Cosmic-ray neutron demography

Abstract

The equilibrium spatial and energy distribution is calculated for neutrons made in the earth's atmosphere by cosmic rays. The neutron current leaking into space is found, and the density of neutron decays in the vicinity of the earth is computed for a future determination of importance as a source for the Van Allen belts. The spectrum and the leakage current below 10 Mev are determined from multigroup diffusion theory; the leakage above 10 Mev (<1 per cent of total) is approximated from geometrical arguments. An integrated source over each square centimeter of earth surface (at geomagnetic latitude 44°N) of 6.2 neutrons/sec (1.2 from ‘knock‐on’ processes above 10 Mev and 5.0 from evaporation processes below 10 Mev) gives an equilibrium spectrum in agreement with the ±25 per cent accuracy of measured values. This source corresponds to a global average of 4.6 neutrons/cm2/sec, of which 0.8 leaks into space, 2.9 form C14, and 0.9 is absorbed in other processes. Gravitationally trapped neutrons (<0.66 ev) amount to less than 1 per cent of the total leakage, but they contribute substantially to the decay density near the earth (e.g., 40 per cent of total decays at 1/2 earth radius).

Integral quantification of seasonal soil moisture changes in farmland by cosmic-ray neutrons

“…Cross sections units in barn (1 barn = 10 −24 cm 2 ) and values were extracted from Sears (1992). Calculations are based on equations presented in Rinard et al (2009) and Krane (1988) (Hess et al, 1961), penetrate the soil. They are scattered and randomly distributed below-and above-ground losing kinetic energy in the course of several successive collisions with nuclei in the soil, land surface cover and near-surface atmosphere, while some are absorbed at some stage.…”

Investigating temporal field sampling strategies for site-specific calibration of three soil moisture–neutron intensity parameterisation methods

“…A recent technology that may help fill this scale gap, is the Cosmic-Ray Neutron Sensor (CRNS) (Zreda et al, 2008. The CRNS detects fast neutrons, which are produced from high-energy neutrons of cosmic origin and are further attenuated as they travel through the soil (Hess et al, 1961;Zreda et al, 2008). Because of the high attenuation power of hydrogen for these cosmic-ray neutrons, fast neutron intensity decreases with increasing hydrogen content within the sensor footprint (Zreda et al, 2008).…”

Monte Carlo Simulation of Neutrons, Protons, Ions and Alpha Particles Involved in Soft Errors in Advanced Memories

“…5) The energy range of interest is 100 keV-200 MeV because atmospheric neutrons are very abundant in this energy range. 12) The physics of DHORIN is mainly based on the 2D-exciton model, 13) the Hauser-Feshbach formulation 14) and the generalized evaporation model. 15) The main advantage of this code is that it is able to calculate all the needed quantities (cross sections, level densities and transmission coefficients) for all nucleus that have to be treated during a reaction.…”