# Accession Number:

## ADA238884

# Title:

## Green's Function Approach to the Atmospheric Albedo Neutron Transport Problem

# Descriptive Note:

## Master's thesis,

# Corporate Author:

## AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING

# Personal Author(s):

# Report Date:

## 1991-03-01

# Pagination or Media Count:

## 127.0

# Abstract:

This study investigated the reflection of neutron radiation off of the earths upper atmosphere, with the goal of generating a quick-running computer algorithm to estimate the albedo free field flux at any point above the atmosphere. This thesis involved analytic development in the construction of the algorithm and employed Monte Carlo simulation for generating the energy and angle distributions of the reflected radiation. The Greens function approach to modeling the neutron transport process involved approximating each energy bin of the source spectrum as a Dirac pulse in energy and summing the contribution from each source bin. The computer program integrates over the surface of the atmosphere and uses the Monte Carlo data to calculate the albedo flux at any specified time and location. Run time was maximum of six minutes for a flux calculation, but a gain on the order of one thousand should be achieved on mainframe computer systems. The albedo flux from an instantaneous point source raises quickly to a maximum and then falls off over time. Albedo fluxes as much as 10-16 neutronssquare cm secsource neutron were calculated. The accuracy of the algorithm is greatly affected by the fineness of the energy bins involved.

# Descriptors:

- *COMPUTER PROGRAMS
- SIMULATION
- ANGLES
- SOURCES
- RADIATION
- COMPUTATIONS
- DISTRIBUTION
- COMPUTERS
- FLUX(RATE)
- ACCURACY
- REFLECTION
- MONTE CARLO METHOD
- FREE FIELD
- SPECTRA
- CONSTRUCTION
- GAIN
- COMPUTER APPLICATIONS
- GREENS FUNCTIONS
- NEUTRONS
- UPPER ATMOSPHERE
- EARTH ATMOSPHERE
- ALBEDO
- NEUTRON TRANSPORT THEORY
- ALGORITHMS

# Subject Categories:

- Radioactivity, Radioactive Wastes and Fission Products