I-Xe dating: intercomparisons of neutron irradiations and reproducibility of the Bjurböle standard

Parameters for a number of neutron irradiations are examined and results intercompared for the Bjurböle meteorite; data for the 1967 Valecitos-1 irradiation are presented. Apparent I-Xe ‘formation’ ages are reproducible for three different samples of Bjurböle, suggesting isotopic homogeneity for initial iodine in the bulk material. The systematics of neutron capture in ¹³⁵Xe (produced from ²³⁵U neutron fission) are examined and verified in irradiated BCR-1.     

Elemental interferences in the analysis of uranium by delayed-neutron counting

Major physical and elemental effects influencing U analysis were investigated at the fully automated Risø delayed-neutron counting facility. Changes in the physical conditions at the analytical facility can be closely controlled and most physical interference parameters are of minor importance for the analysis. Experiments were performed with artificial granitic and basaltic rocks to estimate the actual influence of Be, B, Li, Al, Na, Mn, Fe, rare earth elements and Th on the U analysis. The neutron counting rate from U is increased by about 1% when 1000 ppm Be are added to a 5-g sample. For the strong neutron absorbers B and Cd the correction factors are about −1 and −2%, respectively, per 1000 ppm interfering element present. For the rare earth elements Sm and Gd these correction factors were −2.2% and −10.2% per 1000 ppm added element, respectively. High gamma-radiation fluxes from Al, Mn and Fe have no significant effect on the U analysis.     

The spin-down mechanism of the X-ray pulsar 4U 2206+54

Observations of the X-ray pulsar 4U 2206+54 obtrained over 15 years show that its period, which is now 5555 ± 9 s, is increasing dramatically. This behavior is difficult to explain using traditional scenarios for the spin evolution of compact stars. The observed spin-down rate of the neutron star in 4U 2206+54 is in good agreement with the value expected in a magnetic-accretion scenario, taking into account that, under certain conditions, the magnetic field of the accretion stream can affect the geometry and type of flow. The neutron star in this case accretes material from a dense gaseous slab with small angular momentum, which is kept in equilibrium by the magnetic field of the flow itself. A magnetic-accretion scenario can be realized in 4U 2206+54 if the magnetic-field strength at the surface of the optical counterpart to the neutron star is higher than 70 G. The magnetic field at the surface of the neutron star is 4 × 10¹² G in this scenario, in agreement with estimates based on an analysis of X-ray spectra of the pulsar.     

Uranium and thorium abundances in Indian kimberlites

Abundances of U and Th have been determined in 21 kimberlites from India by delayed fission neutron technique. Whole-rock U ranges from 1.87 to 3.93 ppm but Th shows wider variation from 14.02 to 60.44 ppm. Average Th/U ratios in three main diatremes are 7.9, 8.8 and 10.0. The interrelationships between U, Th and K are variable and complex. A positive correlation exists between P₂O₅ and U and Th. Model calculations suggest that enrichment of U involved considerable mantle reaction during ascent.     

Phosphorus and ChlorinE Content of Eight New U.S.G.S. Standard Rocks

Data on the content of phosphorus and chlorine in eight new U.S.G.S. standard rooks obtained by radiochemical neutron activation analysis are presented and discussed.     

Instrumental Neutron Activation Analysis of Nine New Reference Materials from the Geological Survey of Japan

Nine reference materials, recently distributed by the Geological Survey of Japan (JA-1, JB-la, JB-2, JB-3, JG-la, JGb-1, JP-1, JR-1 and JR-2) have been analysed by instrumental neutron activation analysis using well proven experimental techniques. Results for the twenty elements determined (selected rare earth elements, Fe, Ba, Co, Cr, Cs, Hf, Rb, Sc, Ta, Th and U) are assessed for accuracy and precision and show good agreement with previously published data.     

TRACE ELEMENT ANALYSIS OF TEN U.S. GEOLOGICAL SURVEY ROCK STANDARDS BY NEUTRON ACTIVATION USING A LOW FLUX REACTOR

Ten U.S. Geological Survey rock standards have been analyzed for trace elements by instrumental neutron activation using a low flux reactor and Ge detectors. Results compare favorably with the current working values for all elements except Mo. REE values that have been determined are generally slightly lower than accepted values. Data obtained for rocks that have very low trace element concentrations (e.g., BIR-1) will aid in refining the working values for these standards.     

