Measurements were made to determine the initial conversion ratio C0 in a low-power UO₂-H₂O assembly. Special fissile foils were developed for the purpose, and the coincidence counting technique was extended for application to the Al catcher foils used. The conversion ratio obtained was 0.495±0.043.

View full abstract

A new principle is presented for obtaining absolute reactor power by processing the random fluctuation of neutron flux based on the stochastic nature of nuclear reactions. The required com-bination of instruments to carry out experiments is described, and experimental results obtained in a swimming pool reactor are reported. The power spectral density of the output current of an ion chamber located near the reactor core is determined by reactor kinetic parameters such as delayed neutron yield, life time, ν(mean number of neutrons generated per fission) and counter efficiency as well as by the total number of neutrons in the core, which is a measure of absolute power.
Using either logarithmic amplifier or reactivity meter, absolute reactor power can be measured without any information about detector efficiency. This method has such merits as easiness and simplicity in operation, ability to measure absolute power in the range 0.01-100 W where other methods are inapplicable, and negligible effect of changes in core configuration or in detector position.
The results of actual reactor experiments with this method proved to agree fairly well with those of absolute measurement by gold foil activation.

View full abstract

Highly radioactive fallout particles resulting from the first Chinese nuclear explosion of 16 Oct., 1964, have been studied by X-ray microanalysis, X-ray microdiffraction and neutron activation analysis. Most of these particles are quite or nearly spherical, blakish colored, 10-15 μ in diameter and fairly hard. They appeared to bear some internal stress, and were of amorphous structure. Qualitative and quantitative analyses of one of these particles by means of an electron probe X-ray microanalyzer revealed a large portion of Al, a fair portion of Fe, Ca and Ti as well as a very small portion of K. These elements are not uniformly distributed on the particle surface.

View full abstract

A description is given of the design and performance of a whole-body counter at the University of Tokyo. The apparatus is intended for use in medical research and as control measure for radiation protection. Three types of detectors are installed for whole body counting of the human subject: (a) 5" NaI(Tl) scintillation probe, (b) 2.5" NaI(Tl) scintillation probes, and (c) large plastic scintillation probes. Output signals from the detectors are analyzed in a 400-channel pulse height analyzer. The subject is measured either on: (a) stretcher, (b) chair, or (c) V-bottom bed. In using the plastic scintillation probes, counting for a period of 15 min suffices to detect 150g of potassium in the body, allowing for a statistical counting error of 2.2%. Spectra from some human subjects are presented.

View full abstract