Question: Who was the scientist that generated Hydrogen nuclei from reactions between nitrogen gas and alpha particles?
About the article "Atomic number", section "The proton and the idea of nuclear electrons".

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[[File:Rutherford gold foil experiment results.svg|right|upright|thumb|"Top:" Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.<br>"Bottom:" Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge.
Note that the image is not to scale; in reality the nucleus is vastly smaller than the electron shell.
]]Rutherford remains the only science Nobel Prize winner to have performed his most famous work "after" receiving the prize.
Along with Hans Geiger and Ernest Marsden in 1909, he carried out the Geiger–Marsden experiment, which demonstrated the nuclear nature of atoms.
Rutherford was inspired to ask Geiger and Marsden in this experiment to look for alpha particles with very high deflection angles, of a type not expected from any theory of matter at that time.
Such deflections, though rare, were found, and proved to be a smooth but high-order function of the deflection angle.
It was Rutherford's interpretation of this data that led him to formulate the Rutherford model of the atom in 1911 – that a very small charged nucleus, containing much of the atom's mass, was orbited by low-mass electrons.
Before leaving Manchester in 1919 to take over the Cavendish laboratory in Cambridge, Rutherford became, in 1919, the first person to deliberately transmute one element into another.
In this experiment, he had discovered peculiar radiations when alphas were projected into air, and narrowed the effect down to the nitrogen, not the oxygen in the air.
Using pure nitrogen, Rutherford used alpha radiation to convert nitrogen into oxygen through the nuclear reaction 14N + α → 17O + proton.
The proton was not then known.
In the products of this reaction Rutherford simply identified hydrogen nuclei, by their similarity to the particle radiation from earlier experiments in which he had bombarded hydrogen gas with alpha particles to knock hydrogen nuclei out of hydrogen atoms.
This result showed Rutherford that hydrogen nuclei were a part of nitrogen nuclei (and by inference, probably other nuclei as well).
Such a construction had been suspected for many years on the basis of atomic weights which were whole numbers of that of hydrogen; see Prout's hypothesis.
Hydrogen was known to be the lightest element, and its nuclei presumably the lightest nuclei.
Now, because of all these considerations, Rutherford decided that a hydrogen nucleus was possibly a fundamental building block of all nuclei, and also possibly a new fundamental particle as well, since nothing was known from the nucleus that was lighter.
Thus, Rutherford postulated hydrogen nuclei to be a new particle in 1920, which he dubbed the "proton".
In 1921, while working with Niels Bohr (who postulated that electrons moved in specific orbits), Rutherford theorized about the existence of neutrons, (which he had christened in his 1920 Bakerian Lecture), which could somehow compensate for the repelling effect of the positive charges of protons by causing an attractive nuclear force and thus keep the nuclei from flying apart from the repulsion between protons.
The only alternative to neutrons was the existence of "nuclear electrons" which would counteract some of the proton charges in the nucleus, since by then it was known that nuclei had about twice the mass that could be accounted for if they were simply assembled from hydrogen nuclei (protons).
But how these nuclear electrons could be trapped in the nucleus, was a mystery.
Rutherford's theory of neutrons was proved in 1932 by his associate James Chadwick, who recognized neutrons immediately when they were produced by other scientists and later himself, in bombarding beryllium with alpha particles.
In 1935, Chadwick was awarded the Nobel Prize in Physics for this discovery. 
In 1915 the reason for nuclear charge being quantized in units of Z, which were now recognized to be the same as the element number, was not understood.
An old idea called Prout's hypothesis had postulated that the elements were all made of residues (or "protyles") of the lightest element hydrogen, which in the Bohr-Rutherford model had a single electron and a nuclear charge of one.
However, as early as 1907 Rutherford and Thomas Royds had shown that alpha particles, which had a charge of +2, were the nuclei of helium atoms, which had a mass four times that of hydrogen, not two times.
If Prout's hypothesis were true, something had to be neutralizing some of the charge of the hydrogen nuclei present in the nuclei of heavier atoms.
In 1917 Rutherford succeeded in generating hydrogen nuclei from a nuclear reaction between alpha particles and nitrogen gas, and believed he had proven Prout's law.
