Hisayoshi Nakayama

Muon spin resonance by strong pulsed r.f. field with pulsed muons

Muon spin resonance experiments have been performed for the μ+ in H2O and for some other cases, and the first observation has been made of the time-differential pattern of muon spin resonance, namely, spin precession around the r.f. field vector under various resonance conditions. In the present experiment, a high-power pulsed r.f. field was effectively applied to the pulsed muon beam in our laboratory of the KEK-Booster Meson Facility (BOOM). Potential uses of muon spin resonance, particularly for research in the border regions of solid state and nuclear physics, are discussed in comparison with the conventional spin rotation method.

Long-lived muonium in water revealed by pulsed muons

Abstract The relaxation rate of muonium in pure water has been found to be smaller than 0.05 × 10 6 s −1 . With the aid of pulsed muong. μSR and MuSR measurements have been carried out over a longer time range than ever achieved. The results indicate a stability of thermal muonium in water from 3 to 29°C.

High Spin States above the 8+ Isomer in 88Zr

High spin states above the 8 + isomer in 88 Zr have been studied using the 86 Sr(α, 2nγ) 88 Zr reaction. Several high spin states above the isomer and lower excited states have been identified. The energy levels and transition properties are discussed on the basis of the shell model.

On the Triaxial Deformation in Transitional Odd-A Nuclei

The essential difference as well as the apparent identity between the triaxial-rotor model and the gamma-vibrational model have been discussed. From the gamma decay mode, the [19/2 - ] 1 states of the j =11/2 - family in 187 Ir and 189 Ir have been identified as the K = j +4 states, the presence of which contradicts the particle plus triaxial-rotor model.

Structure of the transitional nucleus 149Eu

The level structure of the transitional nucleus 149Eu was studied by means of in-beam γ-ray spectroscopy using the 150Sm(p, 2nγ)149Eu reaction. The 152−(994.3 keV) and 192−(1609.3 keV) favoured states of the decoupled band based on the 112− isomeric state were found, and the unfavoured 132−(1175.8 keV) state was also found. The positive-parity Δ I = l bands based on the 52+ ground state and the 72+ first excited state were assigned. These states are discussed in terms of a simple particle-plus-rotor model.

Beam-pulsing system for the IMS cyclotron

Abstract An external beam-pulsing system to produce pulsed beams of various time characters (several tens of nanoseconds to seconds) out of a cyclotron beam has been installed for the purpose of studying delayed-γ-ray phenomena. It is composed of two parts. For short time ranges a sinusoidal electric field sweeps the beam horizontally to obtain one out of every 2, 3, 4, 6 or 12 natural beam pulses. For longer time ranges ( > 1 μs) a rectangular pulse-shaped electric field is used to deflect unwanted beams vertically. A combination of the two deflectors makes a versatile time range available for experiments. The design and construction of the system and some experiments performed are described.

Critical phenomena in nickel studied with pulsed μSR

Abstract Pulsed μSR studies were applied to probe critical phenomena in nickel by measuring critical indexes for paramagnetic Knight shift (γ), transverse paramagnetic relaxation ( w ), and ferromagnetic hyperfine fields (β) with field corrections experimentally determined. The indexes β and γ are consistent with magnetization measurements. The measured w (1.1 ± 0.1) is different from those obtained by PAC experiments.

Reinvestigation of the Decay of 2.2 Hour 138Pr

The excited states of 138 Ce following the decay of 2.2 hour 138 Pr were reinvestigated with a Ge(Li) and NaI(T1) detectors. Weak gamma rays of 0.389 and 0.546 MeV, which were reported previously, were confirmed in a Ge(Li) singles and NaI(T1)–NaI(T1) coincidence spectra. Two levels at 2.206 and 2.752 MeV in 138 Ce are proposed.

Lifetimes of the 7− states in 186, 188Os

Abstract The isomeric states are identified to be located at 1775 keV in 186 Os and at 1771 keV in 188 Os and their half-lives were measured to be 10.5 ± 1.0 nsec and 14.0 ± 1.0 nsec, respectively. The result of the angular distribution measurement supports the previous spin-parity assignment of 7 − for these states.

High spin states above the 8+ isomer in 92Mo

Abstract High spin states above the 8+ isomer in 92Mo have been studied using the 90Zr(α, 2nγ)92Mo reaction. The 10+ (5118 keV) and 12+ (5858 keV) states and several negative-parity states have been proposed in the present work and compared with a shell model calculation.