Chushiro Yonezawa

The characteristics of the prompt gamma-ray analyzing system at the neutron beam guides of JRR-3M

Abstract A reactor-neutron-induced prompt γ-ray analyzing system was constructed at JRR-3M. The system can be set at cold and thermal neutron beam guides with a neutron flux at the sample position of 1.1 × 10 8 and 2.4 × 10 7 n cm −2 s −1 , respectively. The system was designed to achieve the lowest γ-ray background. This is done by using lithium fluoride tiles as neutron shielding, by placing the samples in a He atmosphere, and by using a Ge-BGO detector system for Compton suppression. The γ-ray spectrometer is equipped to acquire three modes of spectra simultaneously: single mode, Compton suppression mode, and pair mode in an energy range of up to 12 MeV. Due to the cold neutron guide beam and the low background system, sensitivities and detection limits better than those in other PGA systems have been achieved. For typical elements such as H, B, Cd, and Gd, analytical sensitivities with the cold neutrons are 10 to 18 times higher, and detection limits are lowered by factor of 6 to 8, compared to the case with thermal neutrons under the same geometrical condition. Detection limits down to a range of 2 to 7 ng were recorded for B, Cd, Sm, and Gd by the cold neutrons. Hydrogen, one of the most important elements in material studies, could be detected down to 1.0 and 2.8 μg by cold and thermal neutrons, respectively.

Boron contents of Japan Trench sediments and Iwate basaltic lavas, Northeast Japan arc: estimation of sediment-derived fluid contribution in mantle wedge

Mantle wedge below the Northeast Japan arc contains hydrous fluids that dehydrated from two parts of the descending slab: a sediment layer and an altered oceanic crust (AOC). In order to estimate the weight percent of a sediment-derived fluid in the mantle wedge, we determine boron and other element contents of Japan Trench sediments and Iwate basaltic lavas on the Northeast Japan volcanic front. Trace element contents of the trench sediments are used to estimate those of the sediment-derived fluid, and previously reported trace element contents of the AOC are used to estimate those of the AOC-derived fluid. Examination of mobile/immobile element ratios (B/Sm, Ba/Sm, K2O/Sm, B/Zr, Ba/Zr, K2O/Zr) of the two slab-derived fluids and Iwate basaltic lavas, indicates a mixing ratio between the AOC-derived fluid and the sediment-derived fluid is 90:10 in the mantle wedge beneath the Northeastern Japan arc. The mobile/immobile element ratios also suggest that the subducted sediment recycle to the mantle wedge beneath Northeast Japan as sediment-fluid rather than sediment-melt. Since the weight fraction of the total slab-derived fluid in the mantle wedge is estimated to be less than 1 wt%, an addition of a small amount (<0.1 wt%) of the sediment-derived fluid to the mantle wedge fulfills the boron and other trace element contents in the Iwate basaltic lavas.

Prompt gamma-ray analysis (PGA) of meteorite samples, with emphasis on the determination of Si

Neutron-induced prompt gamma-ray analysis (PGA) was applied to seven meteorite samples (Allende, Zagami, Acfer 209, ALH77005, ALH84001, EET79001 and Neagari). Samples were irradiated in both the thermal neutron and the cold neutron guided beams of JRR-3M at JAERI. Multiple samples of an Allende standard powder were analyzed for Si using two different methods: (1) the comparison method, using a Si standard, and (2) the mono-standard method, using Fe as an internal reference element. The Si concentrations determined by these two methods are in good agreement with literature values. The analytical sensitivity for Si using the cold neutron guided beam is∼14.3× higher than that for the thermal neutron guided beam. Other elements determined (B, Ca, Ti and S) also showed higher sensitivities using the cold neutron beam. The other meteorites studied showed some anomalous B and S values likely due to the effects of terrestrial weathering/contamination.

Efficiency calibration of a Ge detector in the 0.1–11.0 MeV region

Abstract An efficiency curve was constructed for a large-volume Ge detector located at the thermal-neutron beam line of the JRR-3M reactor at the Japan Atomic Energy Research Institute (JAERI). The calibrations for γ-ray energies below 2754 keV were accomplished with a large number of radioactive sources and above 2754 keV with the 12 C(n,γ) and 14 N(n,γ) reactions. This detector and its efficiency curve were subsequently used to determine accurately the photon emission probabilities of γ rays from the decays of 56 Co (T 1/2 =77 d ) and 66 Ga (9.5 h ) and from the 35 Cl(n,γ) reaction. These radiation sources can serve as secondary standards for efficiency calibrations.

