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Manuscript Title: DENTS: a Fortran program for analysing continuous neutron spectra.
Authors: C.A. Ciarcia, W.A. Schier, G.P. Couchell, D.J. Pullen, R.S. Tanczyn, M.H. Haghighi, Q. Sharfuddin
Program title: DENTS
Catalogue identifier: AAFA_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 39(1986)233
Programming language: Fortran.
Computer: HP1000/2100A.
RAM: 32K words
Word size: 32
Peripherals: disc.
Keywords: Reactor systems, Neutron, Time-of-flight spectrum, Response function.
Classification: 22.

Nature of problem:
The program DENTS was written to assist in the unfolding of delayed- neutron time-of-flight (TOF) spectra measured on the University of Lowell 1-MW swimming pool reactor and the 5.5-Mv Van de Graaff accelerator following neutron induced U-235, PU-239 or u-233 fission. The code was designed to: (1) Make corrections to the continuous neutron TOF spectra for neutrons that have not traversed a well defined flight path. These neutrons are represented by long tails on the low- energy side of the spectrometer time response functions for monoenergetic neutrons. They are superimposed on the lower-energy data and therefore must be subtracted. (2) Convert TOF spectra into neutron energy spectra. (3) Correct energy spectra for neutron detector efficiency. The DENTS program primarily manipulates files. The four types of files that must be prepared prior to the operation of DENTS are: (1) a background-subtracted neutron time-of-flight spectrum, (2) a tail-to-peak area ratio file obtained from measured response functions to monoenergetic neutrons, (3) an 'average' tail shape file derived from the measured response functions, and (4) a relative detection efficiency file which can be obtained, for example, from a Cf-252 prompt neutron fission spectrum measurement. Since the time- of-flight spectrometer incorporates two sets of detectors, Pilot U for En>100keV and Li-6 glass for En<400keV, each set of detectors has its own type (1), (2), (3) and (4) files. The DENTS software package also incorporates an optional file creation routine for type (2), (3) and (4) files where the prepared files can be read into permanent storage and accessed for future analyses through their file name designations.

Solution method:
The spectra are analyzed as linear combinations of monoenergetic neutron time response functions, each approximated by the sum of a weighted Dirac-delta function plus a weigthed low-energy tail function. The code DENTS subtracts these tails from the continuous spectra through an iterative process using the approximation that the tail shape is energy independent. The spectra are then converted to an energy independent. The spectra are then converted to an energy scale and corrected for neutron detection efficiency.

Restrictions:
Experimental measurement and observation of a broad range of response functions for monoenergetic neutrons has shown that the position and shape of the tail function is nearly independent of neutron energy. Using this approximation an 'average' tail shape was defined and used. However, this procedure is now being modified to take into account the small variations in the tail shape observed at different energies by fitting the spectra in a least-squares fashion with measured response functions. Our delayed-neutron spectra will not be significantly effected by this modified procedure.

Running time:
The program is user interactive. The actual CPU time for tail subtraction is 11.5 seconds per iteration.