Toshiro Ohsaki

Scientific feasibility of incineration in scnes

Abstract We confirm the simultaneous realization of burning or transmutation of radioactive nuclides and of net energy generation. An investigation of the neutron balance in a reactor core is carried out. It is numerically shown that the neutrons can burn all the transuranium elements (TRUs) produced in the core as fuel in the SCNES reactor. It is numerically found that the fission products (FPs) whose half-lives are longer than one year can be contained and transmuted into harmless nuclides in the core without losing the neutron balance. It is shown that isotope separation of the FPs is required to realize the SCNES. As an example, we investigate the required energy for a scheme of the atomic vapor laser isotope separation (AVLIS) of FPs. It is shown that, in principle, the energy required for the isotope separation is much lower than the generated fission energy. The SCNES is scientifically realized in principle.

Measurement of keV-neutron capture cross sections and capture gamma-ray spectra of 99Tc

The capture cross sections of 99Tc were measured in the incident neutron energy region from 8 to 90 keV and at 190, 330, and 540 keV. A neutron time-of-flight method was adopted with a ns-pulsed neutron source by the 7Li(p, n) 7Be reaction and with a large anti-Compton NaI(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture gamma-ray pulse-height spectra to derive capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of 99Tc were obtained with the error of about 5%. The present results were compared with other measurements and the evaluated values in JENDL-3.2 and 3.3 and ENDF/B-VI. Capture gamma-ray spectra were obtained by unfolding observed capture gamma-ray pulse-height spectra. A change of slopes was observed at 2.2 MeV in the spectra. The multiplicities of observed gamma rays were obtained from the gamma-ray spectra.

Neutron capture nucleosynthesis in the universe

Abstract First, the nucleosynthesis in the universe was reviewed. In particular, the neutron capture nucleosyntheses in the Big-Bang and the s- and r-processes were reviewed in detail. It was pointed out that keV-neutron capture cross sections were important for the study on the neutron capture nucleosynthesis. Second, our measurement of keV-neutron capture cross sections was explained briefly, and the results on 7Li, 12C, and 16O were shown and compared with previous experimental values and the predicted values from the 1/v law and the thermal neutron capture cross sections. The results at 30 keV on 12C and 16O were much larger than the 1/v predictions, while the result at 30 keV on 7Li was in good agreement with the 1/v prediction. The large values for 12C and 16O were ascribed to the non-resonant p-wave neutron capture from the analysis of observed capture g-ray spectra and the neutron energy dependence of derived partial capture cross sections. As for 7Li, the good agreement was ascribed to the peculiarity of bound states of its residual nucleus, which strongly suppresses the non-resonant p-wave neutron capture. Finally, it was shown that the non-resonant p-wave neutron capture is predominant in the neutron capture nucleosynthesis of light nuclei in the universe.

Measurement of ke V-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 147,148,149,150,152,154Sm

The neutron capture cross sections and capture γ-ray spectra of 147,148,149,150,152,154Sm were measured in the neutron energy region of 10 to 90 keV and at 550 keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the 7Li(p, n)7Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained with the error of about 5% by using the standard capture cross sections of 197Au. The present results were compared with the evaluated values of JENDL-3.2 and previous measurements. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra of 150,152,154Sm, and the energy position of the shoulder was consistent with the systematics obtained in our previous work.

Fast neutron capture reactions in nuclear astrophysics

The cross sections of the neutron capture reaction on light nuclei, protons,12C and16O, were measured at astrophysically relevant energies between 10 and 300 keV. They are not only important for estimating yields of elements in the primordial nucleosynthesis, stellar nucleosynthesis of s-, r-, and p-processes, but also to study the role of meson exchange currents, the nuclear structure and the reaction mechanism. In the measurement, we used a prompt γ-ray detection method, combined with a pulsed neutron beam, and a recently developed Monte-Carlo code, TIME-MULTI, to correct for neutron multiple-scattering effects in a sample.

