B.W. Wehring

Gadolinium neutron capture therapy

A computer study of the dose distribution for gadolinium neutron capture therapy is carried out to determine its feasibility. Gadolinium is a potential neutron capture therapy (NCT) agent that produces gamma radiation, conversion electrons, and Auger electrons. The dose distribution from neutrons, neutron-induced gammas, and the reaction products from neutron capture in gadolinium were modeled using the Los Alamos National Laboratory Monte Carlo neutron photon computer code. The results of these calculations are that gadolinium has promise as an NCT agent. Using two parallel opposed epithermal neutron beams for a tumor at an 8.0-cm depth with a gadolinium loading of 100[mu]g/g, the tumor to peak normal tissue dose was determined to be 1.48.

PROMPT GAMMA ACTIVATION ANALYSIS WITH THE TEXAS COLD NEUTRON SOURCE

A Prompt Gamma Activation Analysis (PGAA) facility is being developed at The University of Texas at Austin (UT). The UT-PGAA facility will utilize a focused cold-neutron beam from the Texas Cold Neutron Source (TCNS). the TCNS consists of a cold source cryostat and a curved neutron guide. the use of a guided focused cold-neutron beam will provide a high capture reaction rate and low background. The UT-PGAA facility will be used in the nondestructive determination of B, Cd, Gd and S in biological and environmental samples.

The University of Texas Cold Neutron Source

Abstract A cold neutron source has been designed, constructed, and tested by the Nuclear Engineering Teaching Laboratory (NETL) at The University of Texas at Austin. The Texas Cold Neutron Source (TCNS) is located in one of the beam ports of the NETL 1-MW TRIGA Mark II research reactor. The main components of the TCNS are a cooled moderator, a heat pipe, a cryogenic refrigerator, and a neutron guide. 80 ml of mesitylene moderator are maintained at about 30 K in a chamber within the reactor graphite reflector by the heat pipe and cryogenic refrigerator. The heat pipe is a 3-m long aluminum tube that contains neon as the working fluid. The cold neutrons obtained from the moderator are transported by a curved 6-m long neutron guide. This neutron guide has a radius of curvature of 300 m, a 50 × 15 mm cross-section, 58 Ni coating, and is separated into three channels. The TCNS will provide a low-background subthermal neutron beam for neutron capture and scattering research. After the installation of the external portion of the neutron guide, a neutron focusing system and a Prompt Gamma Activation Analysis facility will be set up at the TCNS.

Transmission of Fast Neutrons Through an Iron Sphere

Integral Experiments have been performed using a homogeneous iron spherical shell to test neutron cross-section data. Neutron leakage spectra from the shell were measured using /sup 252/Cf-fission and (deuterium-tritium) D-T-fusion neutron sources and an Ne-213 spectrometry system. An associated particle detector was used to monitor the absolute D-T neutron source strength as well as any accompanying deuterium-deuterium neutron contamination. The leakage spectra were calculated using the continuous-energy Monte Carlo code VIM and the discrete ordinates S/sub n/ code ANISN employing ENDF/B-IV. For neutron energies between 1 and 5 MeV, the calculations underpredicted the leakage spectrum by factors of 1.4 to 2 for the Californium neutron source and 2 to 3 for the D-T neutron source. The large discrepancies are attributed to inadequate representation of cross-section resonance structure (namely, minima); inadequate representation of the angular and secondary energy distributions for continuum inelastic scattering and (n,2n) reactions also contribute to these discrepancies.

Neutron focusing system for the Texas Cold Neutron Source

Abstract A “converging neutron guide” focusing system located at the end of the Texas Cold Neutron Source (TCNS) “curved neutron guide” would increase the neutron flux for neutron capture experiments. Our design for a converging guide is based on using several rectangular truncated cone sections. Each rectangular truncated cone consists of four 20-cm long Si plates coated with NiC-Ti supermirrors. Dimensions of each section were determined by a three-dimensional Monte Carlo optimization calculation. The two slant angles of the truncated cones were varied to optimize the neutron flux at the focal area of the focusing system. Different multielement converging guides were designed and their performance analyzed. From the performance results and financial considerations, we selected a four-section 80-cm long converging guide focusing system for construction and use with the TCNS. The focused cold neutron beam will be used for neutron capture experiment, e.g., prompt gamma activation analysis and neutron depth profiling.

