Physics and Engineering of Radiation Detection

44 Chapter 1. Properties and Sources of Radiation

spent fuel of nuclear reactors where they are produced as byproducts of the fission
reaction.

Table 1.6.2: Common electron emitters and their half lives.

Element Isotope Energy (Emax) T 1 / 2

Sodium^2411 P 1. 393 MeV 14.959 hours

Phosphorus^3215 P 1. 71 MeV 14.262 days

Chromium^5124 Cr 752. 73 keV 27.702 days

Cobalt^6027 Co 318. 13 keV 5.271 years

Copper^6429 Cu 578. 7 keV 12.7 hours

Strontium^9038 Sr 546. 0 keV 28.79 years

Yttrium^9039 Y 2. 28 MeV 64.0 hours

Iodine^12553 I 150. 61 keV 59.408 days

Cesium^13755 Cs 513. 97 keV 30.07 years

Thallium^20481 Th 763. 4 keV 3.78 years

The emission of aβ-particle by a radionuclide was described earlier through the
reaction
n+p
p X→

n+p

p+1Y+e+ ̄ν.

The energy released in the reaction is taken away by the daughter, the electron, and
the neutrino. The daughter nucleus, being much more massive than the other two
particles, carries the least amount of kinetic energy. This energy, also calledrecoil
energy, is too low to be easily detected^7. Therefore, for most practical purposes, we
can assume that the recoil energy is zero. Most of the energy is distributed between
the electron and the neutrino. There is no restriction on either of these particles
for the amount of energy they can carry. Although the energy of the neutrino can
not be detected by conventional means, it can be estimated from the measuredβ-
particle energy. Fig.1.6.9 shows a typicalβ-particle energy spectrum. The electrons
can carry energy from almost zero up to theendpoint energy, which is essentially
the decayQ-value.

(^7) For detection through ionization, the particle must carry energy greater than the ionization threshold
of the medium. In this case, the recoil energy is generally lower than the ionization threshold. However,
one can utilize other methods of detection, such as scintillation, where the interacting particle excites the
medium such that it emits light during de-excitation. Measurement of recoil energy, not necessarily related
toβ-decay, is not uncommon in particle physics research.