Ernest Rutherford Gold Foil Experiment: The Wild Life of the Father of Nuclear Theory  

Discover alpha and beta radiation, Radon, and the nucleus! 

In 1909, a quirky and engaging New Zealander named Ernest Rutherford gave his co-worker’s new assistant some busy work to get him used to the equipment.  Rutherford wasn’t expecting to find any results.  Instead, the assistant found something startling.  Rutherford decided that the only way these results made any sense was if almost all the mass was smushed in a tiny area, an area he called the nucleus!  What did this assistant do and why did that lead Rutherford to determine that everything is almost completely nothing?  Well, I’ll tell you.  Ready?  Let’s go.

Ernest Rutherford’s life changed, which caused the world to change when a Chemist named J. C. Maclaurin decided to get married in August of 1895.  Why did this change Rutherford’s life?  Well, Maclaurin had been granted a scholarship to study abroad, however, the wedding invalidated the scholarship so it went to the only other applicant, 24-year-old Rutherford.  Supposedly, when Rutherford got the news he was working at the family farm and threw down his shovel, exclaiming, “That’s the last potato I’ll ever dig[1]

Ernest Rutherford
Ernest Rutherford

Ernest Rutherford (Ern to family and friends) was the son of a Scottish farmer and an English schoolteacher who had both made the perilous 6-month boat ride to New Zealand as children (dad at 4 years, mom at 13).   When Ern was 5 they moved to a farm in a town called Foxhill, to “raise a little flax and a lot of children[2]”.  As Ernest was the fourth of twelve children, the second part was certainly true.   Ern always excelled at school, but also was a rough and tumble country boy who enjoyed rugby and fishing and everything except dancing which he inexplicably detested[3].  His mother insisted that “all knowledge is power” although Rutherford put it as, “We didn’t have the money so we had to think. [4]”  With several scholarships, Rutherford got a master’s degree in mathematics and science and a bachelor of science degree in chemistry and geology.  At the time New Zealand had a total of 126 engineers in the entire province (it wasn’t a country at the time), so Rutherford decided to become a schoolteacher, which was not a success.  A former student recalled, “He was entirely hopeless as a schoolmaster [and] disorder prevailed in his classes.”  When a student was sent out for misbehaving, they only had to, “stay out of the classroom long enough for Rutherford’s enormous mind to have bulged in some other direction, sneak back to his seat and he would inevitably not be noticed. [5]”    

In 1888, Rutherford’s father moved the family again and Ern stayed at a boardinghouse, where he eventually fell in love with the landlady’s daughter, Mary Newton.  In 1894, Ern asked Mary for her hand in marriage, but Mary wisely refused as she didn’t want to “be a handicap” to his education, saying, it, “would be idiotic,” to get married.  However, she would wait for him, telling Rutherford, “I wouldn’t dream of marrying anyone else.”  At the same time, Rutherford then decided to publish his work on magnetizing iron with radio waves in the Proceedings of the Royal Society of New Zealand.  To give you a sense of how important Physics was in New Zealand at the time, his article was published in the “Miscellaneous” section, the same section as an article about preserving human heads[6]!  In addition, Rutherford applied for the scholarship I mentioned at the beginning of this video. 

Ernest Rutherford Gold Foil Experiment

In August of 1895, Rutherford sailed to England and sent his paper to the famous JJ Thomson who was the head of the Cavendish laboratories as Thomson had just changed the rules at Cavendish to let “aliens”, or non-Cambridge graduates go to graduate school there.  Thomson immediately hired Rutherford and Rutherford found his new boss to be, “very pleasant” and “not fossilized at all”.  However, Rutherford found his fellow students to be another matter, writing Mary, “They snigger at us… I’d like to do a Maori war-dance on the chest of one and will do that in the future if things don’t mend.”  However, after a couple of months, Rutherford was asked to give a public talk.  Once again he wrote Mary, “My paper before the Physical Society was a heavy blow to their assumed superiority and now they all offer to help us in any way they can.”

Rutherford arrived in England at quite the opportune time.  Just months after his arrival, on January 5th of 1896, the papers carried a strange story that vacuum tubes called Crookes tubes could make powerful invisible rays that their discoverer, Wilhelm Roentgen, named x-rays.  Soon, as Rutherford recalled later, “Every laboratory in the world took out its old Crookes tubes to produce x-rays, and the Cavendish Laboratory was no exception.[7]”  Rutherford had been working on transmitting signals with radio waves but was convinced by JJ Thomson to switch to the effects of x-rays on gasses (they called x-rays Roentgen rays after its inventor).  By April 24, 1896, Rutherford wrote Mary, “I am working with the professor this term on Roentgen rays.  I am a little full up on my old subject and glad of the change.[8]”  Rutherford was working with Thomson while Thomson discovered the electron.  Now they knew that everything was filled with these teeny tiny negatively charged particles that were at least 1700 times smaller than the smallest atom.  However, they didn’t know what these things had to do with the nature of the atom.  Were they part of an atom or just extra things flowing around?  How in the world did all of this work?  

