University of Frankfurt picture gallery http://www.Th.physik.uni-frankfurt.de/~jr/physpicexp1.html

Professor S. Devons Reminisces on Rutherford's Lab http://www.phy.cam.ac.uk/cavendish/history/years/rutherford.asp  "Students in 1930 were not particularly docile (intellectually at least), so that although, as young neophytes in the presence of the most eminent authority and a benevolently and vigorously magisterial personality, we were always attentive, respectful, and at times a little awestruck, yet we were not wholly and uncritically receptive. To us, Rutherford, then in his sixties, appeared as a patriarchal figure, somewhat archaic, vaguely Victorian in dress and manner - and youth is always apt to feel indulgent in paying its respects to age and  experience. " "Rutherford's own attitude to physical problems was always unambiguously expressed. There was always the demand for the "objective" and, if possible, simple reality. Almost invariably there was the question "What are the facts?". Facts were to be respected and treated quite differently from theory, which was, in a sense, "opinion"." "Rutherford's emphasis on simplicity is proverbial: ("I'm a simple man myself.... "). Simple ideas and simple apparatus, but powerful, conclusive results; simple, unpretentious appearances, but striking inferences: these were the Cavendish trademarks. " "As a research novitiate, either one had to make one's own apparatus, using hand (or foot) operated tools and bits of metal and wood that had been used and reused by generations of research students, or one might inherit and make do with the residue of some earlier research. And of course, one was expected to be able to do one's own glass blowing. " "One would receive occasionally, perhaps once or twice a year, a more-or-less unannounced visit from Rutherford at one's working bench. He would briefly examine the apparatus and then would seat himself on a laboratory stool and put one through a quite searching examination: "What, precisely, are you doing? How? Why?" And of course this led rapidly to the request "Now let's see what the results are."  "... Rutherford's real interest was in the results of experiments and not the methods or techniques or difficulties themselves. However, on the few occasions when, as a very junior research student, I was cross-examined, I recall being very much impressed by the questions and criticisms regarding both the aim and the methods of my work. In a few thrusts Rutherford's questions penetrated right through the limits of my own thinking and stimulated me to do some more. He was clearly acting in the role of teacher, not critic, and the results of his uncompromising, but not hostile, questioning were undoubtedly salutary. This was all very much in keeping with his expressed attitude towards teaching: a student should think for himself, should  ask himself questions; a teacher should not so much supply answers as encourage the student to pose questions to himself. "

J.J Thompson and E. Rutherford

The ability of x-rays  to discharge electrically charged bodies led J.J Thompson to suppose that the x-rays split apart gas molecules into pairs of "ions". Left to their own these ions would recombine, but in the presence of an electrically charged body the ions would drift apart under the action of the electric field to neutralize the charged body.

"On the Passage of Electricity through Gases Exposed to Roentgen Rays",
J.J. Thompson and E. Rutherford in The Philosophical Magazine [5], 1896, 42:392-407
"On the Electrification of Gases Exposed to Roentgen Rays, and the Absorption of Roentgen Radiation by Gases and Vapours", E. Rutherford in The Philosophical Magazine [5], 1897,43:241-255
"The Velocity and Rate of Recombination of the Ions of Gases Exposed to Roentgen Radiation", E. Rutherford in The Philosophical Magazine [5], 1897, 44:422-440
In order to test this hypothesis Thompson brought in as a research student a brilliant young New Zealander, E. Rutherford, to the Cavendish lab at Cambridge. Thompson and Rutherford started experimental work on conduction in gases, but Rutherford went on alone with experiments that drew both the positive and negative species of ions from the gas, determined the rate at which they were produced, their recombination rate, and the speed with which they move in an electric field. In fact, Rutherford found that there was an upper limit to the rate at which an ion could be forced to move in a gaseous conductor.

"Uranium Radiation and the Electrical Conduction Produced by It",
E. Rutherford in The Philosophical Magazine [5], 1899, 47:109-163
In 1898 Rutherford began to investigate in detail the effect of Becquerel's rays on gases, since these were also know to cause elctrified bodies to discharge. He concluded that both x-rays and Becquerel's rays produced ion species of the same type. He found that the rays from Uranium were of two categories. He named the first group "alpha rays", which were easily stopped but produced a high denisty of ionization. The second group he named the "beta rays", which appeared to penetrate the same way that x-rays dir, but produced a lower ionization density than alpha rays.

