K. Nagamine

Method of probing inner-structure of geophysical substance with the horizontal cosmic-ray muons and possible application to volcanic eruption prediction

Abstract One potential use of cosmic-ray muons arriving nearly horizontally along the earth is a probe of the inner-structure of a gigantic geophysical substance, such as a volcanic mountain. A simple detection system comprising a plastic scintillator hodoscope which is expandable to a larger scale was developed. The first successful measurement of the inner-structure of Mt. Tsukuba is described. The future perspective of the application of the present method towards the prediction of volcanic eruption is discussed.

First observation of an antiferromagnetic phase in the Y1Ba2Cu3Ox system

The magnetic properties of four different phases of the YBa2Cu3Ox system, including the famous 90 K superconductor, have been probed by the positive muon spin relaxation method (µ+SR). The oxygen-deficient tetragonal insulating phase (x~6.2) was found to be magnetically ordered, thus most likely antiferromagnetic, near room temperature.

Development of a two-fold segmented detection system for near horizontally cosmic-ray muons to probe the internal structure of a volcano

Abstract Very high-energy cosmic-ray muons penetrating through a mountain enable us to probe internal structure of volcanoes. An improved cosmic-ray muon detection system comprising two segmented detectors with multiplicity cut of the soft-component background of cosmic ray was developed. By applying to the measurement on internal structure of the volcano Mt. Asama, we proved that the volume occupancy in the region of a crater is less than 30%.

Development of the Cosmic-Ray Muon Detection System for Probing Internal-Structure of a Volcano

Very high-energy cosmic-ray muons penetrating through a mountain enable us to probe the internal structure of volcanoes. An improved cosmic-ray muon detection system comprising two segmented detectors with multiplicity cut of the soft components of cosmic rays was developed. The test measurement for the volcano Mt. Asama is described.

Magnetic Order of Cu-Moments in La2-xBaxCuO4 around x=0.12 Observed by Positive Muon Spin Rotation

Positive muon spin rotation (µ + SR) is applied to La 2- x Ba x CuO 4 around x =0.12, where superconductivity is suppressed remarkably. The magnetic ordering of Cu-moments appears below 35 K in the narrow range of 0.11≦ x ≦0.135, where the transition from the low-temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) structure exists. The present study suggests strongly that the magnetic ordering of Cu-moments plays an important role in the suppression of the high- T c superconductivity around x =0.12 in La 2- x Ba x CuO 4 .

Hyperfine field and diffusion of μ+ in Fe single crystals

Abstract In recent positive-muon spin rotation experiment at TRIUMF on single crystal Fe, a clear temperature dependent change has been observed, for the first time, both in frequency and depolarization rates from 300 K down to 23 K. The μ + depolarization was explained by the μ + diffusion through inhomogeneous dipolar fields and the diffusion constant was found to obey an Arrhenius law (activation energy 17 meV) above 70 K but surprisingly deviated from this at lower temperatures, indicating quantum diffusion. We have also found that the μ + hyperfine field has a temperature dependence slightly stronger than that of the magnetization.

Temperature-independent hyperfine field on μ+ in nickel in the temperature range of 0.12–300 K

The hyperfine field on a positive muon at interstitial site in a nickel single crystal has been measured by the muon spin rotation method in the temperature range from 0.12 K to 300 K. The hyperfine field in the low temperature limit was found to be −640.7±2.2 Gauss. While the saturation magnetization decreases by 7% as the temperature increases from 0.1 K to 300 K, the hyperfine field seen by the muon remains nearly constant. Possible mechanisms for explaining this result are considered.

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.

Coexistence of magnetic ordering and superconductivity in LaSrCuO system revealed by positive muon spin relaxation

Abstract The positive muon (μ+) spin relaxation has been measured for single crystal samples of the oxide superconductor (La1−xSrx)2CuO4−δ under zero applied field. For x = 0.04 sample, it is found that both the μ+ initial polarization and the relaxation rates do not show any changes at around the superconducting transition temperature (T c ≌ 11 K ) , while they show a dramatic change at the temperature ∼5 K, indicating an existence of a magnetic transition in the superconducting state. It is found that a similar transition also occurs for x = 0.02 sample, suggesting an existence of a magnetic phase at low temperatures and at the low Sr concentration region.

μ+SR Studies of Magnetic Properties of the YBa2Cu3Ox System

Samples of YBa 2 Cu 3 O x in four different phases have been probed by positive muon spin relaxation (µ + SR) method. Each phase was found to show different magnetic behavior. In the famous orthorhombic 90K superconductor ( x ∼6.9), neither magnetic ordering nor magnetic fluctuations were observed. However, in another orthorhombic superconducting phase ( x ∼6.4, T c ≈60 K) a magnetic fluctuation was observed below 7 K via muon spin-nuclear spin double relaxation. Its magnetic ordering temperature was expected to be below 2.4 K. Similar behavior was observed in an oxygen-rich ( x ∼6.5) tetragonal insulating phase, whereas the oxygen-deficient ( x ∼6.2) tetragonal insulating phase was found to be magnetically ordered, most likely antiferromagnetic, near room temperature. This is the first observation of a magnetically ordered state in the YBa 2 Cu 3 O x system.