Biography_Rutherford_ENG.pdf Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson 1 Storytelling Teaching Model: wiki.science-stories.org Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson The man who formulated the nuclear model of the atom didn’t have a typical childhood. Ernest Rutherford came from a large family. He was one of twelve children born to James and Martha Rutherford, and as a young boy his father’s work often caused the whole family to move. Possi- bly due to the flexibility he needed in childhood to adapt to his changing surroundings, he grew up to be exceptionally open-minded and innovative. Later in life, he stepped up to every challenge, was never scared away, and became one of history’s most prominent scientists. In 1908, he received the Nobel Prize in Chemistry. This biography shows how, step by step, he came to his amazing discoveries. Ernest Rutherford (1871 – 1937), later called the Baron of Nelson and one of the most promi- nent scientists of all time, was born on August 30, 1871 in New Zealand. He was the second son and fourth child of twelve born to James and Martha Rutherford. His father worked making wheels for carts, and as an engineer. Later, his father worked as a flax-miller. In contrast, his mother was an English teacher in a provincial school in Spring Grove. She had excellent teaching results and was prized by the provincial school inspector. As we can imagine, as a young boy Ernest was not only educated in the traditional way, but was able to learn technical skills from his father and develop a sense of humanistic sensitivity from his mother. Education was very important to his par- ents. James Rutherford’s work was also very im- portant to the development of his son’s personality. His father’s work required the family to move quite often. In 1876, James moved his family to Foxhill for farming and railway con- struction. Later, they moved to Havelock in the Marlborough Sounds for flax-milling and finally, in 1888, to Taranaki, also for flax milling. At the age of 10, Ernest read his first science book and started performing his first experiments. In 1887, Ernest won a scholarship to Nelson Col- lege, an all-boys private school where he boarded for the next three years. The next step in his education was Canterbury College in Christchurch, New Zealand. There, he became a very active student, not only in science, but also playing for the rugby team. He also partic- ipated in the Dialectic Society (a student debating group) and the graduation day celebrations, for which he co-wrote a song, a talent that was likely passed down from his mother. Despite talents in many different areas, he chose a career in science. In 1892, he obtained a Bachelor of Arts (BA) degree in Pure Mathematics, Latin, Applied Math- ematics, English, French, and Physics. A significant moment in his science career was winning the only Senior Scholarship in Mathemat- ics available in New Zealand. This success led to him meet Alexander Bickerton, a liberal freethink- er who had an enormous impact on his decision to take physics courses the following year. In 1893, Rutherford obtained a Master of Arts degree with double First Class Honours, in Math- ematics, Mathematical Physics, and Physical Sci- ence (specifically Electricity and Magnetism). After graduation, he had problems finding a permanent job. He applied to be a school teacher, but after multiple failed attempts to obtain a per- manent teaching position, he started doing re- search in the field of electrical science. At the time, there were scholarships initiated by The Royal Commissioners for the Exhibition of 1851 that allowed graduates of universities to go anywhere in the world and work on research of importance to their home country’s industries. Rutherford applied for the scholarship and, through a fortu- nate turn of events, received it. As a result, the next stage in Ernest Ruther- ford’s life took place in Cambridge. In 1895, he left New Zealand. He was only 23 years old, but had a reputation as being an outstanding researcher and innovator working at the forefront of electrical technology. He chose to work with Professor Jo- seph John Thomson at Cambridge University’s Cavendish Laboratory. It was a very successful venture, and it marked the first time that a non- 2 Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson Storytelling Teaching Model: wiki.science-stories.org Cambridge-graduate research student worked at Cambridge University. In Cambridge, he was in- spired by the work of Sir Robert Ball and J. J. Thomson. In 1898, Ernest Rutherford accepted a profes- sorship at McGill University in Montreal, Canada. The laboratories there were very well equipped and gave him the chance to make significant pro- gress in his research. In 1900, Rutherford came back to New Zealand to marry Mary Georgina Newton, the daughter of his landlady in Christchurch. They had one child together, a daughter whom they named Eileen. At McGill, Rutherford began to receive world- wide recognition for his research. His work be- came increasingly more widely known and he was elected a Fellow of the Royal Society of Canada in 1900 and of London in 1903. His first book, Radi- oactivity, was published in 1904. In 1908, he was awarded the Nobel Prize in Chemistry due to his research into the radioactive decay of elements and the chemical properties of radioactive sub- stances. Rutherford said then: “All science is either physics or stamp collecting.” Although he received many propositions from American universities and institutions (Yale and the Smithsonian Institute, for example), he re- mained at McGill for quite a long time. This changed when he received an enticing offer from Professor Schuster from Manchester University, who offered to step down if Rutherford would take over his position as Chair. Rutherford accepted the offer, and began working there in 1907. In the Manchester laboratory, the famous gold foil ex- periment was conducted by Hans Geiger and un- dergraduate student Ernest Marsden in 1909, under Rutherford’s supervision. In 1909, Geiger needed an experiment for Marsden. Rutherford gave him the task of looking for alpha-particle scattering at large angles. Geiger and Marsden then investigated the scattering of alpha particles, which came from radioactive ra- don-222 and were directed at a piece of gold foil. The scattering of the alpha particle should have only been deflected by one or two degrees. A few days later, Marsden reported that he saw about one in 10,000 alpha particles scattered at larger angles, even directly backwards, which surprised Rutherford. Geiger and Marsden published their measurements in July, 1909 issue of the Proceeding of the Royal Society. Such huge deflections could not be explained by Thomson's model of the atom, where charge was distributed evenly throughout the atom. Rutherford, who at that time was also the head of the Physics Department at Manchester University, interpreted the experimental results in a famous paper, “The scattering of alpha and beta particles by matter and the structure of the atom.” In this paper Rutherford described and explained the experiments which led him to formulate the nuclear model of the atom, definitively rejecting J. J. Thomson's plum pudding model of the atom. In 1919, Rutherford arrived in Cambridge, where he became the Director of Cambridge Uni- versity’s Cavendish Laboratory. It was there that he gained international fame. Twice he spoke in the House of Lords. As a famous scientist, he often spoke publicly, and his opinion was highly re- spected by many people. He campaigned for Cambridge University to grant women the same privileges as men and defended the award of scholarships to overseas universities. In 1933, when Hitler carried out his non-Aryan policy, Ernest Rutherford helped displaced academics. Ernest Rutherford died on October 19, 1937, at the age of 66. His remains were interred at West- minster Abbey in London. References: Campbell, J. (2011). Ernst Rutherford’s Path to the Nuclear Atom. Science Teaching, Vol 39, 2011,26. Rutherford E. (1911) The Scattering of α and β Particles by Matter and the Structure of the Atom (http://www.chemteam.info/Chem-History/Rutherford- 1911/Rutherford-1911.html). http://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_ex periment http://www.nobelprize.org/nobel_prizes/chemistry/laureates/ 1908/rutherford-bio.html http://www.rutherford.org.nz/ http://www-outreach.phy.cam.ac.uk/camphy/nucleus /nucleus1_1.htm Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson 3 Storytelling Teaching Model: wiki.science-stories.org © 2012, S@TM Research Group Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson was edited by Sarah Dietrich and is based, in part on Historical Background: Atoms written by Peter Heering. Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson was written by Elżbieta Kawecka & Marta Kawecka with the support of the European Commission (project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and Polish Association of Science Teachers, Poland. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein. EN_Guidelines_Rutherford.pdf Suggestions to Teachers (Ernest’s Nuclear Atom) 1 Storytelling Teaching Model: http://science-story-telling.eu Suggestions to Teachers (Ernest’s Nuclear Atom) Expected results After the lesson, the students are expected to: 1. Describe the Rutheford’s experiment, with which was formulated his atomic model. 2. Experiment with the simulations concerning the J.J. Thompson’s atomic model and the Rutherford’s atomic model. 3. Design the courses of the a rays in the J.J. Thompson’s atomic model and the Rutherford’s atomic model. 4. Locate the differences between the J.J. Thompson’s atomic model and the Rutherford’s atomic model, based on their experimentations. 5. Describe the Rutherford’s atomic model, based on the narration as well as their experimentations. 6. Describe how science functions, based on the narration. 7. Locate the characteristic of science and the ways it develops, based on the narration as well as the lesson activities, according to the McComas’s list. 8. Write the differences and the similarities between the Rutherford’s atomic model and the Democritus’ atomic theory. 9. Compare and write the differences between the philosophical and the scientific view, based on Democritus’ atomic theory about the structure of matter and Rutherford’s atomic model. About the activities of students The proposed students' activities are indicative and they aim at the accomplishment of the above expected outcomes. Moreover, the teacher may choose some of them for the teaching process in relation to its aims, the needs of students and the available time. Finally, she/he can create her/his own activities.About the emergence of the characteristics of science in the narration, these characteristics are quoted in the website, comprehensively (in classification of the stories by NOS). About the locating of the characteristics of Nature of Science in the proposed activities, indicatively, we can quote the following: A) The activity 2 concerns the characteristics of Nature of Science: a) “Science demands and relies on empirical evidence”, b) “Science has a subjective element” and c) “Scientific knowledge is tentative but durable”. B) The activity 3 concerns the characteristic of Nature of Science: “Science demands and relies on empirical evidence” C) The activity 4 concerns the characteristics of Nature of Science: “Science demands and relies on empirical evidence”. 2 Suggestions to Teachers (Ernest’s Nuclear Atom) Storytelling Teaching Model: http://science-story-telling.eu D) The activity 5 concerns the characteristics of Nature of Science: “Knowledge production in science includes many common features and shared habits of mind”. E) The activity 6 concerns the characteristics of Nature of Science, which are quoted in the activities: 2, 3, 4 and 5 and the next activity. G) The activity 7 concerns the characteristics of Nature of Science: “Science demands and relies on empirical evidence”. Suggestions to Teachers (Ernest’s Nuclear Atom) were written by Aikaterini Rizaki and Panagiotis Kokkotas with the support by the European Commission (Project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and the NKUA of Greece. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained there in. EN_LA_Rutherford.pdf Student’s Learning Activities (Ernest’s Nuclear Atom) 1 Storytelling Teaching Model: http://science-story-telling.eu Student’s learning activities (Ernest’s Nuclear Atom) Activity 1 You will watch a video with narration or listen to a story from your teacher about Ernest Rutherford and his model of the atom. Please write the most important points of the story according to your view and discuss them in your group. (Indicative important points for this story: relations between Rutherford, J.J. Thompson, Hans Geiger and Ernest Marsden, description of Geiger’s experimental apparatus, process of the experiment, experimental results which guided Rutherford to change the model of J.J. Thompson, ways which the science is developed,…) …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………… Activity 2 Please make a sketch of Geiger’s experimental apparatus, based on the narration. Please draw here: 2 Student’s Learning Activities (Ernest’s Nuclear Atom) Storytelling Teaching Model: http://science-story-telling.eu Activity 3 Please go to the electronic address http://www.youtube.com/watch?v=kHaR2rsFNhg and watch the presentation of Rutherford’s experiment. On the basis of the information you will collect, correct the sketch you have designed for your previous activity. Draw the amended apparatus here: Activity 4 http://www.youtube.com/watch?v=kHaR2rsFNhg Student’s Learning Activities (Ernest’s Nuclear Atom) 3 Storytelling Teaching Model: http://science-story-telling.eu Please visit the website http://phet.colorado.edu/en/simulation/rutherford-scattering and download the relevant application. Activate it and study it carefully. Find the controls with which you can choose a model of the atom. Make visible the orbit and amend the energy of the alpha particles. You should also learn how to recognize the symbols for protons, electrons, neutrons and alpha particles. 1. Please choose the ‘plum pudding model’ and observe the orbit of the alpha particles. Draw a simple sketch in the space below to demonstrate the ‘plum pudding’ and the rotation of the alpha particles. 2. Please choose the Rutherford’s model and observe the orbit of the alpha particles. http://phet.colorado.edu/en/simulation/rutherford-scattering 4 Student’s Learning Activities (Ernest’s Nuclear Atom) Storytelling Teaching Model: http://science-story-telling.eu 3. What do you predict that will happen if you increase the energy of the alpha particles that are launched towards the target? Please make the necessary adjustments in your controls and verify your predictions. Which is your conclusion? …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………… Activity 5 Please discuss in your group the dialogues between Rutherford and Geiger. Based on them what conclusions can you draw about the function and the evolution of science? Write some of them. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… Student’s Learning Activities (Ernest’s Nuclear Atom) 5 Storytelling Teaching Model: http://science-story-telling.eu …………………………………………………………………………………………………………………………………………………… ………………………………………………………………… Activity 6 Using the list of ideas that describe the characteristics of science and the ways it develops, try to locate and write these ideas in the story you heard and the activities of this lesson. These ideas that scientists call Nature of Science (Nature Of Science-NOS- ) are: Characteristics of Nature of Science (NOS) 1. Science demands and relies on empirical evidence. 2. Knowledge production in science includes many common features and shared habits of mind. 3. Scientific knowledge is tentative but durable. 4. Laws and theories are related but distinct kinds of scientific knowledge. 5. Science is a highly creative endeavor. 6. Science has a subjective element. 7. There are historical, cultural, and social influences on science. 8. Science and technology impact each other, but they are not the same. 9. Science and its methods cannot answer all questions. Scientists argue that in order to learn science one must first understand what exactly science is. Because it is difficult to define science, scientists give a list of its characteristics. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………..………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………… Activity 7 Please compare the atomic model of Rutherford with the atomic model of Democritus. 1. Find and write the differences and similarities between the two atomic models. 