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Manuscript Title: Monte Carlo simulation for Compton suppression spectrometer.
Authors: R.H. Tsou, S.C. Lin, L.L. Kiang
Program title: CSSM
Catalogue identifier: ACVH_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 83(1994)30
Programming language: C.
Computer: HP9000/750.
Operating system: UNIX, DOS.
RAM: 200K words
Word size: 32
Keywords: Particle physics, Elementary, Detector design, Monte carlo, Compton suppression Spectrometer, Photoelectric effect, Compton scattering, Pair production, Annihilation process, Hpge, Nai(tl).
Classification: 11.7.

Nature of problem:
Due to the Compton scattering, the gamma-ray spectrum will be ruined by the Compton backgrounds, any small peak in the Compton continuum generated by the intensed gamma peak will become invisible. To overcome this problem, a Compton suppression spectrometer is designed for the reduction of the Compton backgrounds.

Solution method:
A guard detector is added to the main detector for suppressing the Compton effects, typically, the main detector can be fully or partially covered by the guard detector. If any gamma-ray was scattered out of the main detector and detected by the guard detector, the Compton counts would be removed. Here we use Monte Carlo method to simulate the spectra that may have been measured by the Compton suppression spectrometer.

In the program the simulation is restricted to the photon energy below 6 MeV, for the Bremsstrahlung radiation not yet being considered [2]. The program presented in our instruments' setting is the T and L shape Compton suppression spectrometer [1] and we use closed-end coaxial HPGe as the main detector and annular NaI(Tl) as the guard detector.

Unusual features:
1. The influence to the spectrum due to changes of the detector's shape, geometries and positions can be simulated directly.
2. The program is separated into several independent files. It is convenient to change the material and geometry of the main detector and the guard detector.
3. The cross-section absorption coefficient is given by a data table, and the simulation coefficient is obtained by interpolation [3].
4. The program is written in C instead of the conventional Fortran code.

Running time:
The mean running time for 60Co 480,000 events on the HP9000/750 is 136 seconds for the channel=1024 mode, 124 seconds for the channel=4096 mode.

[1] L.L. Kiang, R.H. Tsou, W.J. Lin, Simon C. Lin, G.C. Kiang, P.K. Teng, S.T. Li, Nucl. Instr. and Meth. A327 (1993) 427.
[2] William R. Leo, Techniques for Nuclear and Particle Physics Experiments (Springer-Verlag, Berlin, 1987) p35.
[3] S.T. Li, G.C. Kiang, P.K. Teng, Simon C. Lin, L.L. Kiang, Annual Report of the Institute of Physics, Academica Sinica, Vol. 18 (1989) 31.