Measuring radioactivity

• What is ionising radiation?
• Measuring methods
• Measuring devices
• Influencing factors and informative value of the measurement results
• Professional radioactivity measurements
• View measured values online
• Classify and evaluate radioactivity readings

Measuring instruments for measuring radioactivity in the environment

"Radioactivity" describes a natural physical phenomenon. If atomic nuclei can decay by themselves without external influence and emit high-energy radiation (ionising radiation) in the process, they are referred to as being "radioactive".

Natural radioactivity is everywhere in the environment. No one can escape it. Artificial radioactivity occurs when radioactive atomic nuclei are produced artificially (e.g. by nuclear fission or neutron activation).

The ionising radiation produced by radioactive decay cannot be seen, heard, felt, smelled, or tasted. However, there are methods and devices that can be used to measure it.

What is ionising radiation?

Ionising radiation occurs when certain atomic nuclei decay radioactively, thereby emitting alpha, beta, gamma, and/or neutron radiation. Ionising radiation can also be produced through technical means. This is the case with X-ray radiation.

When ionising radiation hits atoms or molecules, it can "ionise" them. Ionisation means that electrons are "ejected" from the shell of atoms or molecules. The atom or molecule that remains is then (at least briefly) positively charged. Electrically charged particles are referred to as ions.

When atomic nuclei decay, they often emit alpha radiation in the form of ejected helium atomic nuclei or beta radiation in the form of electrons or positrons ejected from the atomic nucleus – depending on which atomic nuclei are involved. In most cases, short-wave and high-energy gamma radiation occurs at the same time as alpha or beta radiation.

If ionising radiation penetrates human tissue, it can damage tissue cells. Whilst alpha radiation is absorbed by only a few centimetres of air and cannot penetrate the human skin, beta radiation can penetrate up to a few metres of air and can thus enter the human body a few millimeters to centimeters through the human skin. Gamma radiation and neutron radiation can readily penetrate various types of matter.

Units of measurement

Measuring methods

Because ionising radiation cannot be observed directly, suitable measurement methods must be used in order to determine the type and intensity of the radiation.

Depending on the type of radiation (alpha, beta, and neutron radiation or X-rays and gamma radiation), different measurement methods are required. This means that it is not possible to measure all types of radiation produced by radioactive decay using a single method.

The purpose of the measurement also plays an important role. If, for example, the type of radioactive substance is to be determined in addition to the intensity of the radiation, different measurement methods are necessary.

Physical interactions of radiation with matter

All methods for measuring ionising radiation are based on physical interactions of the radiation with matter.

In the process, energy is transferred from the radiation to the detector material used. Depending on the detector used, this leads to various effects that can then be measured and made visible (e.g. by means of a display) and/or audible (e.g. by means of cracking noises in a loudspeaker).

Measuring devices

The measuring methods are used in different measuring devices such as Geiger-Müller counters (colloquial: "Geiger counters"), semiconductor detectors, scintillation counters, and passive detectors/film dosimeters.

Depending on the type and intensity of the radiation, the measuring devices mentioned here are better or worse suited for detecting the respective type of radiation. For example, scintillation probes can measure much lower activities or dose rates than a Geiger-Müller counter.

Possible conclusions

Even though measuring devices can be equipped with different types of detectors and thus use different measuring methods in parallel, it is fundamentally not possible to draw conclusions about the "total radiation" at a location based on the result of a single measurement of a certain type of radiation.

However, under certain conditions, conclusions can be drawn about the radioactive material present. These, in turn, allow estimates of the "total radiation". If a measurement is carried out at a location in which not only the intensity but also the energy of the (gamma) radiation present is determined, it may be possible to identify and quantify the radioactive substances present. This allows statements to be made about the total radiation.

Influencing factors and informative value of the measurement results

Qualified statements on radioactivity measurement results can be made only by experts with the appropriate professional equipment. In radiation protection, higher-quality measuring devices are generally used. These are calibrated and subject to regular quality control and calibration.