2. Find and write the differences between the philosophical and scientific view. …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………………… 6 Student’s Learning Activities (Ernest’s Nuclear Atom) Storytelling Teaching Model: http://science-story-telling.eu …………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………… Student’s Learning Activities (Ernest’s Nuclear Atom) were written by Ioannis Vlachos and Aikaterini Rizaki with the support by the European Commission (Project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and the NKUA of Greece. This publication reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained there in. Ernest's Nuclear Atom.pdf Ernest’s Nuclear Atom 1 Storytelling Teaching Model: http://science-story-telling.eu Ernest’s Nuclear Atom Ernest Rutherford was born in New Zealand into a poor farming family in 1871. When the young “Ern,” as his family called him, received his first science book at the age of ten, he was hooked; nevertheless, he still had to keep working at the farm chores. He was very studious and managed to obtain university scholarships. Throughout his university days in New Zealand, he studied and invented high-frequency electrical circuits and worked with radio waves. After he graduated with his Master’s degree, he looked for a job as a school teacher. Evidently, he must not have been very good at it because, even after his third try, he could not get a permanent job. When he fell in love with the beautiful Mary Newton, he decided that without a good job, they could not afford to get married. Failing to get a job, he went back to his parents’ farm to help with the work. At the same time, Ernest applied for a science research scholarship, with which he would be able to take his doctorate anywhere in the world. He was on the field digging potatoes when his mother came running with the news, “Ern, you won’t be- lieve this—you’ve got the scholarship anyway…”. The twenty-four-year-old Ern dropped his potato fork and said, “That’s the last potato I will ever dig!” What a major stroke of luck—although he had placed second in the scholarship competition, the prize had been awarded to him when the win- ner decided not to take it. The second major turning point in his life oc- curred when he chose Professor J. J. Thompson (known as JJ by his students) at Cambridge Uni- versity’s Cavendish Laboratory as his doctoral su- pervisor. Cambridge had just instituted the new “Doctor of Philosophy” degree, and Rutherford was among the first few to earn this degree. By 1898, at the age of 27, with JJ’s help, Rutherford obtained his first job as professor at McGill Uni- versity in Montreal, Canada. Finally, he was also able to marry his sweetheart, Mary, who had waited for him all this time. At McGill, Rutherford made his first great dis- covery–that the atom is composed of parts and that its character can change. One of the atomic parts he discovered and identified was the alpha particle, which is, in effect, just a helium atom with its electrons stripped off. His discoveries in this field were considered so important, that he received the Nobel Prize in Chemistry in 1908 “for his investigations into the disintegration of the ele- ments, and the chemistry of radioactive sub- stances.” By then, he had been induced to move to Manchester, England to accept his second job as head professor of physics there. One spring day, in March of 1909, Ernest Rutherford was sitting at his desk, deep in thought. He realized that he had achieved a level of success that other scientists could only dream of—a Nobel Prize at age 37! Why, then, did he still have these nagging thoughts of dissatisfaction? “For all I have discovered, I still have no clue of what the atom really looks like,” he mused. “I cer- tainly don’t accept JJ’s theory that the atom is some sort of blob of positive and negative charge distributed, more or less, uniformly.” His mind went back to his experiment of shooting a beam of alpha particles at a sheet of mica and taking a pic- ture of the beam on the other side with a photo- graphic plate. What should have been a sharp, bright point was not so; it was fuzzy. Why? Surely, the heart of the atom could not be a positive charge concentrated in a small area, could it? Surely, the alpha particles were not bouncing like marbles from the center of the atom, were they? Rutherford’s thoughts were interrupted by a faint knock at the door. “Come in!” his voice boomed. His research associate, Hans Geiger, en- tered with a young man in tow whom Rutherford had not met before. “Professor, this is Ernest Marsden, one of our students who is in need of an undergraduate re- search project. I have been training him in radio- active methods. Do you think that he might begin a small research project with us?” Hans spoke with a thick German accent, having recently arrived from Germany to take up the John Harling re- search fellowship at Manchester in order to work with Rutherford. 2 Ernest’s Nuclear Atom Storytelling Teaching Model: http://science-story-telling.eu “I think that is a good idea, provided that Ernest is willing to work at the arduous task of observing scintillations.” “Scin-Scintillations, sir? What are they?” stam- mered Ernest. “They are the tiny flashes of light when alpha particles strike a fluorescent screen. Of course, you can’t see them unless you use a microscope, and your eyes can’t detect them unless you first sit in total darkness for at least a half hour with your eyes open. Then, you must be prepared to stare into the microscope and hold your eyes open without blinking for at least two minutes at a time and count all the flashes you see. It’s not easy.” “Sir, I am willing,” replied the young Marsden. Rutherford had a flash of inspiration. “Then, why don’t we have Marsden, here, look for alphas that are scattered through a large angle? It has never been done before.” “Agreed,” said Geiger. “Then we will go ahead,” replied Rutherford, and Marsden nodded. Rutherford, though, had a sheepish look on his face. What he had not said is that he had no confidence that Marsden would succeed. What if he failed? How would that affect the student’s future studies? Three days later, Rutherford, as usual sitting at his desk and writing, was interrupted by a loud knock at the door. Rutherford jumped, his con- centration having been broken. “Come in!” he said with his usual booming voice. The door swung open and Geiger strode in, obviously in an excited state. “Professor, Profes- sor, we have made the most incredible discovery— some of the alpha particles are coming backward towards the source!” For a moment, Rutherford was at a loss for words. Then, he replied, “Hans, explain yourself!” Geiger continued, “We have used a radium source to project alpha particles at a gold foil mounted on a thin, glass plate and find that about one in twenty-thousand of the alpha particles have their directions changed to such an extent that they emerge again at the side of incidence.” Rutherford was stunned. “That is incredible. If the atom is, indeed, like JJ says it is, that would be about the equivalent of shooting a 15-inch artillery shell against a target of tissue paper and having it bounce back towards the gunner!” Geiger laughed, “I hadn’t thought of it quite that way….” Rutherford’s eyes glazed over as he spoke to himself, “This means that we must, indeed, revise our picture of the atom. I wonder….” Geiger interrupted, “Sir, should we complete the experiment and write it up for publication?” “Yes, indeed. Let us do it with all haste.” The next two years passed like a whirlwind, with experiment after experiment revealing more detail about the scattering of alpha particles when passing through matter. It was the Sunday before Christmas in 1911 and the Rutherfords had de- cided to host a Christmas dinner for their friends and colleagues. After supper, Mrs. Rutherford served the traditional Christmas plum pudding. Instead of digging right in, Rutherford just stared at his pudding. “Is something the matter, dear? Why don’t you eat your pudding?” Mrs. Rutherford asked. Rutherford uncharacteristically ignored her question and, instead, began to speak excitedly, “Now, I see it—why JJ’s model cannot be right— and what the atom must be like. It cannot be like this pudding with the negative charges like the plums and the positive charge like the dough. The positive charge must be concentrated in a small region in the center, and the negative charge must be located, perhaps, like a cloud around the cen- ter.” The dinner guests were suitably impressed by Rutherford’s insight, and an animated conversa- tion took place. The next morning at the