Questions and Answers
What is the primary use of the Model 44-2 sodium iodide gamma scintillator?
What is the size of the NaI crystal in the Model 44-2 detector?
What is the recommended instrument input sensitivity for the Model 44-2 detector?
How does the Model 44-2 detector respond in the 100 keV range?
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What is the thickness of the aluminum housing of the Model 44-2 detector?
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What is the typical sensitivity of the detector in counts per minute per micro-roentgen per hour?
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What is the effect of dead time on the linear range of the detector?
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What is the purpose of the magnetically shielded photomultiplier tube?
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What is the efficiency of the detector for 125I?
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What is the operating temperature range of the detector?
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Study Notes
Model 44-2 Sodium Iodide Gamma Scintillator
- Primarily used for detecting low levels of gamma radiation in the range of 20 keV–1.5 MeV
- Consists of a 2.54 x 2.54 cm (1 x 1 in.) NaI crystal coupled to a photomultiplier tube
- Housed in a 0.157 cm (0.062 in.) thick aluminum housing with a front entrance window of 2.3 mm (0.09 in.) thick aluminum
- Energy dependent, over-responding by a factor of 10 or greater in the 100 keV range and under-responding by a factor of 0.5 above 1 MeV when normalized to 137Cs
Operating Conditions and Applications
- Operates with any Ludlum instruments or equivalent instruments that provide 500–1200 volts
- Recommended instrument input sensitivity is approximately 10 mV or higher
- Common applications include:
- Background radiation monitoring
- Low-level radiation detection
- Spectrum analysis when used with a single or multi-channel analyzer
Specifications of the Instrument
- Compatible with general-purpose survey meters, ratemeters, and scalers
Sensitivity and Dead Time
- Typically 175 cpm per µR/hr for 137 Cs gamma
- Dead Time: approximately 10 µs
- Linear range limited to 5 mR/hr (50 µSv/h) without dead time correction
- Linear range extended to 50 mR/hr (500 µSv/h) with electronics equipped with dead time correction
Energy Response and Background
- Energy response is energy dependent
- Background measurement is 1800 cpm
Operating Conditions
- Operating Voltage: 500–1200 volts
- Dynode String Resistance: 100 megohm
Physical Properties
- Connector type: series ˝C˝ (others available)
- Scintillator size: 2.5 x 2.5 cm (1 x 1 in.) diameter and thickness
- Tube size: 2.9 cm (1.1 in.) diameter, magnetically shielded photomultiplier
Efficiency and Construction
- Efficiency (4 π): 7% for 125I, 10% for 57Co, 3% for 137Cs and 60Co
- Aluminum housing with beige powder-coat finish
Environmental Conditions
- Temperature Range: -15 to 50 °C (5 to 122 °F); optional certification for -40 to 65 °C (-40 to 150 °F)
- Size: 5.1 x 18.5 cm (2 x 7.3 in.) diameter and length
- Weight: 0.5 kg (1 lb)
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Description
A gamma radiation detector used for detecting low levels of gamma radiation in the range of 20 keV–1.5 MeV. It consists of a NaI crystal coupled to a photomultiplier tube and is energy dependent.
