The efficiency of NaI(T1) scintillation counters for the detection of gamma rays is discussed and experimentally determined. Experimental efficiencies, based upon the number of counts above a bias equal to one-half the gamma ray energy and a solid angle defined to the crystal effective centre, for a three-inch-diameter by three-inch long (3 x 3) crystal are given for gamma ray energies of 0.51, 1.275 and 6.14 MeV. Gamma ray spectra at 1.275 and 6.14 MeV are extrapolated to zero energy in order to compare theoretical efficiencies, based upon the integrated primary absorption, with the experimental results. These results show that, with experience, one can expect accuracy to better than 5% at these energies. Tables are given of the theoretical efficiency for 3x3, 2¾ x 4½ and 5x4 crystals for several gamma ray energies and source-to-counter distances of from 0.1 cm to 1 m. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

No description available.

Neutron bombardment of bipolar transistors creates cluster defects in semiconductor material. The clusters are small volumes of semiconductor material containing several hundred atoms displaced from their proper lattice sites owing to collision processes. They act as recombination centers in transistor bases, reducing minority carrier lifetime and consequently reducing transistor current gain. The damage is permanent to the semiconductor device and can only be corrected by thermally annealing the transistor. Copious test data available on bipolar transistors d.c. gain (hFE) response to incident fast neutron fluences confirm their mathematically derivable functional relationships. This report develops a neutron fluence detector system based upon the current gain (hFE) degradation. An approximate model extending these results to include the effects of temperature is developed. A probe containing an npn silicon planar transistor with associated components to allow hFE measurements is designed. A thermal sensor is also designed. More precise neutron data is obtained by correcting for d.c. current gain versus ambient temperature error. The design of the probe is the major contribution in this report. In addition to the computer simulation of the probe model a system architecture and implementation is presented. The detector system is comprised of the probe and associated data acquisition I/O circuitry. A microcomputer processes the probe data to calculate the neutron fluence received.

No description available.

The detonation of a radiological dispersal device (RDD) may result in casualties receiving exposure of radioactive materials. Assessments of potentially contaminated personnel are necessary to determine the level of contamination received in order to prioritize and treat individuals. The use of improvised explosive devices (IEDs) and the number of orphan sources in deployed and combat areas such as Iraq, present an opportunity for terrorists to use an RDD against deployed ground forces. There is limited capability in Iraq to assess radiological casualties, as the process of obtaining and analyzing bioassays is time consuming and not readily available in country. Military units are equipped with AN/VDR-2 and AN/PDR-77 radiac detectors which are capable of detecting gamma radiation. Therefore, a study of the use of these radiac sets in assessing internal contamination was conducted. A model of the detector probe was created using the Los Alamos National Laboratory Monte Carlo N-Particle transport code, MCNP Version 5. This model was experimentally validated and used in conjunction with both reference male and reference female computational Medical Internal Radiation Dose (MIRD) phantoms to compute internal dose. The instrument model was evaluated at the following locations, the posterior upper right torso, the anterior upper right torso, the lateral upper left thigh and the anterior of the neck. Nuclides were distributed throughout the phantoms using the Oak Ridge National Laboratory Dose and Risk Calculation (DCAL) software for inhalation pathways. Based on the likelihood for use in RDDs and the capabilities of the instrument, Co-60, Cs-137 and Ir-192 were evaluated.

Made available in DSpace on 2014-10-09T12:36:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:26Z (GMT). No. of bitstreams: 1 04327.pdf: 2200991 bytes, checksum: 4359f2ee2a626eaa629feb45cdeebc50 (MD5) / Dissertacao (Mestrado) / IPEN/D / Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ - COPPE

Made available in DSpace on 2014-10-09T12:36:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:26Z (GMT). No. of bitstreams: 1 04327.pdf: 2200991 bytes, checksum: 4359f2ee2a626eaa629feb45cdeebc50 (MD5) / Dissertacao (Mestrado) / IPEN/D / Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ - COPPE

published_or_final_version / Physics / Master / Master of Philosophy

No description available.