6.
Di
ff
erentiation of Radiation Types
Di
ff
erentiation of ALPHA, BETA and GAMMA radiation is relatively easy with regard to ALPHA
radiation. ALPHA radiation involves helium nuclei with two positive charges which themselves
have a short range even in air - max. 10 cm and usually not more than 5 cm.
The ALPHA component of radiation can be determined by 2 measurements using the end
window counter tubes (A or G) in which one measurement is carried out with open end window
and the other measurement with an open window which is however covered by a thin
transparent film. The thin transparent film shields against ALPHA particles, so the ALPHA
radiation component follows from the di
ff
erence between the two measurements. If ALPHA
radiation is present the first measurement without transparent film must be correspondingly
higher. The distance for these measurements should be 5 mm.
Separating the BETA radiation from the GAMMA radiation is not so simple because complete
shielding against BETA radiation already absorbs part of the GAMMA radiation even at the
higher energy levels. The BETA radiation up to roughly 1.5 MeV can be shielded by Plexiglass or
plastic plate with a thickness of 4 mm or aluminum with a thickness of 2 mm. A thick ruler is
usually su
ffi
cient. For counter tube A this shielding is carried out with an aluminum cover. So a
3
rd
measurement shielded with 4 mm Plexiglass or plastic plate - produces a di
ff
erence to the
2
nd
measurement corresponding to the BETA component in the radiation.
OPERATING INSTRUCTIONS
for Counter Tube Type G
JS Monday 10 January 2011 Page 6 of 9