Meanwhile, in France, a wealthy third-generation scientist named Henri Becquerel had found that uranium would spontaneously produce rays that, like x-rays, could go through the thick paper and develop film.  Then a Polish immigrant to France named Marie Curie decided to study “Uranium rays” for her dissertation and, using the fact that these rays made gasses electrically conductive had used a sensitive electroscope and found that Thorium also produced these rays and named this process “radio-activity”.  She also found that there must be some tiny amounts of new elements, Polonium, and Radium, hidden in ore.  Now, the search was on to use Chemistry to isolate these new elements.  Rutherford, however, had no interest in Chemistry, famously saying, “All science is either physics or stamp collecting.”  However, as Rutherford had been studying the effects of x-rays on gasses, he thought he might also study the effects of radioactivity on gasses. 

Rutherford's Atomic Models
Rutherford’s Atomic Models

Rutherford put a bit of uranium on a plate separated by another plate by air and measured the current that flowed between the plates as a measure of the radioactivity, a method he copied from Marie Curie.  Then, to systematically study the strength of the radiation, Rutherford measured the current as he added layers of thin metal foil in the way of the uranium rays.  The results were very strange.  At first, the thin layers of metal would quickly diminish the strength of the current.  But then, after a while, the amount seemed almost constant.  What was going on? On September 1, 1898, Rutherford published his conclusion: “uranium radiation is complex, and there are present at least two distinct types of radiation – one that is readily absorbed, which will be termed for convenience the alpha radiation, and the other of a more penetrative character, which will be termed the beta radiation.”[9]  The very next year a French physicist named Paul Villard was given some radium to study by the Curies and discovered a third, even more, powerful ray, that Rutherford eventually called gamma radiation (as alpha, beta, and gamma, are the first three letters of the Greek alphabet).  [If you are still confused about Rutherford’s experiment, let me explain further, at first, the layers of metal were blocking the alpha particles so that more metal equals less radiation until all of the alpha particles were blocked.  However, beta and gamma radiation can go through much more material, so adding more layers of metal leaves didn’t really reduce radiation further.]

At around the same time that Rutherford was discovering alpha and beta radiation, a Physics professor at McGill University in Montreal, Canada retired.  Naturally, the department head wrote JJ Thomson and asked his advice on whom to hire to replace him.  Thomson wrote back, “I have never had a student with more enthusiasm or ability for original research than Mr. Rutherford.[10]”  Rutherford was a little hesitant to leave Cambridge, however, he felt the lingering prejudice against him as an outsider would keep him from getting a fellowship.  Rutherford quickly became excited about the possibility of “having a swell lab[11]” so that he could “knock the shine out of the Yankees![12]”  Also, with this new position he finally earned enough money to get married writing Mary, “Rejoice with me, my dear girl, for matrimony is looming in the distance.[13]”  Still, it took another year and a half to arrange the finances for their long-awaited marriage.

At McGill, an electrical engineer named “Bobby” Owens asked Rutherford for advice on what to study for an upcoming exhibition.  Rutherford suggested examining the radiation from thorium oxide in the same way that Rutherford had studied uranium.   To their shock, “The radiation from thorium oxide was not constant, but varied in a most capricious manner”, whereas “All the compounds of Uranium give out radiation which is remarkably constant.[14]”  Rutherford took over the research and quickly found that “this inconstancy is due to slow currents of air produced in an open room.[15]”  But that was crazy, no radiation that they had ever found would blow hither and thither with the breeze!  Rutherford decided the thorium must have been emanating a gas and this gas must be radioactive and decay within minutes!  JJ Thomson: “the discovery at McGill of the emanation of thorium was a stroke of genius because the new gas had to be endowed with properties not recognized as belonging to any such known substance, as it is a gas which exists for a few minutes only; half of what there is of it always disappears in less than a minute!”  Not only had Rutherford discovered the new element eventually called Radon, but he also discovered the decay pattern of radioactive materials and came up with the idea of the half-life! 

