%0 Journal Article
%T Detector Dead Time Determination and Optimal Counting Rate for a Detector Near a Spallation Source or a Subcritical Multiplying System
%A V. B¨¦cares
%A J. Bl¨¢zquez
%J Science and Technology of Nuclear Installations
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/240693
%X The operation of accelerator-driven systems or spallation sources requires the monitoring of intense neutron fluxes, which may be billions-fold more intense than the fluxes obtained with usual radioactive sources. If a neutron detector is placed near a very intense source, it can become saturated because of detector dead time. On the contrary, if it is placed far away from the source, it will lose counting statistics. For this reason, there must exist an optimal position for placing the detector. The optimal position is defined as the one with the minimal relative uncertainty in the counting rate. In this work, we review the techniques to determine the detector dead time that can be applied with an accelerator-driven subcritical system or a spallation source. For the case of a spallation source, counting rates do not follow Poisson's statistics because of the multiplicity of the number of neutrons emitted by incident proton. It has been found a simple expression that relates the optimal counting rate with the source multiplicity and the uncertainty in the determination of the dead time. 1. Introduction A strong interest in intense accelerator-driven neutron sources for different applications has grown in the last decades. Although a number of reactions is available for neutron production with accelerated particles (photoneutrons, D-Be, and others), preferred technology for these neutron sources is spallation, because it provides the highest neutron yield per unit of energy of the incident particles. Neutron spallation sources consist of a high-energy proton accelerator coupled to a high Z target. Typically, a 1000£¿MeV incident proton beam could produce ~50£¿nucleons per incident proton, approximately half of them neutrons [1]. In this way, very intense neutron fluxes can be obtained (over 1015£¿n/cm2£¿s). Although current mode detectors are generally preferred for monitoring such high fluxes, pulse mode detectors are also of interest because of their ability to record information from the individual detector signals. However, if a pulsed mode detector is used to monitor such high fluxes, it can become saturated because of dead time effects. An important application of spallation sources is to drive accelerator-driven systems (ADSs). An ADS consists of a subcritical reactor driven by an external spallation neutron source. The interest in these systems has risen since the 1990s [2¨C6] as it has been recognized their ability to reduce the volume and radiotoxicity of high-level nuclear waste. Operation of ADSs requires the monitoring of the neutron source
%U http://www.hindawi.com/journals/stni/2012/240693/