Novel Scintillation Material - ZnO Transparent Ceramics

ZnO-based scintillation ceramics for application in HENPA LENPA analyzers have been investigated. The following ceramic samples have been prepared: undoped ones (ZnO), an excess of zinc in stoichiometry (ZnO:Zn), doped with gallium (ZnO:Ga) and lithium (ZnO:Li). Optical transmission, x-ray excited emission, scintillation decay and pulse height spectra were measured and analyzed. Ceramics have reasonable transparency in visible range (up to 60% for 0.4 mm thickness) and energy resolution (14.9% at 662 keV Cs137 gamma excitation). Undoped ZnO shows slow (1.6 {\mu}s) luminescence with maximum at 2.37 eV and light yield about 57% of CsI:Tl. ZnO:Ga ceramics show relatively low light yield with ultra fast decay time (1 ns). Lithium doped ceramics ZnO:Li have better decay time than undoped ZnO with fair light yield. ZnO:Li ceramics show good characteristics under alpha-particle excitation and can be applied for the neutral particle analyzers.Comment: 4 pages, 8 figures, research covered in this paper was presented at SCINT2011 conference as a poster, submitted for publication at IEEE Trans. Nucl. Sc

Location of the Energy Levels of the Rare-Earth Ion in BaF2 and CdF2

The location of the energy levels of rare-earth (RE) elements in the energy band diagram of BaF2 and CdF2 crystals is determined. The role of RE3+ and RE2+ ions in the capture of charge carriers, luminescence, and the formation of radiation defects is evaluated. It is shown that the substantial difference in the luminescence properties of BaF2:RE and CdF2:RE is associated with the location of the excited energy levels in the band diagram of the crystals

<i>In situ</i> diagnostics of the crystal-growth process through neutron imaging:application to scintillators

Neutrons are known to be unique probes in situations where other types of radiation fail to penetrate samples and their surrounding structures. In this paper it is demonstrated how thermal and cold neutron radiography can provide time-resolved imaging of materials while they are being processed (e.g. while growing single crystals). The processing equipment, in this case furnaces, and the scintillator materials are opaque to conventional X-ray interrogation techniques. The distribution of the europium activator within a BaBrCl:Eu scintillator (0.1 and 0.5% nominal doping concentrations per mole) is studied in situ during the melting and solidification processes with a temporal resolution of 5-7 s. The strong tendency of the Eu dopant to segregate during the solidification process is observed in repeated cycles, with Eu forming clusters on multiple length scales (only for clusters larger than ∼50 µm, as limited by the resolution of the present experiments). It is also demonstrated that the dopant concentration can be quantified even for very low concentration levels (∼0.1%) in 10 mm thick samples. The interface between the solid and liquid phases can also be imaged, provided there is a sufficient change in concentration of one of the elements with a sufficient neutron attenuation cross section. Tomographic imaging of the BaBrCl:0.1%Eu sample reveals a strong correlation between crystal fractures and Eu-deficient clusters. The results of these experiments demonstrate the unique capabilities of neutron imaging for in situ diagnostics and the optimization of crystal-growth procedures

Nonproportionality of inorganic scintillators

A scintillator is a transparent material that emits a flash of light when it absorbs a ?-ray photon or an energetic particle. Scintillation crystals are widely used as spectroscopic detectors of ionizing radiation in nuclear science, space exploration, medical imaging, homeland security, etc. This thesis is about nonproportional response of inorganic scintillators to ionising radiation of different energies. Nonproportionality is the nonlinear dependence of the total light output of the scintillator on the detected amount of ionization energy, i.e., the emitted number of photons/MeV at 10 keV is not necessarily the same as at 100 keV or at 1000 keV. This dependence is due to a scintillation efficiency that depends on the density of the ionization track. The production of secondary electrons during slowing down of the primary electron inside the scintillator is a probabilistic process and may occur in different ways for the same absorbed energy. The dependence of the absolute light yield on the energy of secondary electrons and the probabilistic mechanism of their creation result in variability of the total number of photons produced inside the scintillator. This process leads to broadening of the photoabsorption peak in the pulse height spectrum measured by a scintillation detector.Radiation, Radionuclides & ReactorsApplied Science