CHAPTER 12
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ALPHA, BETA AND GAMMA RAY3
12—1.
The Nature of Alpha Particles.—The charge of an alpha
particle is determined by measuring the total charge carried by a
measured number of particles. In the apparatus of gure 12—1,
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alpha particles are emitted in all directions from the radioactive
material (X).
The entire apparatus is evacuated, except the
interior of G, in order to eliminate the ionization which would be
produced by the alpha particles. At rst, a magnetic eld is
applied perpendicularly to the plane of the paper and over the
area indicated by the circle, so that all alpha particles which leave
the source in the solid angle 9 are caught in the Faraday chamber
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12—1.
Apparatus used to determine the charge of the alpha
(F)
Thecha‘rge collected in F each second is measured by means
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elec'trometer (E). This current, multiplied by the
theSOlid angle of a sphere around X (= 47r) to the solid angle6,
is equal
the total charge which leaves the source each second
@ In
a magnetic eld, some of the alpha part1cles
(G)Thlscountercon31sts of a
poin—ted Wire, suchaS
WlthreSPe°“®thecyïmdrmaltubesothat a discharge 0felec