UNITED STATES DEPARTMENT OF THE INTERIOR





                         GEOLOGICAL SURVEY




                    USGS Gamma-Ray Modeling Programs


                         Joseph S. Duval **








                       Open-File Report 97-96



This report is preliminary and has not been reviewed for conformity
with U.S. Geological Survey editorial standards and stratigraphic 
nomenclature.  No guarantees are made regarding the usability or 
accuracy of the computer programs presented in this report.



                            INTRODUCTION

This open file report describes several gamma-ray modeling programs
which allow you to investigate the basic physical parameters which 
affect airborne gamma-ray measurements, to design an airborne 
gamma-ray survey, and model the effects of anomalous finite 
gamma-ray sources.  The programs which allow you to investigate 
the basic physical parameters are named Circle and Strip.

Circle calculates the field of view for a stationary gamma-ray 
detector.  This program allows you to change all of the parameters 
which affect the measurement of the gamma-ray flux from a flat 
homogeneous source which is infinitely thick.  You can calculate the 
percentage of the gamma-ray flux which originates within layers of 
different thicknesses as well as from within circular areas of 
different radii.

Strip calculates the field of view for an airborne gamma-ray detector. 
This program also allows you to change all of the parameters which 
affect the measurement of the gamma-ray flux from a flat homogeneous 
source which is infinitely thick but the effects of the motion of the 
aircraft are included in the calculations.  The results provide 
information about the percentages of the gamma-ray flux which 
originate within strips of ground parallel to the flight path of the 
aircraft.

Gdesign is a program which helps you design an airborne gamma-ray 
survey.  This program allows you to specify parameters related to 
the gamma-ray measurements, the size of the survey area, and expected 
cost of the survey.  The program then attempts to honor the specified 
parameters but makes adjustments as necessary in order to achieve as 
good a survey as possible within the limitations placed upon the 
parameters.

Gmodel1 is a program which simulates an airborne gamma-ray system and 
allows you to estimate the effects of anomalous finite gamma-ray 
sources.  The program offers different types of sources which can be 
circular, rectangular, or long linear sources.  This program requires 
a system-response grid which is calculated using the program Gmodgrd.

Gmodgrd calculates a system-response grid for an airborne gamma-ray 
system.  The program allows you to specify most of the parameters 
which affect the airborne gamma-ray measurements and calculates a 
system-response grid which is saved to disk for use with the modeling 
program Gmodel1.


                            INSTALLATION

SYSTEM REQUIREMENTS:
	Windows 95
	16 Mb RAM
	1.9 Mb free disk space
	Windows 95 Compatible Mouse and Keyboard
	640 by 480 Super VGA Video (800 by 600 preferred)

These programs are designed to run under Microsoft Windows 95.
To begin the installation process you should:
1.  Open Disk 1 of the installation disks using Explorer,
2.  Double-click the mouse on the Setup icon,
3.  Select the suggested location for the data files.
    You can select another disk if you have more than one
    hard-disk drive.  Other changes in the folders suggested
    by the installation script are discouraged.
4.  Insert Disk 2 when requested.

The installation script automatically installs the programs on the
start menu under the name "USGS Gamma-ray Modeling".


**   12201 Sunrise Valley Drive, Mail Stop 954, Reston, VA 20192