Radionuclide Identification Devices (RIDs) or Backpack Radiation Detection Systems (BRDs) are often equipped with NaI(Tl) detectors. We demonstrate that such instruments could be provided with reasonable thermal- and fast-neutron sensitivity by means of an improved and sophisticated processing of the digitized detector signals: Fast neutrons produce nuclear recoils in the scintillation crystal. Corresponding signals are detectible and can be distinguished from that of electronic interactions by pulse-shape discrimination (PSD) techniques as used in experiments searching for weakly interacting massive particles (WIMPs). Thermal neutrons are often captured in iodine nuclei of the scintillator. The gamma-ray cascades following such captures comprise a sum energy of almost 7 MeV, and some of them involve isomeric states leading to delayed gamma emissions. Both features can be used to distinguish corresponding detector signals from responses to ambient gamma radiation. The experimental proof was adduced by offline analyses of pulse records taken with a commercial RID. An implementation of such techniques in commercial RIDs is feasible.
Passive radiation detection systems have been developed to screen passengers, vehicles, and cargo for illicit radioactive
sources by measuring gamma and neutron signatures with separate, specialized sensors. The paper introduces a novel
concept combining neutron and gamma sensing in a single detector, thus reducing the overall expense. Low-cost
converter media capture thermal neutrons and commute neutron flux in energetic gammas, which are then detected by a
common gamma detector. Energy signals above 3 MeV indicate the neutron captures. Two prototype systems are
presented: (1) The NCD-BGO, a segmented 655 ml BGO scintillator with embedded Cd absorber, demonstrated an
intrinsic thermal-neutron detection efficiency of about 50%. (2) The PVTNG, comprising 75 l of PVT scintillator
complemented with PVC panels, exhibited a neutron sensitivity of 1.9 cps/ng of 252Cf, thus almost meeting the
corresponding requirement for Radiation Portal Monitors. Moreover, an unconventional construction of scintillator and
light readout, combined with innovative electronics and proper detector stabilization, improved the gamma detector
performance noticeably and enabled nuclide identification.
CdZnTe, commonly known as CZT is the material of paramount importance for
hard X-ray and gamma ray spectroscopy and imaging applications at room temperature.
Over the years, the quality of CZT crystals and its charge transport properties has
improved significantly making it an attractive detector material especially for homeland
security applications. The applications for homeland security demand large and thick
detectors to provide a sufficient stopping power for fast detection of high energy
gamma photons. In this present report we have grown two inch diameter CZT by
Traveling heater method (THM) technique. The as-grown crystals were characterized
through photoluminescence (PL) mapping for composition uniformity, growth interface
study, Te precipitations/inclusions studies. In order to evaluate our as-grown samples,
charge transport characteristics have been studied for thick samples up to ~16mm thick.
It has been demonstrated that by controlling the growth interface, visualization of large
and thick (~16mm thick) detectors with fairly good response is possible from as-grown
CZT detectors grown by THM technique.
The Travelling Heater Method (THM) for CdZnTe growth is a widely accepted
technique for mass production of detector grade material. Compared to other
characterizations of THM grown CdZnTe, study of the growth interface has been
neglected in the past. In the present report, large grain/single crystalline as-grown
detector grade CdZnTe crystals have been grown by THM technique with diameter up
to 52 mm. The crystals were grown from Te solution and the structure of the growth
interfaces were investigated for both slow cooled and rapid cooled ingots. The
macroscopic shape of the interface was studied and correlated with the grain growth of
the ingots. A detailed microscopic morphology of the interface was studied in order to
investigate the formation of the Te inclusions at the interfaces.
Travelling heater method (THM) has been a great success lately for the growth of large CdZnTe
crystals. In this presentation, indium doped CdZnTe crystals have been grown adapting travelling heater
method (THM) in vertical configuration, using three zone custom designed muffle furnace. Crystals have
been grown with different ampoule diameter and size to study the grain growth. Seedless single crystalline
CdZnTe:In crystals have been gown with 4 cm diameter weighing about 650 grams. Crystals have been
characterized by near IR imaging, both microscopic and full wafer. The average resistivity along the length
of the ingot was found to be about 109 ohm-cm. A resolution 3.2% was obtained at 662 keV. The effect of
annealing of the whole wafer in Cd-Zn alloyed vapor on the resistivity and on the Te precipitations will be
discussed.
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