Optical Hall effect in the integer quantum Hall regime.

Optical Hall conductivity σ{xy}(ω) is measured from the Faraday rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz-frequency regime. The Faraday rotation angle (∼ fine-structure constant ∼ mrad) is found to significantly deviate from the Drude-like behavior to exhibit a plateaulike structure around the Landau-level filling ν=2. The result, which fits with the behavior expected from the carrier localization effect in the ac regime, indicates that the plateau structure, although not quantized, still exists in the terahertz regime.

Study of charged particle activation analysis (II): Determination of boron concentration in human blood samples.

Boron Neutron Capture Therapy (BNCT) is a radiotherapy for the treatment of intractable cancer. In BNCT precise determination of 10B concentration in whole blood sample before neutron irradiation of the patient, as well as accurate neutron dosimetry, is crucial for control of the neutron irradiation time. For this purpose ICP-AES and neutron induced prompt γ-ray analysis are generally used. In Ibaraki Neutron Medical Research Center (iNMRC), an intense proton beam will be accelerated up to 8 MeV, which can also be used for Charged Particle Activation Analysis (CPAA). Thus, in this study, we apply the CPAA utilizing the proton beam to non-destructive and accurate determination of 10B concentration in whole blood sample. A CPAA experiment is performed by utilizing an 8 MeV proton beam from the tandem accelerator of Nuclear Science Research Institute in Japan Atomic Energy Agency. The 478 keV γ-ray of 7Be produced by the 10B(p, α)7Be reaction is used to quantify the 10B in human blood. The 478 keV γ-ray intensity is normalized by the intensities of the 847 keV and 1238 keV γ-rays of 56Co originating from Fe in blood. The normalization methods were found to be linear in the range of 3.27 µg 10B/g to 322 µg 10B/g with correlation coefficients of better than 0.9999.

Characterization of experimental ischemic brain edema utilizing proton nuclear magnetic resonance imaging.

Correlations between T1 and T2 relaxation times and water and electrolyte content in the normal and ischemic rat and gerbil brains were studied by means of both nuclear magnetic resonance (NMR) spectroscopic and imaging methods. In the spectroscopic experiment on excised rat brains, T1 was linearly dependent on tissue water content and T2 was prolonged in edematous tissue to a greater extent than expected by an increase in water content, showing that T2 possesses a greater sensitivity for edema identification and localization. Changes in Na+ and K+ content of the tissue mattered little in the prolongation of relaxation times. Serial NMR imaging of gerbil brains insulted with permanent hemispheric ischemia offered early lesion detection in T1- and especially T2-weighted images (detection as soon as 30 min after insult). The progressive nature of lesions was also imaged. Calculated T1 and T2 relaxation times in regions of interest correlated excellently with tissue water content (r = 0.892 and 0.744 for T1 and T2, respectively). As a result, detection of cerebral ischemia utilizing NMR imaging was strongly dependent on a change in tissue water content. The different nature of T1 and T2 relaxation times was also observed.

A new host record of Camelostrongylus mentulatus (Nematoda; Trichostrongyloidea) from abomasum of a giraffe at a zoo in Japan.

Camelostrongylus mentulatus (Railliet et Henry, 1909) Orloff, 1933 (Nematoda; Trichostrongyloidea) was found from the abomasum of a three-year-old female cape giraffe, Giraffa camelopardalis giraffa, born and died in a zoo park in Yamaguchi prefecture, Japan. This is the new host record from Giraffidae and geographical distribution of C. mentulatus. Present case of C. mentulatus might be infected from other ruminants, e.g., camels, antelopes and goats, kept at a same paddock in the zoo. Risk of imported parasitic diseases by the zoo animals from outside of Japan is discussed.

Some problems on the measurement of 222Rn concentrations by passive cup method.

A passive cup monitor has been constructed by using a 50 mm radius stainless steel hemisphere. The conductive housing has reduced the scatter in track densities. In dwellings with high 220Rn concentrations, it is particularly necessary to measure 222Rn concentration with a monitor having a radon exchange rate less than 0.1 h-1.

On some properties of 222Rn short-lived decay products in air.

Simultaneous measurements were made of such properties as the fraction of charged and uncharged atoms, the balance of radioactive equilibrium between 222Rn and its daughters, and the concentration of aerosol particles and their mean radii in tunnel air. It became clear that the behavior of 222Rn decay products in tunnel air could be expressed well by equations based on a simple model, taking the following into account: the attachment of free atoms to aerosol particles, the deposition of radioactive particles on the tunnel wall, emission of alpha recoils from aerosol particles and the surface of the tunnel wall, and radioactive decay. In addition, the effective attachment coefficient of an observed RaA-atom was found to agree well with that calculated. The results obtained should facilitate in the future estimation of the relation between 222Rn daughters and the lung dose to the population.