Neutron capture cross sections of light nuclei in primordial nucleosynthesis

Abstract Neutron radiative capture cross sections of 7 Li and 12 C were measured at a neutron energy of 30 keV to study the production rate of intermediate-mass nuclei in primordial nucleosynthesis. The reaction cross sections were obtained by using pulsed neutrons and by observing prompt γ-rays from the captured state. The present results favor the nucleosynthesis of intermediate-mass nuclei in the early universe.

Measurement of ke V-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 143,145,146Nd

The neutron capture cross sections and capture γ-ray spectra of 143,145,146Nd were measured in the neutron energy region of 10 to 90 keV and at 550 keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the 7Li(p, n)7Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained with the error of about 5% by using the standard capture cross sections of 197Au. The evaluated values of JENDL-3.2 and previous measurements were compared with the present results. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was observed around 2 MeV in the γ-ray spectra of 145,146Nd, and the energy position of the shoulder was consistent with the systematics obtained in our previous work.

Measurement of keV-neutron capture cross sections and capture gamma-ray spectra of 91,92Zr

The capture cross sections and capture γ-ray spectra of 91,92Zr were measured in an incident neutron energy region from 15 to 100keV and at 550keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the 7Li(p,n)7Be reaction and with a large anti-Compton NaI(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to obtain capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of 91,92Zr were derived with the errors from 5 to 9%. The present results were compared with other measurements and the evaluated values in JENDL-3.3 and ENDF/B-VI. The JENDL-3.3 evaluations for 91Zr were in agreement with the present results, but those for 92Zr largely deviated from the present results. The capture γ-ray spectra of 91,92Zr were obtained by unfolding the observed capture γ-ray pulse-height spectra. The multiplicities of observed γ rays were derived from the γ-ray spectra.

Neutron economy and nuclear data for transmutation of long-lived fission products

In the study of Self-Consistent Nuclear Energy System, the following 29 long-lived fission products (LLFPs) have been selected to be transmuted into stable or short-lived nuclides 106 Ru, 102 Rh, 109 Cd, 125 Sb, 134 Cs, 146,147 Pm, 154,155 Eu, 171 Tm, 85 Kr, 90 Sr, 93m Nb, 113m Cd, 121m Sn, 137 Cs, 151 Sm, 152 Eu, 108m Ag, 158 Tb, 166m Ho, 79 Se, 93 Zr, 94 Nb, 99 Tc, 107 Pd, 126 Sn, 129 I, 135 Cs. In the present study, the number of neutrons necessary for the transmutation of the 29 LLFPs with an FBR was evaluated, and the present status of the (n, γ) and (n,2n) cross section data of the 29 LLFPs in JENDL-3.2 and ENDF/B-VI was investigated. The main results of the present study are as follows: (1)only 0.25 neutron per fission is necessary for the transmutation of the 29 LLFPs with isotopic separation, whereas 6.8 neutrons are necessary with chemical separation, (2)the accuracy of the cross sections is 30 to 100 % except for the (n, γ) cross sections of limited nuclides in limited incident neutron energy regions.

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 140Ce and 141Pr

The neutron capture cross sections and capture γ-ray spectra of 140 Ce and 141 Pr were measured in the neutron energy region of 10 to 100 keV and at 550 keV. Prompt γ rays from a capture sample were detected with a large anti-Compton Nal(Tl) spectrometer, employing a neutron time-of-flight method with a 1.5- ns pulsed neutron source by the 7Li(p, n)7Be reaction. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to extract capture yields. The capture cross sections were derived with the error of about 5% by using the standard capture cross sections of 197Au. The present results were compared with evaluated values in JENDL-3.2 and previous measurements. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous bump was observed around 1.5 MeV in each γ-ray spectrum of 140Ce and 141Pr, and its energy position was consistent with the systematics obtained in our previous work. The multiplicities of the observed capture γ rays were derived from the γ-ray spectra.