Measurement and analysis of the line shape of prompt γ-rays from recoiling 7 Li produced in the 10B(n, α) 7Li reaction

Abstract Prompt γ-ray spectra of recoil 7 Li produced by the 10 B(n, α) 7 Li reaction were measured using neutron beam. The observed Doppler broadening energy spectra were satisfactorily reproduced by a simulation where the velocity degradation of 7 Li within its lifetime of 1.05 × 10 −13 s was estimated using the LSS theory. Our successful line-shape analysis was applied to non-destructive state analysis of trace amounts of boron.

Determination of boron in Japanese geochemical reference samples by neutron-induced prompt gamma-ray analysis

Determination of ppm levels of B in 21 igneous and sedimentary rocks of the Japanese geochemical reference samples prepared by the Geological Survey of Japan (GSJ) has been performed by neutron-induced prompt γ-ray analysis (PGA) using cold and thermal guided neutron beams of the JRR-3M. Owing to the Doppler broadened γ-ray line of B 478 keV, many elements such as Na, Ni, Cl and so on showed spectral interference in the determination of B. The interference was corrected by computer fitting and a reference peak method. The analytical results obtained by the present method almost agreed with the GSJ values recommended in 1994 within the standard deviation of the recommended values. Sodium contents determined by the PGA in the reference rock samples are also reported.

PROMPT GAMMA-RAY ANALYSIS USING COLD AND THERMAL GUIDED NEUTRON BEAMS

A permanent and stand-alone neutron-induced prompt γ-ray analysis (PGA) system, usable at both cold and thermal neutron beam guides of JRR-3M has been constructed. The characteristics of the system, including neutron beam and γ-ray spectrometer were measured. Owing to the absence of fast neutrons and the low γ-ray background, analytical sensitivities and detection limits better than those in other PGA systems have been achieved. Analytical results of ten elements in Standard Reference Material of Coal Fly Ash agreed well with those obtained by other methods. Isotopic analysis of Ni and its application to accurate and precise determination of Ni by stable isotope dilution method were performed.

RAPID DETERMINATION OF SPECIFIC ACTIVITY OF NICKEL-63

For the determination of specific activity of63Ni, a method has been developed for simultaneous assessment of both stable and radionickel. The method comprises solvent extraction of Ni-dimethylglyoxime into xylene for spectroscopic measurement and liquid scintillation counting of the extractant. The application of the method has been successful for63Ni in the corrosion products accumulated on the wall surface in the primary circuiting tube of the reactor.

Multi-element analysis of environmental samples by cold and thermal guided neutron induced prompt gamma-ray measurement

Non-destructive multi-element determination in environmental samples by neutron-induced prompt γ-ray analysis (PGA) has been investigated. Comparative standardization for the elements including H, B, C, N, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Co, Cd, Sm, Gd, Hg by PGA has been carried out using the cold and thermal guided neutron beams of JRR-3M reactor and then several environmental reference materials have been analyzed. Accuracy and precision of better than 20% were found for these elemental analyses except for H, C, N and Cl in biological samples. Detection limits in various environmental matrices were 25 to 820 ng/g for B, Cd, Sm and Gd, 1.1 to 820 μg/g for H, Na, S, Cl, K, Ti, Mn, Co and Hg, and 0.031 to 10% for C, N, Mg, Al, Si, P, Ca and Fe. The present method is being applied to environmental studies of post war Persian Gulf together with INAA and ICP-MS.

Neutron induced prompt gamma-ray and instrumental neutron activation analyses of urban estuarine sediments

Neutron induced prompt γ-ray analysis (PGA) and instrumental neutron activation analysis (INAA) have been applied to the sediments collected from the Tama River estuary in Tokyo, Japan. The vertical distribution of 24 elements in the sediments was determined and the factors goveming the vertical profiles have been discussed. Major elements are distributed depending on weathering that proceeds much with increasing depth. Cadmium is highly concentrated in the deeper layer where sulphate ion is reduced to hydrogen sulphide. The distribution of several rare earth elements is also presented