A. Taniguchi

Qβ Measurements of Neutron-Rich Isotopes in the Mass Region 147≤A≤152

The systematic Q β measurements of 14 neutron-rich nuclei in the mass region from A =147 to A =152 have been performed with an HPGe detector. Neutron rich nuclei were mass separated from the thermal neutron induced fission of 235 U using a He-jet type on-line isotope separator which has been developed at the Kyoto University Reactor (KUR). From β-ray singles and β-γ coincidence measurements, the Q β values of 147 La, 147-150 Ce, 147-152 Pr, 152 Nd and 152 Pm have been determined. The Q β values of 152 Pr and 152 Nd have been measured for the first time. The atomic masses derived from the Q β values are compared with the predictions of theoretical mass calculations.

Precise Intensity Measurements in the 14N(n, γ)15N Reaction as a γ-Ray Intensity Standard up to 11MeV

The main γ-ray intensities in the 14N(n, γ)15N reaction were determined at an accuracy of 0.3–1.0% based on the intensity balance principle. Measurements were performed at the supermirror neutron guide tube at the Kyoto University reactor (KUR). A liquid nitrogen target and a deuterated melamine (C3D6N6) one were used. We prepared a full-energy-peak efficiency curve by combining the measured and calculated efficiency curves. The previous values widely used as intensity standards agreed with the present results within 4–5% in the 2–11 MeV region, but the ratio to the present values showed a monotonic decrease with the increase in _-ray energy. The results reported by Belgya in 2006 agreed with the present one within 2–3% in the 2–8MeV region; nevertheless, the ratio showed a small oscillation versusγ-ray energy.

Beta Decay of 151Pr into Levels in 151Nd

The β-decay of 151 59 Pr 92 to the levels in 151 60 Nd 91 has been studied from the fission products of 235 U using an on-line isotope separator (KUR-ISOL). Gamma-rays and conversion electrons have been measured. Conversion coefficients have been determined for the first time. The precise decay scheme is proposed up to 2430 keV. The newly observed 65 γ-rays and 16 levels are incorporated in it. The deduced level scheme of 151 Nd was compared to the calculated level scheme on the basis of the rotation-vibration coupling model with a Nilsson potential. Low-lying levels were well reproduced by this model.

Low-Lying Levels in 147Nd in the Decay of 147Pr

The level structure of 147 Nd has been studied from the decay of 147 Pr. The radioactive sources of 147 Pr were separated from the fission products of 235 U using the on-line isotope-separator KUR-ISOL and chemical separation techniques. A decay scheme has been constructed involving 93 γ-rays and a newly observed 1261.1 keV level. The half-lives of 49.9, 127.8 and 214.6 keV levels were determined to be 1.0 ±0.3 ns, 0.4 ±0.1 ns and 4.53 ±0.06 ns, respectively. Conversion coefficients of 15 transitions were determined. The parities for the levels at 49.9, 127.8, 214.6, 314.7 and 463.5 keV are deduced to be odd. Spins and parities for the 769.3 and 792.6 keV levels are deduced to be 3/2 + . The properties of transition probabilities between the low-lying triplet hole states are similar to that of three particle states in the N =85 isotones.The level structure of 147 Nd has been studied from the decay of 147 Pr. The radioactive sources of 147 Pr were separated from the fission products of 235 U using the on-line isotope-separator KUR-ISOL and chemical separation techniques. A decay scheme has been constructed involving 93 γ-rays and a newly observed 1261.1 keV level. The half-lives of 49.9, 127.8 and 214.6 keV levels were determined to be 1.0 ±0.3 ns, 0.4 ±0.1 ns and 4.53 ±0.06 ns, respectively. Conversion coefficients of 15 transitions were determined. The parities for the levels at 49.9, 127.8, 214.6, 314.7 and 463.5 keV are deduced to be odd. Spins and parities for the 769.3 and 792.6 keV levels are deduced to be 3/2 + . The properties of transition probabilities between the low-lying triplet hole states are similar to that of three particle states in the N =85 isotones.

Measurement of response functions of HPGe detectors for monoenergetic electrons and positrons in an energy range of 6.0–9.0 MeV

Abstract For precise determinations of β-ray endpoint energies of nuclei far from the line of β stability, the response functions of HPGe detectors have been measured for monoenergetic electrons and positrons in an energy range of 6.0–9.0 MeV. Electron and positron beams were produced by hitting a tungsten target with electron beams from the KURRI-LINAC. Based on the response functions obtained, the QEC value of the high-spin isomer of 126La has been determined to be 7700(100) keV for the first time.