Influencing factors that experts take into account in selection and evaluation include

• the suitability of the measuring device for the measuring task:
  Does the measuring device provide reliable results for the type of radiation to be determined, and is the response capacity sufficient?
• the framework conditions of the measurements:
  Which aspects must be considered when evaluating the measurement results? What influence does the measurement geometry (i.e. the distance to the measurement location and any shielding that may be present) have? Measurement results can be compared only if measurements are taken at the same location, in the same measurement geometry, and with a comparable measuring device.

Limited informative value of measurements with simple devices

As a rule, a qualified, reliable, and resilient measurement result cannot be produced by private measurements because the informative value of measurements with simple, commercially available devices is limited. Private measurements with simple measuring devices can, at most, give a rough indication. There are many reasons for this.

• As a rule, there is no continuous calibration and/or verification of the simple commercially available devices.
• If a calibration is available, it is usually related to a specific radionuclide. That means the calibration is valid only for a specific measurement task such as the detection of caesium-137.
• Inexpensive Geiger-Müller counters are often not suitable for all measurement situations. Deviations of the measured values from those of expensive professional devices may therefore occur, especially in lower dose ranges.
• In the case of inexperienced use of unknown detectors, it is easy to make operating errors or use measuring devices that are unsuitable for the type of radiation to be measured (e.g. if devices are not suitable for the type of radiation to be determined or the measurable dose rate is outside the measuring range of the device).
• Simple, commercially available devices are often susceptible to external influences such as temperature fluctuations, humidity, and electromagnetic fields.

The measured values obtained with simple measuring devices can be assessed in a meaningful way only if comparative values are available. This means that a measurement of the "normal" background value was carried out with the same measuring device under the same external influences and at the same measuring distances as the newly determined measured values.

Because all types of radiation can usually not be measured using a single measuring device, measurements with a single measuring device are almost always incomplete.

Notes and recommendations

The Federal Office for Radiation Protection (BfS) cannot make any recommendation for specific measuring devices or providers. However, the BfS recommends taking various aspects into account when considering the purchase of a measuring device.

The measuring range of the measuring device should thus extend downwards to about 0.1 microsieverts per hour because this roughly corresponds to natural ambient radiation. It also makes sense to display the dose rate in microsieverts per hour because this makes it easier to compare the results with each other and with limit values.

However, it should also be noted that the quality of the components used and the expertise of the manufacturer play a role. Inexpensive devices often do not produce as accurate and reliable results. For example, Geiger-Müller counters for private use are often much less expensive than professional meters because they usually are not – and cannot be – calibrated.

Professional radioactivity measurements

Overall, the environment in Germany is closely monitored for radioactivity. Different institutes are responsible for different areas of the environment. In addition to the BfS, at the federal level,

• the German Meteorological Service (DWD),
• the Thünen Institute,
• the German Federal Institute of Hydrology (BfG),
• the Federal Maritime and Hydrographic Agency (BSH),
• and the Max Rubner Institute (MRI)

carry out measurements.

There are also measuring points operated by the federal states. The operators of facilities where radioactive substances are handled also operate radioactivity measuring stations. The BfS is also involved in international measuring networks and participates in international data platforms.

Measurements of the BfS

https://odlinfo.bfs.de provides online monitoring data of radiactivity in Germany

The BfS measures radioactivity with the help of many different measuring methods as well as appropriately equipped laboratories and measuring devices. Examples include:

• the ODL measuring network consisting of around 1,700 measuring probes distributed across Germany; these continuously measure natural radiation exposure
• in situ measurements using mobile germanium gamma spectrometers
• aerogamma measurements with helicopter-based measuring systems in cooperation with the Federal Police
• highly sensitive measuring equipment for trace analysis (e.g. at the BfS measuring station on Mount Schauinsland near Freiburg), which can detect the smallest traces of radioactive substances in the air (trace analysis)
• laboratories for the analysis of radionuclides in various media; these can determine ionising radiation in water, soil, air, and foodstuffs

The measuring devices necessary for measuring alpha, beta, gamma, and neutron radiation are available in different versions at the BfS and are subject to regular quality management through calibration and verification. For example, a BfS radon calibration laboratory accredited by the Deutsche Akkreditierungsstelle (DAkkS) ensures the quality of measurements of radon and radon decay products.

