1932 February, when British physicist chadwick read Iorio Curie's paper on "bombarding beryllium with A particles will produce uncharged particles with strong penetrating power", he was keenly aware that it was wrong to explain this phenomenon with Compton effect of strong gamma rays. Chadwick repeated the experiments of Aurio and Curie, and successively used this radiation to irradiate several elements with different weights. The results show that this kind of radiation is really not gamma rays: because the lower the density, the easier it is to be absorbed, unlike gamma rays, which are easily absorbed by substances with high density; Moreover, this ray will bounce back when it bombards the hydrogen nucleus, indicating that it is a neutral particle flow with a certain mass. By measuring the momentum of recoil nucleus and using the law of conservation of momentum, chadwick estimated that the mass of recoil nucleus is almost the same as that of proton. At this point, chadwick combined intuitive knowledge, logical thinking and experimental research, and boldly pointed out that this kind of beryllium radiation was the "neutron" that Rutherford had predicted and he had been looking for for for a long time. 1932 February 17, chadwick announced the discovery of "neutron".