Sajid Khan

A Study of Radioactive Contamination of

A calcium molybdate (CaMoO₄) crystal scintillator, with molybdenum enriched in ¹⁰⁰Mo and calcium depleted in ⁴⁸Ca (⁴⁰Ca¹⁰⁰MoO₄), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta (0<i>ν</i>ββ) decay of ¹⁰⁰Mo. We are planning to use about 10 kg of ⁴⁰Ca¹⁰⁰MoO₄ crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of CaMoO₄ and ⁴⁰Ca¹⁰⁰MoO₄ crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.

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The crystals of 0.02%, 0.05%, 0.1%, and 0.5% Sn doped Lil are grown by the vertical Bridgman technique. The luminescence and scintillation properties of the grown crystals are investigated. X-ray excited emission spectrum of Lil (Sn) showed a broad emission band between 400-650 nm wavelength range at room temperature. Such emission is attributed to Sn2+ ion. Scintillation properties such as energy resolution, decay time profiles, and light yield are measured under 662 keV (137Cs) -y-ray excitation at room temperature. A maximum light yield of 6000 ± 600 ph/MeV is measured at room temperature. Lil (Sn) single crystals showed two exponential decay components under y-ray excitation. The dependence of scintillation properties on the temperature is also presented. Changes in the decay time and light yield are measured from 295 K down to 10 K. The light yield of Lil (Sn) at 50 K is found to be nine times higher than that at room temperature.

Ca

Bismuth tri-iodide is a promising candidate for room temperature radiation detection because of its wide band gap energy. This material has higher effective atomic number as compared to germanium and CdZnTe. Its higher density results in improved stopping power for photons. But the presence of impurities limits the expected properties up to a large extent. Reduction of impurity concentration can lead to significant improvement in the properties like resistivity, charge transport and spectroscopic performance of detectors. In this study, zone refining technique has been employed to get detector grade refined material. ICP-MS technique was used to analyze the impurity concentration before and after zone refining. Bismuth tri-iodide single crystals were grown using Bridgman technique. Electrical contacts of Initial detectors are made using gold and silver paste. Detectors were tested by measuring their leakage current and resistivity.

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Mixed crystals Li₆Y_xGd_1-x(BO₃)₃:Ce³⁺ (LYGBO) (where, x = 0.0, 0.2, 0.5, 0.8, 1.0) are grown by using Czochralski method with different proportions of Li₆Y(BO₃)₃ and Li₆Gd(BO₃)₃. All crystals are doped with 3 mole% optimized concentrations of Ce³⁺ ions. The grown crystals are 20-70 mm in length and 5-10 mm in diameter. Detailed sintering and crystal growth procedure is presented in this study. The required phase of the grown crystals is confirmed by powder X-ray diffraction (XRD) analysis. Ultraviolet (UV) photoluminescence and X-ray induced luminescence of the grown crystals at room temperature are measured. Various scintillation properties such as energy resolution, light yield, α/β ratio and fluorescence decay time under the excitation by ¹³⁷Cs γ-ray and ²⁴¹Am particles are also presented.

MoO

A calcium molybdate (CaMoO₄) crystal scintillator, with molybdenum enriched in ¹⁰⁰Mo and calcium depleted in ⁴⁸Ca (⁴⁰Ca¹⁰⁰MoO₄), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta (0<i>ν</i>ββ) decay of ¹⁰⁰Mo. We are planning to use about 10 kg of ⁴⁰Ca¹⁰⁰MoO₄ crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of CaMoO₄ and ⁴⁰Ca¹⁰⁰MoO₄ crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.

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A calcium molybdate (CaMoO₄) crystal scintillator, with molybdenum enriched in ¹⁰⁰Mo and calcium depleted in ⁴⁸Ca (⁴⁰Ca¹⁰⁰MoO₄), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta (0<i>ν</i>ββ) decay of ¹⁰⁰Mo. We are planning to use about 10 kg of ⁴⁰Ca¹⁰⁰MoO₄ crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of CaMoO₄ and ⁴⁰Ca¹⁰⁰MoO₄ crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.

Crystals for the AMoRE Experiment

We have successfully grown pure and Pr3+-doped NaGd(WO4)2 (NGW) single crystals using the Czochralski pulling method. By employing a suitable rotation and pulling rates, good quality crystals of pure and Pr3+-doped NGW have been grown from the solution melt. Structural analyses of the grown samples are studied by X-ray diffraction (XRD). The x-ray induced emission spectrum shows a broad emission band in the wavelength range from 400 nm to 650 nm for the pure NGW crystal, while that of Pr3+-doped NGW crystal excited by X-ray was composed of eight bands. Emission spectrum of pure NGW crystal excited by 266 nm UV solid state laser was obtained at room temperature. The emission band includes two spectral regions: one consists of a wavelength band spanning 360 nm to 450 nm wavelengths peaking at 410 nm, and the other consists of a wavelength band spanning at 450 nm to 700 nm peaking at 530 nm, respectively.