J. Katakura

Electromagnetic structure of 98Mo

Abstract The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

Vectorization of the KENO IV code

The multigroup criticality safety code KENO-IV has been vectorized and tested on the FACOM VP-100 vector processor. At first, the vectorized KENO-IV on a scalar processor was slower than the original one by a factor of 1.4 because of the overhead introduced by vectorization. Making modifications of algorithms and techniques for vectorization, the vectorized version has become faster than the original one by a factor of 1.4 on the vector processor. For further speedup of the code, some improvements on compiler and hardware, especially on addition of Monte Carlo pipelines to the vector processor, are discussed.

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.

New Method for Calculating Aggregate Fission Product Decay Heat with Full Use of Macroscopic-Measurement Data

We propose a new “hybrid” method for calculating the aggregate decay heat from fission product nuclides after a fission burst. The decay heat from a given fissioning system is expressed as a linear combination of macroscopic-measurement data for other fissioning systems with a small residual term. This method is based on the linearity of the decay heat to the fission yield. The coefficients in the linear combination are obtained from fitting the fission yield of the given fissioning system with a linear combination of fission yields of other fissioning systems. To demonstrate usefulness of this method, it is applied to examining the consistency among measured decay heat powers of five fast and three thermal neutron induced fissions. The hybrid-method calculations agree well with the measurements and usual summation calculations at cooling times before 4,000 s, except for a γ component measurement of the 235U thermal fission at about 2,000 s. These results indicate the consistency and reliability of the decay heat evaluation for these systems with the above exception. Furthermore, they also imply usefulness of the present method in predicting the decay heat of other fissioning systems, for which no measurements have been performed so far.

Rotational bands of 155Gd

Abstract High spin states of 155 Gd have been investigated using the 150 Nd( 12 C, α3n) reaction. Three rotational bands have been observed. Two of them have been extended up to (51/2) + and 45/2 − , respectively, and another band has been newly observed. The backbending and blocking effects are discussed in comparison with the calculation of cranked shell model. The routhians and the B (M1/BE2 ratio of the high-Ω rotational band are compared with the calculation by the tilted axis craking model. In addition the ground state rotational band of 156 Gd has been extended up to 22 + .

Comparison of Burnup Calculation Results Using Several Evaluated Nuclear Data Files

Burn-up calculation and comparison of the results were carried out to clarify the differences among the following latest evaluated nuclear data libraries: JENDL-3.2, ENDF/B-VI and JEF-2.2. The analyses showed that the differences seen among the current evaluated nuclear data libraries are small for evaluation of the amounts of many uranium and plutonium isotopes. However, several nuclides important for evaluation of nuclear fuel cycle as 238Pu, 244Cm, 149Sm and 134Cs showed large differences among used libraries. The chain analyses for the isotopes were conducted and the reasons for the differences were discussed. Based on the discussion, information of important cross section to obtain better agreement with the experimental results for 238Pu, 244Cm, 149Sm and 134Cs was shown.

Analysis of Uncertainties in Summation Calculations of Decay Heat Using JNDC FP Nuclear Data Library.

Uncertainties of decay heat summation calculations are derived for the thermal fission of 235U and 239Pu and the fast fission of 238U through sensitivity analyses using data given in the JNDC FP nuclear data library. The uncertainties analyzed are those relevant to decay energies, fission yields and decay constants among the nuclear data contained in the summation calculation. For nuclides lacking complete experimental data, the uncertainties of the decay energies are theoretically calculated. Thus analyzed, the maximum uncertainties of burst fission are 2.8 % for 235U, 3.2%” for 239Pu and 4.2% for 238U in the range of cooling time between 1 and 109s, and in the case of infinite irradiation, the corresponding level of maximum uncertainty is below 1.6% for all three fissioning nuclides.

Calculation of the Delayed Gamma-Ray Energy Spectra from Aggregate Fission Product Nuclides

The beta-delayed emission process of gamma rays was treated with a gross theory of beta decay and a cascade gamma transition model. The method proposed was applied to calculations of the delayed gamma-ray energy spectra for short-lived fission product nuclides that lack experimental information on their gamma-ray transition properties. The calculated results are used to complement the summation calculation of the aggregate gamma ray spectrum from an irradiated sample of fissile material after a short cooling time. A satisfactory agreement was obtained between the calculated and the measured spectra, which supported the appropriateness of the coupled gross beta and cascade gamma model. The method was also applied to the calculation of the equilibrium energy spectrum of the delayed gamma rays in operating reactors. The resulting shape resemble the prompt fission-gamma-ray spectrum.

A position-sensitive particle detector for Coulomb excitation experiment

For Coulomb excitation experiments using a γ-ray detector array, a position-sensitive particle detector system that has a good angular resolution, capability of managing a high-counting rate, robustness for a radiation damage, compactness (under 110 mm φ) and easiness of handling is necessary. For this purpose we developed a new device utilizing plastic and yttrium aluminum perovskite activated by cerium (formula YAlO3:Ce abbreviated YAP Ce) scintillators and a position-sensitive photomultiplier tube. The detector system could operate at a high-counting rate (about 105), and with a good position resolution of 0.5–1.2 mm, which was enough for Doppler correction of the γ rays. It could sustain the radiation damage caused by Coulomb excitation experiments with heavy ions for more than 50 days. The detector chamber was well fitted in the 110 mm φ diameter of the internal space of a compact γ-ray detector array, GEMINI. This was much easier to handle than the position-sensitive gas counter. In Coulomb excitati...

Multi-quasiparticle excitations in 145Tb

High-spin states in145Tb have been populated using the118Sn (32S, 1p4n) reaction at beam energy of 165 MeV. The level scheme of145Tb has been established up toEx≈7.4 MeV. The level scheme shows characteristics of a spherical or slightly oblate nucleus. Based on the systematic trends of the level structure in the neighboringN=80 isotones, the level structure in145Tb below 2 MeV excitation is well eplained by coupling anh 11/2 valence proton to the even-even144Gd core. Above 2 MeV excitation, most of the yrast levels are interpreted with multi-quasiparticle shell-model configurations.