Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl/sup +/ concentrations under electron and alpha particles excitations

Hamadaa, M.M.; Costa, F.E.; Pereira, Maria da Conceição Costa; Kubota, Shinzou

doi:10.1109/23.958740

Cited by 36 publications

(23 citation statements)

References 10 publications

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“…Continuing in Table III, the radiative rate of an STE trapped on Tl + , R 1Et , is the reciprocal of the published T + * lifetime measured in CsI by direct uv excitation of Tl 65 . The next 4 parameters in the table are the effective values for electron diffusion coefficient, electron mobility, bimolecular recombination of electrons from Tl 0 with holes trapped as Tl ++ and deep defect trapping of electrons while untrapped from Tl 0 .…”

Section: Materials Parameters and Proportionalitymentioning

confidence: 99%

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Bizarri

et al. 2015

Phys. Rev. B

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A high-energy electron in condensed matter deposits energy by creation of electron-hole pairs whose density generally increases as the electron slows, reaching the order of 10 20 eh/cm 3 near the end of its track. The subsequent interactions of the electrons and holes include nonlinear rate terms and transport as first hot and then thermalized carriers in the nanometer-scale radial dimension of the track. Charge separation and strong radial electric fields occur in a material such as CsI with contrasting diffusion rates of self-trapped holes and hot electrons. Eventual radiative recombination has a nonlinear relation to the primary electron energy because of these interactions. This socalled intrinsic nonproportionality of electron response limits achievable energy resolution of a given scintillation radiation detector material. We use a system of coupled transport and rate equations to describe a pure host (3 equations) and one dopant (4 more equations per dopant). Applying it first to the experimentally well-characterized system of CsI and CsI:Tl in this work, we use results of picosecond absorption spectroscopy, interband z-scan measurements of nonlinear rate constants, and other experiments and calculations to determine most of the more than 20 rate and transport coefficients required for modeling. The model is solved in a track environment approximated as cylindrical and is compared to the proportionality curve and total light yield of undoped CsI at temperatures of 295 K and 100 K, as well as thallium dopant in CsI:Tl at 295 K. With this degree of validation, the space-and time-distributions of carriers and excitons, both untrapped and trapped, are examined within the model to gain an understanding of the main competitions controlling the nonproportionality of response.

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Section: Materials Parameters and Proportionalitymentioning

confidence: 99%

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Bizarri

et al. 2015

Phys. Rev. B

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“…In Fig. 3.1, a comparison of 3 He count rate as a function of SCA threshold is shown for runs with and without an HDPE shielding block placed between the source and detector. The shape of the plot shows that our threshold selects neutron interactions including the triton and proton escape events (wall effect).…”

Section: Chapter 3 Resultsmentioning

confidence: 99%

“…In summary, alkali halide scintillators with 6 Li conversion layers may be useful in the near term as thermal neutron detectors for 3 He replacement. We demonstrated a thermal neutron detection efficiency of ∼ 0.5% with natural Li foil and CsI(Tl), and extrapolate a single-foil efficiency of ∼ 7%, close to the theoretical maximum limited by the range of the reaction products in the Li foil.…”

Section: Resultsmentioning

confidence: 99%

“…PSD in alkali halides is not commonly used in radiation detection, but has been studied [1,2,3]. Since the underlying sensitive medium has gamma sensitivity and good energy resolution, the resulting detectors are well suited for gamma spectroscopy as well as thermal neutron detection.…”

Section: Telephonementioning

confidence: 99%

“…For the doped detector, the measured efficiency was 5.2%, giving an extrapolated 6 Li-enriched efficiency of 53%, to be compared with the goal of 5%. As a point of reference, 3 He detector efficiency for thermal neutron detection can be up to ∼ 50-60%, depending on gas pressure, threshold, etc. Uncertainty ±20% (rel.)…”

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Thermal neutron detection using alkali halide scintillators with Li-6 and pulse shape discrimination