He called the new heavy nuclear particles protons in 1920 (alternate names being proutons and protyles).
It had been immediately apparent from the work of Moseley that the nuclei of heavy atoms have more than twice as much mass as would be expected from their being made of hydrogen nuclei, and thus there was required a hypothesis for the neutralization of the extra protons presumed present in all heavy nuclei.
A helium nucleus was presumed to be composed of four protons plus two "nuclear electrons" (electrons bound inside the nucleus) to cancel two of the charges.
At the other end of the periodic table, a nucleus of gold with a mass 197 times that of hydrogen, was thought to contain 118 nuclear electrons in the nucleus to give it a residual charge of + 79, consistent with its atomic number.
In 1917 Rutherford bombarded nitrogen gas with alpha particles and observed hydrogen nuclei being emitted from the gas (Rutherford recognized these, because he had previously obtained them bombarding hydrogen with alpha particles, and observing hydrogen nuclei in the products).
Rutherford concluded that the hydrogen nuclei emerged from the nuclei of the nitrogen atoms themselves (in effect, he had split a nitrogen).
From his own work and the work of his students Bohr and Henry Moseley, Rutherford knew that the positive charge of any atom could always be equated to that of an integer number of hydrogen nuclei.
This, coupled with the atomic mass of many elements being roughly equivalent to an integer number of hydrogen atoms - then assumed to be the lightest particles- led him to conclude that hydrogen nuclei were singular particles and a basic constituent of all atomic nuclei.
He named such particles protons.
Further experimentation by Rutherford found that the nuclear mass of most atoms exceeded that of the protons it possessed; he speculated that this surplus mass was composed of hitherto unknown neutrally charged particles, which were tentatively dubbed "neutrons".
In 1928, Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles.
It was later discovered that this radiation could knock hydrogen atoms out of paraffin wax.
Initially it was thought to be high-energy gamma radiation, since gamma radiation had a similar effect on electrons in metals, but James Chadwick found that the ionization effect was too strong for it to be due to electromagnetic radiation, so long as energy and momentum were conserved in the interaction.
In 1932, Chadwick exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles which could not be massless like the gamma ray, but instead were required to have a mass similar to that of a proton.
Chadwick now claimed these particles as Rutherford's neutrons.
For his discovery of the neutron, Chadwick received the Nobel Prize in 1935. 
The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period.
As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms (which he called "protyles"), based on a simplistic interpretation of early values of atomic weights (see Prout's hypothesis), which was disproved when more accurate values were measured.
In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases.
However, since particles from different gases had different values of charge-to-mass ratio (e/m), they could not be identified with a single particle, unlike the negative electrons discovered by J. J. Thomson.
Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge.
This was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra.
In 1917, (in experiments reported in 1919) Rutherford proved that the hydrogen nucleus is present in other nuclei, a result usually described as the discovery of the proton.
Rutherford had earlier learned to produce hydrogen nuclei as a type of radiation produced as a product of the impact of alpha particles on hydrogen gas, and recognize them by their unique penetration signature in air and their appearance in scintillation detectors.
These experiments were begun when Rutherford had noticed that, when alpha particles were shot into air (mostly nitrogen), his scintillation detectors showed the signatures of typical hydrogen nuclei as a product.
After experimentation Rutherford traced the reaction to the nitrogen in air, and found that when alphas were produced into pure nitrogen gas, the effect was larger.
Rutherford determined that this hydrogen could have come only from the nitrogen, and therefore nitrogen must contain hydrogen nuclei.
One hydrogen nucleus was being knocked off by the impact of the alpha particle, producing oxygen-17 in the process.
This was the first reported nuclear reaction, 14N + α → 17O + p. (This reaction would later be observed happening directly in a cloud chamber in 1925).
Rutherford knew hydrogen to be the simplest and lightest element and was influenced by Prout's hypothesis that hydrogen was the building block of all elements.
Discovery that the hydrogen nucleus is present in all other nuclei as an elementary particle, led Rutherford to give the hydrogen nucleus a special name as a particle, since he suspected that hydrogen, the lightest element, contained only one of these particles.