Helium-3 and boron-10 concentration and depth measurements in alloys and semiconductors using NDP

Abstract Neutron Depth Profiling (NDP) is a nondestructive near surface technique that is used to measure concentration versus absolute depth of several isotopes of light mass elements in various substrates. NDP is based on absorption reaction of thermal neutrons with the isotope of interest. Charged particles and recoil atoms are generated in the reaction. The depth profiles are determined by measuring the residual energy of the charged particles or the recoil atoms. The NDP technique has became an increasingly important method to measure depth profiles of 3 He and 10 B in alloys and semiconductor materials. A permanent NDP facility has been installed on the tangential beam port of the University of Texas (UT) TRIGA Mark-II research reactor. One of the standard applications of the UT-NDP facility involves the determination of boron profiles of borophosphosilicate glass (BPSG) samples. NDP is also being used in combination with electron microscopy measurements to determine radiation damage and microstructural changes in stainless steel samples. This is done to study the long-term effects of high-dose alpha irradiation for weapons grade plutonium encapsulation. Measurements of implanted boron-10 concentration and depth profiles of semiconductor materials in order to calibrate commercial implanters is another application at the UT-NDP facility. The concentration and depth profiles measured with NDP and SIMS are compared with reported data given by various vendors or different implanters in order to verify implant quality of semiconductor wafers. The results of the measurements and other possible applications of NDP are presented.

Performance of the University of Texas cold-neutron prompt gamma activation analysis facility

The University of Texas cold-neutron prompt gamma-activation analysis (PGAA) facility is operational at the 1-MW UT TRIGA research reactor. The UT-PGAA facility utilizes a guided cold neutron beam produced by the Texas Cold Neutron Source. The cold neutrons are transported to the PGAA chamber via a 6-m long curved neutron guide followed by an 80-cm long converging neutron guide. A program of testing, optimizing, and calibrating the UT-PGAA facility is currently underway. Preliminary results for the sensitivities and detection limits of boron, hydrogen, and silicon in semiconductor materials are given.

Application of cold-neutron prompt gamma activation analysis at the University of Texas reactor

Abstract A cold-neutron prompt gamma activation analysis (PGAA) system is operational at the University of Texas (UT) 1 MW TRIGA research reactor. A 6 m long curved neutron guide followed by an 80 cm long converging (focusing) neutron guide transports cold neutrons from the Texas Cold Neutron Source to the PGAA chamber. The UT-PGAA system will be used to determine hydrogen and boron in semiconductor materials, gadolinium in neutron capture therapy samples, and multielementals in environmental and industrial samples.

Neutron depth profiling at the University of Texas

A neutron depth profiling (NDP) facility has been developed at the University of Texas at Austin (UT) Nuclear Engineering Teaching Laboratory. The UT-NDP utilizes thermal neutrons from a tangential beam port of the 1-MW TRIGA Mark II research reactor. Aspects of the designs of the thermal neutron beam and target chamber for the UT-NDP facility are given in this paper. Also, a brief description of NDP and possible applications are included.

Neutron depth profiling applications at The University of Texas research reactor

The neutron depth profiling (NDP) technique has become an increasingly important method to nondestructively measure the absolute concentration versus depth of various elements in substrates. A permanent NDP facility is operational at a tangential beam port of the 1-MW TRIGA Mark II research reactor at The University of Texas at Austin (UT). This facility was developed to perform materials research, specifically measurements of interest to the microelectronics industry. Applications of the UT-NDP facility include measurements of boron-10 profiles in borophosphosilicate glass samples and helium-3 depth profiles of implanted helium-3 in metals, alloys and amorphous materials. A study is underway to determine radiation damage and microstructural changes in stainless steel samples by helium irradiation using NDP and Transmission Electron Microscopy. Another study, currently planned, is to measure surface wear by measuring the depth profiles of implanted beryllium-7 and sodium-22 in various materials.