Beta Decay of 153Nd and Reflection Asymmetric Deformation in 153Pm

The level structure of 153 Pm has been studied from the decay of 153 Nd. The radioactivities of 153 Nd were separated from the fission products of 235 U using the upgraded KUR-ISOL. A precise decay scheme of 153 Nd has been constructed up to 2 MeV and 115 γ-rays and 36 levels were involved in the decay scheme, in which 107 γ-rays and 28 levels were newly observed. The multipolarities and E2/M1 mixing ratios of 11 γ-transitions were deduced from the measurement of internal conversion electrons. From the results of the angular correlation measurements, the spin values of 450.5, 105.4 and 32.3 keV levels were deduced to be 3/2 + , 7/2 + and 5/2 + , respectively and the previous assignments were confirmed. The half-lives of 32.3 and 105.4 keV levels were determined to be 1.2(1) ns and 0.44(2) ns, respectively and the enhanced E1 transitions with B ( E1)=10 -3 ∼10 -4 W.u. were observed. The 153 Pm level structure was compared with the result of a calculation with a rotation-vibration coupling model (RVCM) and ...

Relative intensities of prompt γ-rays from the 35Cl(n,γ)36Cl reaction with thermal neutrons as secondary γ-ray intensity standards.

The relative intensities of 16 prompt γ-rays from the (35)Cl(n,γ)(36)Cl reaction with a thermal neutron were precisely determined as secondary γ-ray intensity standards with HPGe detectors. The detection efficiencies were calibrated from 0.2 to 10.8 MeV using the standard sources (152)Eu and (56)Co and the (14)N(n,γ)(15)N reaction. We performed appropriate analyses for the evaluation of doublet peaks, subtraction of mixing with escape γ-rays and other corrections; consequently, the values were determined within 1% accuracy. Relative intensities in the range of 0.7 to 8.6 MeV are proposed as reliable secondary standards for 16 γ-rays.

Decay scheme of 126La isomers

The beta+/EC decay of 126La produced by the 94Mo(36Ar, 3pn) reaction has been studied using the on-line isotope separator connected to an AVF cyclotron. Gamma-ray singles, gamma-gamma angular correlation and internal conversion electron measurements were carried out. From analysis of these data, 33 new levels in 126Ba were found and the decay scheme containing 137 gamma-rays and 50 excited states was constructed. The probable spin and parity of the two beta-decaying states in 126La were found to be 4+/-, 5+/- for the high-spin isomer with a half-life of 54(2) s and 0-, 1+/-, 2- for the low-spin isomer with a half-life shorter than 50 s.

Studies of interaction between He and elements with mass number 140 in Fe by time-differential perturbed-angular-correlation measurements

Room-temperature time-differential perturbed-angular-correlation (TDPAC) spectra of 140Ce arising through 140Ba-140La from 140Cs in He-doped Fe, unannealed and annealed in vacuum at various temperatures, were obtained in order to examine whether Ce (or rather, La and Ba) and He form complexes having a definite geometrical structure in Fe, as suggested by first-principles density-functional theory calculations. No clear signal of such complexes was observed in the TDPAC spectra. However, the TDPAC spectra indicate that Ce and He form complexes having a variety of geometrical structures. Comparison with reported TDPAC results on 111Cd arising from 111In in He-doped stainless steel shows that the parent atoms (La and Ba) of 140Ce trap He atoms more efficiently than In atoms do, indicating stronger bonding of He to the former atoms, while different from the present case, 111Cd (In)–He complexes form a unique geometrical structure.

Reliability of Prompt γ‐Ray Intensities for the Measurement of Neutron Capture Cross Sections

We examined the reliability of prompt {gamma}-ray intensities by measuring ratios of thermal neutron capture cross sections on 23Na, 27Al, 51V, 55Mn, 64Ni, 65Cu, 141Pr, 186W, and 197Au at the Kyoto University Research Reactor Institute. The cross sections were obtained by two methods: the first is detecting prompt {gamma}-rays (which we call the prompt-{gamma} method), and the other is detecting {gamma}-rays following {beta}-decay (the activation method). Intensities of prompt {gamma}-rays and decay {gamma}-rays have been reported to have an uncertainty of about 5% and 1%, respectively. It is found that values of 65Cu and 186W have large discrepancies in the results of the two methods, by about 30%. The disagreement would be caused by inaccuracy of the absolute intensities of prompt {gamma}-rays. The inaccuracy is estimated to be due to the incompleteness of level schemes and the detector efficiency of prompt {gamma}-rays. We need to examine absolute intensities of prompt {gamma}-rays when we use the prompt-{gamma} method.