In the Summer of 1899 Rutherford was appointed as a Macdonald Professor of Physics at McGill University in Montreal. He started a collaboration with R. B. Owens, a professor of electrical engineering. Owens wanted to study the ionization power of the rays from Thorium. In 1898 it had been independently discovered by G. Schmidt in Germany, and M. Curie in France that Thorium too emitted penetrating rays like Uranium. Owens's results on the ionizing power of thorium were at first erratic. There were sudden shifts in the ionization of the air produced by his samples of thorium oxide. For example, even the opening of the door to the laboratory could cause the ionization to diminish significantly. Eventually Owens traced the cause to air currents. If he closed his system in a box, and blew air through the box he could reduce the level of radioactivity. If he left the oxide sample quiet for a period of about 1/4 hour, it would regain its previous activity. Owens left this puzzling situation in Rutherford's hands.

"A Radio-active Substance Emitted by Thorium Compounds", E. Rutherford in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science [5], 1900, 49:1-14
"Radioactivity Produced in Substances by the Action of Thorium Compounds", E. Rutherford in The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science [5], 1900, 49:161-192
In these papers he showed that the radioactivity was not induced into the air surrounding the thorium oxide samples. It had rather to be of a substantial, material nature. He shows in this paper that the radioactivity induced on objects distant from the thorium oxide does is not produced directly by the thorium oxide. Rather, there is an "emanation" from the oxide which has the power to induce substance to become radioactive.
"The phenomena exhibited by thorium compounds receives a complete explanation if we suppose that, in addition to the ordinary radiation, a large number of radio-active particles are given out from the mass of the active substance. This "emanation" can pass through considerable thicknesses of paper. The radio-active particles emitted by the thorium compounds gradualy diffuse through the gas in its neighborhood and become centres of ionization throughout the gas."

"The emanation gradually loses its radioactive-power."
(The emanation, we now know is from Radon-220.)

Rutherford measured the decay curve for the emanation and fitted it to an exponential curve. Rutherford introduces the concept of half life. The emanation has a half life of about one minute.

"The emanation passes through a plu of cotton-wool without any loss of its radioactive powers. It is also unaffected by bubbling through hot or cold water, weak or strong sulfuric acid. In this respect it acts like an ordinary gas."

The nature of the emanation is uncertain. They were still trying to determine if this was a chemical effect, which was the only kind of effect they had a reason to expect.
"The emanation may possibly be a vapour of thorium. If the radio-active powers of thorium is possessed by the molecules of the sunstance , it would be expected that the vapour of the substance would be itself radio-active..."

"Experiments, which are still in progress, show that the emanation possesses a very remarkable property. I have found that the positive ions produced in a gas by the emanation possess the power of producing radio-activity in all substances on which it falls."
(We note that the Curies also noted this effect because Pierre complained that everything in their laboratory was beginning to show signs of radioactivity.)

"In order to confine the induced radioactivity produced by thorium compounds to any particular conductor, it is necessary that it should be charged -(negative) and all other bodies in the field +(positive).

Rutherford also shows in these papers that the half-lives from the induced radioactivty and the thorium emanation are different. He attempted to affect the properties of the radioactive surfaces by mechanical and chemical actions. The induced radioactivity was found to be on the surface of exposed materials. Many chemical tests were performed on a platinum surface he had exposed. The resulting loss of radioactivity from the surafce was mixed. Sometimes the surface lost its radioactivity, othertimes not. In those cases where the surface lost its radioactivity he found that the residue was strongly radioactive. He could change the amount of radioactivity on the surface, but this appeared somewhere else. The total radioactive power was not lost.

Rutherford mentions that phosphorescence, as an explanation of the induced radioactivity, is not consistent with his results on thorium. He mentions a contemporary paper by Curie in which Curie suggests that the radioactivity induced by thorium or uranium compounds is possibly a phophorescence.

