Content Summary
In the new year of 2024, and with the new semester, the ShanghaiTech EHS WeChat account is launching a brand new column called Laboratory Safety #YouAskIAnswer#. Here, you can ask any questions about all aspects of laboratory safety, and we will invite professors and experts to answer them for you.
This Issue's Guest
Cao Guohua
Associate Professor, Researcher, PhD Supervisor
School of Biomedical Engineering, ShanghaiTech University
Hot Questions
Question 1
In the laboratory, there are various radiation sources, such as 22Na and 241Am. How can one ensure the minimum absorbed dose during handling?
— Yang Yalong, School of Biomedical Engineering
Answer
Sodium-22 (nuclide symbol 22Na, half-life 2.6019 years, 22Na source emits positron radiation) is a common radioactive isotope, mainly emitting positrons (β+) and gamma rays. When handling 22Na, due to the strong penetration power of its β+ particles and gamma rays, specific safety measures are needed to ensure the minimum absorbed dose.
Americium-241, nuclide symbol 241Am, with a half-life of 432.2 years, is an alpha emitter. During decay, it releases three groups of alpha particles and a certain amount of X-rays and gamma rays. The alpha particles from 241Am have very low penetration ability but can cause severe damage to local tissues if they enter the body through the respiratory tract or open wounds. Additionally, 241Am also emits X-rays and gamma rays, requiring appropriate protection to reduce radiation exposure.
Here are some key safety measures when handling 22Na and 241Am:
Time: Minimize exposure time by planning experimental steps efficiently to reduce the duration of exposure.
Distance: Increase distance from the radiation source as radiation dose decreases with the square of the distance. Use long-handled tools (such as long tongs or tweezers) to minimize contact.
Shielding: Appropriate shielding materials are necessary:
For 22Na: Proper shielding is needed to reduce exposure to β+ and gamma rays due to positron annihilation gamma rays produced when β+ particles interact with matter. Thick lead shielding or other suitable materials for gamma rays are commonly used. Low Z (atomic number) materials like plastic can effectively reduce annihilation radiation for β+ particles.
For 241Am: Use appropriate shielding materials. Although alpha particles can be blocked by paper or a few layers of plastic, considering the accompanying gamma radiation, heavy metals like lead provide additional protection. Operate within a shielded fume hood to reduce exposure and prevent the spread of radioactive materials.
Personal Protective Equipment (PPE): Wear appropriate PPE based on the operation, such as lab coats, radiation-resistant gloves, goggles, or face shields. In cases where radioactive dust or aerosols might be generated, wear suitable respiratory protection.
Monitoring: Use radiation detectors (e.g., Geiger counters or scintillation counters) before, during, and after handling to monitor radiation levels in the work area, ensuring dose control within safe limits.
Work Area Control: Operate within a designated area (e.g., a shielded fume hood) specifically designed for handling radioactive materials to minimize exposure to the surrounding environment and personnel.
Training and Procedures: Ensure all operators are trained in radiation safety and are familiar with specific safety procedures for handling 22Na and 241Am. Follow laboratory safety procedures and national regulations, manage and store radioactive materials properly.
Emergency Preparedness: Be familiar with emergency procedures to respond effectively in case of leaks or other incidents.
Cleaning and Waste Disposal: Thoroughly clean the work area after operations and safely dispose of all radioactive waste. Follow proper waste disposal procedures to ensure all radioactive materials are safely managed.
By implementing these comprehensive measures, radiation exposure during laboratory operations with 22Na and 241Am can be minimized, ensuring the safety of operators and the environment.
Question 2
Do different radiation sources require different protection measures?
— Yang Yalong, School of Biomedical Engineering
Answer
Yes, different radiation sources indeed require different protection measures, primarily due to the different types of radiation they emit (such as alpha particles, beta particles, gamma rays, neutrons) which have different physical properties, including their penetration abilities and interaction modes. These differences dictate the protective measures needed. Here are basic protection principles and measures according to different radiation types:
Alpha Particles:
Penetration Ability: Very limited, can be blocked by paper, human skin, or a few centimeters of air.
Protection Measures: The main focus is to prevent inhalation, ingestion, or entry through skin wounds because internal exposure can cause severe damage. Practical measures include using gloves, protective clothing, and operating in an appropriate ventilated environment.
Beta Particles:
Penetration Ability: Moderate, can be blocked by a few millimeters to centimeters of materials (such as plastic or light metals).
