Takayoshi Aoki

Tables of linear-polarization mixing coefficients☆

Abstract Linear-polarization mixing coefficients for mixed dipole and quadrupole γ radiations have been listed as functions of mixing ratios for integer and half-integer spins up to 26. A familiar type of the Compton polarimeter is briefly discussed in connection with these coefficients.

Level structure of 124Ba

Abstract Excited states of 124 Ba have been investigated by means of in-beam γ-ray spectroscopy via reactions of 111 Cd( 16 O, 3n) and 112 Cd( 16 O, 4n). The decay of 124 La to the levels in 124 Ba has also been studied by γ-ray spectroscopy. The high-spin states have been observed up to J π = 18 + . Several side bands including a quasi-γ-vibrational band have been newly established. Systematic behaviours of the quasi-γ-vibrational band and the band crossing in barium isotopes are discussed

The band structure and triaxial shape in 118Xe

Abstract High-spin states of 118 Xe have been investigated by means of γ-ray spectroscopy using the 92 Mo( 29 Si,2pn) reaction at a bombarding energy of 110 MeV. Several new side bands as well as the yrast band were established. The first band crossings both in the yrast sequence and in the even-spin sequence of the γ-band were observed at ħω c = 0.39 MeV and ħω c = 0.31 MeV respectively. The γ-dependent cranked shell-model calculation was performed to interpret the band crossing in the γ-band.

QUASI-MULTIPLE SPIN ECHOES IN A LARGE MAGNETIC FIELD GRADIENT

Abstract The characteristics of multiple spin echoes observed in NaCl in a large magnetic field gradient are reported. By means of the vector model incorporating relaxation it is shown that this type of multiple echoes can be explained as an extension of Hahns secondary echo.

The 12 UD pelletron accelerator at the University of Tsukuba

Abstract The 12 UD Pelletron installed at the Tandem Accelerator Center of the University of Tsukuba has been in operation for nearly four years. The installation of the accelerator is described and the operational experience with the accelerator and associate facilities are summarized.

Low-lying intrinsic states in 173Ta

Abstract Lifetime measurements were tried for low-lying Nilsson intrinsic states with an aim of examining a level of scheme of 173 Ta proposed by previous authors. The half-life of the 165.84 keV 99 22 − [514] state was 225±15 ns and that of the 35.65 keV 77 22 + [404] state was less than 5 ns. Experimental reduced E1 and E2 transition probabilities were deduced and were compared with those for neighbouring odd- A Ta and Lu isotopes. It was found that the experimental reduced transition probability for 35.65 keV E1 transition from the 77 22 + [404] state to the 51 22 − [541] state was larger by about the order of 10 5 than those for inverse transitions from the 51 22 − [541] states to the 77 22 + [404] states in the neighbouring isotopes. Also it was recognized that a newly found 166 keV n =2-fold K -forbidden E2 transition from the 99 22 − [514] state to the 51 22 − [541] state seemed to be a K -allowed transition because of its great value of the probability. These findings may lead to a contradiction to the assignment of the 51 22 − [541] state in 173 Ta.

Multipurpose beam pulsing system for the 12UD pelletron tandem accelerator at the university of Tsukuba

A beam pulsing system has been developed for a 12 MV tandem accelerator. The system consists of a pre-acceleration chopper, a klystron buncher and a post-acceleration chopper. The pre-acceleration chopper comprises a slow chopper and a fast travelling-wave chopper. Pulsed beams with widths in the range from 10 µs to ~2 s are obtained with the slow chopper, and the repetition periods can be varied from 70 µs to 4 s. The fast chopper produces ion bursts having widths between 0.05 and 0.8 µs with a duty factor of ~10%. The buncher is operated with the two choppers to obtain beam pulses as narrow as a few nanoseconds. Time-of-flight measurements yielded pulse widths 2–4 ns (FWHM) wide for ions in the mass range 1A28. The ratio of the dark to peak ion current was usually of the order of 10-4.

Band structure of118Xe

High spin states of118Xe have been investigated by means of γ ray spectroscopy using the92Mo(29Si,2pn) at a bombarding energy of 110 MeV. Several new side bands as well as the yrast band were established. A band crossing between the ground state and super bands was observed at ħωc = 0.39 MeV. A negative parity band with two quasi particle excitation, and a quasi γ band were also identified.

Magnetic moment of the three-quasiparticle state in 177Ta

Abstract An experimental investigation was made of the γ-transitions feeding or de-exciting the 1355 keV isomeric state in 177Ta. The E2/M1 mixing ratios for the 311 keV interband transition from the isomer and for the 271 keV and the 295 keV intraband transitions within the rotational band on the isomer were determined to be δ = 0.29−0.06+0.11, 0.25−0.03+0.05 and 0.30−0.08+0.06, respectively, employing combined measurements of the linear polarization and angular distribution of the γ-rays with the aid of conversion electron measurements. Spin and parity assignments of the isomer were confirmed to be 21 2 − . The half-life of the isomer was remeasured to be T 1 2 = 5.0 ± 0.2 μ s and the magnetic moment was found to be μ = 0.080 ± 0.014 μN. The gK and gR factors for the band on the isomer were deduced separately to be g K = 2 21 2 − 0.062 −0.008 +0.11 and g R = −0.56 −0.13 +0.09 . Comparing the experimental gK factor with the theoretical value, it was found that the configuration of the isomer is 21 2 − ( P 7 2 + [404] N 5 2 − [512] N 9 2 + [624] . The B(E2) and B(M1) probabilities for the interband transitions were deduced. Discussion concerning the mixed state which caused the interband transitions is based on the experimental B(E2) ratio within the framework of single Km, mixing.