Safety

All biological responses to ionizing radiation are due to the same basic processes of ionization and excitation of atoms and molecules. These processes can disturb the physicochemical equilibrium and ultimately the metabolism of the cell, resulting in various functional and morphological changes, at the end of which is the biologically tangible radiation effect. This depends on the properties of the irradiated tissue, on the ionization density of the respective radiation (alpha, beta, gamma at different energies), on the dose rate, i.e. the absorbed radiation energy per target unit and mass, and on the size of the irradiated body volume. The latter results from the arrangement of the radiation source to the body and the penetrating ability of the radiation.

The activity of a radioactive substance is expressed in Becquarel (Bq). l Bq = 1 decay per second. For the previously used unit Curie (Ci) applies: 1 Ci = 3.7 x 10^10 Bq. The absorbed dose is defined as a measure of the primary damage to the tissue. It is the quotient of the energy transferred by the ionizing radiation to the material in a volume element and the mass in this volume element. It has the unit Gray (Gy). 1 Gy corresponds to an energy output of 1 J/kg. The biological effect (quality factor) depends not only on the amount of absorbed radiation energy, but also on the ionization density along the path of the ionizing particles. The main types of densely ionizing radiation are: Fast neutrons or the recoil protons triggered by them, alpha particles and protons along with alpha particles produced as a result of nuclear reactions with slow neutrons in tissue. Their biological effectiveness is very high compared to that of gamma radiation. If one wants to compare the effect of any radiation on tissues, one uses the term of the equivalent dose. Its unit is the sievert (Sv). The aquivalent dose is the product of the absorbed dose and the quality factor. The latter is 1 for X-rays, gamma and beta radiation, and 20 for alpha radiation from radioactive decay.

As one works with weak radioactive preparations in the practical course, the effects of high doses are not to be dealt with here. However, the permanent exposure to small doses must not be overlooked. There is no principle lower limit for the occurrence of damage, only a practical one. The clarification of the effect of weak continuous irradiation is important for the determination of tolerance doses. This problem leads to the question of natural radiation exposure to which the organism is exposed as a result of environmental conditions. It is composed of external and internal radiation exposure. The former includes cosmic radiation and that of the surrounding air and building walls, as well as earth radiation. The average annual cosmic radiation exposure in our latitudes is 0.35 mSv/a, the contribution caused by concrete buildings can reach 1 mSv/a, while the earth radiation depends strongly on the rock support (Ra, K) and ranges from 0.55 to 2.5 mSv/a. The internal radiation exposure derives from the totality of all radioactive substances present in the organism. In particular, these are 226Ra, 40K, 14C, as well as thorium and radium emanation present in the air, which reaches the lungs. It is estimated that the internal radiation exposure is 0.25 - 2.5 mSv/a. Thus, it can be concluded that in our latitudes the organism is exposed to a natural continuous exposure of at least 2 mSv/a. A biological effect of this radiation exposure is assumed, but could not be clearly detected until now because of the small size of the effect. If the radiation sources in the practical course are handled as prescribed, the additional radiation dose is below the natural exposure. The most radiation-sensitive tissues of the body are the lymphatic organs, furthermore bone marrow and gastric mucosa. In the lymph nodes, significant damage is already found after 250 mSv, although it usually heals quickly. Genetic radiation effects also play a role in determining the tolerance limit. There is a correlation between the total radiation dose administered and the frequency of genetic mutations. Therefore, it is recommended that radiation exposure be kept as low as possible until the end of the reproductive period. For occupationally exposed persons, a total dose of 400 mSv must not be exceeded.

All persons who have contact with ionizing radiation are subject to radiation monitoring. It is performed with film badges. With the badge, the radiation exposure is determined from the blackening of the film. In front of the film there are absorber foils of different thicknesses next to each other. From the ratio of the blackening behind the absorbers, the type of radiation and the dose are inferred. In order to keep radiation exposure as low as possible, the following rules must be observed: All work with radioactive substances should be carried out as quickly as possible. It should be remembered that the radiation exposure decreases quadratically with the distance from the specimen. The easiest way to shield a source is in its immediate vicinity. With relatively low total weight of the absorber material, the solid angle on which the protection affects is maximum here. If the radioactive sources are handled properly in the practical course, following the instructions of the supervising tutor, the radiation exposure due to alpha, beta and gamma radiation is less than the natural radiation exposure. The radioactive preparations used in the practical course are tightly enclosed in inactive preparation holders so that there is no risk of contamination or incorporation. If a preparation is damaged while performing an experiment, immediately notify the supervisor responsible for your experiment, the internship director, or the radiation protection officer, Dr. G. Reicherz, NB 2/127, tel. 23542.
The radioactive preparations are largely shielded in safes with lead. In some experiments you have to work with different preparations one after the other. In these cases, use the shielding devices provided and keep your distance from the preparations not currently in use. The trainees are responsible for all preparations handed out to them as well as those present in the measuring apparatus for the entire duration of the experiment. After the experiment, preparations that are not permanently installed must be locked away by the supervisors in the appropriate safes.