Protection Measures: Use gloves and protective eyewear to prevent direct skin and eye exposure, and appropriate shielding materials to prevent radiation penetration. Note that beta particles may produce Bremsstrahlung (X-rays) when interacting with materials, so additional shielding might be necessary.
Gamma Rays and X-rays:
Penetration Ability: High, requiring dense shielding materials such as lead or concrete to reduce radiation.
Protection Measures: Use adequate lead shielding, maintain sufficient distance, and limit exposure time. Wear personal protective equipment such as lead aprons, and use lead glasses and shielding walls when necessary.
Neutron Radiation:
Penetration Ability: Very high, similar to gamma rays, but requires different shielding strategies.
Protection Measures: Neutrons interact uniquely with matter (mainly by striking atomic nuclei), so effective shielding materials often include hydrogenous materials (such as water, polyethylene) to slow down neutrons, and heavy elements (such as boron, cadmium) to absorb slowed-down neutrons.
Comprehensive Protection Measures:
Time, Distance, and Shielding: Regardless of the type of radiation source, the basic principles of reducing exposure time, increasing distance from the source, and using appropriate shielding should be followed.
Personal Protective Equipment (PPE): Choose suitable PPE based on the type and activity level of the radiation source, such as protective clothing, gloves, glasses, etc.
Monitoring and Training: Regularly monitor radiation levels and ensure all operators receive proper training, understanding the specific safety procedures for the radiation source.
In conclusion, protection measures for different radiation sources should be tailored according to their radiation type, energy level, and specific usage scenarios to ensure operational safety and minimize radiation exposure risks.
Question 3
How do the principles of time, distance, and shielding vary with the type of radiation source?
— Yang Yalong, School of Biomedical Engineering
Answer
The principles of time, distance, and shielding are the most fundamental concepts in radiation protection. Reducing exposure time, increasing distance from the radiation source, and using appropriate shielding materials are universal principles in radiation protection. For all types of radiation sources, the absorbed radiation dose decreases proportionally with reduced exposure time and inversely with the square of the distance from the source. Because different radiation sources emit radiation types (such as alpha particles, beta particles, gamma rays, neutrons) with different physical properties, including their penetration abilities and interaction modes, the specific application of these principles needs to be analyzed based on the radiation type emitted by the source.
Time:
For all types of radiation sources, reducing exposure time directly reduces the absorbed radiation dose. This is universally applicable regardless of whether the source emits alpha, beta, gamma rays, or neutrons. Minimizing contact time with the radiation source is an effective method to reduce dosage.
Distance:
Depending on the type of radiation emitted by the source, the impact of distance on the user's radiation dose can vary:
Alpha Particles: Due to the very low penetration ability of alpha particles, they are generally completely blocked within a few centimeters of air or by very thin shielding materials. Therefore, even a small increase in distance can effectively reduce the radiation received from alpha radiation.
Beta Particles: Beta particles have stronger penetration than alpha particles, but their impact quickly weakens beyond a few meters. Increasing distance from beta radiation effectively reduces the received dose.
Gamma Rays and X-rays: These radiations have high penetration abilities, and increasing distance can reduce the received dose, but due to their penetrative nature, a significant dose reduction might require a greater distance.
Neutrons: The behavior of neutrons depends on their energy (fast or slow neutrons). Like gamma rays, increasing distance can reduce the received dose, but the required distance might be greater than for alpha or beta radiation.
Shielding:
Different types of radiation require different shielding materials:
Alpha Particles: Even a piece of paper or a few centimeters of air is sufficient to block alpha particles, making shielding against alpha radiation relatively easy.
Beta Particles: Beta particles can be shielded by a few millimeters to centimeters of plastic or metal. Note that beta particles may produce Bremsstrahlung (X-rays) when passing through some materials, so additional shielding may be necessary.
Gamma Rays and X-rays: Dense materials (such as lead or concrete) are needed for effective shielding. The thickness of the shielding depends on the energy of the radiation, with high-energy gamma rays requiring thicker shielding.
Neutrons: Shielding neutrons is more complex and requires specific strategies. Fast neutrons first need to be slowed down using light element materials (such as water or polyethylene), turning them into thermal neutrons, which are then captured using neutron-absorbing materials containing boron or other elements.
In summary, the principles of time, distance, and shielding in radiation protection need to be adjusted based on the specific radiation type and characteristics of the radiation source to ensure effective reduction of radiation exposure.
