The New York herald., 1922-07-02

I are present in such relative proper
tions as to make the average atomic
weight s5.46. These different kinds OF
chemically similar atoms. with differ
ent masses, are called isotopes. 1t has
been found that isotopes exist In a
large number Of the chemical ele.
ments, but that the weight Of every
| individual atom or Nisotope Is an exact
multiple of that of the fundamental
unit.
| If positive electrons. or the massive
part of hydrogen atoms, are parts OF
the structure of all atoms we might
expect to be able to break up heavier
atoms into hydrogen. This has ac-
tually been done by Prof. Rutherford
in the case Of nitrogen, aluminium and
number of other elements.
How EIectrons Are Arranged In
Atoms by Rutherford Method d
Thus we have both direct and In
direct evidence that atoms are struc-
lures built out of positive and mega
tive electrons. The next question is,
How are these electrons arranged In
the various atoms?" A good deal is
known about this arrangement, as l
shall proceed to indicate. but there is
much more which Is still unknown.
The Nuclear Structure of Atoms
Radium and the other radioactive ele-
ments owe their unusual properties to
the fact that they emit positively and
negatively charged particles, called A
and B particles respectively, with tre-
mendous velocities. By the bending
of their paths In electric and magnetic
fields, or by other methods, it is found
that the B particles are negative cleo
irons which have velocities as large as
81 per cent. of the velocity Of light, or
about 10000 miles per second. Sim
larly, the A particles are atoms of
helium which have lost two negative
electrons and which consist. therefore,
Of four positive and two negative cleo
irons, forming very compact and
stable group. These have veiocities as
large as about one-tenth that of light.
The B particles set up oscillations OF
negative electrons In neighboring
atoms which they strike, and these
oscillations produce radiation called
Y radiation or wave motion in the
ether. The atoms Of radium do not
explode" In this manner frequently.
In fact the occurrence is so rare that
the chances are even that any given
atom will or will not explode within a
time of 1000 years. When 1t does
explode there remains not an atom of
radium (atomic weight 226), but an
atom of radium emanation (atomic
weight 222) and particle (helium.
atomic weight A..
In spite of their smaller velocity the
A particles possess much greater
kinetic energy than do the B particles.
being nearly 7,400 times heavier. 1t
was by means of bonbardment of
nitrogen and other atoms by these A
particles that Prof. Rutherford has
effected their atomic disintegration,
yielding hydrogen as a product.
When the A particles shoot out
through a gas. such as air, their paths
may be seen and photographed, pro-
vided the air is saturated with water
vapor and suddenly cooled by expan-
sion. The air molecules in the path of
the A particles have negative cleo
irons forced out of them by the action
of the positively charged A particle as
it comes very close. These positively
and negatively charged residues Of the
air molecules serve as nuclei for the
condensation of water vapor. Thus
the path of the A particle is visible as