Radiation protection measures - shielding of gamma radiation with highly filled plastic compounds
The myth: Only high-density metallic materials can provide reliable shielding from gamma radiation.
The best solution comes from injection molding!
This article explains how heavy plastics with a density of up to 15 g/ccm provide safe radiation protection based on PlastFormance technology.
Radiation protection requirements in practice
Radiation protection is a pressing issue in many fields, such as nuclear power and nuclear medicine. Shielding against gamma radiation is one of the most important radiation protection measures for humans. Tungsten compounds from PlastFormance offer an optimal alternative to conventional lead products in this regard.
Human exposure to ionizing radiation occurs from natural sources, such as the radioactive noble gas radon or cosmic radiation, and from man-made sources, such as the nuclear power industry or nuclear medicine. This includes, among other things, diagnostic imaging using X-rays, as well as nuclear medicine diagnostics with the use of radioactive pharmaceuticals.
Sources of radiation of technical origin include, among others, security checks of baggage and people, for example at airports, radioactive substances in watches, or emitters that play a key role in nuclear energy generation.
Radiation protection essentially means protecting people and the environment from the harmful effects of ionizing radiation. The necessary radiation protection measures are regulated and defined in Germany by the Radiation Protection Act (StrlSchG). The Federal Office for Radiation Protection (BfS) is the competent authority in Germany for raising awareness of radiation-related risks and for the radiation protection of the population. [1]
222
Gamma radiation and ionizing radiation
Gamma radiation knocks electrons out of various atoms. What remains is a positively charged atom, also called an ion. For this reason, gamma radiation is classified as ionizing radiation. This alteration of matter can cause significant damage to living cells and organisms.
Alpha and beta radiation have a shorter range in air compared to gamma and X-ray radiation, and therefore a lower penetration depth. The greatest danger lies in inhaled and incorporated radioactive particles, which can release their energy over short distances within the body, thus damaging tissue. While gamma and X-ray radiation have a lower biological potency, they penetrate deeper into tissue and are therefore more dangerous in their overall effect (incorporation and direct external exposure).
Figure 1: Shielding of gamma radiation compared to alpha, beta and X-ray radiation
Ionizing radiation alters or destroys a cell's DNA. DNA contains the information for cell reproduction and repair. Therefore, gamma radiation in particular can be destructive to humans, animals, and the environment. In the best-case scenario, the damaged DNA can be repaired by the cell. If the radiation dose is too high, the cell dies and is expelled. However, if the cell repair is faulty, this change can be passed on to other cells, potentially leading to diseases such as cancer. [2]
Energy dose:
The energy dose is the amount of energy absorbed by a mass of matter. The unit is gray [Gy], which is equivalent to one joule [J] per kilogram [kg].
Organ dose:
Since different types of radiation have varying effects on body tissue, the energy dose is multiplied by a weighting factor to obtain the specific organ dose. For gamma and X-rays, this factor is 1, for example. The resulting unit of measurement is the Sievert [Sv].
Effective dose:
The effective dose is obtained by summing all individual organ doses, which have been multiplied by the corresponding tissue weighting factors. It is a measure of the total body dose and is used as a key factor in radiation protection measures. The unit is also the Sievert [Sv].
Effective dose:
Dose per unit of time, usually based on one hour [Gy/h; Sv/h]
Radiation protection measures are therefore vital for human survival when dealing with ionizing radiation. While alpha and beta radiation can be easily shielded by paper or aluminum, respectively, shielding gamma radiation requires more complex measures (see Figure 1).
Materials currently used
Selecting the right materials for creating a high-quality product to implement radiation protection measures is a constant challenge. Since alpha radiation can be shielded even with paper only a few millimeters thick, the main effort lies in shielding gamma radiation, as well as beta and X-ray radiation. Currently, beta radiation is mostly shielded using a combination of polymers and lead. Its shallow penetration depth makes shielding beta radiation relatively easy; however, a problem arises with the resulting bremsstrahlung, which is generated by the interaction of beta radiation with matter. This requires the addition of lead.
Gamma radiation shielding is usually achieved using lead products. These are manufactured using complex processes involving alloys of lead, and nowadays also of tungsten.
In general, materials with a high Z-value, i.e., a large atomic number and a high density, are suitable for shielding against gamma radiation.
