BRIEF INSTRUCTIONS FOR USE OF THE MONTE-CARLO EFFICIENCY CODE Abridged and modified from the original instructions of N.R. Stanton, COO-1549-92, February 1971 (Ohio State U.), unpublished. A. USER DATA FILE 1. A comment line. 2. A second comment line. 3. A line containing the array NSW and the variable NDUMP (6I1,I4). The 6 elements of NSW give the initial settings of the simu- lated sense switches which control the detail in which the output is printed; these are ordinarily set to 2. NDUMP is the number of individual histories to print out in detail. 4. A comment line. 5. A line containing the variables TBIAS, DTIM, and DPOS for the timing and position study [10F8.3]. TBIAS is the threshold (in MeVee) at which the "measurements" of time and position are taken; DTIM and DPOS are the bin widths (in nsec and in inches, respectively) for the accumulated histograms. 6. A comment line. 7. A line containing ELOPE(2) and ELOPE(3) [2F6.2], the light levels (in MeVee) corresponding to one photoelectron for the two values of resolution smearing desired. 8. A comment line. 9. The random number generator seed [I5]. 10. A comment line. 11. The scintillator density and H/C ratio [2F8.3]. 12. A comment line. 13. The light output coefficients for protons [2F12.5]. 14. A comment line. 15. The light output coefficients for alphas [2F12.5]. 16. A comment line. 17. A line containing the variables XB, YB, ZB, IGEO, and IRANP [3F6.2, 2I2], giving the dimensions and geometry of the scintillator, and whether the neutron illumination is point or uniform. If IGEO = 0, the scintillator is taken to be a rectangular prism +-XB inches wide, +-YB inches high, and ZB inches deep; IRANP = 0 will send in all neutrons at the point specified below, while IRANP = 1 will distribute the neutrons uniformly over the front face of the detector. If IGEO = 1, the scintillator is taken to be a cylinder of radius XB = YB inches and depth ZB. If IRANP = 0, all neutrons will enter at the point specified below; if IRANP = 1, the flat face will be uniformly illuminated. If IGEO = 2, neutrons will be incident on the cylindrical surface of a cylindrical scintillator. (The neutrons' direction is normal to a plane tangent to the cylindrical surface.) 18. A comment line. 19. A comment line. 20. A comment line. 21.-XX. Any number of lines, one for each group of histories desired. Each line has FORMAT (3F5.2, 3F7.4, 2F8.3, I8, F8.3). a. The initial position vector XI(I) in inches, if IRANP = 0 (see above). The center of the coordinate system is at the center of the front face of the counter. IF IGEO = 0 and IRANP = 1, the front face of a rectangular detector will be uniformly illuminated; if IGEO = 1 and IRANP = 1, the flat face of a cylindrical detector will be uniformly illuminated; if IGEO = 2 and IRANP = 1, the cylindrical surface of a cylin- drical detector will be uniformly illuminated. b. The initial direction cosines CI(I). For normal incidence these are 0.0, 0.0, 1.0. c. The average neutron energy E1 (MeV) and the energy bin width E2 (MeV). If E2 is zero, all neutrons will be assigned initial energy E1; otherwise the initial energy will be randomly chosen from a uniform distribution of width E2 about E1. d. The number of histories to be run, NEV. e. The bin width (in MeVee) for the output differential and integral (efficiency) pulse height spectra. B. CROSS SECTION DATA FILE The necessary cross sections for the Monte-Carlo code are contained in a separate input data file, called CROSEC.IN. Normally, it is not necessary to alter these cross sections. See the reference in D. below for the latest description of the choice of the various channel cross sections. In case the user should wish to modify these cross sections, we give the input format here. 1. A comment card. 2. N lines [8F5.3], each containing an energy EDAT(I) (in MeV) and eight total cross sections SDAT(I,J) (in barns) for each of the eight channels listed below: J = 1 NP elastic scattering J = 2 NC nondiffractive elastic scattering J = 3 N + C = N + C + gamma J = 4 N + C = alpha + 9Be J = 5 N + C = N + 3alpha J = 6 N + C = P + 12B and N + C = N + P + 11B J = 7 NC diffractive elastic scattering J = 8 N + C = N + N + 11C (Note: The labeling of reaction channels J returned by subroutine SIGTOT is slightly different. See SIGTOT listing for details.) 3. A comment line. 4. A line containing the number M of anglular distribution coefficient lines to follow. [I3]. 5. A comment line. 6. M lines [10F8.3], each containing an energy ED(I) (in MeV) and five coefficients AD(I,J) for describing NC nondiffractive elastic scattering. C. TIME, CORE, AND LIBRARY REQUIREMENTS The execution time for a fixed number of histories depends on the thickness of the counter and on the neutron energy; simulating interactions takes time. In particular, low energy neutrons often interact several times in scintillators of typical size. As a guide, a sample run of 100,000 neutrons of 120 MeV impinging on a scintillator 5 inches in diameter and 4 inches deep takes about 4 minutes on a VAX 750 (with a floating point accelerator), whereas 100,000 neutrons of 40 MeV take about 10 minutes. The program occupies about 60K Bytes of memory. Note that the random number generator subroutine calls should be checked for proper operation on each new computer system. The uniformity of the random numbers generated is crucial. The statistical accuracy of the calculated efficiency is approximately that expected from a sample with a number of counts equal to the number of incident neutrons times the calculated efficiency. D. REFERENCES The code is an improved version of the original code due to N.R. Stanton at Ohio State U. [COO-1549-92, February 1971, unpublished]. The improved version is described in R.A. Cecil, B.D. Anderson, and R. Madey, Nucl. Instr. and Meth. 161, 439 (1979). Various experimental tests of this code include: B.D. Anderson et al., Nucl. Instr. and Meth. 169, 153 (1980); J.W. Watson et al., Nucl. Instr. and Meth. 215, 413 (1983); and J.D'Auria et al., Phys. Rev. C30, 1999 (1984).