160
10 Identification of Radioactive Isotopes
energy spectrum emitted by the source with the help of a pulse-height analyzer. If
isotope is confirmed to emit α-particles, for example, then either a semiconductor
detector or a gas-flow proportional counter or a liquid phosphor scintillation counter
is preferred for measuring its activity.
10.3 Energy Determination
It is useful to find out the energy of radiation emitted by the isotope. β-particles fortunately can be classified by evaluating their maximum energy known as E max . For
this purpose, one normally uses a scintillation counter to get the entire spectrum or a
G.M. counter to get the absorption spectrum. α-particles or γ -rays, being monoenergetic radiations, their energies can be found out by measuring their spectrum. These
techniques are discussed here.
10.4 β-Spectrometry
While discussing applications of scintillation and proportional counting systems in
the previous chapters, it was pointed out that with the help of a pulse-height analyzer,
the spectrum of β-particles can be obtained. Since β-particles possess energy ranging
from zero to a maximum value known as E max , one is normally interested in knowing
the value of E max rather than the entire spectrum of β-particles. E max value gives an
idea in regards to penetration power of β-particles. This is a very useful information
for deciding the method of counting and for protecting human body from the health
hazard point of view. Though it is difficult, to get an idea of E max from the βspectrum, nevertheless it is preferred to measure this value from the absorption curve
of β-particles.
10.4.1 β-Absorption Law and Its Spectrum
The absorption of β-particles closely follows the law of exponential nature i.e.,
I = I 0 e
−μx
(10.1)
where I 0 is initial number of β-particles reaching one end of the absorber (i.e., when
x = 0), I is number of β-particles penetrated out of the absorber (i.e., for thickness
10 Identification of Radioactive Isotopes
energy spectrum emitted by the source with the help of a pulse-height analyzer. If
isotope is confirmed to emit α-particles, for example, then either a semiconductor
detector or a gas-flow proportional counter or a liquid phosphor scintillation counter
is preferred for measuring its activity.
10.3 Energy Determination
It is useful to find out the energy of radiation emitted by the isotope. β-particles fortunately can be classified by evaluating their maximum energy known as E max . For
this purpose, one normally uses a scintillation counter to get the entire spectrum or a
G.M. counter to get the absorption spectrum. α-particles or γ -rays, being monoenergetic radiations, their energies can be found out by measuring their spectrum. These
techniques are discussed here.
10.4 β-Spectrometry
While discussing applications of scintillation and proportional counting systems in
the previous chapters, it was pointed out that with the help of a pulse-height analyzer,
the spectrum of β-particles can be obtained. Since β-particles possess energy ranging
from zero to a maximum value known as E max , one is normally interested in knowing
the value of E max rather than the entire spectrum of β-particles. E max value gives an
idea in regards to penetration power of β-particles. This is a very useful information
for deciding the method of counting and for protecting human body from the health
hazard point of view. Though it is difficult, to get an idea of E max from the βspectrum, nevertheless it is preferred to measure this value from the absorption curve
of β-particles.
10.4.1 β-Absorption Law and Its Spectrum
The absorption of β-particles closely follows the law of exponential nature i.e.,
I = I 0 e
−μx
(10.1)
where I 0 is initial number of β-particles reaching one end of the absorber (i.e., when
x = 0), I is number of β-particles penetrated out of the absorber (i.e., for thickness