Neutron

There most probably is a neutron, smallest bit, last resolvable particle of Matter. Last Summer when Dr. W. Pauli of Zurich propounded the idea at Pasadena, the fact was less certain (TIME, June 29). Last week there was almost no doubt. Dr. James Chadwick of Cambridge University's Cavendish Laboratory, brightest spot of British science, declared for the existence of neutrons. Ernest Baron Rutherford, director of the Cavendish Laboratory, confirmed the investigation. And no brash statements ever come from Professor Rutherford, 1908 Nobel Laureate, the man who established the existence and nature of radioactive transformations, the electrical structure of all matter, the nuclear structure of atoms.

It was by following the clues of radio-activity that Drs. Pauli and Chadwick separately reached their conclusions. Recently Professor Walther Bothe of Giessen, Germany, bombarded the element beryllium with alpha particles. Something happened to the alpha particles. The particles contained four units of positive electricity (protons) and two of negative electricity (electrons) when they crashed into the beryllium. Two protons of an alpha particle seemed to cling to the nucleus of a beryllium atom (thereby theoretically transmuting that atom of beryllium into an atom of carbon). The particle's other two protons and the two electrons seemed changed into what Professor Bothe considered an artificial gamma ray, which like a light ray is an electromagnetic phenomenon.

Dr. Pauli, on his part, observed that when beta rays pop away from a substance like radium, the substance loses a certain amount of energy. But the energy of the departing rays is always less than the substance's energy loss. What happens to the difference? Dr. Pauli surmised that it rides away on what he called a neutron.

Dr. Chadwick repeated the Bothe experiment at his Cavendish Laboratories last week. Protons and electrons were on the loose. What might happen to them?

A proton, which is 1,845 times as heavy as an electron, might make an electron its satellite. Such a simple system of one electron revolving around one proton makes up a common atom of hydrogen, simplest of the 92 elements. (Helium, next simplest, has an alpha particle for its core, two electrons for satellites. Other atoms have more protons, more electrons.)

In another possible arrangement, the electrically positive proton might join with the negative electron. Generally, physicists believe, the two cancel each other. Their energy disappears. But last week Dr. Chadwick thought, "not always." The proton and electron in such case may join together like the knobs of a dumbbell.

That is the neutron. It lacks electrical characteristics. The charges of proton and electron have bound and balanced each other. A particle has been formed halfway between nascent electricity and atomic hydrogen. It hops out of radioactive substances as do alpha particles.

Neutrons move much faster than alpha particles, and they have great penetrating powers. They can travel through a mile of air, several feet of lead. They apparently weigh 200,000,000,000,000,000,000,000 to the ounce. It is only by the finest of discernment that they can be distinguished from unentangled quanta of energy. Streams of them may be what Dr. Robert Andrews Millikan calls cosmic rays. But Dr. Chadwick doubts that. Neutrons may be, because they have opposite poles, the long sought units of magnetism. Whatever they are, neutrons are fine things for physicists to play with and to guess about. They are, declared Lord Rutherford last week, the greatest discovery since the artificial disintegration of the atom.

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