labora- tory, Rutherford met with Geiger, as usual. Triumphantly, Rutherford announced, “Hans, I know what the atom looks like and how we must explain the large scattering of alpha particles. Most of its mass is concentrated near the center as the positive charge, and the negative charge in the form of electrons is much smaller and further away from the center.” Geiger appeared somewhat concerned. “Profes- sor, that is certainly a revolutionary idea and will not be viewed too kindly by JJ.” Confidence rang in Rutherford’s voice. “If JJ had not put forward a theory of his own, he would Ernest’s Nuclear Atom 3 Storytelling Teaching Model: http://science-story-telling.eu have to admit that I am right, as the evidence is very strongly against him.” Rutherford published the details of his new model of the atom, but not too many people be- lieved him at the start. It remained up to Niels Bohr to join Rutherford and devise his Bohr atomic model, which was a refinement of Ruther- ford’s idea and the first model that explained the atom in a way that was consistent with all the known observations. So, that is the story of how the idea of the nu- clear atom was born, but it was not until two years later that Rutherford first used the word “nucleus” to describe the center of the atom. References Geiger, H., & Marsden, E. (1909). On a diffuse reflection of the alpha particles. Proceedings of the Royal Society of Lon- don A, 82, 495–500. Moon, P. B. (1974). Ernest Rutherford and the Atom. London: Priory Press Limited. Niaz, M. (1998). From cathode rays to alpha particles to quantum of action: A rational reconstruction of structure of the atom and its implications for chemistry textbooks. Science Education, 82, 527–552. Reeves, R. (2008). A Force of Nature: The frontier Genius of Ernest Rutherford. New York, N.Y.: W. W. Norton & Company, Inc. Rutherford, E. (1911). The scattering of alpha and beta parti- cles by matter and the structure of the atom. Philosophical Magazine, 21, 669–688. Wilson, D. (1983). Rutherford: Simple genius. Cambridge, MA: MIT Press. Ernest’s Nuclear Atom was edited by Cathrine Froese Klas- sen with the support the European Commission (project 518094-LLP-1-2011-1-GR-COMENIUS-CMP) and The University of Winnipeg, Canada, and is based, in part, on Historical Background: Atoms written by Peter Heering and on Biography: Ernest Rutherford, 1st Baron Rutherford of Nelson written by Elżbieta Kawecka and Marta Kawecka. Ernest’s Nuclear Atom was written by Stephen Klassen with the support the European Commission (project 518094-LLP- 1-2011-1-GR-COMENIUS-CMP) and The University of Winnipeg, Canada. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein. 4 Ernest’s Nuclear Atom Storytelling Teaching Model: http://science-story-telling.eu Historical background atoms.pdf Background Atomsatoms 1 Storytelling Teaching Model: http://science-story-telling.eu Background atoms The concept of Atoms is fundamental to our modern scientific understanding of the world. The em- inent physicists Richard P. Feynman pointed out that “[i]f, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of crea- tures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms – little particles that move around in perpetual motion, attracting each other when they are little distance apart, but repelling upon being squeezed into one another” (Feynman et al. 1963, I- 3). This quotation is for several reasons relevant with respect to this historical background: On the one hand, Feynman is pointing out extremely clear how important the concept of an atomic struc- ture of matter is to modern science. Yet, he also raises implicitly another issue that is very relevant if the genesis of this concept is analysed: Feynman speaks in this introduction to the first lecture of the ‘atomic hypothesis (or the atomic fact, or whatever you wish to call it)’, and in doing so he ad- dresses and ignores at the same time a crucial detail: is the existence of the atom an hypothesis, or is it a fact, and if so, what really is part of this fact – which level of description can still be taken as being a fact, which are additional hypothesis. Feynman ignores this issue by leaving it to the reader how she or he wishes to call it – this appears to be a crude form of relativism that can possibly be explained by looking at the date of the publication: Feynman’s lectures date from the early 1960s, for that time it appears to be questionable whether a different position could be expected in epis- temological or in nature of science categories. Such a statement appears to be somewhat irritating from our point of view, yet, it demonstrates how far the knowledge about the nature of science has developed in recent decades. In order to teach this central concept, one aspect gets relevant which was also important in the historical development but will not be discussed in this historical background: The notion of a chemical element is a prerequisite for the formulation of the atomic model – this can be seen in the historical analysis booth for the development in the Greek antiquity as well as for the modern period, and it can also be identified in the educational conceptions. How- ever, the historical development of the concept of elements will not be discussed in this back- ground material but is assumed to already ex- ist. Ancient discussions about the structure of matter The question how the material world is structured has been discussed in particular in Greek Antiquity (a knowledge which is in part due to the transfer of knowledge from this pe- riod to the Early Modern Era in Europe).1 In this respect, the topic of a prime element that 1 There is evidence that models of the material world existed also in the Indian culture as well as in Babylonian culture, however, documentation is poorer and these concepts have not played any role in the introduction of an atomic theory into Europe- an science – thus they are not discussed in the back- ground. constitutes all the other substances becomes relevant, however, it is of course not even syn- onymous with a simplistic atomic concept as this prime element could exist without any corpuscular structure. Philosophers such as Thales of Miletus, Anaximenes, Heraclites and Empedocles were among those scholars who developed or promoted respective conceptions. About 450 BC, two philosophers developed ideas that are relevant to the introduction of the atomic conception: Democritus and Leucip- pus. Both postulated that the material world is made from very tiny particles, which them- selves cannot be any further separated into smaller parts. These atoms were distinguished from each other by their shape and size. Ac- cording to Democritus, these atoms move in the empty space and collide with each other. By specific combinations of atoms, other sub- stances are formed, yet, these combinations are not permanent but the atoms can separate again. However, the concepts of Leucippus and Democritus were not accepted by their con- temporaries: “Two factors weighed against any widespread acceptance of the classical version of atomism. The first factor was the uncom- promising materialism of this philosophy. By explaining sensation and even thought in terms of the motions of atoms, the atomists chal- lenged man’s self-understanding. Atomism seemed to leave no place for spiritual values. 