Radioactivity

Radio activity

Radioactive material in a laboratory is usually a specific isotope of an element, for example carbon‑14 (¹⁴C) or radium‑226 (²²⁶Ra). Radioactive nuclei are unstable and emit radiation (decay) in order to reach a more stable state. Most substances emit several types of radiation, and the nucleus changes accordingly depending on how much energy (and sometimes also mass) is emitted with the radiation. If the atomic number of a substance changes during the radiation process, a different element is formed; if not, a different isotope of the same element is produced.

Radiation from radioactive substances can be:

Alpha radiation: a particle with mass number 4 and a +2 charge is emitted from the nucleus (a helium nucleus, α).
Beta radiation: a particle similar to an electron is emitted from the nucleus (β⁻), but it can also be positively charged (a positron, β⁺).
Gamma radiation: electromagnetic radiation is emitted from the nucleus that has neither mass nor electric charge (γ).
Neutron radiation: a neutron (n) is emitted from the nucleus; it has a mass number of 1 and no electric charge.

Alpha, beta, and neutron radiation are often collectively referred to as particle radiation. The activity of radioactive substances is measured in nuclear transformations per second and has the unit becquerel.

1 Bq = one nuclear transformation per second

The becquerel is a small unit and is most often used with multiplying prefixes such as M (mega) or G (giga). An older unit for radioactivity is the curie (Ci), which is a very large unit.
1 mCi = 370 MBq.

When radioactive substances decay, their quantity decreases, and thus their activity decreases as well. The time it takes for the amount (and activity) of a substance to decrease to 50% of its original amount is called the half‑life. The type of radiation emitted by a substance and its half‑life vary greatly between substances but are characteristic of each individual type of nucleus. It is therefore possible to identify a substance by the radiation it emits and to predict its lifetime.

Radiation source

Hazard posed by radioactive materials

The hazard posed by radioactive materials lies in the fact that they can cause radiation exposure to people. When working with sealed radiation sources, there is only a risk of external exposure, that is, the body is exposed to radiation from the outside. However, when working with open radiation sources, there is also a risk of internal exposure, meaning that radioactive material can enter the body and irradiate it from within.

Radioactive materials vary greatly in how dangerous they are, and therefore the requirements placed on those who use them also vary. Alpha radiation is very dangerous if the material enters the body (through wounds, the mouth, or the nose), but its range is very short (a few micrometres), so it only irradiates the area where the radioactive material is located.

Beta radiation is dangerous both inside and outside the body, although the damage it causes is less severe than that caused by alpha radiation. The range of beta radiation is long enough (a few millimetres) to cause skin burns on unprotected skin.

Gamma radiation causes less damage than particle radiation, but on the other hand, gamma radiation is highly penetrating and difficult to shield against. The penetration and effects of neutron radiation on the body depend greatly on the energy of the radiation, and protective measures must always be planned in accordance with the available information about it.

Radiation sources are classified into hazard categories 1–5, with the most dangerous materials in category 1. Radiation sources in hazard categories 1–3 are highly radioactive, and special regulations apply to them. For more information, see publication GR20:02 and Regulation No. 1298/2015 on sealed radiation sources.

Laboratories in which radioactive materials are used are classified into categories A–C, with the most hazardous activities in category A. For further details, see the publications of the Icelandic Radiation Safety Authority, GR04:02 on laboratory classification, and Regulation No. 809/2003 on open radiation sources.

Basic protection

When working with open radiation sources, protection against both external and internal radiation exposure is required.

Protection against internal radiation primarily involves preventing radioactive material from entering the body. Based on the properties of the material (for example, whether it emits particle radiation or is volatile), the amount being handled at any given time, and the nature of the work, it must be assessed what kind of protective equipment is necessary.

Protective clothing, gloves, and masks are used both to prevent radioactive material from entering the body and to prevent it from spreading beyond the work area.

Open radiation sources must never be handled without gloves, and special care must be taken to ensure that radioactive contamination is not spread via the gloves. When working with beta‑emitting materials, particular attention must also be paid to the risk of skin burns.

Protection against external radiation is based on the following three fundamental principles, whether working with open or sealed radiation sources:

Distance from the radiation source: Radiation decreases with the square of the distance, so increasing distance is an effective protective measure.
Time: Radiation exposure to the body increases in direct proportion to the time spent in the radiation field; therefore, the time spent there should be limited.
Shielding: Shielding refers to the use of materials that significantly attenuate radiation in order to reduce radiation from a source to its surroundings. Radiation sources must always be stored in some form of shielding.

The use of sealed radiation sources generally involves opening access to radiation from the source (for example, opening a window on a source housing) or temporarily removing the source from its shielding. When a source is removed from shielding or access to its radiation is opened, the radiation field around it increases manyfold. Information about the radiation field should be available in the instructions for use of the radiation source.

When selecting materials for shielding, it is important to know the type and energy of the radiation emitted by the radioactive material in question.

All use of radiation sources should be arranged so that people are exposed to as little radiation as possible. The combined application of distance, time, and shielding should be optimized during work to ensure this. If the use of radiation sources may result in radiation exposure to people exceeding the maximum annual dose limits for the general public, those working with the radiation source are classified as radiation workers. For further information, see the publication of the Icelandic Radiation Safety Authority GR19:06.

Law and regulation

Rules of the University of Iceland on the Use of Radioactive Materials and Radiation‑Emitting Devices