I am afraid neutrons will not be of any use to any one.

I remember the spring of 1941 to this day. I realized then that a nuclear bomb was not only possible—it was inevitable. … And I had then to start taking sleeping pills. It was the only remedy, I’ve never stopped since then. It’s 28 years, and I don’t think I’ve missed a single night in all those 28 years.

If we ascribe the ejection of the proton to a Compton recoil from a quantum of 52 x 10⁶ electron volts, then the nitrogen recoil atom arising by a similar process should have an energy not greater than about 400,000 volts, should produce not more than about 10,000 ions, and have a range in the air at N.T.P. of about 1-3mm. Actually, some of the recoil atoms in nitrogen produce at least 30,000 ions. In collaboration with Dr. Feather, I have observed the recoil atoms in an expansion chamber, and their range, estimated visually, was sometimes as much as 3mm. at N.T.P.
These results, and others I have obtained in the course of the work, are very difficult to explain on the assumption that the radiation from beryllium is a quantum radiation, if energy and momentum are to be conserved in the collisions. The difficulties disappear, however, if it be assumed that the radiation consists of particles of mass 1 and charge 0, or neutrons. The capture of the a-particle by the Be⁹ nucleus may be supposed to result in the formation of a C¹² nucleus and the emission of the neutron. From the energy relations of this process the velocity of the neutron emitted in the forward direction may well be about 3 x 10⁹ cm. per sec. The collisions of this neutron with the atoms through which it passes give rise to the recoil atoms, and the observed energies of the recoil atoms are in fair agreement with this view. Moreover, I have observed that the protons ejected from hydrogen by the radiation emitted in the opposite direction to that of the exciting a-particle appear to have a much smaller range than those ejected by the forward radiation.
This again receives a simple explanation on the neutron hypothesis.

The neutron was difficult to catch. Other particles can be seen and their actions watched, but the neutron we could not see and it left no traces of its passage.

There was, I think, a feeling that the best science was that done in the simplest way. In experimental work, as in mathematics, there was “style” and a result obtained with simple equipment was more elegant than one obtained with complicated apparatus, just as a mathematical proof derived neatly was better than one involving laborious calculations. Rutherford's first disintegration experiment, and Chadwick's discovery of the neutron had a “style” that is different from that of experiments made with giant accelerators.

In that same year [1932], the number of [known] particles was suddenly doubled. In two beautiful experiments, Chadwick showed that the neutron existed, and Anderson photographed the first unmistakable positron track.

I am glad that Dr. Chadwick has stuck to the view that it [the neutron] is a combination of a proton and electron. Some people have said it was a new kind of ultimate particle. It was really too much to believe—that a new ultimate particle should exist with its mass so conveniently close to that of the proton and electron combined. It was nothing but a bad joke played on its creator and on the rest of us. Still, there is no doubt this neutron business is going to have many developments.

The discovery [of the neutron] is of the greatest interest and importance—possibly the greatest since the artificial disintegration of the atom.

When alpha rays are photographed, the plate is all cluttered up with traces of rays which fail to reach their objective inside the atom and usually they hide the most interesting part of the picture. In the case of neutrons, [the advantage is that they are not seen, so] the photograph gives clear evidence of the disrupted atom.