Secondary particles with multiplicity greater than 1

The differences in the treatment of secondary particles with multiplicity exceeding 1, e.g., (n, 2n$\gamma$) reactions, derive from the fact that the energy distribution data is the average for the two particles. Note also that the output of endep includes the particle multiplicity in the average energy deposition. That is, the output file contains pairs

(E_yi,$$\mu$$$$\langle$$E_yo$$\rangle$$)

where E_yi is the energy of the incident particle, $\langle$E_yo$\rangle$ is the average energy of the secondary particle yo as computed from the integral (16), and $\mu$ is its multiplicity.

Another difference arises from the fact that some decision has to be made about how to apportion the energy between the multiple secondary particles. For the sake of clarity, I describe how endep handles (n, 2n$\gamma$) reactions. This is treated as a 2-step reaction, with the first step being continuum inelastic scattering as described in Section 3. The second step is emission of the second neutron by continuum decay as discussed above. The important point to note is that the same average neutron energy, $\langle$E_yo$\rangle$ from the integral (16), is used in both processes. If the model were changed, for example by apportioning more energy to the first neutron emitted than to the second, the average energies $\langle$E_res$\rangle$ and $\langle$E_$\gamma$$\rangle$ would change, but the sum $\langle$E_res$\rangle$ + $\langle$E_$\gamma$$\rangle$ would stay constant.