In simplest terms, the

probability that a given

fusion reaction. However, it is expressed as an area. That area is the effective

target area that a stationary

fuel ion presents to an oncoming

projectile fuel ion. It is determined

experimentally and therefore takes into account all of the difficult to calculate

quantum effects.

Several interesting things pop out of this: first, cross-section is not constant; it depends on projectile energy. Second, cross-section peaks at a given energy for each fuel combination. Assuming the target ion is at rest, the total cross-section in barns (sigma), as a function of **E**, the energy of the projectile in keV, can be fitted by the following equation:

sigma_{T}(**E**) = {A_{5}+{(A_{4}-A_{3}**E**)^{2}+1}^{-1}A_{2}}/{**E**{exp(A_{1}**E**^{-1/2})-1}}

The coefficients A_{j} are called Duane coefficients and vary for each fuel combination. Duane coefficients for several common reactions may be found on pp 45 of the 1998 Revised NRL Plasma Physics Formulary. I may post them later as an addendum to this writeup.