Table of Content
- The Basics of Gamma Radiography
- Radiation Hazards and Safety Measures
- How Radiation is Measured
- Practical Tips for Using Radiation Detection Devices
- Real-Life Example: Avoiding an Accident
- Conclusion
Gamma radiography is a powerful technique used in industrial testing to inspect materials like steel castings and welded joints. Its ability to penetrate thick materials makes it invaluable, especially in industries like construction, oil and gas, and manufacturing. However, with its benefits come significant safety risks, and understanding these is critical for safe and effective work.
The Basics of Gamma Radiography
Gamma Radiography uses radioactive materials, such as radium or modern isotopes like Iridium-192, to create images of the internal structure of materials. These isotopes are selected for their specific properties: they emit gamma rays with high energy capable of penetrating dense materials like steel, and their half-lives are optimized for practical usage, offering a balance between effective imaging and manageable radioactive decay. For example, Iridium-192, with a half-life of 73.8 days, provides strong gamma emissions while ensuring relatively straightforward handling and replacement logistics in industrial settings. Unlike X-rays, which have limitations on material thickness, gamma rays can penetrate up to 30.5 cm (12 in.) of steel, making them ideal for testing heavy components.
Key Applications:
- Inspecting welds in pipelines.
- Checking for cracks or flaws in castings.
- Verifying the integrity of critical components in pressure vessels and storage tanks.
Gamma radiography stands out due to its portability and ability to work in remote locations, which is critical for industries that often operate in challenging environments. For example, oil and gas pipelines laid across vast terrains can only be inspected effectively using gamma radiography because of its robust penetration and minimal equipment requirements compared to X-ray setups.
Radiation Hazards and Safety Measures
Working with gamma radiography involves exposure to radiation, which can harm the body if proper precautions are not taken. Long-term health risks from radiation exposure can include an increased risk of cancer, genetic mutations, and organ damage. These risks underscore the importance of adhering to safety protocols and using protective equipment at all times. Here are the main hazards and safety practices to remember:
Major Risks:
1. Intense Radiation:
Gamma sources emit highly penetrating radiation. A small source can cause severe injuries in seconds if mishandled.
2. Small Source Size:
These compact sources have extremely high radiation intensity on their surface. Direct contact can result in severe burns.
Image Credit: Dontwastemichigan.org
Right hand of a pioneer radiologist. The first injury was seen in 1899. The hand was amputated in 1932 and death from cancer occurred in 1933.
3. Challenging Work Conditions:
Radiography often happens in busy, high-pressure environments, increasing the likelihood of accidents if procedures are rushed.
Avoiding Accidents:
Most accidents occur due to:
- Failing to return the gamma source to its shielded container.
- Skipping radiation surveys to confirm the source is secure.
- Neglecting to lock the source after use.
Radiographers should also be aware of the cumulative nature of radiation exposure. Even low levels of exposure, when accumulated over time, can lead to significant health risks. Monitoring exposure consistently and maintaining accurate records is essential to manage this risk.
Tip: Always follow your company’s operating and emergency procedures, and never rush radiography work. Your safety and that of others depend on your actions.
How Radiation is Measured
Radiographers use specific tools to detect and measure radiation, as relying on multiple instruments ensures comprehensive monitoring. Different tools provide unique data, such as dose rates, total doses absorbed, or real-time exposure alerts, and together they help mitigate risks by confirming readings and identifying inconsistencies. This layered approach to radiation detection enhances safety and accuracy in radiographic operations.
Survey Meters:
Image Source: ASNT Book “Working Safely in Radiography”
Gamma and X-radiation sensing devices: (a) geiger-mueller survey meter with three ranges: 0-10 mR/h, 0-100 mR/h, and 0-1000 mR/h, (b) survey meter with an external detector, (c) survey meter with automatic audible alarm, (d) survey meter with an external detector, (e) ion chamber survey meter.
- Measure radiation dose rate (mSv/h or mR/h).
- Common types include ionization chambers and Geiger-Mueller meters.
- Note: Some Geiger-Mueller meters can malfunction in high-intensity fields, so always double-check readings.
Dosimeters:
- Measure the total radiation dose absorbed (mSv or mR).
- Include devices like direct-reading dosimeters, film badges, and thermoluminescent dosimeters (TLDs).
Alarm Rate Meters:
Image Source: NDE-ED ORG
An audible alarm dosimeter.
- Emit an audible alarm when entering high-radiation areas (≥5 mSv/h or 500 mR/h).
- Essential for alerting radiographers to unexpected exposure.
The use of multiple tools is critical for accurate monitoring because no single device provides a complete picture. For example, survey meters give real-time data on radiation levels in an area, while dosimeters track cumulative exposure over time. Combining these tools ensures that both immediate and long-term risks are effectively managed.
Practical Tips for Using Radiation Detection Devices
1. Survey Meters:
Always verify the source is secure after use by performing a radiation survey.
2. Pocket Dosimeters
- Charge and record initial readings before starting work.
- Check periodically during the job and note the final reading.
3. Film Badges and TLDs
- Wear them between your neck and waist during Radiography.
- Protect them from heat, water, and damage. Report any loss or damage immediately.
4. Alarm Rate Meters
- Test alarms before starting work.
- Use vibrating or flashing models in noisy environments.
Proper usage of these devices not only enhances personal safety but also helps radiographers comply with regulatory requirements. Regularly calibrating these instruments is equally important to ensure accurate measurements and reliable performance.
Real-Life Example: Avoiding an Accident
Imagine a scenario where a radiographer forgets to confirm the gamma source is fully retracted. Without using a survey meter, they unknowingly enter a high-radiation area. The alarm rate meter sounds, allowing them to leave quickly and avoid severe overexposure. This incident highlights why consistent use of safety devices is non-negotiable.
Another common scenario involves skipping the use of a dosimeter during extended shifts. Over time, this negligence can lead to undetected overexposure. By wearing a dosimeter and tracking cumulative exposure, radiographers can ensure they stay within safe limits, preventing long-term health issues.
Conclusion
Gamma radiography is an essential NDT Technique with unmatched capabilities, but it requires strict adherence to safety protocols. By understanding the hazards, using detection tools correctly, and following established procedures, you can ensure your safety and excel in your role as an NDT technician. Always prioritize training and never hesitate to ask questions or seek guidance when in doubt.
As a new technician, embracing a culture of safety and continuous learning will prepare you to handle gamma radiography with confidence. Remember that this field is not just about technical proficiency but also about protecting yourself, your colleagues, and the environment from the risks associated with radiation exposure.
Author: Amit Gabani
