File 6 - N-Body Phase-Space Distributions (LAW=6)

In the absence of detailed information, it is often useful to use n-body phase-space distributions for the particles emitted from neutron and charged-particle reactions. These distributions conserve energy and momentum, and they provide reasonable kinematic limits for secondary energy and angle in the LAB system.

The phase-space distributions are described by the following formulas:

where

E: is the projectile energy in the laboratory;
E',μ: are the energy and cosine for the outgoing particle, both in the lab or CM, depending on LCT;
E_i^max: is the maximum possible CM energy for particle i;
E_CM: is the energy of the CM motion in the laboratory;
E_a: is the energy available in the CM for a one-step reaction;
M: is the total mass of the n particles being treated by this law;
m_i: is the mass of the particle being described in this section of File 6;
m_p: is the projectile mass;
m_T: is the target mass; and
Q: is the reaction QI values from File 3.

Note that M may be less than the total mass of products for reaction like

α + ⁹Be -> n + 3α

where the neutron can be treated as a two-body event and the alphas by a 3-body phase-space law. The parameter APSX is provided so the E_i^max can be determined without having to process the other subsections of this section.

The following quantities are defined for LAW=6:

APSX: total mass in neutron units of the n particles being treated by the law; and
NPSX: number of particles distributed according to the phase-space law.

Only a CONT record is given for a LAW=6 subsection:

   [MAT, 6, MT/ APSX, 0.0, 0, 0, 0, NPSX] CONT

23 January 1998

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