May you explain the discovery of the neutron and the proton?

Question

May I have a few bits of information on the discovery of the neutron and the proton, to get me started on a Physics essay.

Answer 1

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proton has a + charge and a neutron has a netural charge

Answer 2

Start with Rutherford. Look up his experiment and how he figured out that all the positive charge in the atom is concentrated in a tiny nucleus instead of being smeared out through the atom.

Rutherford went on to discover that this positive charge is due to the proton.

The neutron doesn't have a charge, so it doesn't affect charges the way protons do. So how was it discovered? That was due to James Chadwick, who was experimenting with radioactivity like Rutherford. He figured out that he was observing neutral particles and calculated what their mass had to be.

That should give you plenty to search on. You should probably get the details on both Chadwick's and Rutherford's experiments and the deductions from those.

Answer 3

Ernest Rutherford is generally credited with the discovery of the proton. In 1918 Rutherford noticed that when alpha particles were shot into nitrogen gas, his scintillation detectors showed the signatures of hydrogen nuclei. Rutherford determined that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggested that the hydrogen nucleus, which was known to have an atomic number of 1, was an elementary particle.

In 1931 Walther Bothe and Herbert Becker in Germany found that if the very energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. At first this radiation was thought to be gamma radiation, although it was more penetrating than any gamma rays known, and the details of experimental results were very difficult to interpret on this basis. The next important contribution was reported in 1932 by Irène Joliot-Curie and Frédéric Joliot in Paris. They showed that if this unknown radiation fell on paraffin or any other hydrogen-containing compound it ejected protons of very high energy. This was not in itself inconsistent with the assumed gamma ray nature of the new radiation, but detailed quantitative analysis of the data became increasingly difficult to reconcile with such a hypothesis.

Finally, in 1932 the physicist James Chadwick in the George Holt building at the University of Liverpool performed a series of experiments showing that the gamma ray hypothesis was untenable. He suggested that in fact the new radiation consisted of uncharged particles of approximately the mass of the proton, and he performed a series of experiments verifying his suggestion. These uncharged particles were called neutrons, apparently from the Latin root for neutral and the Greek ending -on (by imitation of electron and proton).

The discovery of the neutron immediately explained a known puzzle involving the spin of the nitrogen-14 nucleus, which had been experimentally measured to be 1 basic unit of angular momentum. It was known that atomic nuclei usually had about half as many positive charges as if they were composed completely of protons, and in existing models this was often explained by proposing that nuclei also contained some "nuclear electrons" to neutralize the excess charge. Thus, nitrogen-14 would be composed of 14 protons and 7 electrons to give it a charge of +7 but a mass of 14 atomic mass units. However, it was also known that both protons and electrons carried an intrinsic spin of 1/2 unit of angular momentum, and there was no way to arange 21 particles in one group, or in groups of 7 and 14, to give a spin of 1. All possible pairings gave a net spin of 1/2. However, when nitrogen-14 was proposed to consist of 3 pairs of protons and neutrons, with an additional unpaired neutron and proton each contributing a spin of 1/2 in the same direction for a total spin of 1, the model became viable. Soon, nuclear neutrons were used to naturally explain spin differences in many different nuclides in the same way, and the neutron as a basic structural unit of atomic nuclei was accepted.