Naoshi Mutsuro

Angular Distributions of Fast Photoneutrons from Pb, Bi and Ta

Using a stilbene scintillation detector, the angular distributions of fast photoneutrons of energies greater than two bias values of 7.4 MeV and 8.7 MeV were measured for Pb, Bi and Ta at 25.5 MeV end point energy of the bremsstrahlung. For Pb and Bi, the angular distributions were found to be asymmetric about 90 degrees with respect to the gamma-ray beam axis and were strongly peaked in a forward direction, but in the case of Ta not so obviously. The angular distributions were fitted to W(θ)=A+Bsin 2 θ+Ccos θ, using a least squares analysis. The present experiment indicates that, in the high energy region of the (γ, n) spectrum, C/A increases with the detecting threshold energy for neutrons and on the otherwise B/A decreases with the energy.

Photoneutron Cross Sections for Ag107, Mo92 and Zr90

Photoneutron cross sections and the yield curves were taken by the residual activity method for Ag 107 , Mo 92 and Zr 90 . Threshold energy were obtained as 9.35±0.1 MeV, 9.15±0.1 MeV, 12.38±0.1 MeV and 12.3±0.1 Mev for Ag 107,109 , Mo 92 and Zr 90 respectively. The energy for the maximum cross section was obtained as 14.5 MeV for Ag 107 , 16.5 MeV for Mo 92 and 17 MeV for Zr 90 . The giant resonance widths were measured about 5.3 MeV, 2.7 MeV and 2.9 MeV respectively. Intrinsic quadrupole moment determined from above data was (1.9±0.7)×10 -24 cm 2 for Ag 107 .

Structure of the giant resonance in the Al27(p, γ) reaction

Abstract The variation of the cross section for Al27(p, γ0 + γ1)Si28 with proton energy from 7.5 to 14.7 MeV, reveals the full structure of the giant resonance. Gamma ray yields for transitions to the ground and first excited states of the product nucleus were measured using a large NaI(Tl) crystal spectrometer. The width of the giant resonance is of the order of 4 MeV, with many resonance peaks and possibly with a splitting due to deformation.

Nuclear Magnetic Resonance on Oriented 175Ta and 177Ta

175 Ta and 177 Ta nuclei were oriented at low temperature as dilute impurities in Fe. The magnetic hyperfine splitting frequencies ν=|µ B HF / I h | of the 175 Ta and 177 Ta ground states have been measured to be 320.45(11) and 317.552(55) MHz by using the technique of NMR-ON. Taking the known hyperfine field of 181 Ta in Fe, the magnetic moments have been deduced: |µ( 175 Ta, 7/2 + )|=2.270(45) and |µ( 177 Ta, 7/2 + )|=2.250(45)µ N . These values of the magnetic moments are discussed in the framework of the rotational model.

g -Factor of the Ground State of 73 Se

Nuclear magnetic resonance on oriented 73 Se in an iron host has been observed at about 7 mK. From resonance-shift measurement, the magnetic hyperfine-splitting frequency ν M , g -factor and magnetic hyperfine field were derived as ν M =102.61(3) MHz, | g (9/2 + )|=0.188(16) and B HF ( 73 Se Fe )=716(81) kG. The experimental values of the g -factors of the g 9/2 neutron states, in the neighborhood of the neutron number 40, are compared with the theoretical values based on the core-polarization model.

On the Study of P31(γ, n) and S32(γ, n) Reaction

Photoneutron cross sections of P³¹ and S³² were measured up to 24 Mev by using bremsstrahlung from a 25 Mev betatron. Each neutron yield point was the result of four or five measurements involving a count of about 10⁴ for each point. Cross section curves and characteristic constants are shown. (W.D.M.)

Photoneutron Reaction of S32

The photoneutron cross section of S 32 was observed up to 22 MeV with good energy resolution, together with the photoneutron spectrum using a stilbene scintillation spectrometer. Fine structures were observed in either of the two measurements. Taking into account the threshold energy and the excitation energies of the residual nucleus, these structures have been shown to be consistently related with each other. Experimental results were discussed using the statistical model calculation, assuming that the emitted particles were only p -wave and f -wave particles. The integrated cross section ratio for S 32 (γ, n ) to P 31 (γ, n ) reaction and the same ratio for S 32 (γ, p ) to S 32 (γ, n ) reaction were well explained by the calculations. The difference between the energy spectrum of the photoprotons from P 31 and that from Si 28 also seemed to be well explained qualitatively. In the appendix, the contributions of the f -wave protons for the energy spectrum of photoprotons were shown. Summarizing the discu...

Structure of Giant Resonance in Al27(p, γ) Reaction

The 90 deg yields of gamma radiation produced from proton capture by Al/ sup 27/ were measured at proton energies of 7.5 to 14.5 Mev. The relative cross section data combined with these of Canberra revealed a giant resonance of width on the order of 4 Mev and with many peaks. Three resonances at 7.61, 8.75, and 10.13 Mev can be attributed to the excited state of Si/sup 28/. The giant resonance is interpreted from the standpoint of spheroidal deformation of a compound nucleus. (D. L.C.)

He3-Alpha Scattering

Differential cross sections for scattering of He 4 by He 3 have been measured at E α =27.7, 28.5, 29.4, 30.0, 32.0, 33.4, 34.7, 36.5, 38.4, 41.0 MeV using a scintillation counter spectrometer, at the center of mass angles from ∼30° to ∼150°. Three distinct minima were found at about 45°, 100°, and 140°. The absolute cross-section and the pattern of the angular distribution showed no appreciable change in the energy range investigated: thus, there was found no sharp resonance in the He 3 +He 4 system corresponding to an excited state of Be 7 between 13.4 and 19.2 MeV. Differential cross-sections of the protons from He 3 (α, p )Li 6 Li 6* were observed. Differential cross-sections of alpha-alpha scattering were also measured at E α =33.5 and 35.5 MeV.

Pulse shape discrimination with a P-I-N solid state detector

Abstract A new technique of pulse shape discrimination with a single p-i-n solid state detector is described. The technique was found suitable for the identification of photoprotons in the strong gamma-ray and electron background in photoreactions by bremsstrahlung X-rays.