No abstract

Two‐group neutron diffusion theory has been applied to two concentric cylindrical regions representing borehole and formation to show that the ratio of thermal neutron flux at two appropriately large distances along the axis is virtually identical to the epithermal flux ratio, and is a measure of a single epithermal parameter of the formation, viz., the slowing down length. The slowing down length is most strongly dependent on hydrogen content. It is shown that variations in salinity of the liquid in the formation or the borehole and uncertainties in borehole size have relatively little effect on the flux ratio. Experiments in a borehole model showed that the thermal flux ratio does not depend on eccentricity of location of the logging tool in the borehole. Fits of theory to experiment allowed determination of slowing down lengths for Pu‐Be neutrons in salt water filled sandstone at two porosities for which experimental values have not previously been available. These investigations suggest that an improved porosity log can be obtained by use of 70‐ and 90‐cm source‐detector spacings with a neutron source of [Formula: see text] neutrons/sec or greater. Proportional counters containing [Formula: see text] are recommended as detectors. Such a system employing flux ratios is expected to be insensitive to casing and cement in cased holes.

No abstract

The cross section for S 32 (w,^)P 32 has been measured for incident neutron energies up to 15 Mev. The data at high energies differ from previously published measurements. The cross section for S 34 (w,a)Si 31 also has been measured for incident neutron energies up to 14.1 Mev.

Three instrumEmt packages containing Geiger tubes ,were flown into the inner Van Allen belt to, altitudes up' to 1500 km. Various absorber thicknesses were used to obtain range ' speetra for penetrating particlel3. Magnetic ,separation .of electrons and protons was perfoOlled on ~ounters with absorber 'thicknesses ranging from 1.7' mg/cm" of mica to 36 mg/cm" of aluminum. The electron spectrum ' observed ' with counters having electron energy thresholds of 30, 160, 190, !lend 460 kev' appears 'considerably softer than a neutron beta-decay spectrum. Counts in cowrters with higher thresholds are a~med to, be due to trapped protons and the measurements are compare, d 'with those obtained with ,nuclear ' emufl3ion experiIDents on similar trajectories. Absolute flux v!1lues are reported.' '