View measured values online

BfS-Geoportal

Qualified radioactivity readings are made available online by the BfS and other institutes:

• The ODL measuring network of the BfS – with its important early warning function to quickly detect increased radiation from radioactive substances in the air in Germany – makes its measured values available online at https://odlinfo.bfs.de around the clock. In the event of the spread of a radioactive cloud of pollutants, these could be tracked almost in real time – an essential prerequisite for initiating targeted measures to protect the population at short notice.
• In the BfS Geoportal, the BfS provides not only its own measurement data but also measurement data from federal, state, and other partner authorities. Most of these are data from the Integrated Measuring and Information System (IMIS).
• Measured values of the local dose rate from the member states of the European Union (EU) are published collectively by the Joint Research Centre (JRC) of the EU.

Citizen science networks such as SAFECAST also make measured values available online – the values are not quality-assured but can nevertheless provide rough indications of whether radioactivity readings have increasing or decreasing tendencies.

Various retrospective reports on environmental radioactivity and radiation exposure supplement the current measured values available online. In addition to publishing its own reports, the BfS also supports the Federal Environment Ministry in its national and international reporting obligations.

Classify and evaluate radioactivity readings

Radioactive decay occurs in our natural environment at all times, and radioactive doses are absorbed accordingly. This naturally occurring radioactivity can hardly be influenced. In contrast, (artificial) radiation exposure from technical facilities can be influenced – and thus regulated by limit values.

Comparative values

Everyone is exposed to radiation from natural and man-made radiation sources.

In Germany, the natural radiation background ranges from 0.6 millisieverts per year in the North German lowlands to more than 1.2 millisieverts per year in the low mountain ranges depending on the region.

Ionising radiation also reaches us from space – in the form of cosmic radiation. At sea level, this radiation is equivalent to about 0.3 millisieverts per year. But even at the altitude of aircraft (at about 10 kilometers), the cosmic equivalent dose rate is about 100-fold greater.

The total natural radiation exposure in Germany – or more precisely, the effective dose of an individual in Germany – is 2.1 millisieverts per year on average. Depending on the individual’s place of residence and their dietary and living habits, this value ranges from 1 to 10 millisieverts.

In medical diagnostics, radiation exposure can be particularly high in complex X-ray examinations. A single computer tomography scan can produce about as much radiation exposure as natural radiation exposure over 10–50 years.

What does an increase in radioactivity readings mean?

Radioactivity readings are often subject to natural fluctuationsSchwankungen

An increase in measured values can essentially mean an increase in radiation intensity.

However, radioactivity readings are often subject to natural fluctuations. In the case of current measured values (e.g. from probes of the ODL measuring network), short-term increases in the local dose rate of two- to three-fold the normal values can occur.

Such increases in radiation intensity can be caused by various weather influences such as rain or wind and do not pose a danger.

At what measured values does it become dangerous?

Consequences of acute radiation exposure

Whilst it is difficult to establish precise cause and effect relationships for the slow and long-term uptake of low doses of radiation, the effects of severe radiological accidents with large uptakes of radiation are known and well investigated.

Thus, severe tissue damage – and even death – is inevitable with the short-term intake of a single dose of a few thousand millisieverts of ionising radiation. However, such a high dose can be reached only in exceptional radiological situations with massive releases of radioactivity in the immediate vicinity of human settlements or in irradiation facilities. This was the case for the operating staff and fire-fighters in the initial phase of the reactor disaster in Chornobyl.

Strict limits for the handling of radioactivity and for the general public are laid down in legal regulations such as EU regulation 96/29/EURATOM and the German Radiation Protection Act: Adults exposed to ionising radiation through their occupational activities may not absorb more than 100 millisieverts in five years with no more than 50 millisieverts in any single year. This corresponds to about 20-fold the natural radiation exposure. For all other persons, a maximum of 1 millisieverts equivalent dose per year may be absorbed through technical installations or artificially introduced radioactive substances.