This article provides an overview of the operation, accuracy, and reliability of Blackline Safety’s Gamma sensor.
Overview
The gamma sensor detects gamma radiation using a scintillation crystal detector integrated with a silicon photomultiplier (SiPM). The scintillation crystal detector is a large, Nal (TI) doped crystal (1.5 inches by 1.5 inches), which is highly sensitive to gamma rays and supports high photon count rates. The crystal’s material, size, and geometry determine the detector’s sensitivity and accuracy.
Gamma radiation photons typically pass through most materials, but when a photon collides with a scintillation crystal, the crystal emits visible light. The SiPM detects the light and converts it into an electrical signal, which is amplified and recorded.
Higher concentrations of gamma photons increase the likelihood of these collisions, resulting in more light emissions and stronger signals. By factory-calibrating the EXO Gamma device with known radioactive sources, measurements can be quantified in standard units, such as sieverts or rem per hour.
Device Placement
Gamma sources emit radiation in all directions. As EXO 8 Gamma is most sensitive to gamma rays towards the front of the device, you should face the device towards the area you are monitoring. The device can still accurately detect gamma radiation from other angles, but the gamma radiation sensitivity is lower towards the back of the device as photons are weakened by the density of the battery pack.
Sensor Accuracy
Operating Range
The sensor has a broad operating temperature and relative humidity range, making it suitable for a variety of environments.
-
Temperature: -20°C (-4°F) to 50°C (122°F)
-
Humidity: 0% to 93% RH
-
IP66 Ingress
Detection Range
-
Dose Rate Range: 0.01 to 2000 µSv/h (1 to 200,000 µRem/h)
-
Photon Energy of Incident Radiation: 200keV to 6MeV
-
Calibrated to Cs-137 (662keV)
-
Gain compensated across operating temperature range: ±10%
Sensor Reliability
Specific factors can impact the gamma sensor’s performance, potentially affecting its accuracy and reliability.
-
Sensor drift: < 1%, short and long term
-
Rapid temperature changes: May cause an increase in gamma detection errors, such as inaccurate radiation readings that appear overly high or low.
CAUTION: Operation or storage of the sensor outside of the specified range may permanently damage the sensor.
Calibration and Bump Testing
The gamma sensor does not require calibration. EXO 8 Gamma is factory calibrated and is ready for use on arrival.
The gamma sensor does not require bump testing, but it can be performed as a confidence check. Confirm applicable laws in your country prior to bump testing to determine what check source type/size is appropriate.
To perform a bump test, hold a check source (Cs-137 is the standard) near the device and confirm that the displayed dose rate increases.
Please consult your local Health and Safety group or an Industrial Hygienist for further information and guidance at your location.
