W. Mengesha

Intrinsic energy resolution of NaI(Tl)

The light output for +10 mm � 10 mm and +75 mm � 75 mm NaI(Tl) crystals and energy resolution were measured for g-ray energies ranging from 16–1333 keV. These measurements enabled the observation of the light yield nonproportionality behavior and allowed the determination of the intrinsic resolution after correctingfor the measured resolution for photomultiplier tube (PMT) statistics. The intrinsic resolution was then compared with the nonproportionality component. The latter was calculated usingmeasured electron response, Monte Carlo N Particle code (MCNP4B), and the simplified cascade sequence for NaI(Tl). This comparison allowed the identification of the intrinsic resolution component associated with d-rays. Consequently, it was shown that the d-ray component is the most dominant component of the NaI(Tl) intrinsic resolution. r 2002 Elsevier Science B.V. All rights reserved.

Light yield nonproportionality of CsI(Tl), CsI(Na), and YAP

CsI(Tl), CsI(Na), and YAP light yield nonproportionality has been characterized using the Compton Coincidence Technique. Measured electron responses were used to calculate photon responses of the scintillators studied. These calculated photon responses were then compared with measured photon responses. In addition results from electron response measurements and photon response calculations were compared with previously reported results. While the CsI(Na) electron response was observed to have the largest deviation from proportionality (about 40%), YAP was observed to have a nearly proportional response. The CsI(Tl) calculated photon response was observed to agree to within 1% with measured photon response in this study for all measured photon energies. While the CsI(Na) calculated photon response agreed to within 1% of measured data for photon energies above 60 keV, deviations up to 4% were observed below 60 keV.

Generalized multicoincidence analysis methods

The ability to conduct automated trace radionuclide analysis at or near the sample collection point would provide a valuable tool for emergency response, environmental monitoring, and verification of treaties and agreements. Pacific Northwest National Laboratory is developing systems for this purpose based on dual gamma-ray spectrometers, e.g., NaI(TI) or HPGe, combined with thin organic scintillator sensors to detect light charged particles. Translating the coincident signatures recorded by these systems, which include betagamma,gammagamma, and betagammagamma, into the concentration of detectable radionuclides in the sample requires generalized multicoincidence analysis tools. The development and validation of the Coincidence Lookup Library, which currently contains the probabilities of single and coincidence signatures from more than 420 isotopes, is described. Also discussed is a method to calculate the probability of observing a coincidence signature which incorporates true coincidence summing effects. These effects are particularly important for high-geometric-efficiency detection systems. Finally, a process for verifying the integrated analysis software package is demonstrated using GEANT 4 simulations of the prototype detector systems

Electron and photon responses of Gd/sub 2/SiO/sub 5/(Ce/sup 3+/) and BaF/sub 2/

Gd/sub 2/SiO/sub 5/(Ce/sup 3+/) (GSO) and BaF/sub 2/ electron responses were characterized using the Compton Coincidence Technique (CCT). The CCT has been used previously to characterize several scintillators and has proven to be an accurate and reliable technique. The GSO measured electron response was observed to increase by 28% as the electron energy increased from 5 keV to 445 keV. BaF/sub 2/ measured electron response increased by 22% as the electron energy increased from 18 keV to 436 keV. The observations made with GSO and BaF/sub 2/ in this study are consistent with the general trend reported for previously characterized non-alkali halide scintillators. The GSO and BaF/sub 2/ measured electron responses were further used to calculate their respective photon responses. MCNP4C together with simplified electron cascade sequences for GSO and BaF/sub 2/ were used in these photon responses calculations. Calculated photon responses for both crystals are in good agreement with measured photon responses. This agreement confirms the accuracy of the GSO and BaF/sub 2/ measured electron responses.