Investigation of nano MgO loaded polyvinyl chloride polymer in protective clothing as a nonlead materials.

Recently, investigation of advanced shielding materials to be used as an alternative to lead apron has become important. In the current study, MgO loaded into PVC matrix as a non-lead modern shielding composite was modeled to evaluate its performance on radiation protective clothing (RPC). Parameters such as mass attenuation coefficient (MAC), mean free path (MFP), flux buildup factor (FBF), transmission factor (TF) and lead equivalent value (LEV) of samples were calculated using MCNPX Code. The simulation of the MCNP code was validated, by comparing the mass attenuation of concrete sample, with standard XCOM data and very good agreement was attended between XCOM and MC Code results. The MAC of nano and micro-sized samples were also compared with pure PVC and it was found that the nano MgO particle exhibits higher attenuation compared to micro MgO particle and pure PVC. The results show that, the MAC of samples increased to 63.13 % in 1.332 MeV with increasing filler concentration of nano MgO to 50 wt% relative to pure PVC. Investigation of LEV shows that nano MgO sample has more effective than Pb in 1.173 and 1.332 MeV gamma ray energy so that it provides 36.46 % and 11.13 % lighter RPC than Pb ones.

Compact shielding and irradiator design of a 252Cf neutron source.

New developments are under way to reduce the weight and volume of neutron shielding structures using multi-layered materials. The present study aimed at designing and simulating an appropriate neutron shielding material based on a 252Cf source using MCNPX code. The proposed design is composed of concentric cylinders and sphere layers with a source. The shielding matter consists of paraffin and paraffin +10% graphite as a moderator, beryllium as a reflector and multiplier and boron carbide and lead tungsten as a thermal neutron and gamma absorber, respectively. The results indicate that, compared to previously reported shielding assemblies, the volume and the weight of the proposed design could be significantly reduced by about 97% and 75%, respectively. Thermal and fast neutron fluxes in the irradiation channel were optimized to achieve maximum values for NAA, PGNAA and other applications.

Calculation of the exposure buildup factors for x-ray photons with continuous energy spectrum using Monte Carlo code.

Exposure buildup factors are very important for the calculation of radiation shielding and also applied radiation. We must distinguish the monoenergetic and continuous energy spectrum gamma source in order to calculate the exposure buildup factors. In this study, the exposure buildup factors for two x-ray continuous energy spectra (bremsstrahlung) with 5 and 10 MeV endpoint energies were calculated up to depths of 10 mfp of water. It was observed that there is a large difference between the obtained exposure buildup factors due to the monoenergetic and continuous energy spectrum gamma sources. The calculation results show that the relative differences in 5 MeV energy for 1 mfp to 10 mfp are 114% to 44%, respectively, and also the relative differences in 10 MeV energy for 1 mfp to 10 mfp are 87% to 38%, respectively. Actually, the main purpose of this paper is to illustrate the fact that there is a significant difference between the exposure buildup factors due to the continuous and monoenergetic gamma sources. Therefore, radiation staff must pay more attention to calculating the thickness of radiation shields for continuous energy gamma sources.

Diaphragm correction factors for the FAC-IR-300 free-air ionization chamber.

A free-air ionization chamber FAC-IR-300, designed by the Atomic Energy Organization of Iran, is used as the primary Iranian national standard for the photon air kerma. For accurate air kerma measurements, the contribution from the scattered photons to the total energy released in the collecting volume must be eliminated. One of the sources of scattered photons is the chamber's diaphragm. In this paper, the diaphragm scattering correction factor, kdia, and the diaphragm transmission correction factor, ktr, were introduced. These factors represent corrections to the measured charge (or current) for the photons scattered from the diaphragm surface and the photons penetrated through the diaphragm volume, respectively. The kdia and ktr values were estimated by Monte Carlo simulations. The simulations were performed for the mono-energetic photons in the energy range of 20 - 300keV. According to the simulation results, in this energy range, the kdia values vary between 0.9997 and 0.9948, and ktr values decrease from 1.0000 to 0.9965. The corrections grow in significance with increasing energy of the primary photons.

INVESTIGATION OF THE HUMIDITY EFFECT ON THE FAC-IR-300 IONIZATION CHAMBER RESPONSE.

The free-air ionization chamber is communicating with the ambient air, therefore, the atmospheric parameters such as temperature, pressure and humidity effect on the ionization chamber performance. The free-air ionization chamber, entitled as FAC-IR-300, that design at the Atomic Energy Organization of Iran, AEOI, is required the atmospheric correction factors for correct the chamber reading. In this article, the effect of humidity on the ionization chamber response was investigated. For this reason, was introduced the humidity correction factor, kh. In this article, the Monte Carlo simulation was used to determine the kh factor. The simulation results show in relative humidities between 30% to 80%, the kh factor is equal 0.9970 at 20°C and 0.9975 at 22°C. From the simulation results, at low energy the energy dependence of the kh factor is significant and with increasing energy this dependence is negligible.

Calculation of the exposure buildup factors for X-ray photons with continuous energy spectrum by Monte Carlo code.

The exposure buildup factors are very important for the calculation of radiation shielding and also applied radiation. We must distinguish the monoenergetic and continuous energy spectrum gamma source in order to calculate the exposure buildup factors. In this study, the exposure buildup factors for two X-ray continuous energy spectrum (bremsstrahlung) with 5 and 10 MeV endpoint energy were calculated up to depths 10 mfp of water. It was observed that there is a large difference between the obtained exposure buildup factors due to the monoenergetic and continuous energy spectrum gamma source. The calculation results show that the relative differences in 5 MeV energy for 1 mfp to 10 mfp are 114% to 44%, respectively, and also the relative differences in 10 MeV energy for 1 mfp to 10 mfp are 87% to 38%, respectively. Actually, the main purpose of this paper is to illustrate the fact that there is a significant difference between the exposure buildup factor due to the continuous and monoenergetic gamma source. Therefore, radiation staffs must pay more attention to calculate the thickness of the radiation shields for continuous energy gamma source.