Radiation shielding mechanisms in the material
The decisive processes in the interaction of gamma radiation with the absorber material are the photoelectric effect, the Compton effect and the pair formation, the partial cross-sections of which add up to the total effective cross-section.
Other relevant material parameters for shielding materials are the absorption coefficient and the attenuation coefficient, which characterise the absorption capacity of a certain material. The half-value layer thickness indicates the thickness of a material that reduces the ion dose rate by a factor of two.
In order to achieve effective shielding of gamma radiation, the material thicknesses must at least correspond to the maximum range of charged particle radiation in the respective material. [2]
Why the use of lead is problematic
Lead was favored for shielding gamma radiation because of its high density (11.3 g/cm³), high atomic number (Z = 82), and high absorption capacity. However, its drawbacks include high toxicity due to accumulation in the human body, environmental hazards, and the costly and complex recycling process as hazardous waste. [4]
Since 2003, lead has been listed under the RoHS Directive (Restriction of Hazardous Substances). This means that the defined maximum concentration of lead is limited to 0.1% by weight in homogeneous materials. [5]
3
Radiation shielding with PlastFormance plastics
In radiation protection, tungsten is increasingly becoming an alternative to lead. The atomic number of tungsten (Z = 74) and its higher density (19.25 g/cm³) are attractive material properties for shielding against gamma and X-ray radiation. [4]
3
Figure 2: Density comparison: (from left to right), tungsten, lead, tungsten alloy for sintering process and PlastFormance heavy plastic
PlastFormance technology makes it possible to incorporate pure tungsten as a filler in the compound and to produce materials with a higher density (see Figure 2) than lead. Polyamides form the plastic base of our heavy plastics. However, the special feature also lies in the transferability to other plastic classes.
Tungsten compounds as a substitute for soft lead
The aforementioned advantages of tungsten over lead can be optimally incorporated into the technology patented by PlastFormance. Compared to conventional sintering processes, injection molding offers a significantly higher degree of design freedom. Complex component geometries, in particular, can be realized without time-consuming machining. Furthermore, the manufacturing costs of injection molding are considerably lower than those of conventional methods for producing and post-processing sintered tungsten alloys (see Figure 3).
Figure 3: Advantages of the PlastFormance solution compared to the conventional sintering process
Radiation-shielding plastic in practice
The tungsten heavy plastic developed by PlastFormance has already been used to develop initial products for nuclear medicine and the nuclear power industry.
Syringe shielding in nuclear medicine
Sample containers in the nuclear power industry and natural sciences
In the control and analysis of overburden from the nuclear power industry, regular handling of radioactive samples is common. To prevent exposure of personnel to the radionuclides used, sample containers made of lead are usually used. Aicher Tröbs Produktentwicklung GmbH has therefore developed a sample container based on the PlastFormance tungsten compound (see Figure 5), which has already proven itself in use.
Figure 5: Sample container for shielding against gamma radiation
Outlook
In nuclear medicine, radioactive contrast agents are administered to patients via syringe during diagnostic imaging procedures. These agents, for example in PET (positron emission tomography), cause certain body regions to appear particularly intense. Depending on the organ being analyzed, various short-lived radionuclides, such as tetrachloroethylene (Tc) or fluorine (F), are used. To reduce the risk of radiation exposure for medical personnel, syringe shields are used.
99m
18
Figure 4: PlastFormance syringe shielding for implementing radiation protection measures in medicine
Aicher Tröbs Produktentwicklung GmbH has developed a syringe shield based on the PlastFormance tungsten compound for this purpose. The increased design freedom in injection molding enables particularly good handling compared to competing products (see Figure 4).
In addition to these possible applications, PlastFormance's heavy plastic offers a wide range of applications for shielding gamma radiation and implementing suitable radiation protection measures. Do you have any questions, requests or suggestions? Then contact us at any time! We look forward to working with you to find a solution.
Conclusion
Lead is no longer the only option for shielding against gamma radiation. While sintered tungsten does not have the same toxicity, it is much more expensive to process. The use of tungsten compounds from PlastFormance technology opens up entirely new possibilities for radiation protection measures against gamma radiation.
Replacement of toxic lead products
High design freedom thanks to injection molding.
Simplification in the manufacturing process compared to tungsten/lead alloys
Flexibility of the plastic base; even shielding soft plastic products are possible.
Cost savings in the overall system