Luminescence and radiation resistance of undoped NaI crystals

• The performance of NaI scintillators depends on luminescence properties.
• A criterion of crystals’ purity level is radiation colorability at room temperature.
• The traces of the most dangerous impurities were detected.
• Crucial role in efficiency of pure NaI scintillator play the crystal perfection.

Undoped NaI single crystal is an excellent scintillator at low temperature. However, scintillation parameters of different quality crystals vary in a wide range, significantly exceeding measurement error. Experimental data demonstrate the features of luminescence, radiation induced coloration, and afterglow dependence on the quality of nominally pure crystals. It is found that defects level that allows to elucidate artefacts introduced by traces of harmful impurities corresponds to 3 × 1015 cm−3 that significantly overhead accuracy of chemical and absorption analysis. It is shown that special raw material treatment before and during the single crystal growth allows to reach NaI purity level that avoids impurities influence to the basic luminescence data.

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