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1.Multi-elemental Neutron Activation Analysis of Chinese GeoChemical...
Zhang Yun jun,Li Xing bin,Song Lin shanInstitute of Geophysical and Geochemlcal Prospecting, Ministry of Geology and Mineral Resources of ChinaYuan Ling, Chen Bao guanInstitute of Atomic Energy, Academia SinicaChen Bing ru,Wang Yu qi,Sun Jing xinInstitute of High Energy Physics,Academla SinicaThe concentrations of 36 elements in geochemical reference samples issued by the Ministry of Geology and Mineral Resources of China were determined by neutron activation analysis.Three main variants of the technigue, instrumental,epithermal,and preirradiation separation neutron activation analysis（INAA, ENAA, PRAA）, were employed in a systematic study of the samples by three laboratories: the Institute of Atomic Energy of the Academia Sinica（INAA,ENAA）,the Institute of High Energy Physics of the Academia Sinica（INAA）, and the Institute of Geophysical and Geochemical Prospecting of the Ministry of Geology and Mineral Resources（INAA, PNAA）.Both long and short irradiations and both Ge（Li）and HPGe detectors were used.A supplementary software package for data processinq was developed.About 81%of the data determined by neutron activation agreed with recommended values with in 15%.The Institute of Geophysical and Geochemical Prospecting of Ministry of Geology and Mineral Resources bas prepared three series of geochemical reference samples: stream sediments（GSD）, soils（GSS）, and rocks（GSR）.The eight stream sediment samples,GSD 1-8, were selected from areas believed to be representative of the types of sediments found in China.The provinces where the sampling sites are located and the lithology of the rocks in the basins sampled are given in a parer by Xie
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（1）.EXPERIMENTALStandardsPrimary solution standards were used for standardization.Sets of 3-5 elements with no mutual interferences of main energies were combined to form multielement standards.Reference samples USGS GXR 1-6, USGS-AGV-1,NES-SRM-1362a, and CCRMP SY-2 and SY-3 were also used.Predetermined volumes of solution standards were pipetted onto plastic films or onto circular pieces of filter paper and the films or the papers were packed into aluminium foils of high purity
（2）.Sample preparation and irradiationThe homogeneous sample powders were dried in an oven at 90 ℃－110℃ for over 3 hours and sample portions（20-100mg）were then precisely weighed onto aluminium foils.All samples and standards were placed in aluminium irradiation containers for INAA and PNAA, and in boron nitride（BN3）container for ENAA.The irradiation times were 2 to 5 min for Dy and Mn,72 to 150 hr for Ag and 3-23 hr for other elements.Both swimming pool and heavy-water reactors were used for irradiation.The thermal neutron fluxes were（1-2.4）*1013n1cm-2s-1and（5-7）*1013n1cm-2s-1respectively.Preirradiation separation techniques were used to improve the analytical sensitivities for gold and the rare earths.For gold the sample portion（10-20g）was dissolved in aqua regia and the Au then absorbed on activated carbon, whereas for the rare earths, sample portions（1g）werefused in sodium peroxide and the rare earths were extracted by PMBP（1-Pheny1—3-Methy1-4-Bnzoyl-5-Pyrazolone）.Equipment and measurementTwo types of CANBERRA data acquisition systems（SCORPIO-3000 and JUPITER）were used for measuring the gamma spectra.The coaxial Ge（Li）detector covers the energy range from 60 to 2000 keV and the planar high purity germanium（HPGe）detector from 30 to 3
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