N. Shinohara

Efficiency calibration of a Ge detector in the 0.1–11.0 MeV region

Abstract An efficiency curve was constructed for a large-volume Ge detector located at the thermal-neutron beam line of the JRR-3M reactor at the Japan Atomic Energy Research Institute (JAERI). The calibrations for γ-ray energies below 2754 keV were accomplished with a large number of radioactive sources and above 2754 keV with the 12 C(n,γ) and 14 N(n,γ) reactions. This detector and its efficiency curve were subsequently used to determine accurately the photon emission probabilities of γ rays from the decays of 56 Co (T 1/2 =77 d ) and 66 Ga (9.5 h ) and from the 35 Cl(n,γ) reaction. These radiation sources can serve as secondary standards for efficiency calibrations.

Rapid preparation of high-resolution sources for alpha-ray spectrometry of actinides in spent fuel

Abstract A method for rapid preparation of high-resolution α-sources by electrodeposition using isopropyl alcohol and by direct drop deposition using tetraethylene glycol was investigated, in order to determine the actinides (U, Np, Pu, Am and Cm). Each actinide can be electrodeposited quantitatively within 15–20 min, and the energy resolution of the α-ray spectrum is 14–18 keV FWHM. By the direct drop deposition method, the actinides in spent fuel can be deposited simultaneously; the energy resolution obtained by measuring the source is 20–30 keV FWHM.

Isomeric yield ratios of 134I and 136I in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U

Short-lived nuclides of iodine produced in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U were separated with a rapid chemical separation system SISAK. Relative yields of the nuclides were determined by γ -ray spectrometry to obtain the isomeric yield ratios of 134mI/134gI and 136mI/136gI. Angular momenta of the fission fragments, 134I and 136I, were derived from the measured isomeric yield ratios by the spin-dependent statistical model. In the light- and heavy-ion fission, variation of the observed angular momenta can be explained by the excitation energies of the fissioning nuclei and the spherical shell structure with N = 82.

Measurements of delayed neutron decay constants and fission yields from 235U, 237Np, 241Am, and 243Am

Delayed neutron yields and decay constants for 235 U, 237 Np, 241 Am, and 243 Am were measured at the Texas AM Waldo, Karam, and Meyer; and Tuttle. Very good agreement was obtained, especially for 235 U.

Mass separation of neutron-rich isotopes using a gas-jet coupled thermal ion source

A gas-jet coupled thermal ion source was installed in the isotope separator on line at the JAERI tandem accelerator. It was used for separation of neutron-rich isotopes produced in the reaction 238U(15 MeV-p, fission). The separation efficiencies of the whole system were measured to be 3.3% for 140Cs (T12 = 63.7 s), 2.0% for 144La (T12 = 40.8 s), 2.2% for 148Pr (T12 = 2.0 m), 1.2% for 156Pm (T12 = 26.7 s) and 1.0% for 160Eu (T12 = 44 s). A long sticking time of La atoms on the ionizer surface gave a low efficiency of about 0.1% for 148La (T12 = 1.05 s). The first observation of a new isotope 166Tb was carried out using its monoxide ions from this ion source: T12(166Tb) = 21±6 s.

Comparison Method for Neutron Activation Analysis with γ-γ Matrix

A comparison method, utilizing neutron activation analysis followed by multidimensional spectrum analysis was proven to provide accurate quantification of the multi-element samples. In this study, 23 elements were detected simultaneously in a sample containing standard elements for neutron activation analysis. The method presented here can be applied for about 50 elements.

A High-sensitivity and Non-destructive Trace Element Analysis Based on Multiple Gamma-ray Detection

A new trace-element quantification method has been developed by combining multiple gamma-ray detection and neutron activation analysis. This method is characterized by high sensitivity and simultaneous analysis for multielements. The quantification accuracy amounts to 3–20% depending on statistics. It has been successfully applied to the analyses of igneous rock samples, long-lived radionuclide, 129I, and geologic samples. Future perspectives for an innovative pulsed neutron source and a new detector system will be presented.

Multiple Coulomb excitation of a 76Ge beam

A multiple Coulomb excitation experiment on a 76Ge beam was performed using a natPb target. The relative excitation probabilities were measured as a function of the projectile scattering-angle. 15 E2 matrix elements, including diagonal ones, for seven low-lying states were determined using the least-squares search code GOSIA. The expectation values of centroid for the magnitude of the intrinsic frame E2 properties Q2 show that the ground state is weakly deformed, while the shape of the 02+ level is almost spherical. The 22+ state is found to be a band head of the γ vibrational band and the 42+ state is a member of this band.

Status of six-group delayed neutron data and relationships between delayed neutron parameters from the macroscopic and microscopic approaches

Work performed in part for an American Nuclear Society Standards Committee Subgroup (ANS 19.9) to assess the status of delayed neutron data is summarized. Recent measurements of delayed neutron emission conducted at Texas A and M University are also described. During the last 10 yr, there have been advances in nuclear data libraries (e.g., improved fission product yields) that make it possible to quantitatively predict delayed neutron emission from basic data. The six-group delayed neutron data available in the literature from both macroscopic level experiments and microscopic level calculations for several actinide isotopes are compared. Results are also presented from recent experimental measurements of delayed neutron emission and delineates some of the relationships between these measurements and microscopic level predictions. For example, from the experimental measurements, Keepin`s delayed neutron group 1 is shown to correspond mainly to a single isotope. {sup 87}Br, as expected from microscopic level theory, and Keepin`s group 2 is shown to correspond to primarily two separate isotopes. {sup 137}I and {sup 88}Br. In the future, it may be useful to use properties of specific isotopes to replace Keepin`s delayed neutron groups 1, 2, 3, and 4 for prescribing delayed neutron data for actinides.

Measurements of neutron-induced fission cross section of Americium-243 from thermal neutron energy to 15 keV using lead slowing-down spectrometer and thermal neutron facility

The neutron-induced fission cross section of 243Am was measured relative to that of 235U from thermal neutron energy to 15 keV making use of a double fission chamber with 243Am and 235U electrodeposited layers. The data above 0.05 eV were measured using a lead slowing-down spectrometer coupled to an electron linear accelerator. A relative measurement to the 10B(n, α) reaction was also made using a BF3 counter at energies below 1 keV, and normalized to the absolute value obtained by using the cross section of the 235U(n,/) reaction between 200eV and IkeV. The existing experimental data by Wisshak and Kappeler, and by Knitter and Budtz-Jorgensen are in general agreement with the current measurement in the relevant energy region. However, the data by Seeger are considerably higher. The evaluated nuclear data in JENDL-3.2, ENDF/B-VI and JEF-2.2, whose data were broadened by the energy resolution function of the spectrometer, have been compared with the measured result. The fission cross section for thermal ne...