Biomedical subjects

A X da Silva

Publications and source records attributed to A X da Silva.

3 recordsLinked to original sources

PubMed2002

Explosives detection using prompt-gamma neutron activation and neural networks.

This work describes a study of the application of a neural network to determine the presence of explosives using the neutron capture prompt gamma-ray spectra of the substances as patterns which were simulated via Monte Carlo N-particle transport code, version 4B. After the training of the neural networks, it was possible to determine the presence of the C-4 explosive, even when they were occluded by several materials. The neural network was a powerful tool, able to recognize prompt gamma-ray explosive patterns in spite of the presence of occluding materials. Besides that, the network was able to generalize, identify the presence of explosive in cases in which it had not been trained. In that way, it was revealed as a potential tool for in situ inspection systems.

Explosions↗

PubMed2001

Moderator-collimator-shielding design for neutron radiography systems using 252Cf.

This paper is concerned with the presentation of a study of the general design of an optimized neutron radiography system that utilizes 252Cf. Moderation, collimation and shielding aspects are considered. A Monte Carlo code, MCNP, was used to obtain a maximum and more homogeneous neutron flux in the collimator outlet next to the image plane, taking into account geometric characteristics and an adequate radiation shielding strategy that complies with the radiological protection rules. Among the various moderator materials investigated, the high density polyethylene proved to be the most efficient, with a thermalization factor of 56 cm2. Using a collimator design assembly it was possible to obtain a normalized thermal neutron flux, at the image plane, equals 6 x 10(-6) n cm(-2) s(-1) at an effective collimator ratio of 7.5, or 3.2 x 10(-7) n cm(-2) s(-1) at an effective collimator ratio of 50. The total dose equivalent rates were significantly reduced by the shielding optimization process.

Journal Article↗

PubMed2001

Shielding design studies for a neutron irradiator system based on a 252Cf source.

This study aims to investigate a shielding design against neutrons and gamma rays from a source of 252Cf, using Monte Carlo simulation. The shielding materials studied were borated polyethylene, borated-lead polyethylene and stainless steel. The Monte Carlo code MCNP4B was used to design shielding for 252Cf based neutron irradiator systems. By normalising the dose equivalent rate values presented to the neutron production rate of the source, the resulting calculations are independent of the intensity of the actual 252Cf source. The results show that the total dose equivalent rates were reduced significantly by the shielding system optimisation.

Boron Neutron Capture Therapy↗