Beta Particle Transmission Through Materials

The estimation of the beta particle transmission through an absorber has almost exclusively been approximated by an exponential function. This approximation is accurate for absolute thicknesses up to only 50% of the maximum energy electron range. Often the electron fluence is needed at depths greater than 50% of the range in cases such as beta dosimetry. The transmission of a pencil beam of beta particles through an absorber was investigated experimentally using a gas flow proportional counter to detect the transmitted radiations. Foil absorbers ranged in atomic number from 13 to 47. Beta sources ranged in maximum beta energy from 0.22 to 2.28 MeV. A quasi-theoretical model was developed to calculate the transmission of beta particles using the mono-energetic electron transmission and the beta particle energy distribution. The mono-energetic electron transmission was calculated using the electron range distribution generated by the EGS4 Monte Carlo code. The results are compared with theoretical results based on transport theory for materials ranging in atomic number from 6 to 82 and energies from 0.1 to 4.0 MeV. The experimental method used a collimated beam of beta particles and a large detector, where as the theoretical calculation was for a pencil beam of beta particles. The experimental results are generally within 20% of the theoretical calculations for a pencil beam down to 1% transmission.