He named this new fundamental building block of the nucleus the "proton," after the neuter singular of the Greek word for "first", πρῶτον.
However, Rutherford also had in mind the word "protyle" as used by Prout.
Rutherford spoke at the British Association for the Advancement of Science at its Cardiff meeting beginning 24 August 1920.
Rutherford was asked by Oliver Lodge for a new name for the positive hydrogen nucleus to avoid confusion with the neutral hydrogen atom.
He initially suggested both "proton" and "prouton" (after Prout).
Rutherford later reported that the meeting had accepted his suggestion that the hydrogen nucleus be named the "proton", following Prout's word "protyle".
The first use of the word "proton" in the scientific literature appeared in 1920. 
In the years 1899 and 1900, physicists Ernest Rutherford (working in McGill University in Montreal, Canada) and Paul Villard (working in Paris) separated radiation into three types: eventually named alpha, beta, and gamma by Rutherford, based on penetration of objects and deflection by a magnetic field.
Alpha rays were defined by Rutherford as those having the lowest penetration of ordinary objects.
Rutherford's work also included measurements of the ratio of an alpha particle's mass to its charge, which led him to the hypothesis that alpha particles were doubly charged helium ions (later shown to be bare helium nuclei).
In 1907, Ernest Rutherford and Thomas Royds finally proved that alpha particles were indeed helium ions.
To do this they allowed alpha particles to penetrate a very thin glass wall of an evacuated tube, thus capturing a large number of the hypothesized helium ions inside the tube.
They then caused an electric spark inside the tube, which provided a shower of electrons that were taken up by the ions to form neutral atoms of a gas.
Subsequent study of the spectra of the resulting gas showed that it was helium and that the alpha particles were indeed the hypothesized helium ions.
Because alpha particles occur naturally, but can have energy high enough to participate in a nuclear reaction, study of them led to much early knowledge of nuclear physics.
Rutherford used alpha particles emitted by radium bromide to infer that J. J. Thomson's Plum pudding model of the atom was fundamentally flawed.
In Rutherford's gold foil experiment conducted by his students Hans Geiger and Ernest Marsden, a narrow beam of alpha particles was established, passing through very thin (a few hundred atoms thick) gold foil.
The alpha particles were detected by a zinc sulfide screen, which emits a flash of light upon an alpha particle collision.
Rutherford hypothesized that, assuming the "plum pudding" model of the atom was correct, the positively charged alpha particles would be only slightly deflected, if at all, by the dispersed positive charge predicted.
It was found that some of the alpha particles were deflected at much larger angles than expected (at a suggestion by Rutherford to check it) and some even bounced almost directly back.
Although most of the alpha particles went straight through as expected, Rutherford commented that the few particles that were deflected was akin to shooting a fifteen-inch shell at tissue paper only to have it bounce off, again assuming the "plum pudding" theory was correct.
It was determined that the atom's positive charge was concentrated in a small area in its center, making the positive charge dense enough to deflect any positively charged alpha particles that came close to what was later termed the nucleus.
Note: Prior to this discovery, it was not known that alpha particles are themselves atomic nuclei, nor was the existence of protons or neutrons known.
After this discovery J.J. Thomson's "plum pudding" model was abandoned, and Rutherford's experiment led to the Bohr model (named for Niels Bohr) and later the modern wave-mechanical model of the atom.
Rutherford went on to use alpha particles to accidentally produce what he later understood as a directed nuclear transmutation of one element to another, in 1917.
Transmutation of elements from one to another had been understood since 1901 as a result of natural radioactive decay, but when Rutherford projected alpha particles from alpha decay into air, he discovered this produced a new type of radiation which proved to be hydrogen nuclei (Rutherford named these protons).
Further experimentation showed the protons to be coming from the nitrogen component of air, and the reaction was deduced to be a transmutation of nitrogen into oxygen in the reaction 14N + α → 17O + p  This was the first-discovered nuclear reaction.
To the pictures on the right: According to the energy-loss curve by Bragg it is recognizable that the alpha particle loses indeed more energy on the end of the trace.