Development of a Compact, High Efficiency Fast-Neutron Detector
V. V. Massawe1,3, D.N. Phuong2, and S. Hameer 1
1
Department of Sustainable Energy Science and Engineering. The Nelson Mandela African Institute of
Science and Technology. P. O. Box 447, Arusha-Tanzania.
2
Institute of Physics, University of Freiburg, Freiburg, Germany
3
Department of Electrical and Electronics Engineering. Mbeya University of Science and Technology.
P.O. Box 131, Mbeya-Tanzania
Detection of neutrons is of value for purposes of scientific research as well as radiation damage concerns
related to the health of natural habitat, including humans. Major sources of neutrons are the nuclear power
reactors and particle accelerators. The upper atmospheric conditions also generate fast neutrons causing
concern of radiation to communications instrumentations.
Unlike the detection of charged particles, which leave ionization trails along their paths, the detection of
neutrons poses a major challenge. The task is a bit easier for thermal neutrons which exhibit cross
sections of a few thousand barns for absorption by 10B, 3He and Gd materials. These reactions resulting
in emissions of alphas or gamma rays permit compact systems for large area monitoring.
So far, with a few exceptions, the detection of fast neutrons employs large arrays of plastic scintillator
with an efficiency of 1% per one centimeter path length. The other approach is to let the fast neutrons
pass through moderators such as water columns to thermalize them and then accomplish detection
through thermal neutron detectors such as boron counters.
We are exploring a detector design to exploit the advantage of thin plastic scintillating fibres to achieve
high efficiency. In conventional large scintillators, one detects the scintillation produced by secondary
protons due to neutron interactions in the medium. The large scintillators suffer from low light collection
efficiency. The modern scintillating fibres, extensively used for charged particle tracking and active
targets offer an attractive option to explore.
A multi-purpose Monte Carlo radiation transport code (MCNPX) has been modified to analyze the
interaction of neutrons with fiber bundles of different sizes so as to get optimum size. A C++ program has
been written to create the MCNP input files with input variable including: the type of source particles, the
source particle energy, the source location, fiber material type, the diameter and length of the scintillating
fibers, cladding material type, shielding, and the number of fibers along the x- and y-axis. The
simulations have been carried out to determine the useful dimensions of individual fibres and overall
bundle sizes.
The talk will present preliminary results of our simulations and the readout systems we plan to
implement. We will also present our plans for the validation of the simulations at an accelerator facility.
It is anticipated that such a high efficiency compact detector will be useful in scientific research and
applications concerned with the safety of nuclear power reactors. The compact detectors will also be
appealing to radiation research in the upper atmosphere.