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

Angular distributions of absorbed dose of Bremsstrahlung photons and secondary electrons at a wide range of emission angles from 0 to 135 degrees, were experimentally obtained using an ion chamber with a 0.6 cm 3 air volume covered with or without a build-up cap. The Bremsstrahlung photons and electrons were produced by 18-, 28-, and 38-MeV electron beams bombarding tungsten, copper, aluminum, and carbon targets. The absorbed doses were also calculated by multiplying simulated photon and electron energy spectra with simulated response functions of the ion chambers, using the MCNPX code. Our simulation results agree with the experimental results, within a factor of 2, over wide ranges of emission angles, incident electron energies, and atomic numbers of targets. The angular distributions of absorbed doses at forward angles for incident energies are similar to those for targets. On the other hand, the absorbed doses at backward angles depend on target species. The dependences of absorbed doses on electron energy and target thickness were compared between the measured and simulated results, and showed good agreement. We also measured the attenuation profiles of absorbed doses of Bremsstrahlung beams at 0, 30, and 135 degrees to the electron beam axis. Simulated attenuation profiles agree, in relative values, with the experimental results at incident electron energies and angles. To achieve further accuracy of calculation, angular absorbed-dose measurements are necessary for bremsstrahlung radiation dosimetry.

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“…Photoneutrons produced at the targets were observed by Kosako [7]. These photoneutrons show smaller fluxes than electron and photon fluxes.…”

Section: Uncertainties In Experimental Datamentioning

confidence: 95%

Angular distributions of absorbed dose of Bremsstrahlung and secondary electrons induced by18-, 28- and 38-MeV electron beams in thick targets

Takada¹,

Kosako

Oishi

et al. 2012

Radiation Protection Dosimetry

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“…The copper were selected as a target using widely in the medical LINAC. The calculation condition is the same as in the experiment at the 45 MeV electron linear accelerator of Hokkaido University as described later [7,8]. The tallies were the point detectors to estimate the photon and neutron fluxes.…”

Section: Calculation Conditionmentioning

confidence: 99%

Optimum shielding structure for the wall of medical LINAC facility

Kosako

Oishi

Nakamura

et al. 2014

Progress in Nuclear Science and Technology

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When considering the space limit of high energy LINAC facility in a hospital, the design of shielding wall is strongly required to optimize the wall thickness. Shielding wall usually consists of concrete, and iron plate is sometimes added in concrete to decrease the wall thickness. We investigated the optimum design of the shielding wall in medical LINAC facility by simulation. The calculations were carried out by the three-dimensional Monte Carlo code, MCNP5. The electron energy used in this investigation is 28 MeV. In the calculations, the wall thickness was fixed to 100 cm from the viewpoint of durability and reliability and the cost to build the shielding wall. In the shielding wall consisting of iron and concrete, the suitable configuration was found to have 40-50 cm-thick iron at the front side. But it was insufficient to achieve the required attenuation rates of 2 x 10 -6 and 5 x 10 -8 for effective neutron and photon doses, respectively. We further searched the optimum combination of shielding materials to get the most efficient attenuation profile and finally obtained the optimum arrangement of 100 cm thick shielding wall having the multi-layered structure of iron 40 cm, polyethylene 10 cm, iron 20 cm, lead 10 cm, polyethylene 10 cm, and concrete 10 cm in this order. In order to investigate the shielding capability of this multi-layered shielding wall, the neutron and photon dose rates were measured using the 45 MeV electron linear accelerator of Hokkaido University to verify the MCNP5 calculated results. The MCNP5 calculation was found to give good accuracy within 30% for the multi-layered shielding structure.

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“…High energy (greater than 10 MeV) linear electron accelerators (linacs) often produce photoneutrons due to the energies of the generated bremsstrahlung photons being greater than that of the neutron binding energies of the materials they are likely to interact with [1]. These materials include the components of the linac itself in addition to the nearby structures within a shielded vault where the linac is housed.…”

Section: Introductionmentioning

confidence: 99%

Computational study of radiation doses at UNLV accelerator facility

et al. 2017

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Abstract.A Varian K15 electron linear accelerator (linac) has been considered for installation at University of Nevada, Las Vegas (UNLV). Before experiments can be performed, it is necessary to evaluate the photon and neutron spectra as generated by the linac, as well as the resulting dose rates within the accelerator facility. A computational study using MCNPX was performed to characterize the source terms for the bremsstrahlung converter. The 15 MeV electron beam available in the linac is above the photoneutron threshold energy for several materials in the linac assembly, and as a result, neutrons must be accounted for. The angular and energy distributions for bremsstrahlung flux generated by the interaction of the 15 MeV electron beam with the linac target were determined. This source term was used in conjunction with the K15 collimators to determine the dose rates within the facility.

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

Cited by 18 publications

References 19 publications

Angular distributions of absorbed dose of Bremsstrahlung and secondary electrons induced by18-, 28- and 38-MeV electron beams in thick targets

Angular distributions of absorbed dose of Bremsstrahlung and secondary electrons induced by18-, 28- and 38-MeV electron beams in thick targets

Optimum shielding structure for the wall of medical LINAC facility

Computational study of radiation doses at UNLV accelerator facility

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