Chapter 10
FACTORS AFFECTING NEUTRON MEASUREMENTS
AND CALCULATIONS
Part D. Trace Elements in Granite
Satoru Endo, Masaharu Hoshi, Kiyoshi Shizuma, Hiromi Hasai
Introduction
Ruhm et al. (Chapter 10, Part C) pointed out that the neutron spectrum near the ground might
be distorted by trace elements such as Gd, Li, B and Sm in soil, which have large cross sections
for thermal neutrons. T. Imanaka has theoretically tested the effects of neutron energy distortion
caused by trace elements and found that trace elements do not affect the neutron spectrum in air
above the ground. However, trace elements might improve the depth-profile calculation of
thermal activation in granite or concrete (Chapter 8, Part C). To calculate precisely the depth
profile of neutrons, Dy, Gd, Eu, Sm, Cd, Li and B concentrations in the Motoyasu Bridge granite
have been analyzed. We present the results of the concentrations of these elements and list other
major elements from previous measurements.
Materials and Methods
Sample Preparation
The measurements were carried out in the Japan Chemical Analysis Center. An amount of 0.1
g of Motoyasu Bridge granite sample was heat-dissolved by a microwave dissolution device with
ClO4/HF/HNO3. The concentration of trace elements in the solution was then analyzed by two
methods: (1) Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), and (2) Inductively
Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Trace elements to be measured
were classified into three groups: (1) Dy, Gd, Eu and Sm, (2) Cd and Li, and (3) B. For the
measurement of groups (1) and (3), In or Y was added to the solution, respectively, as an internal
standard. Densities of the added standard reagent were balanced to 10 ng/ml for the former and
1 µg/ml for the latter. Group (2) was measured directly by ICP-MS.
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Trace Element Analysis
For group (1), ion intensities of Dy, Gd, Eu, Sm and In that were in the solution sprayed into
the plasma were measured by ICP-MS. Each density of group (1) was calculated from the known
In density. For group (2), ion intensities of Cd and Li were directly obtained by ICP-MS. For
group (3), luminescent intensities of B and Y in the solution sprayed into the plasma were
measured by ICP-AES. The density of B was calculated from the known density of Y. For each
group, the measurements were carried out five times. The mean values and standard deviations
were then obtained.
Major Elements in Previous Measurements
Hasai et al. (1987) analyzed the major elements in the Motoyasu Bridge granite sample in
1987 (see also Chapter 10, Part F). Analysis of the chemical composition except for Eu and water
was performed at KTEC Co. Ltd., Kawasaki, Chiba, Japan. The Eu concentration was estimated
by the neutron activation method using the research reactor of Kiniki University (UTR-KINKI).
The water content in granite is discussed in other sections of this report by Iwatani et al. (Chapter
10, Part F) and Komatsubara et al. (Chapter 10, Part E).
Results and Discussions
The results of the measurements of the concentrations of trace elements are summarized in
Table 1 together with results for other major elements. The Eu concentration from a previous
measurement is also listed. The two values of the Eu concentration are consistent within
estimated errors. The new result of the Eu concentration is obtained with a better accuracy of 1%.
The concentration of B could not be obtained. Therefore the upper limit of the 99.7% confidence
level, which was estimated by the standard deviation (3σ) in five repeated measurements, is
indicated only.
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The water content is discussed in Chapter 10, Parts E and F by Komatsubara et al. and
Iwatani et al., respectively. Their values are summarized in Table 2. Komatsubara et al. directly
measured the proton components to be 0.29 ± 0.11% as the water mass content in granite by
using elastic proton-proton scattering. On the other hand, Iwatani et al. measured the mass
changing of granite by heating. They classified the water content into three components;
adsorptive water (I), adsorptive water (II) (H2O−), and bound water (H2O+). The sum of three
components was 0.51 ± 0.10% as the water mass fraction in granite. In comparing the two values,
the direct measurement of the hydrogen component gives a lower fraction than that by Iwatani et.
al. For convenience, atomic concentrations for all of the measured elements (Hasai et al. 1987)
are summarized in Table 3.
Reference
Hasai, H.; Iwatani, K.; Shizuma, K.; Hoshi, M.; Yokoro, K.; Sawada, S.; Kosako, T.; Morishima, Y.
“Europium-152 Depth Profile of a Stone Bridge Pillar Exposed to the Hiroshima Atomic Bomb: 152Eu
Activities for Analysis of the Neutron Spectrum.” Health Phys. 53: 227-239; 1987.
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