Angular Distribution of Photoneutrons from Copper and Tungsten Targets Bombarded by 18, 28, and 38 MeV Electrons

Abstract Following the angular distribution measurement of bremsstrahlung, we measured the angular distribution of photoneutrons between 0 and 120 degrees from copper and tungsten targets bombarded by 18, 28, and 38MeV electrons at the electron linac of Hokkaido University. The activation detectors and neutron dosimeters were applied to the measurement. The measured results were compared with the results calculated with the Monte Carlo code MCNP5 to verify the calculated results. The calculated results of both the reaction and ambient dose equivalent rates were in good agreement with the measured ones between 20 and 120 degrees in the cases of 28 and 38MeV electrons, but the calculation underestimated the measured data by a factor of 1.5 to 2.5 for 18MeV electrons. A large disagreement was observed at small forward angles of around 0 degrees. It was clarified that this disagreement was due to the contributions of photonuclear reactions in the detectors and dosimeters themselves, and of (e,n) reactions in the target. KEYWORDS: photoneutronangular distributionactivation foilreaction ratedose rateradiotherapylinacMonte CarloMCNPelectron