Transmutation of the Elements !
In 1900 and 1901 Rutherford continued investigating the emanation from thorium, and a similar one from radium (²²⁶Ra). A young chemist, Frederick Soddy, joined his research group at McGill. This collaboration was an intensive chemical analysis into the radioactive power of thorium.
Because of the complex chain of decays, the fact that they had no model of the atom which could explain radioactivity, and the extremely small quantities of active material responsible for radioactivity there were cases of error in their conclusions. For example,
- Rutherford had concluded that the emanation from radium, ²²²Rn, had an atomic mas between 40 and 100.
In the following paper Rutherford and Soddy come to an ambigous/contradictory conclusion about the source of the thorium emanation and radioactivity.
There are three points made:
1) The emanation is from thorium, and not from something else mixed in with it. (See point 4 !)
2) Thorium oxide which had been highly heated could have its emanating "power" restored if it was converted to a soluble compound, dissolved in water, and recovered from solution.
3) The emanation has the chemical behavior of an inert gas of the argon series.
4) There is a component, they called ThX, which also possesses the radioactivity and emanation of thorium. (See point 1 !)

"The Radioactivity of Thorium Compounds - I. An Investigation of the Radioactive Emanation", E. Rutherford and F. Soddy in, Journal of the Chemical Society, Transactions, 1902, 81: 321-350
After a sequence of chemical preparations they ask if the radioactive residue has the same properties of radioctivity as thorium. They answer this in a way that points to future nuclear spectroscopic techniques.
"If the rays from various radioactive substances are made to pass through successive layers of aluminum foil ... a curve can be plotted with the thickness of metal penetrated as abscissae, and the intensity of the rays after penetration as ordinates... . The curves so obtained are quite different for different radioactive substances. The radiations from uranium, radium, thorium, each give distinct  and characteristic curves, whilst that of the last named is again is quite distinct from that given by the exicted radioactivity produced by the thorium emanation."

There was no known mechanism by which the energy released by radioactive substances could be accounted for. There were no apparent external sources of energy, as there were for the case of phophorescence. The Curies produced a list of several current models, among which they listed transformation of radioactive elements. They were not in favor of this idea. Some comments from one of their papers:
"Sur les corps radio-actifs", by P. Curie and Mme S. Curie, in Compte rendus de l'Academie des Sciences, Paris, 1902, 134:85-87 (13 January)

"Since the beginning of our research, we have taken radioactivity to be an atomic property of substances."

"Each atom of a radioactive substance functions as a constatnt source of energy."

"Experiments over several years show that for uranium, thorium, radium, and probably also actinium, the radiant activity is rigorously the same every time the radioactive substance is brought back to the same chemical and physical state, and that this activity does not vary with time."

"If we seek to fix the origin of the energy of radioactivity, we make may make various assumptions, which group around tow quite general hypotheses:
(1) each radioactive atom possess in the form of potential energy the energy it releases;
(2) the radioactive atom is a mechanism which at each instant draws in from outside itself the energy it releases.

"According to the first hypothesis, the potential energy of radioactive substances should at length exhaust itself. although the experience of several years has shown no variation up to the present. ... After four months no variation can be observed in the weights of radium-bearing substances... .
The theories of Perrin and Becquerel are likewise theories of atomic transformation. Perrin likens each atom to a planetary system from which certain negatively charged particles could escape. Becquerel explains induced radioactivity by a progressive and complete dismemberment of the atoms."

"The hypotheses of the second group ... are those according to which radioactive ubstances are transformers of energy. This energy might be borrowed, in violation of Carnot's principle, from the heat of the surroundings medium, which would undergo cooling. It might again be borrowed from unknown sources, for example from radiations unknown to us. it is indeed probable that we know little about the medium that surrounds us, since our knowledge is limited to phenomena which can affect our senses, directly or indirectly."

In January 1902 after the Christmas break Soddy and Rutherford return to their laboratories to try and make sense out of ThX. With their new extremely pure thorium nitrate from Germany they discovered that ThX was being produced from thorium at a steady rate ( half life 14GY). ThX then decayed by an exponential law of decay. From this they concluded that thorium X came into being as a transmutation of thorium! This conclusion was radical. It contradicted the view of the Curies and also the long held belief, based mainly on experience, that the "elements" could not transform. This would, obviously, not make them elements! The conclusion was so radical that Rutherford in Montreal felt compelled to write to Crookes asking his help in making sure the publication of the paper was not delayed.