2 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu Surely the values of friendship, courage, and worship cannot be reduced to the concourse of atoms. Moreover, the atomists left no place in science for considerations of purpose, whether natural or divine. The second factor was the ad hoc nature of the atomists’ explanations”. (Loose 2001, 25) Additionally, there was a rival concept which appeared superior as it ex- plained the behavior of matter: the four ele- ments conception which explained all existing matter as well as its properties through four elements: Water, Air, Fire, and Earth.2 A central, if not the central figure for the re- jection of this atomic theory was Aristotle, who advocated the four elements theory and added as a fifth: ether, which filled the space between the celestial bodies. This was relevant as – ac- cording to Aristotle – no empty space could exist – the horror vacui, nature’s ‘fear’ of emp- tiness. Moreover, according to his conception, everything in nature is intentional; there is no superfluous action in nature. Additionally, each object has a natural position, and if displaced, it aims at getting back to this position. Conse- quently, Aristotle was able to explain observa- ble processes with his principles. The atomists were not only unable to propose a superior explanation, even more: they assumed the ex- istence of particles no one could see. This was a major criticism Aristotle made against the atomic theory, apart from that he did not ac- cept the idea of the empty space which was according to his own conception impossible. And a permanent motion appeared absurd in Aristotle’s understanding. All in all he opposed the atomic concept which was in contradiction to several of his central beliefs. Yet in some sense he is still relevant to the modern devel- opment of the atomic theory as the original works of Leucippus and Democritus were lost and were actually known only through his criti- cism. Aristotle’s works were kept and expanded in the Islamic culture, and through this culture, they came back to Europe and the Christian culture. For the scholastic period, this Aristote- lian understanding became dominant, particu- larly as it was considered to be coherent with 2 It has to be understood that these elements were not what we call Earth, Fire, Air, and Water, but they are elementary principles (see also the background on the development of the Periodic Table). the Bible. Yet, astronomers and slightly later natural philosophers developed a different understanding of natural processes – conse- quently the authority of Aristotle was more and more questioned throughout the 17th and 18th centuries – at the end of this period, it was the experimenting enlightened natural philosopher who was considered to be able to uncover the laws and structure of nature. In this process some experiments and considerations were developed that seemed to strengthen the an- cient atomic hypothesis. Of particular im- portance was the demonstration of the exist- ence of the vacuum.3 In another argumentation it was discussed that if a tiny bit of incense is burned, it can be smelled in the entire room. As this room is significantly bigger than the space the incense initially occupied, the initial piece has to be divided into more than 750.000.000 parts – these calculations were intended to show how small the particles have to be that form the piece of incense (see Beer & Pricha 1997). However, such a discussion remained on the level of simple calculations, there was no claim whatsoever that atoms exists or what their properties might be. Such an understand- ing was only developed in the early 19th centu- ry. Structuring matter: Dalton When looking into the genesis of modern science, probably the first scholar to establish an atomic conception is John Dalton, a chemist who was following Lavoisier’s new, quantita- tive approach towards chemistry. Using a bal- ance to analyze chemical reactions formed a major achievement of Lavoisier’s new chemical system, and this enabled chemists to take a different perspective on chemical reactions. Lavoisier himself established the difference towards classical chemistry and the novelty of his approach several times, to give but one ex- ample: “Lavoisier wrote in the Opuscules phy- siques et chimiques (1774) that he ‘applied to chemistry not only to the apparatus and meth- ods of experimental physics but also the spirit of precision and calculation which characteriz- es that science’.” (Nye 1993, 35). Yet, it was not only the methodological step or conceptual modifications that made Lavoisier’s chemistry 3 On some of the controversies with respect to the existence of a vacuum and the related philosophical implications see Shapin & Schaffer 1989. Background Atoms 3 Storytelling Teaching Model: http://science-story-telling.eu distinct to the previous understanding. A key element in his chemistry was the different no- tion of chemical reactions that helped him to use the quantitative description, and the un- derstanding that ‘simple substances’ can be interpreted as elements that cannot be decom- posed any further. In this respect, Lavoisier stated explicitly: “I shall, therefore, only add upon this subject, that if, by the term elements, we mean to express those simple and indivisi- ble atoms of which matter is composed, it is extremely probable we know nothing at all about them; but if we apply the term elements, or principles of bodies, to express our idea of the last point which analysis is capable of reaching, we must admit, as elements, all the substances into which we are able, to reduce bodies by decomposition.“(Lavoisier 1794, xxiii) Remarkably, Lavoisier is already using the term ‘atom’, even though he is not using an atomic theory. However, this notion of element that gets evident in this quotation is also rele- vant to the introduction of the atomic theory. A key understanding resulted from the quantitative observations at the end of the 18th century: most compounds are the result of the reaction of specific ratios of masses of the ele- ments that form this compound. This rule be- came known as the law of constant composi- tion. Even though this law appeared to be valid for the chemical reactions that had been ana- lyzed quantitatively, there was another striking aspect, and this was first characterized by John Dalton. Dalton realized that there were some chemical reactions in which different com- pounds were formed through a combination of the same elements (i.e. from a reaction of cop- per with oxygen two different compounds can result, likewise carbon and oxygen, and so on). The resulting compound depended on the amount of the two initial substances that react- ed with each other. However, there was also some regularity that Dalton noticed: there was a ratio of small integer numbers between the masses of element A that reacted with the same amount of element B to two different com- pounds. From this finding Dalton formulated another law. the law of multiple proportions characterizes that if two elements possibly re- act to more than one compound, then the masses of element A reacting with the same amount of B are small integer multiples. This law, together with the law of constant composi- tion, forms the starting point towards the stoi- chiometric approach in chemistry. However, even though this law was based on empiric evidence, it was not the only conclu- sion that Dalton drew from his experiments: In a lecture delivered at the Royal Institution London4, he proposed the following ideas which form the basis of the modern atomic theory of matter: “All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements.”5 Evidently, Dalton’s use of the term atom is different to the one of Lavoisier. Dalton’s con- ception of the atom is characterized by their countability, they have a certain weight and so on, whilst in Lavoisier’s conception it is more their chemical property which is relevant, and it is even unclear whether this is an actual par- ticle. This assumption enabled Dalton to prepare an explanation of the stoichiometric laws he and others had formulated. According to this understanding, the law of constant composition results both from the understanding that all atoms of the same element are identical, and that chemical reactions are a result of the rear- rangement of the atoms. The law of multiple proportions can then be interpreted as being the result of different arrangements of the at- oms that result in different compounds. In do- ing so, the knowledge about quantitative chem- ical analysis became based on a first paradigm in the Kuhnian sense (and in this respect, one could argue that this achievement turned stoi- chiometric chemistry into a science in the Kuhnian sense). Yet, things were not that easy: Even though Dalton’s theory was adopted by several chemists very quickly, others rejected it. A key problem was the assumption that each element was formed by a different atom, as a result there were about thirty different atoms at the beginning of the 19th century, and their number was increasing. Thus, instead of simpli- fying the structure of matter, Dalton’s atomic 4 According to Clarke (1803), the first presentation was made at the Manchester Philosophical Society. 5 http://www.rsc.org/chemsoc/timeline/pages/1803 .html, last access April 18, 2012 4 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu theory made nature more complex. Despite this criticism, the stoichiometric laws were used by chemists, and some of them used fractional numbers to express the ratio of masses – indi- cating that there was no inseparable particle. This was not just a problem of initial ac- ceptance, even sixty years later, reservations against this theory were stated very explicitly, e.g. the President of the Chemical Society Wil- liamson stated in a speech in 1869: “… that on the one hand, all chemists use the atomic theo- ry, and that, on the other hand, a considerable number of them view it with distrust, some with positive dislike.