Technology to Grow Single Crystals of NaI:Tl and
Fabrication of Radiation Detectors

INTRODUCTION

Single crystals of alkali halide inorganic scintillators are useful as nuclear radiation detectors in gamma-ray spectroscopy and radiography applications. These crystals are grown in silica crucibles using the vertical Bridgman technique. Crystals of NaI:Tl coupled to photo-multiplier tubes have exhibited excellent energy resolution of less than 7% at 662 keV, suitable to be used as radiation detectors in gamma-ray spectroscopy applications.

BARC has developed a novel crystal growth system based on the modified Bridgman technique to grow high quality, crack-free single crystals of NaI:Tl. Easy extraction of the grown crystal is achieved using a uniquely designed silica crucible and an ingenious furnace design that has precise temperature control mechanism and highly accurate motor for lowering the crucible. Single crystals of NaI:Tl up to 50 mm in diameter and 60 mm in length could be grown with almost 100% yield. The technology also covers processing of the grown NaI:Tl crystals and fabrication of scintillator detectors using photo-multiplier tubes (PMT).

SPECIFICATIONS

Crystal dimension (mm)	: Diameter : 50 mm, : Length : 60 mm
Density [g/cm3]	: 3.67
Melting point [°C]	: 651
Thermal expansion coefficient [°C-1]	: 47.4x10-6
Cleavage plane	: <100>
Hardness (Mohs)	: 2
Hygroscopic	:Yes
Wavelength of emission max. [nm]	: 420
Refractive index @ emission max	: 1.85
Primary Decay time (ns)	: 250
Light yield [photons/keVγ]	: 38
Energy resolution	: Less than 7% at 662 keV

APPLICATIONS

• Gamma-ray spectrometer
• High energy radiation detectors
• Nuclear Physics Experiments
• Area monitor
• Whole body counting
• Oil well logging
  

REQUIREMENTS FOR COMMERCIAL PRODUCTION

Infrastructural Requirements

Space :

• About 600 sq feet (25x25 sq. ft) roofed area with proper arrangement of cleanness (preferably Class 10,000), dust proof with controlled temperature (25±1°C) and humidity (<55%) with continuous electricity

• Growth Furnace
• Dehydration unit
• Weighing balance
• Glove Box with humidity control (RH < 1%)
• Cutting machines
• PMT and associated electronics for testing
• Glass blowing facility for sealing
• Laminar flow bench

• Vacuum desiccators
• Quartz crucible
• Raw material
• Process chemicals (alcohol, optical grease, oil)
• Emery papers
• Alumina powder
• Liquid nitrogen

Manpower Requirement

• One B.Sc. (Physics) and one M.Sc. (Physics) or equivalent degree.

Electrical Power Requirement

• 220 V, 50 Hz, Single phase, 15 A

For details contact :
   

    Head, Technology Transfer & Collaboration Division,
    BHABHA ATOMIC RESEARCH CENTRE,
    TROMBAY, MUMBAI - 400 085
    Fax : 091-022-25505151
    Email : technology@barc.gov.in