1. NAME AND TITLE

ELBA: Electron and Bremsstrahlung Dose Rate Code.

2. CONTRIBUTOR

Space Sciences Laboratory, NASA George C. Marshall Space Flight Center, Huntsville, Alabama.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

ELBA takes an incident isotropic electron flux with a given differential energy spectrum and calculates the dose rate received from bremsstrahlung produced in a plane aluminum shield placed in front of the receiver. There is an option to also calculate the electron dose rate from the same source.

5. METHOD OF SOLUTION

The electron differential spectrum as a function of depth is inferred by assuming that electrons travel straight ahead and that distance traveled and energy are related by a range-energy relationship. The electron dose rate at a given depth is calculated by integrating, over energy and direction, the product of the electron flux, the stopping power, and the appropriate flux-to-dose rate conversion factor.

The bremsstrahlung source is assumed to be plane and isotropic at a given depth. This source is defined as the integral over energy and direction of the product of photon energy, the differential bremsstrahlung spectrum from electrons of a given energy, and the electron flux differential spectrum. The differential bremsstrahlung spectrum is derived from the Born approximation cross section multiplied by a correction factor. The bremsstrahlung dose rate is obtained by integrating, over photon energy and slab volume, the product of the bremsstrahlung source, photon energy flux-to-dose rate conversion factor, buildup factor, and attenuation kernel. The buildup factor assumed is a plane isotropic buildup factor generated by Monte Carlo calculations. The integrations are performed by evaluating the integrand at the midpoint of each integration step, multiplying by the step width, and summing the result.

The incident electron spectrum, dose rate conversion factors, and range formula coefficients are input by the user. The buildup factor information is contained in three DATA statements in subroutine BURP.

6. RESTRICTIONS OR LIMITATIONS

There are limitations on the dimensions of certain arrays, but these dimensions probably can be increased to meet the user's requirements.

7. TYPICAL RUNNING TIME

Estimated running time of the packaged sample problem on the IBM 7090: 13.8 minutes; considerably less time required for the IBM 360/370.

8. COMPUTER HARDWARE REQUIREMENTS

The code was written for the IBM 7094, and was converted to run on the IBM 360/370.

9. COMPUTER SOFTWARE REQUIREMENTS

A FORTRAN IV compiler is required.

10. REFERENCES

M. O. Burrell, J. J. Wright, and John W. Watts, Jr., "The Calculation of Electron and Bremsstrahlung Dose Rates," NASA-SP-169 (ANS-SD-5) pp. 529-538 (1968).

Informal note, Printed Output from Sample Problem.

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code and input for a sample problem. The output from running the problem is included in the referenced document.

12. DATE OF ABSTRACT

August 1971; updated August 1981, February 1985, September 1991.