Measurement of the thermal neutron absorption cross section of rock samples by a pulsed source method
Conference
·
OSTI ID:4064946
- eds.
Small portable accelerators have been used in oil well logging for the past decade. The uses of these accelerators for neutron logging have been supported by a continuing program of theoretical studies as well as experimental model measurements. For quantitative interpretation of field logs a measurement of the macroscopic thermal neutron absorption cross section, $Sigma$/sub a/, of common rock materials is required. A pulsed neutron source technique for making such measurements in the laboratory is described. The method requires only one thermal neutron lifetime determination for a mixture of crushed rock saturated with pure water. The error in determining $Sigma$/subrock/ is less than or equal to 1 c.u. (capture unit = 10$sup -3$ cm$sup -1$). However, to reduce the effect of thermal neutron diffusion relative to absorption it is necessary to use crushed rock samples weighing approximately 15 to 20 kg. Although this limitation precludes application of the technique to small core samples, the method can be used to determine $Sigma$/sub rock/ for any laboratory model whose material of construction is available. Results are given for both igneous and sedimentary rocks which outcrop in various parts of the United States. Most of the measured cross sections exceed the cross sections one would calculate for a given rock on the basis of its primary minerals. It is concluded that most of the rocks probably contain strongly absorbing trace elements such as boron or gadolinium.
- Research Organization:
- North Texas State Univ., Denton (USA)
- NSA Number:
- NSA-33-023302
- OSTI ID:
- 4064946
- Report Number(s):
- CONF-741040--P2
- Country of Publication:
- United States
- Language:
- English
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