Low Flux Reactor Research Articles

Low-flux neutron imaging for Californium-252-based thermal neutron radiography : Wada, N. neutron radiography, proceedings of the second world conference, Paris (France), 16–20 Jun. 1986. pp. 223–230. D. Reidel Publishing Company

In Boron Neutron Capture Therapy the 10B(n, α)7 Li reaction is used to create a tumour-destructing field of high Linear Energy Transfer (LET) particles. The therapy requires a high boron concentration in the tumour and a low boron concentration in the healthy tissue. The boron neutron capture reaction is accompanied by the emission of a photon of energy 478 keV. It is investigated whether measuring of these photons can serve as a tool to determine the boron concentration during therapy in the tumour as well as in the healthy tissue. Such a measurement is complicated by the presence of a large background photon field. To study the feasibility, an experimental configuration has been designed at a test facility of the Low-Flux Reactor (LFR). The LFR provides an epithermal neutron beam for irradiation of a head phantom which simulates a human head with a tumour. This paper shows that the reconstruction of the position and the size of the tumour as well as the ratio of the boron concentrations appeared to be possible. In a second stage it is shown that these measurements can be expanded to experiments with the therapy neutron beam of the High-Flux Reactor (HFR).

Superconductivity induced by irradiation in La 2CuO 4

Superconducting transition below a resistivity peak is observed in La 2CuO 4 irradiated with low flux reactor radiation at 350 K. The transition temperature increases with increasing irradiation dose up to T c (onset) = 48.9 K at 4.8 ×10 16 n/cm 2 ( E > 0.1 MeV). The result is compared with previous irradiation experiments.

A new method for99mTc generator preparation

The authors report here a new approach for making99mTc generators based on neutron irradiation of metallic molybdates and direct elution eliminating intermediate chemical processing steps. This approach tested using zirconium molybdate was found to yield99mTc with good yield and purity. This seems to be the simplest way of making column type99mTc generator even using low flux reactors and merits further detailed evaluation.

Trace Element Analysis by Neutron Activation With a Low Flux Reactor (Slowpoke ‐ II): Results for International Reference Rocks

A low‐flux reactor (SLOWPOKE II) may be used to determine a large number of trace elements by neutron activation. Details of this technique are given along with results for 22 elements in 22 international reference rocks. Our results are compared with published “best values”; the agreement is favourable in most cases.

Analysis of self-powered gamma ray detector with directional discrimination

The results of a combined Monte Carlo simulation and experimental investigation of the directional and energy dependent response of a self-powered gamma detector with a flat plate Pb-C central electrode are presented. The electron yield of the central electrode in a three dimensional mockup of the detector was calculated for photons of several discrete energies, emanating from an infinitely thin planar source, incident on the outer surface of the detector. Separate computations were done with the source facing the lead side and carbon side of the central electrode. Experimental measurements with a detector that closely matched the design used in the simulation were conducted in a graphite column next to a neutron leakage face of a low flux reactor. A localized gamma ray source was created by positioning a 235U strip between the leakage face of the reactor and the detector. A comparison of results obtained in both cases showed good agreement. Also experimental measurements to determine the effect of the thickness of lead shielding surrounding the outer wall of the detector and space charge in the vacuum insulator between the central electrode and the inner wall on the response of the detector were performed.

Direct Determination of Uranium-235 Capture-to-Fission Ratio in a Zero-Power Reactor

An experimental method for the determination of the spectral average of the capture-to-fission ratio ᾱ for materials inserted in a low-flux reactor is described. The procedure involves a comparison of reactor response to oscillated samples of a fissile material, an absorber, and a spontaneous fission neutron source, plus an experimental determination of fission rate for the fissile material and capture rate for the absorber. In addition, it is necessary that the neutron source be calibrated. These experimental results, combined with a knowledge of the number of neutrons per fission for the fissile material, yield a value of the quantity 1 + ᾱ. This method has been tested in Hi-C Core 10, a critical assembly of 3%-enriched-UO2 fuel pins, moderated and reflected by light water, in a lattice spacing which yields a H-to-238U atom ratio of 2:91. The oscillator and absolute counting data yield a value of 0.217 for the central capture-to-fission ratio of 235U, with a standard deviation of ± 0.015. This agrees well with values derived from a combination of measured 235U fission cadmium ratios and calculated thermal and epithermal values for α.

Influence of neutron-irradiation at 78°K on the critical field of superconducting lead

Measurements on the critical field of neutron-irradiated lead are given. Lead wires, soft-annealed for 2 hours at 200 un. Concent 85% C in vacuo, were encapsulated in an evacuated silica tube and subsequently irradiated in a low flux reactor for a period of eleven days at a temperature of 78 un. Concent 85% K. The integrated flux was about 10/sup 18/ fast neutrons cm/sup -2/. Values of the residual resistivity measured before irradiation and after recovery for 20 minutes at 353 un. Concent 85% K are listed. (C.E.S.)