When was the proton found

This scientific phenomenon was described by William Bragg at that time. In , the American physicist Ernest O. Lawrence and his associates were the first to invent the cyclotron to accelerate proton to an energy high enough for cancer treatment applications.

A decade later, his advanced version of the synchrocyclotron, which is inches in diameter, is capable of producing MeV protons Figure 2. Figure 1 American physicist Ernest O. Lawrence [], photographed in adjusting the ion source of his inch cyclotron.

Chadwick's own research focused on radioactivity. In Rutherford had discovered the proton, a positively charged particle within the atom's nucleus. But they and other researchers were finding that the proton did not seem to be the only particle in the nucleus.

As they studied atomic disintegration, they kept seeing that the atomic number number of protons in the nucleus, equivalent to the positive charge of the atom was less than the atomic mass average mass of the atom.

For example, a helium atom has an atomic mass of 4, but an atomic number or positive charge of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass. One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons.

So in the helium example, there would be four protons and two electrons in the nucleus to yield a mass of 4 but a charge of only 2. Unfortunately, not long after he arrived, WWI broke out and Chadwick ended up spending the next four years in a prison camp there.

This did not entirely stop his scientific studies. To keep from being bored, he and some fellow prisoners formed a science club, lectured to each other, and managed to convince the guards to let them set up a small lab. Though many chemicals were hard to get hold of, Chadwick even found a type of radioactive toothpaste that was on the market in Germany at the time, and managed to persuade the guards to supply him with it.

Using some tin foil and wood he built an electroscope and did some simple experiments. Chadwick was able to continue to work on radioactivity, now with more sophisticated apparatus than tin foil and toothpaste. In , Chadwick was appointed assistant director of Cavendish Laboratory. Rutherford had discovered the atomic nucleus in , and had observed the proton in However, it seemed there must be something in the nucleus in addition to protons. For instance, helium was known to have an atomic number of 2 but a mass number of 4.

Some scientists thought there were additional protons in the nucleus, along with an equal number of electrons to cancel out the additional charge. In , Rutherford proposed that an electron and a proton could actually combine to form a new, neutral particle, but there was no real evidence for this, and the proposed neutral particle would be difficult to detect.

Chadwick went on to work on other projects, but kept thinking about the problem. Around , several researchers, including German physicist Walter Bothe and his student Becker had begun bombarding beryllium with alpha particles from a polonium source and studying the radiation emitted by the beryllium as a result.