Ulexite-galena intermediate-weight concrete as a novel design for overcoming space and weight limitations in the construction of efficient shields against neutrons and photons.

Recently, due to space and weight limitations, scientists have tried to design and produce concrete shields with increased attenuation of radiation but not increased mass density. Over the past years, the authors' had focused on the production of heavy concrete for radiation shielding, but this is the first experience of producing intermediate-weight concrete. In this study, ulexite (hydrated sodium calcium borate hydroxide) and galena (lead ore) have been used for the production of a special intermediate-weight concrete. Shielding properties of this intermediate-weight concrete against photons have been investigated by exposing the samples to narrow and broad beams of gamma rays emitted from a 6°Co radiotherapy unit. Densities of the intermediate-weight concrete samples ranged 3.64-3.90 g cm⁻³, based on the proportion of the ulexite in the mix design. The narrow-beam half-value layer (HVL) of the ulexite-galena concrete samples for 1.25 MeV 6°Co gamma rays was 2.84 cm, much less than that of ordinary concrete (6.0 cm). The Monte Carlo (MC) code MCNP4C was also used to model the attenuation of 6°Co gamma-ray photons and Am-Be neutrons of the ulexite-galena concrete with different thicknesses. The 6°Co HVL calculated by MCNP simulation was 2.87 cm, indicating a good agreement between experimental measurements and MC simulation. Furthermore, MC-calculated results showed that thick ulexite-galena concrete shields (60-cm thickness) had a 7.22 times (722 %) greater neutron attenuation compared with ordinary concrete. The intermediate-weight ulexite-galena concrete manufactured in this study may have many important applications in the construction of radiation shields with weight limitations such as the swing or sliding doors that are currently used for radiotherapy treatment rooms.

EchoSeed Model 6733 Iodine-125 brachytherapy source: improved dosimetric characterization using the MCNP5 Monte Carlo code.

This study primarily aimed to obtain the dosimetric characteristics of the Model 6733 (125)I seed (EchoSeed) with improved precision and accuracy using a more up-to-date Monte-Carlo code and data (MCNP5) compared to previously published results, including an uncertainty analysis. Its secondary aim was to compare the results obtained using the MCNP5, MCNP4c2, and PTRAN codes for simulation of this low-energy photon-emitting source. The EchoSeed geometry and chemical compositions together with a published (125)I spectrum were used to perform dosimetric characterization of this source as per the updated AAPM TG-43 protocol. These simulations were performed in liquid water material in order to obtain the clinically applicable dosimetric parameters for this source model. Dose rate constants in liquid water, derived from MCNP4c2 and MCNP5 simulations, were found to be 0.993 cGyh(-1) U(-1) (±1.73%) and 0.965 cGyh(-1) U(-1) (±1.68%), respectively. Overall, the MCNP5 derived radial dose and 2D anisotropy functions results were generally closer to the measured data (within ±4%) than MCNP4c and the published data for PTRAN code (Version 7.43), while the opposite was seen for dose rate constant. The generally improved MCNP5 Monte Carlo simulation may be attributed to a more recent and accurate cross-section library. However, some of the data points in the results obtained from the above-mentioned Monte Carlo codes showed no statistically significant differences. Derived dosimetric characteristics in liquid water are provided for clinical applications of this source model.

High-performance heavy concrete as a multi-purpose shield.

Concrete has long been used as a shield against high-energy photons and neutrons. In this study, colemanite and galena minerals (CoGa) were used for the production of an economical high-performance heavy concrete. To measure the gamma radiation attenuation of the CoGa concrete samples, they were exposed to a narrow beam of gamma rays emitted from a (60)Co radiotherapy unit. An Am-Be neutron source was used for assessing the shielding properties of the samples against neutrons. The compression strengths of both types of concrete mixes (CoGa and reference concrete) were investigated. The range of the densities of the heavy concrete samples was 4100-4650 kg m(-3), whereas it was 2300-2600 kg m(-3) in the ordinary concrete reference samples. The half-value layer of the CoGa concrete samples for (60)Co gamma rays was 2.49 cm; much less than that of ordinary concrete (6.0 cm). Moreover, CoGa concrete samples had a 10 % greater neutron absorption compared with reference concrete.