Isamu Ishikawa

A method for determination of the 152Eu activity

Abstract A new method for the absolute measurement of the 152 Eu activity was established based on the 4 πβ − γ spectroscopic coincidence method. It consists of a 4 πβ counter and a Ge(Li) detector, in which the effective counting efficiencies of the 4 πβ counter for β-rays conversion electrons, and Auger electrons were obtained by taking the intensity ratios for certain γ-rays between the single spectrum and the spectrum coincident with the pulses from the 4 πβ counter. First, in order to verify the method, three different methods of the absolute measurement were performed with a prepared 60 Co source to find excellent agreement among the results deduced by them. Next, the 4 πβ − γ spectroscopic coincidence measurement was applied to 152 Eu sources prepared by irradiating an enriched 151 Eu target in a reactor. The result was compared with that obtained by the γ-ray spectrometry using a 152 Eu standard source supplied by LMRI. They agreed with each other within an error of 1%.

Test Production of Tritium in 3 TBq Level from Neutron-Irradiated 6Li-AL Alloy Targets

Equipments were constructed for the development of tritium production technology. Gaseous tritium in a level of 3 TBq (∼80 Ci) was extracted from neutron-irradiated 6Li-Al alloy by heating at 1,073 K under vacuum and collected in an activated-uranium getter. The recovery of the tritium was 90% or more and the isotopic purity of the product was about 50%. Throughout the production experiment, no release of tritium out of the equipments to the environment was observed.

Electronic imaging for 252Cf based neutron radiography

For 252Cf based neutron radiography, a photon counting method which performed binary image conversion and minimum ranked-order filtering has been applied using a multi-functional electronic imaging system. The contrast and spatial resolution of the radiograph have been improved by the signal processing method.

High accuracy measurement of the relative efficiency curve and determination of gamma-ray relative intensity for 38Cl

Relative efficiency curves were accurately determined for Ge gamma-ray detectors from measurements for radionuclides which emit two gamma-rays with essentially the same emission probabilities. The relative intensity of the 1643 and 2167 keV gamma-rays from 38Cl was determined to be 0.7496 (11) by using these highly accurate efficiency curves.

The absolute measurement of beta- disintegrating nuclides emitting conversion electrons with appreciable proportions

Abstract A new method was proposed for the 4πβ and 4πβ-γ coincidence absolute measurements of nuclides emitting conversion electrons with appreciable proportions. Correction formulas giving the disintegration rate were shown for 153 Sm, which can be easily extended to general forms. The validity of the derived formulas was examined by performing 4πβ, 4πβ-γ-coincidence, and β-γ-coincidence countings for 153 Sm, 156 Eu and 147 Nd, by comparing the resulting values of the disintegration rate with one another and also with those obtained by other methods, and by examining the consistency of the model. It was concluded that the present method gave satisfactory results for the above three nuclides; that is, we could determine the disintegration rate with an uncertainty of only 0·5 per cent.

4β-γ coincidence absolute measurement of nuclides emitting soft conversion electrons in appreciable proportions

Abstract A correction method has been derived for the disintegration-rate measurement of nuclides emitting soft conversion electrons along the lines of the method developed in our previous paper. The resulting correction formulae have been applied to the 4πβ-γ coincidence absolute measurement of 161 Tb and of the 140 Ba- 140 La mixed activity. The resulting disintegration rate has been found to be a reasonable value with an uncertainty of, at most, 1 per cent in either case. The proposed correction formulae have been concluded to be particularly useful for the absolute determination of nuclides emitting conversion electrons of low energies, ⪅30keV.

Development of a neutron absorption tracer technique for evaluation of fluid dynamics in coal liquefaction reactors

Abstract This article reports on the development of a neutron absorption tracer (NAT) technique for evaluating the hydrodynamic properties in direct coal liquefaction reactors. The plant was constructed at Kashima, Japan, based on the concept of the NEDOL process, and possessed three reactors which were connected in series. The reactors were 1.0 m in diameter and 11.8 m in height, and could treat 150 ton coal/day. In order to determine the residence time distribution (RTD) data of the liquid phase in the reactors, 252 Cf was used as the neutron source, and a fine gadolinium oxide powder was used as the tracer. The tracer slurry was injected into the inlet pipe of the first or third reactor, and the response was detected at the outlet pipe of the first and third reactors. Preliminary tests were performed to obtain the design principles for the neutron howitzer and the instrument system. Low- and middle-energy neutrons were more effective than thermal neutrons for the detection of the RTD of the liquid phase. The tracer particles were estimated to behave in the same manner as the liquid under conditions of coal liquefaction. The tracer injection tests were then performed 64 times during the pilot plant (PP) operation. The accuracy of the NAT technique was confirmed by comparing the gas holdups calculated from the RTD data by the NAT with those directly determined using a shutdown technique of the recycle gas. The RTD data suggested that the flow in the reactors was classified in the homogeneous bubble flow. These results show the applicability and effectiveness of the NAT technique.

Combination source for gamma-ray spectrometry

Abstract An acrylic-resin-made one-eight-sector source in which radioactive material was mounted at the angular position was constructed. The sources of this type may be used in various combinations of up to eight sources of the same or different kinds of nuclides, performing nearly point source configuration. Characterization and performance as well as applications of the combination source were discussed.

A method for estimating the tritium yield from 6Li(n,α) reactions

Abstract A program for producing high activities of tritium (of order TBq) in a nuclear reactor made it desirable to predict tritium yields conveniently, safely and with an accuracy within 10%. This paper describes how this was done by measuring the 60 Co activity from n 7 reactions with cobalt impurities in the aluminium cladding of the 6 Li-Al alloy target, from which the tritium was generated. The cobalt impurity concentration was measured by a neutron activation technique.