Hisao Mabuchi

The half-life of 41Ca

Abstract The 40 Ca-enriched isotope was irradiated by pile neutrons. From the measurement of the activity ratio of two isotopes, 41 Ca and 45 Ca, produced at the same time, the half-life of 41 Ca was determined to be (1·03 ± 0·04) × 10 5 yr.

Radionuclides produits par le rayonnement cosmique dans la météorite Saint-Séverin

Resume On a mesure, apres separation chimique, les activites de 18 radionuclides contenus dans 4 echantillons de la meteorite Saint-Severin. Lexamen des resultats montre que lechantillon DI du fragment D a ete en moyenne moins irradie que les echantillons B2, B3, B4 du fragment B, tant pour les nuclides formes principalement par spoliation (26Al, 53Mn, 54Mn, 55Fe, 57Co) que pour ceux formes par capture de neutrons lents (59Ni, 60Co). La comparaison des valeurs experimentales avec les taux de production calcules suggere que le fragment D etait lie au reste de la meteorite par une surface etroite, et quen outre DI etait situe, sur le fragment D, a loppose du reste de la meteorite.

Evidence of the extinct nuclide146Sm in “Juvinas” achondrite

Abstract The search for the isotopic anomaly of Nd due to the disintegration of 147 Sm and 146 Sm was carried out on separated mineral phases of Juvinas achondrite. An internal isochron of 4.3 ± 2.5 billion years was obtained for 147 Sm 143 Nd pair. This provides the possibility of dating the planetary materials. Anomalies were observed for 142 Nd, giving the isotopic ratio 146 Sm/ 144 Sm at the time of solidification to be 0.39 ± 0.14 . This is the first positive evidence of extinct 146 Sm which may be used as a p-process chronometer.

An extremely low-level x-ray spectrometer

Abstract An extremely low-level X-ray counter system has been constructed with heavy-mass and anticoincidence shieldings. The detector is made of oxygen-free copper and of cylindrical form. It operates as a proportional counter of gas-flow type (argon-methane), inside of which are put samples. It is surrounded by 7mm thick purified mercury, multiwire GM anticoincidence counters, 1 cm thick oxygen-free copper, 12 cm thick iron, and finally 10 cm lead. The whole assembly is built in an underground cell heavily shielded from major cosmic ray components with a rock cover of at least 100 mwe. After careful measurements of the background counting rate, it was found that oxygen-free copper still contains some radioactive impurities, constituting a considerable portion of background count. By coating the inside wall of sample holders with purified nickel or copper, the background counting rate was reduced to a great extent. The definitive background counting rate is 0.1 cpm/keV in the energy region of 4–5 keV for 940 cm 2 of sample area (2π geometry).

Isotopic ratios of Gd, Sm and Eu in “Abee” enstatite chondrite

Abstract This paper presents measurements of the isotopic ratios of Gd, Sm and Eu from the enstatite chondrite Abee, Because the oxidation state of enstatite chondrites is significantly less than that of other chondrites and of the Earth, Miyashiro has postulated that this class of meteorite originated closer to the Sun (although its recent orbit appears to have been significantly beyond 1 A). Depending on the model used for nucleosynthesis, the greater flux of secondary thermal neutrons resulting from proximity to the sun might be observed as isotopic anomalies in these elements, some isotopes of which have very large thermal neutron cross sections. The meteorite Abee was compared with two terrestrial samples, from North and from South America. The isotope ratios Gd 155 Gd 156 , Gd 157 Gd 158 , Sm 149 Sm 150 and Eu 151 Eu 153 are identical for the three samples studied, within maximum experimental uncertainties (i.e. 2-sigma) of 0·15, 0·1, 0·3 and 0·3 per cent, respectively. The uncertainties include possible sources of systematic error as well as statistical errors. On the basis of these results, we conclude that the differential thermal neutron irradiation between Abee and the earth does not exceed 3 × 10 15 neutrons/ cm 2 , for a uniform irradiation model, or that the dilution factor differed by less than 1·2 per cent for the FGH model.