“ (quoted in Tilden & Glasstone 1926, 227). And some renown chem- ists and physicists at the beginning of the 20th century still rejected the atomic theory – we will come back later to this issue. Yet, particu- larly for chemists, the atom became an entity that was used in their analysis of chemical reac- tions. However, it was not considered to be real (neither in the positivistic sense nor in the sense of a relevant theoretical description) but just a heuristic tool which was very adequate in terms of describing chemical reactions, but had nothing to do with the actual understanding of matter (Görs 1999). The atom gets established Despite the discussions amongst the chem- ists who accepted the atom as a useful hypoth- esis, the physicists started to use the atom as a real object with explanatory power. Particular- ly the developing science of thermodynamics played an important role in the establishment of a physical atom that is crucial for the kinetic theory (atoms in motion represent heat). How- ever, this understanding was strongly criti- cized, particularly in the German speaking sci- entific community by eminent scientists such as Ernst Mach, Wilhelm Ostwald and Georg Helm.6 The controversy between these re- searchers (Ostwald was a Nobel Prize winner in 1909, Mach was also very prominent in his times) and the proponents of a statistical inter- pretation (most notably Boltzmann) was not just based on physical issues but involved also deep philosophical questions. A key aspect in 6 For other reasons, also Max Planck initially criti- cized atomism as he understood it in Boltzmann’s statistical interpretation, see Müller (2008). This discussion was not limited to the German speaking community; another example of the opponents of atomism is Poincare this respect was the question whether individ- ual atoms can be seen, or whether there is any evidence for the existence of individual atoms. Actually, at the beginning of the 20th centu- ry, it appeared that the atomic theory was con- sidered to be overthrown, and Boltzmann to be a relic from the 19th century. Things changed significantly when Planck’s theory of radiation was established and at about the same time Einstein and Smoluchowski published their interpretation of Brownian motion. This was a phenomenon described already in the 18th century by several observers. However, it was attributed to the biologist Robert Brown who noticed in the early 19th century that small pollen and dust particles that are floating on water moved in an erratic manner. The re- markable detail about this motion was that it never appeared to stop, moreover, the moving particles were certainly not alive. It remained an open question for about half a century how this motion was to be interpreted. Even though towards the end of the 19th century some re- searchers proposed solutions to this question which correspond to our interpretation, it was only in 1905/06 when Albert Einstein and Mar- ian Smoluchowski presented independently their mathematical analysis of Brownian mo- tion (actually Einstein’s paper was one of the three famous in his annum mirabilis, the other two dealt with the photoelectric effect and the special theory of relativity). Both researchers were able to explain that the motion can be caused by the motion of the particles of water due to their kinetic energy – thus, Brownian motion appeared to be a first macroscopic ef- fect that had to be explained with the assump- tion of small particles and thus forming an em- pirical evidence for the kinetic theory and thus for the atomic theory. Actually, Ostwald is said to have been convinced of the adequateness of the atomic theory through the agreement of the description and the empirical data. At about the same time, there was another empirical evi- dence for the adequateness of the atomic theo- ry, and this one is said to have convinced Mach: When radioactive particles are placed next to a fluorescent screen, minute flashes of light can be observed which are to be interpreted as results of individual α-particles. Thus, within a few years, the understanding of atomism had changed from almost complete rejection to almost complete acceptance. Boltzmann, the great proponent of the atomic theory, was at Background Atoms 5 Storytelling Teaching Model: http://science-story-telling.eu that time already dead – he committed suicide in September 1906. The atom gets a substructure Even before Einstein’s and Smoluchowski’s work helped to establish a consensus about the correctness of the atomic description of matter, some researchers established empirical results that actually contradicted the initial under- standing of the atom as being inseparable: Ac- tually Faraday’s work on electrolysis – which dated from the 1830s –could have been raised questions on the fundamental and inseparable nature of the atom as formulated by Dalton: According to Faraday’s investigation, a certain amount of electricity releases a certain amount of an element in the process of electrolysis. However, this empirical result did not raise questions with respect to the atomic nature of matter, on the contrary: It remained unclear until well into the 20th century whether elec- tricity has an atomic structure, or whether the ratio between electrical charge and released matter was the mean of several reactions that could take place at the same time. Only in the 1920’s, when Millikan’s measurements on the elementary charge were awarded with the No- bel Prize, this issue had been settled (at least for the vast majority of scientists, see Holton 1978). Yet, towards the end of the 19th centu- ry, further evidence was produced that ques- tioned the indivisible character of the atom. Actually, the starting point was research that in retrospect can be taken as being further evi- dence for the atomic theory, even though it was not interpreted in this sense in the historical situation. In the 1860’s, the chemist Bunsen showed, together with the physicist Kirchhoff, that the light emitted from a substance is very characteristic and that only special frequencies (or lines, if the spectrum is analysed) are emit- ted (or absorbed). This provided also a method to identify new elements, and the number of elements increased significantly over the next few years. Analysing spectra was a major issue, and became expanded towards analyzing also cathode rays and their interaction with gases that are filled into the tubes. In doing so, exper- imentalists had hoped to develop a further un- derstanding about the constitution of matter (Müller 2004). Particularly the analysis of cathode rays appeared to be very promising; among the researchers working in this field was J.J. Thomson. Thomson analyzed these cathode rays and established that they are formed by particles7 which have a mass of about 1/1000 of the hydrogen atom. He was also able to determine the mass-charge ratio by deflecting these particles in a magnetic field. However, what might be more relevant to this discussion are his experiments in which he used different cathode materials to emit the rays (which were basically emitted by heating up the cathode, the rays were then accelerated with an electric field). Thomson could show that all particles have similar properties, no matter from which material they were emanat- ed. This could be seen as an indication that these particles (corpuscles, as Thomson called them) were a fundamental part of matter. However, there was a problem: When these corpuscles were that lightweight, but electrical- ly charged, and they form a part of matter, then how can stability be created? Thomson finally came up with a solution: “We suppose that the atom consists of a number of corpuscles mov- ing about in a sphere of uniform positive elec- trification …” (Thomson 1904, 255).8 This meant that the (at this time still disput- ed atom) was no longer indivisible, and that the model of the atom had to be modified. Another modification became necessary soon after- wards, and this was related to another field which emerged in the very early 20th century: radioactivity - which will be discussed in the next chapter. One of the researchers who estab- lished their scientific career in analyzing this phenomenon was Ernest Rutherford, a physi- cist from New Zealand who did his early re- searches (which won him the Nobel Prize) in Canada and then moved to England again. In the Cavendish laboratory two of his assistants – Marsden and Geiger – carried out the experi- ment to scatter α-particles with metal foils (Geiger & Marsden 1909). 