Man's physical universe

xanabras

ATOMS ARE COMPLEX 575

mutation experiments is that they show that all of the elements are

composed of the same material.

In 1940 element 93 of atomic weight 239 was identified. It was produced

by bombarding uranium, element 92, of atomic weight 238, with

neutrons; thus an element

heavier than any previously

known element was produced.

Since that time E.

Fermi and his co-workers

have similarly produced

elements 94 and 95.

In 1940 plans were made

by E. 0. Lawrence to build a

powerful cyclotron, dwarfing

all others by three

times in linear dimensions,

whose huge electromagnet

alone would weigh about

4000 tons; 300 tons of

copper will

windings.

be used in the

Fig. 275.

The 200-ton cyclotron at the University

of California produces atomic particles

with energies as great as 32,000,000 electric

volts. (Courtesy of Ernest O. Lawrence.)

Artificial Radioactivity Is Now a Reality.

In 1934 Madame Irene Curie-Joliot, the daughter of Madame Marie

Curie, and her husband, F. Joliot, discovered that ordinary inactive

elements such as aluminum,

boron, and magnesium,

when bombarded with alpha

rays, were transformed into

substances which exhibited

radioactivity for varying

periods of time after the

bombardment ceased.

Since that time other

workers have produced artificial

or induced radioactivity

by use of protons,

deuterons, and neutrons

Fig. 276. A beam of deuterons with an enr

i

ergy of 16,000,000 electron volts, produced Lawrence, at the University

by the University of California 200-ton of California, has produced

cyclotron. (Courtesy of Ernest O. Lawrence.) radioactive sodium. It is

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