Brubaker

Dibble

Yang

2013

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An ideal3 He detector replacement for the near-to medium-term future will use materials that are easy to produce and well understood, while maintaining thermal neutron detection efficiency and gamma rejection close to the 3 He standard. Toward this end, we investigated the use of standard alkali halide scintillators interfaced with 6 Li and read out with photomultiplier tubes (PMTs). Thermal neutrons are captured on 6 Li with high efficiency, emitting high-energy α and triton ( 3 H) reaction products. These particles deposit energy in the scintillator, providing a thermal neutron signal; discrimination against gamma interactions is possible via pulse shape discrimination (PSD), since heavy particles produce faster pulses in alkali halide crystals. We constructed and tested two classes of detectors based on this concept. In one case 6 Li is used as a dopant in polycrystalline NaI; in the other case a thin Li foil is used as a conversion layer. In the configurations studied here, these systems are sensitive to both gamma and neutron radiation, with discrimination between the two and good energy resolution for gamma spectroscopy. We present results from our investigations, including measurements of the neutron efficiency and gamma rejection for the two detector types. We also show a comparison with Cs 2 LiYCl 6 :Ce (CLYC), which is emerging as the standard scintillator for simultaneous gamma and thermal neutron detection, and also allows PSD. We conclude that 6 Li foil with CsI scintillating crystals has near-term promise as a thermal neutron detector in applications previously dominated by 3 He detectors. The other approach, 6 Li-doped alkali halides, has some potential, but require more work to understand material properties and improve fabrication processes. 3 AcknowledgmentThis work was funded by DOE NNSA NA-22 Office of Non-proliferation Research and Development.4

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Excitation density, diffusion‐drift, and proportionality in scintillators

Williams

Grim

et al. 2010

Physica Status Solidi (b)

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Phone: þ1 336 758 5132, Fax: þ1 336 758 6142.Stopping of an energetic electron produces a track of high excitation density, especially near its end, and consequent high radial concentration gradient. The effect of high excitation density in promoting nonlinear quenching is generally understood to be a root cause of nonproportionality in scintillators. However, quantitative data on the kinetic rates of nonlinear quenching processes in scintillators are scarce. We report experimental measurements of second-order dipole-dipole rate constants governing the main nonlinear quenching channel in CsI, CsI:Tl, NaI, and NaI:Tl. We also show that the second of the extreme conditions in a track, i.e., radial concentration gradient, gives rise to fast ( picoseconds) diffusion phenomena which act both as a competitor in reducing excitation density during the relevant time of nonlinear quenching, and as a determiner of branching between independent and paired carriers, where the branching ratio changes with dE/dx along the primary electron track. To investigate the interplay of these phenomena in determining nonproportionality of light yield, we use experimentally measured rate constants and mobilities in CsI and NaI to carry out quantitative modeling of diffusion, drift, and nonlinear quenching evaluated spatially and temporally within an electron track which is assumed cylindrical Gaussian in this version of the model. 1 Introduction When an energetic electron is slowed and stopped in a scintillator (or any solid material with a band gap), the track of excitations left behind is characterized by at least two remarkably extreme numbers: (i) very high excitation density and (ii) very large concentration gradient of carriers and/or excitations. The first condition of high excitation density has been recognized for some time as crucial for setting rates of second-order (dipole-dipole) and third-order (Auger) quenching of local light yield in the vicinity of the track. However, with very few exceptions, those rate constants have not been determined. Therefore we present measurements of dipole-dipole quenching rate constants at high excitation density for three halide scintillators in the present work.In addition to the promotion of nonlinear quenching by high excitation density in a track, the high concentration gradient promotes radial diffusion of electrons and holes, which can limit the nonlinear quenching rates by rapidly diluting carrier concentration, and may affect linear rates by setting up charge separation. We show by numerical modeling of the diffusion and quenching processes together

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Dependence of scintillation characteristics in the CsI(Tl) crystal on Tl/sup +/ concentrations under electron and alpha particles excitations

Cited by 36 publications

References 10 publications

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Coupled rate and transport equations modeling proportionality of light yield in high-energy electron tracks: CsI at 295 K and 100 K; CsI:Tl at 295 K

Thermal neutron detection using alkali halide scintillators with Li-6 and pulse shape discrimination

Excitation density, diffusion‐drift, and proportionality in scintillators

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