7 Quite remarkably, his son George Paget Thomson was also awarded the Nobel Prize in physics, this time for his work on electron diffraction. In some sense, it could be (admittedly oversimplified) ar- gued that J.J Thomson was awarded the Nobel Prize for demonstrating that electrons were particles, whilst his son was awarded the same honor for demonstrating that electrons are no particles but have also a wave character. 8 Actually the Japanese physicist Nagaoka came up with a similar solution one year earlier. 6 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu Rutherford had already suspected that a scattering is possible when he observed the passage of α-particles through sheets of mica. This experiment was taken up again, and the result was more than irritating (even though not completely unexpected: Geiger and Marsden observed that even though the vast majority of α-particles passed the metal foil (and in the course of the experiment they used gold foil as this could be prepared extremely thin), with some of them being scattered, very few of them were reflected. “In retrospect, Marsden’s discovery was the ‘most incredible event’ that had ever happened to him [Rutherford, PH], almost as incredible, he would say, as if a fifteen-inch shell fired at a piece of tissue paper bounced back and hit the gunner. That the military imagery and the in- credulity are later fabrications we can see easi- ly from a lecture Rutherford delivered … six month after the discovery of the diffuse reflec- tion (Heilbron 1981, 264f.) Be this statement as it may, the result was certainly unexpected to the scientific communi- ty, and Rutherford came up with an explanation that was certainly also unexpected: He calcu- lated from the behavior of the α-particles that the atom had a small positively charged nucle- us that contains almost all the mass, whilst most of the space of the atom was empty, ex- cept for the electrons that moved around somewhere in this space. Atoms can change As already mentioned, Rutherford became famous for his researches in radioactivity – yet he was not the person to open this field. The first researcher who actually observed radioac- tivity was the French physicist Henri Becquerel – his discovery (and one can use this term as this was completely unexpected even though some sensibility for radiation effects certainly existed due to Röntgen’s demonstration of the X-rays) opened a new field. Yet, this field was not entered immediately by Becquerel himself or other scientists, but the rays emitted from Uranium salts were just considered to be a cu- riosity not worth any further scientific atten- tion. It was the collaboration of a young Polish chemist with a French physicists that actually made the importance of this new field evident: Marie and Pierre Curie could use the radiation to show that within several radioactive samples other elements than Uranium have to exist as the radiation was stronger than the one emit- ted from pure Uranium. In a long and laborious analysis, they were finally able to prepare pure samples of the elements Polonium and Radium. Particularly Radium became central to the re- search in the new field of radioactivity as it was fairly active and produced different rays. Yet, it became evident, that a lot more chemical ele- ments have the ability to emit such a radiation. However, there were several things that turned out to be really astonishing – among them cer- tainly the transformation of one element into another in the process of an α- or a β-decay. This gets evident from an anecdote that brings us back to Rutherford: “Rutherford and Soddy found, for example, that radioactive thorium, atom by atom, was gradually turning itself into radium. At the moment he realized this, Soddy … blurted out, ‘Rutherford, this is transmuta- tion!’ ‘For Mike’s sake, Soddy,’ his companion shot back, ‘don’t call it transmutation. They’ll have our heads off as alchemists” (Weart 1988, 5f.). Already the work of the Curies’ had estab- lished a fundamental idea: The radiation of a material is related to some properties of the element. Uranium has a different radiation than Polonium and Radium, and so on. Moreover, it became evident through experiments that the activity of a sample gets reduced over time – which is evident when the transformation of the atoms into those of another element is tak- en into consideration. However, there was also a problem with respect to the decrease of the activity, it became evident that the half-life was not a value that could be used for an individual atom, on the very contrary. The law of radioac- tive decay worked only for a statistical sample, a prognosis of the behavior of the individual atom was not possible. Initially, this was taken to be an indication of the required development in atomic physics, however, it became evident in the end that this is simply not possible and the decay can only be described mathematical- ly in terms of the statistic of the ensemble. Moreover, in analyzing the radiation, three different types could be identified and soon characterized. Another surprise came with the α-rays – they turned out to be helium, an ele- ment that until then was only detected in the Background Atoms 7 Storytelling Teaching Model: http://science-story-telling.eu sun (with spectroscopic methods) and seem- ingly did not exist on Earth. Yet, as the α-rays appeared to be positive particles whilst the β- rays were electrons, this meant that not only the electrons could be emitted from the atom but also some of the positive substance. Physical atoms and chemical atoms Determining the properties of the different rays was one of the first things that experi- menters did once it became evident that this was a relevant topic. Among other things, mass and charge of the particles that formed the rays were determined. This was done by applying a well defined magnetic field rectangular to the direction of the rays – from the deflection the charge/mass ratio could be determined. A comparable set-up was used to analyze atoms, and this provided another insight into their structure as well as it solved one of the remain- ing problems. Particularly through the work of Francis Aston, who modified this set-up into a mass spectrometer, it became evident that even though from a chemical point of view all atoms of an element are indistinguishable, this was not the case from the physical point of view. Aston could demonstrate that for several ele- ments different atoms existed that could be distinguished (and only be distinguished) from their mass. This helped to explain why certain elements had an atomic weight that was not an integer multiple of the mass of the hydrogen atom. From Aston’s data it became evident that the atomic weight was the weighted mean of the atoms’ mass. Looking at the masses of each kind of atoms (which were predicted and called isotopes already before by Rutherford’s collab- orator Soddy) it became evident that the atom- ic weight of each individual isotope was (within the accuracy) an integer multiple of the Hydro- gen atom. Atoms can be changed Whilst most experiments with radioactive substances aimed at analyzing the radiation, some researchers also attempted to modify atoms (artificial ‘transmutation’). Initially, α- particles were used, they were shot towards matter and it could be observed that some at- oms were able to integrate the α-particle in the nucleus, thus forming a new element. The first to establish this experiment was again Ruther- ford who could show that when α-particles are sent through Nitrogen, Hydrogen and Oxygen are traceable. Rutherford’s interpretation was that the Nitrogen nucleus was absorbing an α- particle, and the newly formed nucleus would immediately emit a hydrogen nucleus. This was the first successful attempt to modify an ele- ment and to create a new one – other such ex- periments quickly followed. Yet, it has to be understood that this is not a nuclear fission, this was still considered to be impossible. Rutherford named the Hydrogen nucleus proton, and postulated that this proton is an