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Manuscript Title: MCBETH: liquid scintillation counting spectra computation at the dynodic output of the photomultipliers.
Authors: F. Ortiz, J.M. Los Arcos
Program title: MCBETH
Catalogue identifier: ADCI_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 93(1996)283
Programming language: Fortran.
Computer: 286-type PC.
Operating system: DOS 3.1 or later.
RAM: 256K words
Word size: 16
Keywords: Nuclear physics, Activity detection, Liquid scintillators, Beta-decay, Photomultiplier, Spectra, Monte Carlo simulation.
Classification: 17.6.

Nature of problem:
The detection of beta emitters by liquid scintillation counting (LSC) involves a number of processes, namely, energy deposited, light production, light atenuation, photoelectron generation and signal amplification in a photomultiplier tube (PMT). Besides, a good knowledge of the spectral response of LSC systems is important to characterize accurately some related problems, like wall effect, complex beta-spectra deconvolution, ionization quenching effect, in order to obtain a possible absolute standardization method.

Solution method:
The Fermi spectrum of each radionuclide is evaluated on an energy-band mesh, with a bin width appropriate to the beta-end energy. The emission of a beta particle of energy E is simulated by the Monte Carlo method, which is also used to evaluate the number of photoelectrons and the subsequent electrons generated through the dynodic stages. The electron number obtained at the anode output determines the final pulse height which is classified in a histogram of number of pulses versus pulse height. This process can be applied to LSC systems operating with a single PMT or with two PMTs working in summed-coincidence mode.

Restrictions:
A Poisson distribution is assumed for the response at each PMT stage. The mean number of photoelectrons generated after each energy deposit event is evaluated through a figure of merit which includes the interaction processes of the beta particle in a toluene scintillator and the subsequent generation of photoelectrons. The response of dynodes is described by their respective dynodic gains and no electron losses are assumed to hold between consecutive PMT stages. The final spectrum is so obtained as a function of the figure of merit.

Unusual features:
The output results, number of events versus electron number, is given in 2-column tabular form.

Running time:
6.8 10**-4 seconds per event in a 66 MHz 486-system with mathematical coprocessor.