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

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.     

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

We measured the angular distribution of bremsstrahlung photons between 0 and 120 degrees from copper and tungstentargets bombarded by 18, 28, and 38MeV electrons at the electron linac of Hokkaido University. Activation detectors and two types of dosimeters were applied for the measurement. The measured results were compared with those calculated with the Monte Carlo code MCNP5 to verify the calculated results. The calculated results of both the reaction rates and ambient dose equivalent rates gave good agreement with the measured ones in the case of 18MeV electrons. A good agreement between the measurement and calculation was also observed for relative angular distributions of dose rates from 38MeV electrons; however, the calculation overestimated the measured data by a factor of 1.2 to 2.0. To achieve further accuracy of calculation, improvement of photonuclear reaction data and absorbed dose measurement are necessary for bremsstrahlung radiation dosimetry.     

Monte Carlo estimation of average energy required to produce an ion pair in noble gases by electrons with energies from 1 keV to 100 MeV

This paper describes the results of Monte Carlo estimation of the average energy W required to produce an ion pair in five noble gases by fast electrons. The ENDF/B-VI.8 library was used as the source of electroionization and atomic excitation cross sections for electron energies above 1 keV, as well as the source of all other types of electron and photon interaction cross sections for all energies. The low-energy electroionization and atomic excitation cross sections were taken from three data-sets: ENDF/B-VI.8 and two data-sets posted on the LXCat website (www.lxcat.net), i.e., BIAGI-v8.9 and SIGLO. Calculations were done using MCNP6 and a similar open-source program MCNelectron (http://web.vu.lt/ff/a.poskus/mcnelectron/). By comparing the calculated W-values with experimental ones, it is shown that replacement of the low-energy part of ENDF/B-VI.8 electroionization and excitation cross section data by LXCat data causes a significant improvement of accuracy of the calculated W-value. This accuracy can be improved even more by interpolation between the low-energy LXCat cross sections and high-energy ENDF/B-VI.8 cross sections. It is concluded that the value of W obtained by Monte Carlo simulation using different sets of low-energy electron interaction cross sections can be used as one of the criteria for evaluating accuracy of those data-sets.     

A comparison of the bremsstrahlung yields from 53 keV electrons on gold targets produced by PENELOPE and experiment

We compare the predictions for the bremsstrahlung probability densities for 53 keV electrons on gold targets produced by the Monte Carlo program, PENELOPE, to experimental results. A comparison of the results indicates that bremsstrahlung produced by solid targets is best described by ordinary bremsstrahlung alone and that there are no significant polarizational bremsstrahlung contributions.     

Attenuation of ambient dose equivalent from neutrons by thick concrete, cast iron and composite shields for high energy proton, He, Ca and U ions on Cu targets for shielding design

Data on neutron dose attenuation by thick concrete, cast iron, and cast iron plus concrete composite shields for heavy ions and protons having high energies (200-1000 MeV/u) are necessary for shielding designs of high-powered heavy ion accelerator facilities. Neutron production source terms, shield material attenuation lengths, and neutron dose rate reduction effectiveness of the bulk shielding in the angular range from 0° to 125° were determined by the Particle and Heavy Ion Transport Code (PHITS) for beams of 300 and 550 MeV/u ⁴⁸Ca ions, 200 and 400 MeV/u ²³⁸U ions, 800 MeV/u ³He and 1 GeV protons. Calculated results of interaction lengths of concrete and cast iron were also compared with similar work performed by Agosteo et al., and to experimental and other calculated data on interaction lengths. The agreement can be regarded as acceptable.