elementary component of all nuclei. Yet, the mass of the nuclei does not form integer multi- ples of the mass of the proton, this was still a major problem. At the same time, two more questions still existed: Why can positive pro- tons form the nucleus, and how to explain a β- decay. Rutherford assumed that also electrons exist in the nucleus and form pairs together with protons, and these pairs should keep the elementary particles in the nucleus together. Among the researchers that tried to investi- gate the nucleus and the atom through interac- tion with α-particles were Irène Joliot-Curie (daughter of Marie Curie) and her husband Frédéric. They repeated some experiments which had been carried out in Berlin: Beryllium was irradiated with α-particles; as a result a significant radiation could be observed which they initially took as γ-rays. The particles of this radiation were not charged and appeared to have an extremely high energy. Even though the particles were not charged, they could in- teract with hydrogen and release electrons. Whilst the Joliot-Curies kept their interpreta- tion of the result of their experiments being γ- radiation, James Chadwick, who was working with Rutherford, choose a different interpreta- tion. According to Chadwick this radiation was to be explained with a new corpuscle and thus the radiation was a completely new type. Fur- ther experiments showed that the particles had a rest mass similar to the proton, and could be seen as the particle that replaces the proton- electron-pair Rutherford had assumed to ex- plain the (relative) stability of the nucleus. The neutron enabled further experiments on transmutation, as it is neutral, there is not the repulsive electrostatic force that was a problem in attempting to get an α-particle into the nucleus. Several researchers worked on 8 Background Atoms Storytelling Teaching Model: http://science-story-telling.eu this field as it enabled the creation of new radi- oactive isotopes as well as new products of decay. Among those researchers were the Jo- liot-Curies in Paris, Fermi in Italy, and Hahn and Strassmann in Berlin. Both aimed at getting a neutron into the nucleus of Uranium, at that time the heaviest element to be known. The idea was to produce the so-called transuranium elements, elements with a greater atomic num- ber than Uranium. This appeared to be the only possibility to develop new elements as the Pe- riodic Table was considered to be complete. Particularly the chemist Hahn was very un- satisfied with his results: It appeared that through his experiments, Uranium had been turned into Barium – which has significantly lesser atomic weight than Uranium. Hahn ad- dressed this issue in a letter to the physicist Lise Meitner. She had been working with Hahn for a long time and recently had to flee to Swe- den from the threat of fascist Germany after the so-called Anschluss of Austria. Meitner re- sponded initially that such a result does not seem to be plausible.9 However, as she pointed out in the same letter, there had been so many surprises in the history of radioactivity that one could hardly could say, this or that is impossi- ble. Hahn insisted that he had verified Barium, and Meitner pointed out in another letter writ- ten a couple of days later that at least from the energetic point of view, a fission could have occurred. In a discussion she had with her nephew Frisch, Meitner came to the idea that possibly the model of the atom had to be thought like a drop – if an object with adequate energy hits that drop, breaks this drop into two smaller ones. Hahn finally published his findings (togeth- er with Strassmann) and pointed out that for him as a chemist, he had to state that the result- ing isotopes behave like Barium, yet he claimed that from the point of physics he was still not convinced that this element could be produced in such an experiment. This changed very quickly, and scientists immediately pointed out that in such a reaction not only a significant amount of energy would be released, but also 9 Before these experiments were carried out, how- ever, the concept of nuclear fission had already been formulated by Ida Noddack already in 1934 when she was criticizing the discussion of Fermi in his experiments on transurane elements. other neutrons, thus, a chain reaction appeared possible. Note that some audiofiles with Protagonists such as Thomson, Rutherford, Hahn etc. are to be found at http://www.aip.org/history/mod/fission/fissi on1/01.html I am indebted to D. Metz (University of Win- nipeg) for his careful proof-reading as well as for comments on the previous version of this background material. References Heidelberger, M. (1993). Die innere Seite der Natur : Gustav Theodor Fechners wissenschaftlich- philosophische Weltauffassung. Frankfurt am Main: Klostermann. Heilbron, J. L. (1981). Historical studies in the theory of atomic structure. New York: Arno Press. Holton, G. J. (1978). The scientific imagination : case stud- ies. Cambridge [Eng.]; New York: Cambridge University Press. Lavoisier, A. L. (1794). Elements of Chemistry. Transl. by Kerr, 4th ed., Edinburgh: William Creech. Losee, J. (2001). A historical introduction to the philoso- phy of science. Oxford [England]; New York: Oxford University Press. Morgenweck-Lambrinos, V., & Trömel, M. (2001). Wissen- schaft und Legende: eine Nachbetrachtung zu Lise Meitner, Otto Hahn und die Kernspaltung: eine Legende aus unseren Tagen. NTM, 9, 29--40. Müller, F. (2004). Gasentladungsforschung im 19. Jahr- hundert. Berlin: Verlag für Geschichte der Naturwissen- schaften und der Technik. Müller, I. (2008). Ein Leben für die Thermodynamik. Vom Zweiten Hauptsatz der Thermodynamik zum Planck- schen Wirkungsquantum. In: Physik Journal 7/3, 39-45. Nye, M. J. (1993). From chemical philosophy to theoretical chemistry : dynamics of matter and dynamics of disci- plines, 1800-1950. Berkeley u.a.: Univ. of California Press. Rife, P. (1992). Lise Meitner: ¬Ein Leben für die Wissen- schaft. Hildesheim: Claasen. Shapin, S., & Schaffer, S. (1989). Leviathan and the Air- Pump: Hobbes, Boyle, and the Experimental Life (1st Paperback Edition ed.). Princeton: UP. Sichau, C. (2005). Atomphysik : historische und fachliche Materialien zur Unterrichtsvorbereitung. Oldenburg: Didakt. Zentrum (diz). Background Atoms 9 Storytelling Teaching Model: http://science-story-telling.eu Simonyi, K. (1995). Kulturgeschichte der Physik: von den Anfängen bis 1990 (2. Aufl. ed.). Thun, Frankfurt/Main: Deutsch. Thomson, J.J. (1904). “On the structure of the atom: an investigation of the stability and periods of oscillation of a number of corpuscles arranged at equal intervals around the circumference of a circle; with application of the results to the theory of atomic structure”. In: Philo- sophical Magazine 6 Volume 7, Issue 39, 237-265 Tilden, W. A., & Glasstone, S. (1926). Chemical discovery and invention in the twentieth century. London: Routledge. Weart, S. R. (1988). Nuclear fear : a history of images. Cambridge, Mass.: Harvard University Press. Background atoms was edited by S. Klassen Background atoms was written by Peter Heering with the support of the European Commission (project 518094- LLP-1-2011-1-GR-COMENIUS-CMP) and the University of Flensburg, Germany. This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the infor- mation contained therein Historical Ressources.pdf A Primary Sources Geiger, H./Marsden, E.: On a Diffuse Reflection of the Alpha-Particles, in: Proceedings of the Royal Society of London A 82 (31.07.1909), S. 495–500. Rutherford, Ernest: Radio-activity 1905, avialable online: http://archive.org/details/radioactivity00ruth. Rutherford, Ernest: Radioactive Transformations 1906, avialable online: http://archive.org/details/radioactivetrans00ruth. Rutherford, Ernest: Radioactive Substances and their Radiations 1913, avialable online: http://archive.org/details/radioactivesubst00ruthuoft. B Secondary Sources Andrade, E. N. da C: Rutherford and the Nature of the Atom, Garden City, N.Y. 1964. Heilbron, John L.: Historical Studies in the Theory of Atomic Structure, New York, 1. pub. 1981. Reeves, Richard: A Force of Nature: The Frontier Genius of Ernest Rutherford, New York 2008. Rowland, John: Ernest Rutherford: Atom Pioneer, New York 1957. links.pdf http://www.youtube.com/watch?v=2BV5BYC7On8&feature=youtu.be http://cetera.home.pl/SATM/EN/rutherford_s_experiment/ http://cetera.home.pl/SATM/EN/ernest_atom/
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