Radiation protection measures - shielding of gamma radiation with highly filled plastic compounds
The myth: Only high-density metallic materials can produce safe shielding from gamma radiation.
The best solution comes from injection moulding!
In this article you can find out how heavy-duty plastics up to a density of 15 g/ccm based on PlastFormance technology provide safe radiation protection.
Table of Contents
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]
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]
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).
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).
Incumbent radiation shielding materials
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 key processes in the interaction of gamma radiation with the absorber material are the photoelectric effect, the Compton effect and pair production, the sum of whose partial cross-sections gives the total effective cross-section.
Other relevant material properties for shielding materials are the absorption coefficient and attenuation coefficient, which characterize the absorption capacity of a particular material. The half-value layer thickness indicates the thickness of a material that reduces the ion dose rate by a factor of two.
To achieve effective shielding of gamma radiation, the material thicknesses must be at least equal to the maximum range of the charged particle radiation in the respective material. [2]
Why choosing lead is problematic
Die Verwendung von Blei wurde wegen der hohen Dichte (11,3 g/cm3), seiner hohen Ordnungszahl (Z = 82) und des hohen Absorptionsvermögens für die Abschirmung von Gammastrahlung favorisiert. Die Schattenseite stellt jedoch unter anderem die hohe Toxizität durch Anreicherung im menschlichen Körper, die Gefahren für die Umwelt und das kostenpflichtige, aufwendige Recycling als Sondermüll dar. [4]
Seit 2003 gehört Blei zu den Stoffen der RoHS-Richtlinie (Restriction of Hazardous Substances). Das bedeutet, dass die definierte maximale Höchstkonzentration von Blei auf 0,1 Gew.-% in homogenen Werkstoffen limitiert ist. [5]
Figure 2: Density comparison: (from left to right), tungsten, lead, tungsten alloy for sintering process and PlastFormance heavy plastic
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/cm²) are attractive material properties for shielding against gamma and X-ray radiation. [4]
PlastFormance technology makes it possible to incorporate pure tungsten as a filler into the compound and produce materials with a higher density (see Figure 2) than lead. Polyamides form the base material for our heavy-duty plastics. However, the unique aspect also lies in its transferability to other plastic classes.
Tungsten compounds as a replacement 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
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 99mTc or 18F, are used. To reduce the risk of radiation exposure for medical personnel, syringe shields are used.
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).
Figure 5: Sample container for shielding against gamma radiation
Sample containers in the nuclear power industry and natural sciences
The inspection and analysis of waste rock from the nuclear power industry involves the regular handling of radioactive samples. To prevent personnel exposure to the radionuclides used, lead sample containers are typically employed. Aicher Tröbs Produktentwicklung GmbH has therefore developed a sample container based on the PlastFormance tungsten compound (see Figure 5), which has already proven its worth in practical application.
outlook
In addition to the applications mentioned above, PlastFormance's heavy-duty plastic offers a wide range of possibilities for shielding gamma radiation and implementing suitable radiation protection measures. Do you have any questions, requests, or suggestions? Then please contact us at any time! We look forward to working with you to develop 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
References
[1] Federal Office for Radiation Protection: “Radiation and radiation protection: Responsibility for people and the environment”; BfS (2019)
[2] Krieger, H.: “Fundamentals of Radiation Physics and Radiation Protection”; Springer Verlag (2012)
[3] Grupen, C.: “Basic Course in Radiation Protection: Practical Knowledge for Handling Radioactive Materials”; Springer Verlag (2008)
[4] Binder, H.: "Lexicon of Chemical Elements"; S. Hirzel Verlag Stuttgart (1999)
[5] Directive 2002/95/EC of the European Parliament and of the Council of 27 January 2003 on the restriction of the use of certain hazardous substances in electrical and electronic equipment