Research of Isotopic Reference Material for Improvement of Measurement Precision of Isotopic Ratios in Space and Earth Sciences

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Neodymium isotopic standard requires low impurity. In addition, (1) it should have a high ^<143>Nd/^<144>Nd ratio because of high ratios in island-arc samples generally researched in Japan and (2) should have low rare-earth impurities because of the reduction of isobaric interference by ^<142>Ce and ^<144>Sm. Isotopic ratios and rare-earth impurities were examined in high purity neodymium oxides prepared by six chemical companies, SPEC,JMC,CERAC,MERCK,ShinEtsu and Mitsuwa. The reagent of the ShinEtsu company is preferable. Two bottles of 1kg each, of neodymium oxide reagent from the same lot, were bought from the ShinEtsu company and defined as split 1 and split 2. Upper part of split 1 was discarded. The rest was divided into 725 small bottles, each of them containing 1g reagent, from upper part (position 1) to lower part (position 725) in order.Isotopic ratios of JNdi-1 and LaJolla-Nd were determined by cyclic measurement on 12 mass spectrometers in 11 institutes using specific proce … More dures, except for the using of normalized value, <@D1143@>D1Nd/<@D1144@>D1Nd=0.7219.18 positions of JNdi-l were measured twice to twelve times, respectively. The values of jNdi-1 and LaJolla-Nd by cyclic measurement are defined as A and B,respectively, and F (Factor) vaoues are calculated from the two values, F<@D2n@>D2=2A<@D2n@>D2/(B<@D2n@>D2+B<@D2n+1@>D2). F values of several positions measured by the same instrument and the same procedure in one institute are consistent in the range of their standard deviation (2sigmam). Therefore, the isotopic composition of the reagent in the 1kg bottle is considered to be homogenous. This allows to calculate an average of F values of all 18 positions, that is 1.000503(]SY.+-。[)1 (1sigmam). The isotopic ratio of JNdi-1 which corresponds to 0.511857 of LaJolla-Nd is 0.512114(]SY.+-。[)7. Moreover, to consider the role of standard for variation of <@D1142@>D1Nd produced by decay of <@D1146@>D1Sm, that is the extinct nuclide, <@D1142@>D1Nd/<@D1144@>D1Nd ratios of JNdi-1 were also checked. From the results of the 104 data, it is found that the average of F values is 1.000006(]SY.+-。[)3 (1sigmam). This indicates that the values of JNdi-1 and LaJolla-Nd do not have a significant difference. Geological Survey of Japan has started to distribute the new isotopic standard regent (JNdi-1). Less