"The Radioactivity of Thorium Compounds - II. The Cause and Nature of Radioactivity", E. Rutherford and F. Soddy in, Journal of the Chemical Society, Transactions, 1902, 81: 837-860
"The position is thus reached that radioactivity is at once an atomic phenomenon and the accompaniment of a chemical change in which new kinds of matter are produced. The two considerations force us to the conclusion that radioactivity is a manifestation of subatomic chemical change."

"There is not the least evidence for assuming that uranium and thorium are not as homogeneous as any other chemical element, in the ordinary sense of the word, so far as the action of known forces is concerned. The idea of the chemical atom in certain cases spontaneously breaking up with the evolution of energy is not of itself contrary to anything that is known of the properties of the atoms, for he causes that bring about the disruption are not among those that are yet under our control, whereas the universally accepted idea of the stability of the chemical atom is based solely on the knowledge we possess of the forces at our disposal."

"... the existence of radioactive elements at all in the earth's crust is an apriori argument against the magnitude of the change being anything but small."

"It is a significant fact that the radioactive elements are all at the end of the periodic table. If we suppose that radium is the missing second higher homologue of barium, then the known examples - uranium, thorium, radium, polonium(bismuth), and lead are the five elements of heaviest atomic weight."

"... it seems not unreasonable to hope that radioactivity affords the means of obtaining information of processes occurring within the chemical atom."

In a subsequent submission of the same articel to the Philosophical Magazine( so that physicists would hear the news too) that added a brief section suggesting that the energy emitted in radioactivie decay came out all at once at the time of the transformation.

The Energy Of Radioactivity
Soddy and Rutherford then turned to measuring the energy given off in radioactive decay. Rutherford had determined that the alpha rays coming out of radioactive decay were material bodies consisting of heavy positively charged particles(Phil. Mag. Feb. 1903). He had obtained e/m = 6x10³ for the alpha particles. This is compared to e/m = 10⁴ for the hydrogen atom and e/m = 10⁷ for cathode rays. They conclude that 99% of the energy of the decay is carried away by the alpha particles. For radium they estimated the power output of 1 gram of pure radium as 8200 ergs/sec. They argued that the energy emitted for all the radioactive elements is about the same per alpha particle and conclude that radium's higher power output must mean that radium has a much shorter life time than uranium, on the order of a few thousand years.
"Radioactive Change", by E. Rutherford and F. Soddy in,
The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science [6], 1903, 5:576-591
"If elements heavier than uranium exist it is probable that they will be radioactive. The extreme delicacy of radioactivity as a means of chemical analysis would enable such elements to be recognized even if present in inifitesimal quantity."

"The maintenance of solar energy... no longer presents any fundamental difficulty if the the internal energy of the component elements is considered to be available,i.e., if processes of sub-atomic change are going on."

The alpha particle is recognized as as the helium atom.
Rutherford and Soddy pointed out that the invariable presence of helium in minerals containing uranium indicate that helium might be an end product in radioactive decay (Phil. Mag., 1902, p.582; 1903, p.453 and p 579)

Soddy left Rutherford at McGill to work with William Ramsay. They tested the Soddy- Rutherford hypothesis about helium being an end product of radioactive decay. They examined spectroscopically the gases occulded by radium bromide in the solid state and showed that helium was being formed. There was no doubt about transmutation now.
"Gases Occluded by Radium Bromide", by W. Ramsay and F. Soddy, in
Nature, 1903, 68: 246

In May of 1904 Rutherford was invited to present the Bakerian Lecture to the Royal Society on the transmutation theory. This was a detailed exposition of radioactive decay explaining the intermediate steps of shorter lived products. The lecture appeared under:
"The Succession of Changes in Radioactive Bodies", by E. Rutherford, in
Philosophical Transactions of the Royal Society of London, A, 1905,
204:169-219