Introduction

Beam energy in industrial electron beams is usually found using depth-dose distributions in aluminium or polymers, utilising equations given in Annex 4 of ISO ASTM 51649 [1]. These relationships were derived using results from earlier Monte Carlo codes, with monoenergetic electron beams.

Here, empirical relationships are derived using more realistic spectra, and the results are then compared with those from the earlier equations.

Body

Monte Carlo calculations (EGSnrc [2]) using a wide range of “realistic” (exponentially-modified Gaussian) spectra were used to generate a large number of depth-dose distributions in aluminium and polystyrene, from which new empirical relationships were derived linking measured range parameters R50 and Rp, and average and most probable energy Ea and Ep.

Measurements performed at three facilities for several energies between 1 and 12 MeV in aluminium wedges and polystyrene stacks, were used as a validation of the calculations.

For aluminium:

Similar relationships were identified for polystyrene.

Conclusion

These determinations of Ea and Ep demonstrate that the older equations based on monoenergetic spectra show that those equations are still broadly valid. This work is expected to help in continuing development of the standards in use.

References

1: ISO ASTM 51649: “Standard Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 300 keV and 25 MeV”, www.astm.org, 2014

2: Kawrakow I., Rogers D.W.O. “The EGSnrc Code System: Monte Carlo Simulation of Electron and Photon Transport”. NRCC Report PIRS 701 (1999), National Research Council of Canada, Ottawa