Instrumental Neutron Activation Analysis Of 37 Geochemical Reference Samples

37 geochemical reference samples, issued mostly by the U.S. Geological Survey and the "Centre de Recherches Pétrographiques et Géochi-miques", have been analysed for more than twenty trace elements using instrumental neutron activation technique. The results are compared with published data; in most oases, the agreement is good.     

Precise determination of uranium in rocks and minerals by neutron activation analysis using 133I fission product

A radiochemical neutron activation technique for uranium determination in rock and mineral samples is presented. The method is based on an alkaline fusion, a selective oxidation of iodine by a sodium-nitrite solution, followed by an iodine distillation technique for the isolation of the ¹³³I produced in fission. The outlined scheme is rapid, sensitive and reliable. Determination of uranium in U.S. Geological Survey standard rocks (G-1, W-1, G-2, BCR-1, AGV-1, GSP-1), C.R.P.G. Nancy geochemical standards (GA, GH, BR, Mica-Fe, Mica-Mg), C.A.A.S. reference syenite rocks (SY-1, SY-2, SY-3) and other analysed rock samples are reported. These results are compared with those obtained by other methods.     

Evaluation of uranium and arsenic retention by soil from a low level radioactive waste management site using sequential extraction

The European Communities Bureau of Reference (BCR) and Chunguo sequential extraction procedures were employed to evaluate the retention of U and As by a soil contaminated with low level radioactive waste. Modifications were made to both procedures to optimize the measurement of soil and extractant samples using epithermal neutron activation analysis. Based on the BCR procedure, approximately 20% of the U appeared to be bound to the carbonate fraction, 10% to the mineral oxide fraction and 20% to the organic fraction. In the case of As, the majority was strongly bound in the residue fraction. The results obtained with the Chunguo procedure supported these conclusions to some extent, in that the majority of the U and As was found to be strongly bound to the soil in a manner consistent with its presence in the residue fraction.     

Neutron Activation Analysis of Nine GSJ Sedimentary Rock Reference Samples

Nine rock reference samples "Sedimentary rock series" issued by the Geological Survey of Japan (GSJ) were analysed for up to 31 elements by neutron activation analysis (NAA); 14MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with reported values.     

NEUTRON ACTIVATION ANALYSIS OF FIFTEEN GSJ IGNEOUS ROCK REFERENCE SAMPLES

Fifteen rock reference samples "Igneous rock series" issued by the Geological Survey of Japan were analysed for up to 31 elements by neutron activation analysis (NAA); 14 MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with published values.     

Uranium and thorium in achondrites

The abundances of U and Th in 19 achondrites and two pallasite olivines have been measured by radiochemical neutron activation analysis. Brecciated eucrites are enriched relative to chondrites in both elements by factors between 10 and 20, perhaps as a result of a magmatic differentiation process. Two unbrecciated eucrites are far less enriched, possibly due to their origin as igneous cumulates. The diogenites Johnstown and Shalka contain approximately chondritic levels of U and Th, but Ellemeet is 10 times lower. The abundances in three howardites are in good agreement with those expected from major element data for a mixing model with eucrite and diogenite end members. The high O¹⁸ basaltic achondrites Nakhla, Shergotty and Angra dos Reis have a range of U and Th abundances similar to the brecciated eucrites and howardites, but have systematically higher Th/U ratios. The Bishopville aubrite has U and Th abundances and Th/U ratios similar to those of several enstatite chondrites, suggesting a genetic relationship. The Norton County aubrite has a low Th/U, similar to that observed in recrystallized and metamorphosed terrestrial ultrabasic rocks, indicating a more complex history. Pallasite olivines have low U and Th contents (0.5.4 ppb and 1.4.3 ppb, respectively) similar to those in terrestrial dunites. The Goalpara ureilite has very low U (<0–6 ppb) and Th (2.7 ppb) abundance consistent with an origin from carbonaceous chondrites by partial melting.     

Determination of Niobium in 15 USGS Standard Rocks by NEutron Activation Analysis

The niobium concentrations in 15 U.S.G.S. standard rocks were measured by neutron activation analysis. The niobium was separated from the rock matrix (in the presence of ⁹⁵Nb tracer, which was used to measure the fraction recovered) before irradiation to improve the sensitivity. Results of this work are compared with those obtained by other techniques. Some results obtained by multielement X-ray fluorescence procedures agree well with the present data, but a systematic disagreement exists between these and the spectrophotometric data.     