In March of 1901, Rutherford debated the existence of electrons against a young chemist named Fredrick Soddy[16].  Soddy not only lost the debate but decided to devote himself to helping Rutherford in his studies (a full 19 of Rutherford’s papers in the next 3 years were co-authored by Soddy).   Soddy went to work on determining the properties of radon.  In 1902, he tried to get it to react to any other element, but it stubbornly refused, meaning that it had to be a noble gas.  Soddy then thought it must be Argon gas (although, it turned out to be a new noble gas).  He recalled in his biography, “I remember quite well standing there transfixed as though stunned by the colossal import of the thing and blurting out…’Rutherford, the Thorium is disintegrating and transmuting itself into an argon gas.’  Rutherford replied, “For Mike’s sake, Soddy, don’t call it transmutation.  They’ll have our heads off as alchemists… Make it a transformation.[17]” Soddy then helped Rutherford use this transformation and the knowledge of “half-life” to determine the age of inanimate objects, including the Earth itself!  In 1904, Soddy got a job at the University of Glasgow and their partnership waned although their friendship was as strong as ever.  

Rutherford was incredibly successful but Rutherford still felt “rather out of things” in Canada, complaining to JJ Thomson that, “this feeling of isolation is the great drawback to colonial appointments.[18]”  Finally, in 1907, Rutherford was awarded a job at the University of Manchester and happily went back to the UK where Rutherford gained a new assistant named Hans Geiger.  [Discover the nature of alpha particles]

Even at this new “equipment and apparatus were very simple.  We built our own beta and gamma-ray electroscopes out of large tin cans, on which were placed smaller tobacco or cigarette tins[19]

Rutherford was then surprised to find that in 1908 he won the Nobel Prize in Chemistry for “investigations into the disintegration of the elements, and the chemistry of radioactive substances” (he was particularly surprised as he wasn’t a Chemist).  Unlike the Curies, however, Rutherford loved the fame and attention, and he wrote that he and his wife “had the time of our lives,” in Sweden.  Five years later, he was knighted and made a Lord, and told his 13-year-old daughter Eileen, “Henceforth, young lady, you may address me as ‘Sir Ernest’”.  Rutherford, however, was not about to sit on his laurels, he had secrets of the universe to discover.  First was proving the nature of those alpha particles.        

“Some fool in a laboratory might blow up the universe unawares”

“Don’t let me catch anyone talking about the Universe in my department”

In 1907 the cost to produce a gram of radium was over 100,000 dollars! 

The quickest transformation was the Nobel committee’s “instantaneous transmutation” of him from a physicist to a chemist!

“Geiger is a demon at the work of counting scintillations and could count at intervals for a whole night without destroying his equanimity.  I damned vigorously and retired after two minutes[20]

Roomed next to French physicist Paul Langevin (who ended up being Marie Curie’s lover after her husband’s early death).  When Langevin was asked if they were friends, he replied, “One can hardly speak of being friendly with a force of nature”

August of 1895

He loved to talk, and when one of his portraits was revealed, his wife remarked that she was stunned the artist had managed to capture him with his mouth shut!

Rutherford did a series of experiments to determine what these radiations were[1].  Eventually, he determined that Alpha radiation was helium stripped of two electrons (or a helium nucleus).  Beta radiation turned out to be fast-moving cathode rays, in other words, speedy electrons.  Gamma radiation turned out to be a high-energy electromagnetic wave, like x-rays but more powerful and more deadly.    Anyway, in his desire to figure out all about the different types of radiation, Rutherford wanted to measure the charge for an alpha particle and, in order to do that, he wanted to measure how many alpha particles he was getting overtime.  Working with a young German scientist named Hans Geiger they attempted to create a machine that would count how many alpha particles they had[2].  Unfortunately, the particles seemed to be scattered by the air molecules in the chamber.  Rutherford thought that was strange, as he knew that air particles were very heavy compared to his alpha particles.  Therefore, he decided to recreate Hertz’s experiment by bombarding a thin gold foil, but this time bombarding them with alpha particles instead of cathode rays. 

January 27, 1908 “We have detected a single alpha particle by an electric method… The method is to fire an alpha particle into a small hole covered with thin mica into a cylinder about 60 cm long where the air pressure is about 30 cm.  There is a thin central wire and a voltage is applied of about 1000 until a discharge almost passes.  Under such conditions, the ionization produced in the gas by the alpha particle is magnified 2000 times by collision.  The effect of each alpha particle is marked enough to show an audience”

At first, Rutherford and Geiger did find that the alpha particles went through thin pieces of gold and wrote a paper about how this occurred.  However, in 1909, Geiger asked Rutherford if he thought that Geiger’s graduate student named Marsden should do some research on the project.  Rutherford suggested that Marsden study the large scattering of the particles, basically, as a way to help him be familiar with the equipment as “we knew that the alpha particle was a very fast massive particle, with a great deal of energy…[so] the chance of an alpha particle’s being scattered backward was very small[21].”  A few days later, Geiger told the astonished Rutherford that some of the alpha particles did bounce backward!  Rutherford recalled, “It was quite the most incredible event that has ever happened to me in my life.  It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.[22]”  Rutherford decided that the alpha particles that bounced back must have hit something very massive and positive in the gold.  Thomson’s “plum pudding” model was completely wrong.  Electrons are not swimming in a “sea” of positive charges.  Instead, all the positive charges (which is almost all the mass) must be in a tiny spot in the middle of the atom that Rutherford called the nucleus in 1911.  It was like looking at a forest from a distance, it might seem like a solid wall of the forest, but if you walked into it, you could see that it is composed of trees that can be quite distant from their neighbor.  Of course, this analogy makes one’s head hurt when one gets to the dimensions of actual nuclei in atoms. 

