- What materials can block ionising radiation?
- What are the four main practical principles of radiation protection?
- Can radiation be passed from person to person?
- What is radiation Skyshine - and does it matter to me?
- What is the difference between sealed and unsealed radioactive source?
What materials can block ionising radiation?
The type of material depends on the type of ionising radiation in question.
Alpha Particles - single sheet of paper, the outer dead layer of skin of your body, clothing
Beta Particles - depends in energy of beta particle, but 12mm of a low density material like perspex or plastic will stop all betas
Gamma Ray / X-ray - shielding performance depends on energy of the radiation for a given thickness and density. Higher density shielding such as lead / tungsten will provide the best shielding performance for the least thickness. If space is of little concern high density concrete, normal concrete or even water can be used (but these shields will be thicker).
What are the four main practical principles of radiation protection?
The following four principles are valid for ionising radiation (although not all will apply for individual cases as this will depend on the type of radiation source involved).
Time - Minimise the time of exposure.
Distance - Maximise the distance from the source of radiation.
Shielding - Use radiation shielding where practicable.
Containment - For unsealed radioactive materials use containment to minimise risk of contamination spread and avoid inhalation of ingestion hazards.
Can radiation be passed from person to person?
This question is often asked but needs some clarification before providing an answer. Radiation cannot be passed from person to person, just as visible light cannot be passed from person to person. However, if you mean radioactive material (which emits radiation) then its possible to pass this between individuals. Radioactive material is a physical substance which may take the form of a solid, liquid or gas. Therefore, if the radioactive material is mobile in the environment then it can be passed from person to person.
What is radiation Skyshine - and does it matter to me?
Radiation skyshine is where radiation (predominately gamma or x-rays) scatter within air (and other objects) above a facility which is either open topped (no shielding) or has reduced shielding. Radiation from the bottom of the facility will scatter upwards to the top of the facility, and some of this will then scatter downwards towards the ground - the other side of the facility shielding. It may be that direct measurements from the source of radiation through the shield are negligible. However, as you move away from the facility a peak dose rate will be measured some distance from the shielding (maximum skyshine) before reducing with further distance from the facility. It matters to you as many have ignored this phenomenon and only discovered higher dose rates some distance from the facility many months later.
A more rigorous explanation of Skyshine can be found here: Skyshine – radiation scattering around and over shielding.
What is the difference between sealed and unsealed radioactive source?
Sealed radioactive material is that which is contained or encapsulated in some way so that the radioactive material cannot move within the environment around it. This is sometimes known as a sealed or closed radioactive source. Such sources can only present an external radiation hazard, walking away from the source will reduced radiation exposure to negligible levels. Unsealed radioactive material (or source) is where the material is not contained, and depending on circumstances, can move around the environment. An example could be a radioactive liquid that has been spilled from an open container. This unsealed material is called contamination and could be taken into the body by ingestion, inhalation or through cuts in the skin. Walking away from the container will not necessarily reduce the radiation exposure hazard to zero since this person may already be contaminated.