The energy dependent neutron transmission function of the Cd-filter covering a cylindrical 1/ν-detector was calculated with consideration given to the perturbation effect in the surrounding medium. The results were found to agree well with experiments using lead slowing-down time spectrometer.
The effective Cd cut-off energy for 1mm thick Cd was calculated from the above transmission function, and found to be about 50% larger than the reported values.
The validity of the assumption of 1/E^1+β spectrum in a graphite moderator is discussed, and the β-value determined with an accuracy of 0.01 from the reaction rate ratio of BF₃-counters covered with the different thicknesses of Cd- and B-filters. The region of the 1/E-spectrum neutron field in the graphite standard pile was determined by using this technique.

抄録全体を表示

Asymptotic neutron decay constants were measured in effectively infinite light water systems poisoned with Cd and Gd as non-1/v absorbers, by changing the concentration of the absorbers added. The capture γ-ray counting technique was used for detecting the decaying neutron, to eliminate the spatial higher modes .The effective absorption cross section α and the absorption cooling (or heating) coefficient β derived from the measured decay constant curves vs. concentration were 3, 343±42 barn, (0.61±0.03)×10^-17 barn•cm³ for Cd and 4, 0211±230 barn, (9.6±1.1)×10^-17barn•cm³ for Gd, respectively. For α, the calculations reported so far, based on the Nelkin model, are in good agreement with the measurements, while a significant discrepancy appears in the comparisons on β.

抄録全体を表示

Thermoluminescence from γ-irradiated 3-methylpentane at 77°K has been studied. Two kinds of emission spectra are observed in the visible region according to temperature. The one has its maximum intensity at 425nm and is observed in the temperature range of 77°∼83°K (Spectrum I), the other its maximum at 530nm, appearing at 83°∼90°K (Spectrum II). The effects brought upon the integrated luminescence intensity by differences in radiation dose, by IR and UV bleaching, by the addition of electron or hole scavengers, and by standing in dark were examined, and the results are compared with those obtained from optical absorption in the IR and UV regions under various experimental conditions. The results suggest that the spectrum I is caused by the recombination of positive holes with electrons released by the warming, while the spectrum II would appear attributable the recombination of positive holes with some anionic species produced by the reaction of electrons with radicals.

抄録全体を表示

Measurements of reactor parameters, such as prompt neutron generation time and subcriticality, have been made in the past using band pass filters or else applying the correlation technique. Other new methods of reactor parameter estimation would now appear to be available thanks to the recent developments in optimal filtering technique, such as optimal linear (Kalman) filter and some of the nonlinear optimal filters. Such new methods should prove very promising for on-line estimation of the reactor parameters.
In this paper a description is given of the application of some of these new methods to subcriticality measurements. The results of computer simulation of estimates using the Kalman filter are presented, as also on account of experiments with the actual reactor noise obtained on the Toshiba Training Reactor (TTR-1), using a nonlinear analog filter. The results agreed with those reported by Nomura using conventional methods.

抄録全体を表示

The separation of fission-product La, Ce, Pr, Vd and Y was performed in 4 min by electromigration. As complexing agent, nitrilotriacetic acid was used at two concentrations of the NTA ion selected so as to optimize mutual separation of the elements. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated sample. The purity of the elements thus separated was checked by γ-ray spectrometry. At the higher concentration of NTA (_??_NTA_??_=1.0×10^-2M, pH=4.1) under which all of rare earths and Y migrate toward the anode, the elements were well separated from each other, although appreciable amounts of other F. P. were also found in each fraction. On the other hand, at the lower NTA concentration (_??_NTA_??_=4.0.×10^-3M, PH=2.0) where the F. P. all migrate toward the cathode, each zone contained the isotopes of the respective element almost exclusively, except for a few small photo-peaks attributable to other elements. In each fraction, the 92.5min ¹⁴²La and 14min ¹⁴³La, the 14min ¹⁴⁶Ce (24min ¹⁴⁶Pr), the 24min ¹⁴⁶Pr and 12min ¹⁴⁷Pr, the 1.8hr ¹⁴⁹Nd, the 20.3min ⁹⁴Y and 10.9min ⁹⁵Y were identified from the energies of photo-peaks and their decay rates.

抄録全体を表示

Investigations of reactor noise in water-cooled research reactors show that the power spectral density rises in the low frequency domain. The cause of this phenomenon is often attributed to fluctuations in the coolant temperature, but this has never been proved experimentally. The present experiment is an attempt in this direction.
The temperature fluctuation in a natural convection heat transfer loop decoupled from neutronics was measured and analyzed in the frequency domain. The test section of the loop had a rectangular channel measuring 5mm×50mm in cross section and 500mm in length. This configuration simulated a coolant channel of the MTR-type fuel element used in swimmingpool reactors. The power spectral density of the temperature fluctuation at the channel exit showed a shape similar to the power spectral density of the noise-equivalent source obtained in the Kyoto University Reactor at comparable power levels.

抄録全体を表示

A new approximation is proposed for calculating the first flight collision probabilities in cluster-type fuel lattices, based on the subcell model In this method the unit cluster is divided into subregions of fuel pins (with or without cladding) arranged in rings, associated coolant, and homogeneous annular regions surrounding the fuel region. The fuel pins and associated coolant are treated separately, and each is distinguished ringwise as a different subregion. The collision probability is then calculated for a neutron proceeding from one subregion to another. The method treats rigorously the fuel annulus where a neutron starts with consideration given to the non-uniform structure of the annulus. The other fuel annuli, however, are treated approximately as if each annulus were homogeneous. The values of the homogenized cross sections of the annuli are determined in such manner that the number of outgoing neutrons from the homogenized annuli equals that from the actual non-uniform fuel annuli. The collision probability is then apportioned among fuel pins and coolant in the annulus.
The results of the method compare favorably with those of the exact methods based on direct numerical evaluation of the collision probabilities. Multigroup application of the method shows that the time required for calculation is comparable with the standard multigroup calculation scheme.

抄録全体を表示