Ionizing radiation

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Updated – August 5, 2024

Ionizing radiation is imperceptible to humans; it is odorless, tasteless and invisible. It arises from the decay of atoms of radioactive substances, which occur everywhere in nature.

units

However, this atomic decay can be measured. Antoine Henri Becquerel received in 1903, together with Mary and Pierre Curie, the Nobel Prize for the discovery of radioactivity. After the decay rate, ie the number of decayed atoms per second, was initially given in Curie (Ci), the Bequerel (Bq) unit has been used since 1998.

After the Swedish physician and physicist Rolf Sievert, in 1979, 13 years after his death, the unit sievert (Sv) was established as the international unit for the equivalent dose. It describes the exposure (dose) to a biological organism in joules per kilogram multiplied by that Beam weighting factor.

A distinction is made between equivalence (H), effective (D_eff) and the organ dose (H_T).

The effective dose takes into account the different sensitivity of the organs. The limit value for people who are not occupationally exposed to radiation⁽¹⁾ is 1 mSv/a, for those occupationally exposed to radiation⁽²⁾ at 20 mSv/a.
The organ dose describes the dose absorbed by the respective organ, in Germany for example the eye lens 15 mSv/a⁽¹⁾, or 20 mSv/a⁽²⁾, extremities 50 mSv/a⁽¹⁾, or 500 mSv/a⁽²⁾ according to StrlSchV §71.

Types of radiation

Depending on the type of radiation to be measured, different measuring methods and devices are available.

A Geiger counter named after Johannes Wilhelm Geiger, or Geiger-Müller counter tube, supplemented by the name of his doctoral student Walther Müller, known since 1929, is used to measure the radioactive decay of alpha, beta and gamma radiation. The order also provides information about the increasing penetrating ability of the radiation.

Alpha radiation (α) is found in heavy nuclei such as uranium-238.

Beta radiation (β) is formed when the nucleus of an atom is converted into one of another element. A distinction is made here between β⁺, the element with the next lowest value and β^–, the element of the next higher atomic number. Both are ionizing radiation.

Gamma radiation (γ) is an electromagnetic radiation with a wavelength of only 0.005 nm (corresponding to 59,958,491.6 THz(!)) and is created after α or β decay from the energy released in the process, also referred to as a γ transition. This is not a decay because the number of neutrons and protons contained in the nucleus remains unchanged. When it passes through a body (human, animal, fruit, etc.), the electrons released and the resulting X-rays break chemical bonds, causing cell and DNA damage, among other things.
The Radiation weighting factor is 1 and serves as a reference for other types of radiation with regard to their harmfulness to the organism.

radon (Rn) is a radioactive element, a noble gas that occurs naturally all over the world and is the most stable isotope ²²²Rn with a half-life of 3.8 days, which is produced by the decay of uranium and radium. The reason for the health-stressing moment is primarily the α-particle-emitting decay product polonium (Po) with a half-life of 138 days, especially the isoptopes ²¹⁰Po ²¹²butt, ²¹⁴butt, ²¹⁶butt, ²¹⁸Po. The biological half-life in the body is 50 days.
Alpha radiation is hardly harmful externally, as the penetration depth is already absorbed in the top layer of skin. However, as radon is soluble in drinking water, this is an internal contamination that has a direct effect on cells and can be stored in organs.
The radiation weighting factor is 20 and thus represents a twenty-fold higher level of harmfulness than the effect of γ-radiation over the same unit of time.

Measuring device

The Geiger-Müller counters mentioned above generally detect β and γ radiation in the lower price segment. Measuring devices that detect α-radiation cost more than around 600 euros.

Radon measuring devices including calibration can be purchased for around under 200 euros.

Devices that are sufficient for home users are, for example, the β / γ counter GMC500+ from GQ, as well as the radon detector RadonEye with Bluetooth connection from the South Korean manufacturer FTLab, which is also available in a version - unfortunately twice as expensive - with a WLAN connection.

Both devices have integrated data storage and the numerical and graphical representation of the measurement series.
The replaceable Li-ion battery of the mobile and stationary Geiger counter can be charged using a USB port. The radon detector requires 12V DC, e.g. connected to a power bank via a StepUp DCDC converter or via a plug-in power supply, or via a car 12V connection.

Definition of limit, guideline and reference value

The meaning of these three values is often confused, so here is the correct definition:

• Limit value – must not be exceeded
• Guideline value – should be adhered to in order to ensure that limit values are not exceeded
• Reference value – is the just accepted concentration

Interpretation of the measured values

The natural radioactive radiation is between 0.03 and 0.08 μSv/h. The radiation exposure calculated over a year is determined from (0.03 x 24 x 365) / 100 = 0.2628 mS/a .. (0.08 x 24 x 365) / 100 = 0.7008 mS/a.

Limit values are very subject to interpretation. If we think about the former limit values for X-rays, much lower values apply today because we can now determine which damage is caused by which dose.

Today, around 100 mS/a is considered to be dangerous to health. A single dose of 1 S causes radiation sickness, or 5 S in 50% cases causes death within a month.

The radon pollution varies greatly depending on the soil permeability and uranium or radium occurrence, which results in different radon concentrations recommended as “limit values”.
On average we can say that 100 Bq/m³ as a limit for indoor concentrations, but also 200 Bq/m³ are still considered acceptable in some countries.

Radon is easily soluble in water and can therefore also be absorbed with drinking water or by inhaling the water vapors when cooking or showering. Waterworks reduce radon concentrations by mixing water with a lower concentration from other sources or by aerating it with oxygen, which causes radon to partially escape from the water.