APSD up to 100 kHz dataset measured in the IPEN/MB-01 research reactor facility.

The data presented in this work are from the very accurate reactor noise measurements performed in the IPEN/MB-01 research reactor facility. The quantity inferred from the measured data was the Auto Power Spectral Density (APSD) with the frequency range extended up to 100 kHz. The core configuration considered a short version of the IPEN/MB-01 core, consisted of a 26 × 24 rectangular array of fuel rods with control banks totally withdrawn. The measured reactivity excess for this configuration was equal to (10 ± 3) pcm. The subcriticality was reached by poisoning the reactor water with boric acid (H3BO3) in the concentrations of 286.8 and 578.6 ppm of natural boron. The main goal of these experiments was to test subcritical configurations with uniform poisoning. The average temperature for the experiment with 286.8 ppm of natural boron was (19.82 ± 0.37) °C and that for the 578.6 ppm was (19.89 ± 0.09) °C. The core was driven by the 241Am-Be start-up source (∼1.0 Ci) of the facility placed in the reflector. The APSD (in units of count2/Hz) was inferred employing the IPEN/MB-01 Correlator. The basic measured data arise from the pulses of two 3He Centronic detectors placed in the reflector region.

Physical models, cross sections, and numerical approximations used in MCNP and GEANT4 Monte Carlo codes for photon and electron absorbed fraction calculation.

PURPOSE: Radiopharmaceutical applications in nuclear medicine require a detailed dosimetry estimate of the radiation energy delivered to the human tissues. Over the past years, several publications addressed the problem of internal dose estimate in volumes of several sizes considering photon and electron sources. Most of them used Monte Carlo radiation transport codes. Despite the widespread use of these codes due to the variety of resources and potentials they offered to carry out dose calculations, several aspects like physical models, cross sections, and numerical approximations used in the simulations still remain an object of study. Accurate dose estimate depends on the correct selection of a set of simulation options that should be carefully chosen. This article presents an analysis of several simulation options provided by two of the most used codes worldwide: MCNP and GEANT4. METHODS: For this purpose, comparisons of absorbed fraction estimates obtained with different physical models, cross sections, and numerical approximations are presented for spheres of several sizes and composed as five different biological tissues. RESULTS: Considerable discrepancies have been found in some cases not only between the different codes but also between different cross sections and algorithms in the same code. Maximum differences found between the two codes are 5.0% and 10%, respectively, for photons and electrons. CONCLUSION: Even for simple problems as spheres and uniform radiation sources, the set of parameters chosen by any Monte Carlo code significantly affects the final results of a simulation, demonstrating the importance of the correct choice of parameters in the simulation.

A new human eye model for ophthalmic brachytherapy dosimetry.

The present work proposes a new mathematical eye model for ophthalmic brachytherapy dosimetry. This new model includes detailed description of internal structures that were not treated in previous works, allowing dose determination in different regions of the eye for a more adequate clinical analysis. Dose calculations were determined with the MCNP-4C Monte Carlo particle transport code running n parallel environment using PVM. The Amersham CKA4 ophthalmic applicator has been chosen and the depth dose distribution has been determined and compared to those provide by the manufacturer. The results have shown excellent agreement. Besides, absorbed dose values due to both 125I seeds and 60Co plaques were obtained for each one of the different structures which compose the eye model and can give relevant information in eventual clinical analyses.