Journal of Nuclear Science and Technology
Online ISSN : 1881-1248
Print ISSN : 0022-3131
Volume 11, Issue 10
Displaying 1-5 of 5 articles from this issue
  • Mikio HYAKUTAKE, Masateru SONODA, Akira KATASE, Yoshihisa WAKUTA, Masa ...
    1974 Volume 11 Issue 10 Pages 407-421
    Published: October 25, 1974
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    Using a time-of-flight spectrometer, the differential cross sections were measured for the elastic and inelastic scattering of 14.1 MeV neutrons by 6Li, 7Li, 9Be, 10B and 11B. In the case of elastic scattering by 7Li and 10B, correction was applied to subtract the contribution of in-elastic scattering from the unresolved first excited state, after which, the elastic scattering data were compared with predictions based on the optical model. The potential parameters derived with a seven-parameter search yielded angular distributions agreeing with the present experi-mental data. The expressions for these parameters are presented as a function of mass number.
    The experimental data on inelastic scattering were analyzed with the distorted wave Born approximation. The deformation parameters were estimated to be nearly equal to or larger than unity for these nuclei.
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  • Toshikazu TAKEDA, Kunitoshi KURIHARA, Masaaki YAMAMOTO
    1974 Volume 11 Issue 10 Pages 422-433
    Published: October 25, 1974
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The effect of neutron streaming upon the neutron multiplication factor in a fast critical assembly FCA-VI is estimated by considering the anisotropy of the diffusion coefficient. In this paper, the Benoist formula is adopted to obtain the diffusion coefficient. In his original ex-pression, many effects such as those of neutron angular distribution, multiple collision (correla-tion of different neutron passes) and finiteness of lattice system are included. In order to estimate these effects, the generalized first-flight collision probability method is adopted as in the previous paper, and an improvement is brought over the previous method so as to calcu-late the effective diffusion coefficient in a practical slab lattice cell which is asymmetric about the center of the cell.
    Using the method of calculation described above, the anisotropic effect of neutron stream-ing in the lattices TA, TB, TC and TD used in the FCA VI-1 assembly is estimated. The effect of anisotropy of the diffusion coefficient upon the multiplication factor for the TA, TB, TC and TD lattices is found to be -0.156, -0.181, -0.242 and -0.330% Δk/k, respectively.
    Usually, the effects of neutron distribution, multiple collision and anisotropic scattering are neglected in evaluating the diffusion coefficient when using the Benoist formula. Among these factors, the effect of multiple collision of neutrons has the largest effect upon the dif-fusion coefficient and upon the neutron multiplication factor. For the TA lattice, 30% of the overall effect of anisotropy is attributable to multiple collision.
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  • Masahiko UTSURO
    1974 Volume 11 Issue 10 Pages 434-444
    Published: October 25, 1974
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    An analysis is presented on the slowing-down of cold neutrons in moderators in which molecular or intramolecular rotations play a predominant role. Use is made of two kinds of approximation : (1) the classical approximation in which the rotational effects are taken into account in terms of an effective mass, and (2) the few-level approximation which becomes useful at the lowest limits of temperature. Further, the concept of effective mass is extended to include also the effects of a weak hindering barrier against rotation.
    The expressions derived for the effective cold neutron temperature in low temperature moderators are compared with experimental results obtained on typical materials-ondensed methane and methyl compound, and satisfactory agreement is obtained. The analysis further reveals some particular characteristics inherent in the slowing-down of cold neutrons due to the rotational motions of molecules. Moreover, the present model is found valid for expressing the slopes in the 1/v-region presented by the scattering cross section of ammonium ions in low barrier materials.
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  • Hiroshi OHASHI, Etsuzo NODA, Takashi MOROZUMI
    1974 Volume 11 Issue 10 Pages 445-451
    Published: October 25, 1974
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    The oxidation of UO2 was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO2 to U3O7 significantly influenced the rate of the oxidation of the second stage from U3O7 to U3O8.
    The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These find-ings suggest the existence of a close connection between the rate of formation of the U3O7 phase and the rate of the subsequent oxidation of this phase : A slow formation of U3O7 would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U3O7 at 200° : The increase of annealing time prolonged the induction stage.
    The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y))=(1/2.303)kntn. The time exponent n in this equation varied in the range of 1.02.5, and the rate constant k of 1.15×10-42.04×10-1min-1, depending on the experimental conditions.
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  • Hiroshi TSUBAKIHARA, Touichi OKADA, Tokuo SUITA, Takefumi HORIUCHI, Ki ...
    1974 Volume 11 Issue 10 Pages 452-458
    Published: October 25, 1974
    Released on J-STAGE: April 18, 2008
    JOURNAL FREE ACCESS
    A systematic study has been carried out on Nb-Ti wire of two different kinds of metal-lurgical structure, to examine the effects of neutron irradiation on the critical density Jc. The samples used were Nb-47.6 a/0 Ti (sample #A) and Nb-59.8 a/0 Ti (sample #B), which were aged at 380°C for 0104 min and irradiated to 1.3 × 1018n/cm2 (En>0.1 MeV). The sample temper-ature during the irradiation is believed to have been below 70°C. The values of Jc of both #A and #B aged up to 50 min were found to increase with irradiation. But when aged beyond 100 min, #B had its value of Jc lowered by the irradiation. The presence of Ti enriched precipitates such as α and ω phases in the samples was surmised from the behavior shown by the critical temperature Tc. The Tc of #A and #B changed little by irradiation when aged not longer than 100 min, but with aging beyond 500 min, # B showed a decrease in its value of Tc. This decrease indicates that the Ti concentration in the matrix may have increased through radiation-induced breakup of the above-mentioned precipitates, which, in turn, would have brought about the reduction observed in Jc upon irradiation. It is concluded that super-conducting Nb-Ti wire with Jc endanced by precipitation does not appear very resistant to neutron irradiation. This underlines the importance of the choice of superconducting materials to be used in fusion reactor magnets.
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