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.
Radiation protection requirements in practice
Radiation protection is a current topic in many areas, e.g. nuclear power or nuclear medicine. The shielding of 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 for this purpose.
Human exposure to ionising radiation comes from natural radiation sources, such as the radioactive noble gas Rn or cosmic radiation, and civilisational sources, such as the nuclear power industry or nuclear medicine. These include imaging diagnostics using X-rays, as well as nuclear medicine diagnostics with the use of radioactive drugs.
Radiation sources of technical origin include security checks of luggage and people, for example at airports, radioactive substances in watches, and also emitters, which play a key role in nuclear energy production.
Radiation protection essentially means protecting people and the environment from the harmful effects of this ionising radiation. The respective radiation protection measures required are regulated and specified in Germany by the Radiation Protection Act (StrlSchG). The Federal Office for Radiation Protection (BfS) is the authority responsible in Germany for informing the public about radiation-related risks, as well as for radiation protection. 
Gamma and ionizing radiation
Gamma radiation detaches electrons from various atoms. What then remains is a positively charged atom, also called an ion. For this reason, gamma radiation is considered ionising radiation. This change in matter can sometimes cause considerable damage in living cells and organisms.
Compared to gamma and X-rays, alpha and beta radiation have a shorter range in air and thus a lower penetration depth. The greatest danger is posed by inhaled and incorporated radioactive particles, which can release their energy in the body over a short distance and thus damage tissue. Gamma and X-ray radiation have a lower biological effectiveness, but penetrate deeper into the tissue and are thus more dangerous in their overall effect (incorporation and direct external impact).
Abbildung 1: Abschirmung von Gammastrahlung im Vergleich zu Alpha-, Beta- und Röntgenstrahlung
Ionising radiation alters or destroys the DNA of a cell. The DNA contains the information for the reproduction and reparation of the cell. Thus, gamma radiation in particular can have a destructive effect on humans, animals and the environment. In the best case, the damaged DNA can be repaired by the cell. If the radiation dose is too high, the cell dies and is rejected. However, if the cell is repaired incorrectly, this change can be passed on to other cells so that, for example, cancer can occur as a result. 
Unter der Energiedosis versteht man die Menge an Energie, die von einer Masse an Materie aufgenommen wird. Die Einheit ist Gray [Gy] und entspricht einem Joule [J] pro Kilogramm [kg].
Da die verschiedenen Strahlungsarten unterschiedlich starke Auswirkungen im Körpergewebe verursachen wird die Energiedosis mit einem Wichtungsfaktor multipliziert, um die explizite Organdosis zu erhalten. Für Gamma- und Röntgenstrahlung ist das zum Beispiel 1. Die daraus resultierende Maßeinheit ist das Sievert [Sv].
Die effektive Dosis erhält man nach der Aufsummierung aller Organeinzeldosen, welche vorher mit den entsprechenden Gewebe-Wichtungsfaktoren multipliziert wurden. Sie ist ein Maß für die Gesamtkörperdosis und wird maßgebend für Strahlenschutzmaßnahmen verwendet. Die Einheit ist ebenfalls das Sievert [Sv].
Dosis pro Zeiteinheit, i.d.R. bezogen auf eine Stunde [Gy/h; Sv/h]
Radiation protection measures are therefore essential for human survival when dealing with ionising radiation. While alpha and beta radiation can easily be shielded by paper or aluminium, the shielding of gamma radiation requires more elaborate measures (see Figure 1).
Currently used materials
The choice of material for the creation of a high-quality product for the realisation of radiation protection measures is a constant challenge. Since alpha radiation can already be shielded with millimetre-thick paper, the main effort is to shield gamma radiation, as well as beta and X-ray radiation. Currently, beta radiation is usually shielded by a combination of polymers and lead. The low penetration depth makes it relatively easy to shield beta radiation, but there is a problem with the Bremsstrahlung (Bremsstrahlung) that occurs when beta radiation interacts with matter. For this, additional lead is needed.
Gamma radiation is usually shielded by lead products. For this purpose, alloys of lead, but now also of tungsten, are produced in complex manufacturing processes.
In general, materials with a high Z-value, i.e. a large atomic number and a high density, are suitable for shielding 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. 
Why the use of lead is problematic
The use of lead was favoured because of its high density (11.3 g/cm ), its high atomic number (Z = 82) and its high absorption capacity for shielding gamma radiation. The downside, however, is, among other things, the high toxicity due to accumulation in the human body, the dangers for the environment and the costly, complex recycling as hazardous waste. 
Since 2003, lead has been one of the substances covered by 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. 
Radiation shielding with PlastFormance plastics
In radiation protection, tungsten is increasingly an alternative to lead. The atomic number of tungsten (Z = 74) and its higher density (19.25 g/cm ) are attractive material characteristics for the shielding of gamma and X-ray radiation. 
Abbildung 2: Dichtevergleich: (von links nach rechts), Wolfram, Blei, Wolfram Legierung für Sinterprozess und PlastFormance Schwerkunststoff
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 in the technology patented by PlastFormance. Compared to conventional sintering processes, injection moulding offers a great deal of design freedom. Complex component geometries in particular can be realised without the need for costly and time-consuming reworking. In addition, the costs of injection moulding are much lower than in conventional processes for the production and post-processing of sintered tungsten alloys (see Figure 3).
Abbildung 3: Vorteile der PlastFormance Lösung gegenüber dem herkömmlichen Sinterverfahren
Radiation-shielding plastic in practice
The first products for nuclear medicine and the nuclear power industry have already been developed with the tungsten heavy plastic developed by PlastFormance.
Syringe shielding in nuclear medicine
Sample containers in the nuclear power industry and natural science
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.
Abbildung 5: Probenbehälter zur Abschirmung von Gammastrahlung
In nuclear medicine, radioactive contrast media are administered to patients by means of an injection in the course of diagnostic imaging procedures. In PET (positron emission tomography), for example, these contrast agents produce particularly strong images of certain regions of the body. Depending on the analysis of certain organs, different short-lived radionuclides such as Tc or F are used. To reduce the risk of the resulting radiation exposure for medical staff, syringe shields are used.
Abbildung 4: PlastFormance Spritzenabschirmung zur Realisierung von Strahlenschutzmaßnahmen in der Medizin
For this purpose, Aicher Tröbs Produktentwicklung GmbH has developed a syringe shield based on the PlastFormance tungsten compound. The increased design freedom in injection moulding enables particularly good handling compared to competitor 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.
Lead has long since ceased to be the alternative material for shielding gamma radiation. Sintered tungsten does not have the same toxicity, but is much more expensive to process. The use of tungsten compounds from PlastFormance technology opens up completely new possibilities for radiation protection measures to shield gamma radiation:
Replacement of toxic lead products
High design freedom, due to processing by injection moulding
Simplification in the manufacturing process, compared to tungsten/lead alloys
Flexibility of the soft plastic base, shielding soft plastic products also possible
Cost savings in the overall system