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  • Author or Editor: T. Saito x
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Abstract  

The concentrations of radium isotopes and the progenies (226Ra; 228Ra and 228Th) in three hokutolite samples from Tamagawa hot-spring were measured. These isotopes were analyzed by a well-type HPGe γ-ray spectrometer for the 351, 911 and 583 keV γ-ray from 214Pb, 228Ac and 208Tl, respectively, each being in radioactive equilibrium with precursors. Concentration of 226Ra and 228Ra were observed to be in the range of 52–85 and 7.1–85 Bq/g, respectively. The activity ratios of 228Ra/226Ra and 228Th/226Ra provided the estimation of the growth rate (0.09–0.15 mm/y). Estimated 228Ra/226Ra activity ratios in hot-spring water from surface of three hokutolite were concordant.

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Abstract  

Liquid scintillation counting of40K in ordinary potassium propionate is a highly suitable experimental task in the general education on radioactivity. The counting efficiency is about 90%, depending little on the measurement conditions. Potassium propionate is of suitable properties and can be easily obtained commercially or by conversion from other compounds. The result of counting, about 1,700 cpm/g, is highly impressive to many students, indicating the existence of40K radioactivity unexpectedly high in the normal nature, and can be used for the exercise of calculating our internal radiation exposure.

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Abstract  

The concentration of Ra isotopes in environmental water can be determined from the amount of Ra isotopes recovered in two successive batch operations a using cation exchange resin. The present analytical method is applicable to 10 liter of sample water having a Ra concentration larger than 10 mBq/l and is also applicable to the ordinary underground water of less than 1 mBq/l by use of 50 liter of sample water. In case where Ra concentration is extremely low, Mn-impregnated acrylic fiber can be used with a larger volume of water sample as an absorbent by soaking it in the water.

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Abstract  

The reaction of238U with12C was studied radiochemically with the purpose of elucidating fast fission characteristics. Fast fission component was extracted in far-asymmetric mass region and interpreted as the mass diffusion following the Fokker-Planck equation. Anomalous charge dispersion widths in the corresponding mass region and a sudden increase of the whole mass distribution width at the critical energy were also observed to support the above interpretation. The reaction time of fast fission was determined to be 5·10−21 s from the width and position of the mass distribution.

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Abstract  

The atmospheric concentration of 210Pb and 7Be was observed at Sarufutsu on the coast of the Sea of Okhotsuk in Hokkaido, Japan. Measurements were carried out during the period from February to August, 2001. The atmospheric concentrations of 210Pb and 7Be ranged from 0.2 to 2.5 mBq/m3 and from 0.0 to 4.2 mBq/m3, respectively. The seasonal variation pattern of the atmospheric concentration of 210Pb indicated that the air mass from Chinese Continent reached the coast of the Sea of Okhotsuk.

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Abstract  

For Mössbauer -rays in the in-beam Mössbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mössbauer effect even under high -background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mössbauer experiments.

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Abstract  

A convenient non-destructive method for the determination of low level210Pb and226Ra with an ordinary high-purity Ge-detector is presented. The ordinary Ge-detectors used in this work were available to measure 46.5 keV -rays of210Pb. These detectors were also useful for the non-destructive analysis of low-level226Ra in lime-stone and calcium chemicals when a stream of nitrogen gas was maintained around the detectors. By this method, measurements could be carried out not only for210Pb and226Ra but also for other -emitting radionuclides simultaneously, using the same detector. The detection limits of about 1 Bq per sample for210Pb and about 0.05 Bq per sample for226Ra, respectively, were estimated, when the samples were counted for 1–2 days.

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Summary We have performed low-temperature heat capacity measurements on pellet samples of (DMe-DCNQI)2M (M=Li, Ag) which is known to show spin-Peierls transitions at 51 and 86 K, respectively. A linearly temperature-dependent term in the low-temperature heat capacity has been observed for both the samples: It is attributable to the spin-wave excitations induced by the inhomogeneous pressure effects produced in the pellet forming process. Although the temperature dependences of the magnetic susceptibility in both materials are almost the same, the coefficient of T-linear term of the Ag salt becomes three times larger that that of the Li salt. The peculiar electronic state originating from the competition of the spin-Peierls mechanism and the Coulomb repulsion is suggested.

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Abstract  

The heat capacities and magnetic susceptibilities of powdered samples of FexNbS2 (x=0.14, 0.21 and 0.30) were measured at temperatures from 8 to 303 K and from 5 to 300 K, respectively. For Fe0.14NbS2, the magnetic susceptibility exhibited an anomaly as a shoulder at about 57 K, but no heat capacity anomaly was observed at this temperature, indicating the appearance of a spin-glass state. Anomalies in the heat capacity for FexNbS2 (x=0.21 and 0.30) occurred at 100.5 and 45.0 K, respectively, where the magnetic susceptibility displayed a maximum, corresponding to an antiferro-paramagnetic phase transition. The electronic state of the iron atom is discussed on the basis of entropy analysis.

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