Shoaib Usman

Measurement and Application of Paralysis Factor for Improved Detector Dead-Time Characterization

Abstract This paper describes the finding of an experimental study to measure the detector paralysis factor and the use of this parameter in conjunction with detector dead time to better model detector dead-time response. The idealized one-parameter models, the paralyzable and nonparalyzable models, are inadequate to properly model the dead-time response of any real detector system. To address this deficiency, a more realistic two-parameter model is proposed that incorporates the paralysis factor of the detector in addition to the dead time. The revised two-parameter–based model is an extension of Lee and Gardner’s two-dead-time model. A simple scheme is proposed to deduce these parameters from the recorded data based on the rise and drop of count rates from a decaying source. Measurements were made using 56Mn and 52V. The data collected in this study show that a high-purity germanium (HPGe) detector has a paralysis factor of ˜50 to 77% and a dead time of 6 to 10 μs. Using the data collected by Lee and Gardner, the paralysis factor for a Geiger-Mueller (GM) counter is estimated to be ˜5%. These results are consistent with the approximating assumption that GM counters are nonparalyzing and HPGe detectors are paralyzing.

Natural convection's transient behavior

Transient response of a natural convection system is investigated by numerical simulation using FLUENT code. An integrator circuit analogy was recently proposed for natural convection systems. The proposed analogy was further confirmed by these recent simulations. New simulation results also suggest that a natural convection system acts as a “low-pass” filter for transients. Transmission characteristics of a natural convection system were investigated using sinusoidal temperature at the source-side boundary. Transient transmission factor was found to be a function of both fluid properties and the flow characteristics. Transmission factor was also found to be a strong function of fluctuation frequency. These results may prove a significant design tool for Generation IV natural convection systems, particularly for lead-cooled fast reactors or molten salt reactors.

Dead-Time Correction for Nonparalyzing Detectors When Measuring Short-Lived Nuclides

The purpose of this article is to show that when the half-life of a specimen being measured is comparable to the dead time of the measurement system, an additional correction is required in the classical dead-time correction formula for a nonparalyzing detector. This additional correction accounts for the decay of radioactivity during the dead time, and therefore the expression for the additional correction includes the specimen half-life. This additional correction is significant for some specialized applications involving very short-lived nuclides. These results may be useful for neutron activation analysis of short-lived isotopes and certain medical imaging applications.