See, Rutherford found that about one in 20,000 alpha particles “bounced back”.  From this, he extrapolated that the nucleus must be about smaller than the ??

, as if the nucleus was the width of a tree, in the middle of San Francisco, the next tree would be in Stanford University, over 30 miles away!  And between them, a whole bunch of nothing.  

Rutherford concluded by the percentage of alpha particles that bounced that gold (and all objects) are 99.999999999999999% nothing with the 0.0000000000000001% in a very tiny spot, the ridiculously tiny nucleus [The electrons are so small they don’t count].  To put it another way “if an atom were expanded to the size of a cathedral, the nucleus would be only about the size of a fly.[23]”  It is a mind-boggling thought.  So, if everything is basically nothing then why don’t I just fall through my chair?  Well, it comes back to those pesky electric forces again.  The electrons in the atoms in your pants push against the electrons in the atoms in the chair when they get close enough to each other.  It turns out that even things we thought were touching are actually action-at-a distance.  Just a really, really, really small distance. 

By 1920, Rutherford determined that these nuclei were filled with protons (massive positive particles), where the number of protons tells you what material you have.  By the 1930s other scientists added Neutrons (or massive neutral particles) to the nucleus that act like glue to hold the positive charges together. 

And if you think that it is strange, the world of Physics was about to go completely bat shit crazy.  And although a lot of it is the fault of a third rank patent clerk by the name of Einstein and his put upon the first wife, I will first go back a bit to a conservative Prussian named Planck who wanted to make an equation to model light from an oven. 


[1] where I am sure his graduate work with Thomson helped a lot.

[2] A study that Geiger eventually succeeded in with his Geiger counter.


[1] according to Jorgensen, Timothy Strange Glow: The Story of Radiation p. 244

[2] p 143 “Weird Scientists the Creators of Quantum Physics” Strickland

[3] according to Reeves, Richard A Force of Nature: The Frontier Genius of Ernest Rutherford p. 27

[4] The actual quote is in present tense i.e. “We don’t have the money so we have to think”  

[5] recalled by Gillespie, O and written in Reeves, Richard A Force of Nature: The Frontier Genius of Ernest Rutherford p. 29

[6] Transactions of the New Zealand Institute vol 27, 1894

[7] p 34 “Background to Modern Science” 1938 ‘Forty Years of Physics’ Rutheford

[8] Rutherford, Ernest to Newton, Mary April 24, 1895, quoted in Eve, A. S. Rutherford p. 34

[9] Rutherford, Ernest, “Uranium Radiation and the Electrical Conduction Produced by It” Philosophical Magazine p. 116

[10] Thomson, JJ quoted in Eve, A. S. Rutherford p. 55

[11] Rutherford, Ernest to Newton, Mary Aug 11, 1895, quoted in Eve, A. S. Rutherford p. 56

[12] Rutherford, Ernest to Newton, Mary Aug 3, 1898, quoted in Eve, A. S. Rutherford p. 55

[13] Rutherford, Ernest to Newton, Mary Aug 3, 1898, quoted in Eve, A. S. Rutherford p. 55

[14] Rutherford, E. Owens, R (1899) “Thorium and uranium radiation” Transactions Royal Society of Canada Vol. 2 p. 9

[15] Rutherford, E “A Radioactive Substance Emitted From Thorium Compounds” Philosophical Magazine, Jan 1900p. 1

[16] Reeves, Richard A Force of Nature: The Frontier Genius of Ernest Rutherford p. 48

[17] Soddy, Fredrick, quoted in Schwoerer, H., Magil, J. Beleites, B. Lasers and Nuclei p. 131

[18] Rutherford to Thomson March 26, 1901, quoted in Eve, A.S. Rutherford p. 77

[19] Hahn, Otto “Some Reminiscences of Professor Ernest Rutherford” The Collected Papers of Lord Rutherford of Nelson, Volume 1 p. 167

[20] Rutherford to Bumstead July 11, 1908, quoted in Eve, A. S. Rutherford p. 180

[21] p 48 “Background to Modern Science” 1938 ‘Forty Years of Physics’ Rutheford 

[22] Rutherford, Ernest “Forty Years of Physics” in Background to Modern Science, 1938 p 48 

[23] p 141 “Short history”

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