3. DESCRIPTION OF PROGRAM OR FUNCTION
SPEC is a program for calculating the neutron or charged particles (p, d, t, He3, alpha) induced reactions of medium-heavy nuclei in the incident energy range up to 60 MeV including 6 emission processes. For those reaction channels contributed only by 1-5 emission processes the incident energy can go up to 100 MeV. SPEC is constructed within the framework of optical model, master equation of the exciton model, and the evaporation model. In the first and second particle emission processes, we consider preequilibrium emission and evaporation; in 3-6 particle emission processes, we only consider evaporation. The preequilibrium and direct reaction mechanisms of gamma emission are also included in this program. The effect of recoil nucleus is considered for calculating spectra. Program SPEC includes the first to the sixth particle emission processes.
a+A -> b+B*, a=n, p, alpha, d, t, He3, b=n, p, alpha, d, t, He3,gam B* -> c+C*, c=n, p, alpha, d, t, He3, gamma
C* -> d+D*, d=n, p, alpha, d, t, He3, gamma
D* -> e+E*, e=n, p, alpha, d, gamma
E* -> f+F*, f=n, p, gamma
F* -> g+G*, g=n, p, gamma
When a particle is emitted, the residual nucleus may emit another particle or gamma ray continuously if the excited energy is large enough to overcome the binding energy. Generally speaking, the gamma emission cross section is much less than neutron emission cross section when neutron emission channel is open, we assume that after gamma ray is emitted the residual nucleus do not emit any particle except after the first gamma ray emission process the particle or gamma are allowed to be emitted. Thus, 7 channels can be opened for the first emission process, 49 channels for the second emission process, 252 channels for third emission process, 1080 channels for forth emission process, 2592 channels for fifth emission process, and 5184 channels for sixth emission process.
The Gilbert-Cameron level density formula was applied in program SPEC. The inverse cross sections of the emitted particles used in statistical theory are calculated from the optical model. The partial widths for gamma-ray emission are calculated based on the giant dipole resonance model with two resonance peaks in both the evaporation model and exciton model.
In the optical model calculation, we usually adopt the Becchetti and Greenlees's phenomenological optical potential, which parameters are usually given by a program for automatically searching the optimum optical model parameters. We use Neumanove methods to solve the radial equation in optical model. Coulomb wave functions used in optical model are calculated by the continued fraction method.
SPEC does not calculate the direct inelastic scattering and compound nucleus elastic scattering cross sections, but the calculated direct inelastic scattering cross sections by the collective excitation distorted-wave Born approximation and compound nucleus elastic scattering results by Hauser-Feshbach model can be added by the input data of the program SPEC.
The following nuclear data can be calculated with the program SPEC: total emission cross sections and spectra of all emitted particles; for first to sixth particle emission processes and different pick-up configurations (l,m); the various yield cross sections; total and elastic scattering cross sections (only for neutron as projectile); total reaction cross section; nonelastic scattering cross sections; radiative capture cross section; (x,np), (x,n alpha), (x,2n), (x,3n), (x,4n), (x,5n), (x,6n) cross sections and so on.