The Diffusion Length of Thermal Neutrons in Heavy Water

Abstract

A continuous flux of thermal neutrons was passed into a large cylindrical tank of heavy water that sat on a graphite column containing a source of photoneutrons. The neutron density in the tank was explored with small indium detectors at selected points along two diameters at right angles in each of three horizontal planes and at 10-cm. intervals along the axis of the tank. The transverse measurements were fitted to Fourier–Bessel series in which the amplitudes of the harmonics were relatively small. The effective radius derived from the transverse analysis was the same in the three planes. The relaxation length of the first component was found from the axial measurements. Corrections were applied for the absorption of neutrons in the axial detector tube, enclosed framework, and indium detectors, and in the light hydrogen in the heavy water. The final value of the diffusion length of thermal neutrons in heavy water (100% D2O) is 171 ± 20 cm. Combining this with the known transport mean free path, the capture cross-section is (0.92 ± 0.22) × 10−27 cm.2 per molecule D2O for neutrons of velocity 2200 m. per second.

Thermal neutron capture cross sections forO16,17,18andH2Firestone1, Révay2 2016Phys. Rev. C264701View full textAdd to dashboardCite

“…Most earlier measurements are higher than the current value but the more recent values of Alfimenkov et al [19] and Jurney [20], adopted by Mughabghab [7] are consistent with our new value. Sargent (1947) [21] Pile Oscillator 0.92±0.22 Kaplan (1952) [22] Diffusion a 0.572±0. 10 Jurney (1963) [10] Capture γ-ray 0.60±0.05 Trail (1964) [23] Capture γ-ray 0.36±0.03 Merritt (1967) [24] Activation 0.506±0.010 Merritt (1968) [25] Activation 0.521±0.009 Silk (1969) [26] Diffusion 0.523±0.0.029 Ishikawa (1973) [27] Activation 0.55±0.…”

A deuterated liquid scintillator for supernova neutrino detection

“…See for example at https://www.hwb.gov.in/ 3. We note that a thermal neutron travels ∼ 170 cm in heavy water before capture[37], compared to a few cm in ordinary water[38]. The diffusion length of neutrons in DLS will be much smaller if n-capture dopants, such as Gd, are present.…”

A Note on theUOperator

“…Its use amounts to an additional assumption. The failure of (1) need not be related to convergence or renormalization difficulties We consider the operator equation…”

“…1 A somewhat better insight into the nature of these relations is gained by connecting U r (t) } U a (t) with another special solution of (4):…”