晋北-宁北煤中痕量元素的地球化学特征

应用仪器中子活化 (INAA)、电感耦合等离子体原子发射光谱 (ICP- AES)和原子吸收光谱 (AAS)等方法测定了晋北-宁北一线 5对矿井、 2个露天矿、 5个电厂和 3个洗煤厂煤中环境敏感性痕量元素的含量;通过与中国土壤、其他地区煤以及世界范围煤中痕量元素含量进行对比,总结了研究区痕量元素的分布、富集特征,得知部分地区煤中 Hg、 Cd和 Se的含量较高,在燃烧利用过程中可能对环境造成影响.通过分析痕量元素与灰分、挥发分的相关性以及痕量元素间、痕量元素与 Al、 Fe和 Sp的相关、聚类特性,探讨了痕量元素间及其与矿物质间的亲合性及赋存特征.     

SHRIMP in situ isotopic analyses of REE,Pb and U in micro-minerals bearing fission products in the Oklo and Bangombé natural reactors: A review of a natural analogue study for the migration of fission products

In the Precambrian, parts of the Oklo, Okélobondo and Bangombé uranium deposits of the Republic of Gabon, central Africa, functioned as natural fission reactors. Many elements in the Oklo and Bangombé uranium deposits show variations in isotopic composition caused by a combination of nuclear fission, neutron capture and radioactive decay. Isotopic studies provide useful information to understand the behavior of radionuclides in geological media. In our recent work, in situ REE, Pb and U isotopic analyses of individual tiny minerals in and around reactor zones have been performed using a SHRIMP (Sensitive High Resolution Ion Microprobe). The isotopic results of the SHRIMP analyses on micro-minerals found in and around the Oklo and Bangombé natural reactors are reviewed in this paper. The data suggest the selective uptake behavior of (1) Ra into illite, and (2) Pu into apatite, (3) the formation process of secondary minerals bearing fissiogenic REE and depleted U, (4) evidence of nuggets (?-particles) bearing fissiogenic platinum group elements (PGE), and (5) from the U–Pb systematics of highly altered zircons, the redistribution of U and Pb.     

大别山地面γ能谱资料的统计分析及其铀成矿信息

用GAD－6型4道γ能谱仪对大别造山带各地质体进行了地面γ能谱测定,获1324组eU,eTh,K含量数据。根据113组中子活化分析数据对能谱资料进行了质量检验。在计算能谱特征参数的基础上,将富铀钍地质体划分为铀源体、富铀体和含铀体,并探讨了其空间组合特征及其与铀成矿的关系。     

Some Trace-Element Contents of Biotite, Btt-1, and Hornblende, Hbl-I, by Semiquantitative Spectrographic Analysis and by Instrumental Neutron Activation Analysis

Some trace-element contents of U.S. Geological Survey (USGS) samples, biotite Btt-1 and hornblende Hbl-1, were determined by both computerized semi-quantitative spectrographic analysis and instrumental neutron activation analysis. An equal number of portions of the Centre de Recherches Pétrographiques et Géochimiques (CRPG) samples, biotite Mica-Fe and phlogopite Mica-Mg, were randomized with portions of the USGS samples and analyzed simultaneously to allow direct comparisons of trace elements in the biotites. Mica-Fe has concentrations of Cs, Hf, Ta and Zn that are greater by factors of 3 or more than those in Btt- 1. Although the Co contents of the two biotites are nearly equal, the amounts of Cr, Sc, La and the rare earth elements are significantly greater in Btt-1. Mica-Mg contains larger amounts of Cs and Rb than does Hbl-1, whereas the Cr content of Hbl-1 is 15 times that of Mica-Mg. Btt-1 and Hbl-1 may be useful as comparison samples for the analysis of biotites and hornblendes after other data are available.     

Bismuth in stony meteorites and standard rocks

Bismuth has been determined by alpha counting of the ²¹⁰Po daughter activity of the ²¹⁰Bi formed by thermal neutron activation. Results are presented for thirty chondrites, six achondrites, eight separated meteoritic phases, and six U.S. Geological Survey standard rocks. There is no resolvable difference in Bi abundances among the different groups of ordinary chondrites. Bismuth concentration decreases with increasing petrologic grade among the ordinary chondrites. The enstatite chondrites are separable into two groups on the basis of Bi data.