A. Syntfeld

CdWO/sub 4/ crystal in gamma-ray spectrometry

The properties of CdWO/sub 4/ (CWO) crystals in gamma spectrometry were studied. Several small samples of 10/spl times/10/spl times/3 mm size, typically used in CT X-ray detectors, were tested and then compared to the performance of a larger crystal of 20 mm in diameter and 20 mm in height. The light output, energy resolution, and non-proportionality of the CWO response versus gamma-ray energy, were measured and compared with those of a small BGO to discuss further the origin of the intrinsic resolution of pure undoped scintillating crystals. A high light output of 6500 /spl plusmn/ 200 phe/MeV and a good energy resolution of 6.6 /spl plusmn/ 0.2% for 662 keV gamma rays from a /sup 137/Cs source were measured for the small samples coupled to an XP3212 photomultiplier. Common non-proportionality curves and consequently common intrinsic resolutions of small CWO and BGO suggest that they represent fundamental characteristics of the heavy oxide scintillating material themselves.

/sup 6/LiI(Eu) in neutron and /spl gamma/-ray spectrometry-a highly sensitive thermal neutron detector

Europium doped 6LiI crystals (enriched to 96%6 Li) have been studied in neutron detection and gamma-ray spectrometry. Two crystals, 50 mmtimes5 mm and 30 mmtimes3 mm in size were coupled to a calibrated Photonis XP5200 photomultiplier, were tested. The response of 6LiI(Eu) to neutrons emitted from a paraffin moderated Pu-Be source has been investigated and the thermal neutron peak has been found at a Gamma Equivalent Energy (GEE) of about 3.5 MeV. The high sensitivity of the 6LiI(Eu) crystal is demonstrated by the observation of a neutron peak at a dose equivalent as low as 0.05 muSv/h. Apart from the neutron response, the light output, energy resolution and nonproportionality of the 6LiI(Eu) crystals versus gamma-ray energies have been measured. The light yield of 1.5times104 ph/MeV (about 40% of NaI(Tl)) was obtained and the energy resolution at 662 keV (137 Cs) of 7.5plusmn0.1% was found for the large crystal. The linearity of the light output with energy has been measured and is better compared to NaI(Tl). Due to the high sensitivity to thermal neutrons and good proportionality against gamma-ray energy, the 6 LiI(Eu) crystal was tested with a few samples of nuclear materials. Shielded samples can be recognized via detection of neutrons following spontaneous fission

Study of pure NaI at room and liquid nitrogen temperatures

Three pure NaI crystals grown in different batches by Scionix (Holland) were studied at room and liquid nitrogen temperatures. The room temperature studies performed with photomultiplier readout covered measurements of emission spectra, photoelectrons yield and energy resolution. Moreover, the scintillation light pulses were measured by single photon method. Two crystals showed the photoelectron yield of about 1000 phe/MeV measured at room temperature with an XP2020Q photomultiplier. The energy resolution of the 662 keV photopeak was measured to be about 16% and was limited mainly by a low number of photoelectrons and a large non-proportionality of the light yield. The fast light pulse had the main decay time components of 1 ns and 5 ns. The high initial photon intensity of the tested NaI crystals revealed in the good timing resolution of about 140 ps obtained for /sup 60/Co /spl gamma/-rays. At liquid nitrogen temperatures the measurements of light yield and energy resolution were performed using Advanced Photonix, Inc. avalanche photodiode readout. A high light output above 80000 ph/MeV was measured for the best of the tested crystals. The energy resolutions of the 662 keV photopeak of the three crystals differ a lot, varying from an excellent value of 3.8% to 6.2%. This suggests that the measured energy resolutions depend on the purity of the scintillator samples reflected in the emission spectra. The studies that were performed demonstrate the attractive properties of pure NaI at both room and LN/sub 2/ temperature.

Spectral gamma detectors for hand-held radioisotope identification devices (RIDs) for nuclear security applications

The in-situ identification of the isotope causing a radiation alarm at a border crossing is essential for a quick resolution of the case. Commonly, hand-held radioisotope identification devices (RIDs) are used to address this task. Although a number of such devices are commercially available, there is still a gap between the requirements of the users and what is actually available. Two components are essential for the optimal performance of such devices: i) The quality of the raw data-the gamma spectra, and ii) isotope identification software matching the specifics of a certain gamma detector. In this paper, we investigate new spectral gamma detectors for potential use in hand-held radioisotope identification devices. The standard NaI detector is compared with new scintillation and room temperature semiconductor detectors. The following spectral gamma detectors were included into the study: NaI(Tl), LaCl3(Ce), 6LiI(Eu), CdWO4, hemispheric and coplanar CdZnTe detectors. In the paper basic spectrometric properties are measured and compared in view of their use in RIDs

Evaluation of new Photonis XP1472 nine-channel photomultiplier

The performance of a new Photonis XP1472 nine-channel photomultiplier (PMT) was studied with the main emphasis to the photoelectron numbers and photoelectron collection efficiency, as measured with a 10 mm in diameter NaI(Tl) crystal coupled to the separate channels. Simultaneously, energy resolution and crosstalk were measured for all channels with a Cs-137 source. Time jitter and time resolution for an LSO crystal coupled to the different channels were measured for 511 keV annihilation quanta and compared to those measured earlier with XP2020Q PMTs. The studies confirmed high photoelectron collection efficiency in the PMT due to a new design of the input focalisation system.

Evaluation of new photonis XP1472 nine-channel photomultiplier

The performance of a new Photonis XP1472 nine-channel photomultiplier (PMT) was studied with the main emphasis to the photoelectron numbers and photoelectron collection efficiency, as measured with a 10 mm diameter NaI(Tl) crystal coupled to the separate channels. Simultaneously, energy resolution and crosstalk were measured for all channels with a /sup 137/Cs source. Time jitter and time resolution for an LSO crystal coupled to the different channels were measured for 511keV annihilation quanta and compared to those measured earlier with XP2020Q PMTs. The studies confirmed high photoelectron collection efficiency in the PMT due to a new design of the input focalization system.

/sup 6/LiI(Eu) in neutron and /spl gamma/-ray spectrometry - a high sensitive thermal neutron detector

Europium activated 6LiI crystal (enriched to 96% 6Li) has been studied in neutron and gamma-ray spectrometry. Two crystals of Oslash50 mm times 5 mm and Oslash30 mm times 3 mm size coupled to a calibrated Photonis XP5200 photomultiplier were tested. A response of 6LiI(Eu) to neutrons emitted from a paraffin moderated Pu-Be source has been investigated and the thermal neutron peak has been found to be located at gamma equivalent energy (GEE) of about 3.5 MeV. High sensitivity of the 6LiI(Eu) crystal is demonstrated as the neutron peak is observed at the rate as low as 10-2 counts per second. Apart from neutron spectra a light output, energy resolution and non-proportionality of the 6LiI(Eu) response versus gamma-ray energy have been measured for the two crystals. The light yield of 1.5times104 ph/MeV (about 40% of NaI(Tl)) was obtained and the energy resolution at 662 keV (Cs-137) of 7.5plusmn0.1% was found for the large crystal. The non-proportionality has been measured to have more proportional character as compared to NaI(Tl). Due to the high sensitivity to thermal neutrons and good proportionality against gamma-ray energy, the 6LiI(Eu) crystal was brought under testing with few samples of fissile nuclear materials. Shielded fissile samples can be recognized via detection of neutrons followed spontaneous fission.