4. METHOD OF SOLUTION
The electron differential spectrum as a function of depth is inferred by assuming that electrons travel straight ahead and that distance travelled 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 buil-dup factor assumed is a plane isotropic buildup factor generate 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.