An electrostatic integrating 222Rn monitor with cellulose nitrate film for environmental monitoring.

This paper describes a new type of electrostatic integrating 222Rn monitor designed for the environmental 222Rn monitoring. The window area of the monitor was selected to make the exchange rate optimal. The collecting electrode was positioned on the basis of calculating the internal electric field. A drying agent, P2O5, was placed in the bottom of the monitor, since the collection efficiency of 218Po+ atoms depends on the humidity of the air. The monitors have been calibrated against known 222Rn exposures. The detection limit is 1.2 Bq m-3 for an exposure time of 2 mo. In a small survey, annual mean 222Rn concentrations between 3.7 and 9.5 Bq m-3 in outdoor air and between 6.4 and 11.9 Bq m-3 in indoor air were measured.

The use of the orthographic lexicon in reading kana words.

A lexical decision task was used to investigate the dual-route hypothesis that, in reading words conventionally written in katakana, a Japanese syllabic script, lexical access may be achieved by both a process of assembled segmental phonology and the use of a visual orthographic lexicon. The variables examined were lexicality (words and nonwords), kana type (katakana and hiragana), string length (long and short), and vocal interference (silence and concurrent vocalization). The main effects of the first three variables were significant, but more important, we found that subjects could be divided into two groups--phonological assemblers and orthographic lexicon users. Words that assume sighting were also identified. Collectively, the results were interpreted to uphold the dual-route hypothesis and to reject the common view that kana words are accessed on the basis of phonological mediation alone.

[Magnetic resonance imaging of experimental cerebral ischemia: correlations between NMR parameters and water content].

Recent studies on proton NMR imaging revealed its remarkable sensitivity for detecting cerebral ischemia. Since proton NMR reflects the distribution and state of water in the brain, an NMR imager becomes a sensitive in vivo detector of brain edema developing soon after the energy state is compromized by ischemia. To further clarify the usefulness of NMR imaging to characterize the ischemia-induced changes, correlations between T1 and T2 relaxation times and water content of the normal and ischemic rat and gerbil brain were studied by means of both spectroscopic and in vivo imaging methods. In the spectroscopic experiment on excised rat brain (cortex, white matter, hippocampus and thalamus for normal and ischemia-laden brain), T1 and T2 relaxation times and water content were determined. The ischemic insult was induced for 60 min by the method of Pulsinelli followed by 60 min of reperfusion. All of the T1, T2 and water content significantly increased in the ischemic tissue. Gray-white difference was evident in T1 and T1 was linearly correlated with the water content of the tissue. T2 was by far prolonged in the ischemic tissue compared with the increase in the water content, showing greater sensitivity of T2 for detection of ischemia. In the imaging experiment, coronal NMR imaging at 0.5 tesla was performed employing proton density-weighted saturation recovery (TR = 1.6 s, TE = 14 ms), T1-weighted inversion recovery (TR = 1.6 s, TI = 300 ms, TE = 14 ms) and T2-weighted spin echo (TR = 1.6 s, TE = 106 ms) pulse sequences.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiography of alpha- and beta-emitters using a charged-particle imaging system.

A newly developed charged-particle imaging system was applied to rapid measurements of the distribution of alpha- and beta-emitters. The imaging system consists of a ZnS(Ag) screen, two tapered fibers, an image intensifier, and a Polaroid film. The image obtained with the system shows very good quality, namely, a spatial resolution of more than 6 line pairs (lp)/mm and a distortion of less than 2.5%. As the system is capable of detecting each alpha-particle separately, the distribution of alpha-emitters can be quantitatively determined. The autoradiograms of the sections of mice with beta-emitters administered can be obtained with an exposure time of only 2 min compared with 2 weeks by a conventional technique.

Detection of an X-Ray Hot Region in the Virgo Cluster of Galaxies with ASCA.

Based on mapping observations with ASCA, an unusual hot region with a spatial extent of 1 deg2 was discovered between M87 and M49 at a center coordinate of R.A.=12h27m36s and decl.=9&j0;18' (J2000). The X-ray emission from the region has a 2-10 keV flux of 1x10-11 ergs s-1 cm-2 and a temperature of kT greater, similar4 keV, which is significantly higher than that in the surrounding medium of approximately 2 keV. The internal thermal energy in the hot region is estimated to be VnkT approximately 1060 ergs with a gas density of approximately 10-4 cm-3. A power-law spectrum with a photon index of 1.7-2.3 is also allowed by the data. The hot region suggests there is an energy input due to a shock that is probably caused by the motion of the gas associated with M49, infalling toward the M87 cluster with a velocity greater, similar1000 km s-1.