A Monte Carlo study on the gamma-ray buildup factors for the linear sources embedded in a cylindrical shield

Abstract

While the studies on the photon buildup factors for point gamma sources have been widely made, studies for linear gamma sources, for which the spent nuclear fuel rods and/or brachytherapy seeds could be a relatively good approximation, have become extremely scarce. Buildup factors for linear gamma sources are computed here by means of the MCNPX Monte Carlo code. The exposure buildup factors were calculated for isotropic linear gamma sources with different lengths (1, 10, and 100 cm) and also for different energies (0.1, 0.5, 1, 5, and 10 MeV) in a cylindrical concrete shield up to depths of 10 mean free paths. A number of 45 simulations were done to reach the appropriate results for the linear gamma sources and 5 more simulations were performed for point gamma sources to be compared with the linear sources of photons at the same energies. For validation, we calculated the total mass attenuation coefficients, mass energy absorption coefficients, and uncollided photon flux for some photon energy in concrete and we showed that the simulation results have a good agreement with NIST-XCOM database and theory. Finally, comparisons are shown for the exposure buildup factors of the linear source in terms of the gamma-rays energy, of the length of the linear source and of the cylindrical shield, which can be useful in the design of a suitable shield.

A Monte Carlo investigation of some important radiation parameters and tissue equivalency for photons below 1 keV in human tissues

“…For accurate simulation, we used the MCNP6.1 code with detailed physics (based on PHYS:P card) [46]. In our previous works, we obtained the attenuation coefficients for energies higher than 1 keV using the MCNPX code [50][51][52]. To obtain the desired data through simulation, two computers (Intel ® Core™ i3-6006U processors, Intel ® Core™ i5-2410M) were used.…”

A database of photon mass-energy transfer coefficients for dosimetric materials from 1 keV to 100 MeV

“…where 𝐾 is kerma rate, is photon flux that reached the target, and 𝐸 is photon energy. Mass energy-absorption coefficient (𝜇 en ) was calculated from absorption dose rate ( 𝐷) using the following equation [1,17].…”