Man's physical universe



at a cost of about $400 per ounce; and heavy carbon, atomic weight 13,

as compared with ordinary carbon of atomic weight 12, was made

available at $400 per ounce. Nitrogen of atomic weight 15 was first

separated in 1937. It may now be obtained at about the same cost as

that of carbon of atomic weight 13.

Nonradioactive Elements Have Been Disintegrated by Bombardment

with High-speed Particles.

In 1919 Ernest Rutherford was able to produce protons by the bombardment

of nitrogen atoms with alpha particles. Later he found that

when bombarded by alpha particles, the nuclei of some other elements

would emit protons, while those of certain others would not.

Since 1930 it has been observed that very penetrating radiations are

produced when alpha particles from radioactive elements, such as

polonium, fall upon beryllium or boron. In 1932 Chadwick showed

that this radiation consists of particles of about the same mass as protons

but having no charge. He called these particles neutrons. The

neutron's mass corresponds to that of ordinary hydrogen (now sometimes

called protium). The neutron thus corresponds to an element

with an atomic number of zero.

E. O. Lawrence and M. Stanley Livingston, of the University of California,

have produced rays consisting of a stream of about 10,000,000

neutrons per second, produced by bombardment of beryllium with

high-speed deuterons. (Deuterons are the positively charged nuclei of

deuterium.) These rays are found to be more penetrating than X rays

or gamma rays and will destroy both plant and animal life.

In 1932 Carl D. Anderson, of the California Institute of Technology,

announced the discovery of a positive electron, now called the positron.

This particle has the same mass as the negative electron — i.e.,

1/1845 the mass of the proton — but its charge is positive rather than


In 1937 physicists studying cosmic rays discovered the mesotron

(heavy electron), which is 150-180 times as heavy as the electron but

has the same charge as an electron.


1931 swiftly moving protons, accelerated by traversing electrical

fields of high potential differences, have replaced alpha particles

as projectiles. Since 1932 deuterons and neutrons have also been

employed as projectiles. With these projectiles a great many interesting

transformations have been accomplished; thus, lithium has been

converted into helium, and a large number of other nuclear reactions

have been brought about. About sixty elements have been transmuted

by means of the neutron. The significance of all these trans-

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