What types of radioactive chemicals are there

radioactivity

The title of this article is ambiguous. For the album of the same name by the band Kraftwerk, see radio activity.
DIN 4844-2 warning sign D-W005 Warning of radioactive substances or ionizing radiation (also on shielding containers)(1)

radioactivity (from Latin radius, 'Ray'; Radiation activity), radioactive decay or Nuclear disintegration is the property of unstable atomic nuclei to transform spontaneously with the release of energy. In almost all cases, the released energy is emitted as ionizing radiation, namely high-energy particles and / or gamma radiation.

The term itself (French radioactivity) was minted by Marie Curie in 1898.

Definitions and terms: radioactive substance, decay, radiation

Radioactive substance
Colloquially, occasionally also in technical language, the word 'radioactivity' is also used for radioactive substance second hand.
Radioactive decay
The historical term Decay aptly describes the decrease in quantity of the starting material according to the law of decay. However, this simplified view does not fully characterize the process. On the level of the atoms there is rather one that is defined by law conversion of the respective individual atomic nucleus instead of a certain other atomic nucleus; This individual process is also called disintegration in technical terms.
Radioactive radiation
The terms radioactivity and radiation Often confused with each other or used synonymously: Radioactivity is often not the material but the radiation emitted (emission of particles or energy) - or even ionizing radiation from non-radioactive sources - meant. Conversely, z. For example, when reporting incidents, the term “leaked radiation” is often used when referring to unintentionally released radioactive substances (emitters). The frequently used phrase "radioactive radiation" is pleonastic, da radioactive already radiant means; what is meant here is the Radiation of radioactive substances.

Basics

Every atomic nucleus is either stable or radioactive in its basic state. The term nuclide describes a type of atom with the same nucleus. A radioactive nuclide is called radionuclide for short.

According to current knowledge, some nuclides that used to be considered stable are radionuclides with very long half-lives in the range of up to a few trillion years, for example 152Gd, 174Hf and 180W.[1] Because of these very long half-lives, the correspondingly low level of radioactivity can only be detected with great effort.

Exponential decrease over time

Radioactive decay is not a deterministic process. The time of decay of the individual atomic nucleus is completely random. However, there is a fixed value of for every radionuclide Probability of decay per unit of time; In the case of macroscopic amounts of substance, this means that the decrease in the amount of the substance follows an exponential law to a good approximation. The probability of decay can also be expressed in terms of the half-life, i.e. the period of time after which, on average, half of the atomic nuclei of an initial set have decayed. There are radioactive half-lives ranging from fractions of a second to billions of years. Nuclides, for example, are very long-lived 238U, 235U, thorium232Th and potassium40K. The shorter the half-life, the greater the activity for a given amount of substance.

isotope Half-life specific activity
131I.8 days 4,600,000,000,000 Bq / mg
137Cs30 years 3,300,000,000 Bq / mg
239Pooh24,110 years 2,307,900 Bq / mg
235U703,800,000 years 80 Bq / mg
238U 4,468,000,000 years 12 Bq / mg
232Th14,050,000,000 years 4 Bq / mg

Statistical fluctuations

The activity is the expected value of the number of decays per unit of time. The actual number of decays observed in a fixed time interval randomly fluctuates around the expected value; the frequency with which the individual possible numbers occur follows the Poisson distribution. (If you want to observe the fluctuation by repeated measurements, the half-life must be long compared to the selected duration of the observation interval so that the conditions remain constant.)

If the average number is sufficiently large, the Poisson distribution can be approximated by the Gaussian distribution, which is more convenient for calculations.

history

Alpha radiation is completely absorbed by a sheet of paper, beta radiation is completely absorbed by a metal sheet a few mm thick; to sufficiently attenuate gamma radiation, a thicker layer made of a material with the highest possible density is required (see shielding (radiation)).

In 1896, while trying to explain the X-rays that had just been found by fluorescence, Antoine Henri Becquerel discovered that uranium salt was able to blacken photographic plates. However, the uranium sample was able to do this without pre-exposure, which ruled out fluorescence as the cause. As he later showed, this new radiation could penetrate opaque materials and ionize air without being influenced by temperature changes or chemical treatments of the sample. Marie and Pierre Curie found further radioactive elements in 1898 in thorium as well as two new, much more strongly radiating elements, which they named radium and polonium.

By examining the penetration capacity, Ernest Rutherford succeeded in 1899 in distinguishing two components of radiation. Stefan Meyer and Egon Schweidler as well as Friedrich Giesel were able to show in the same year that these are deflected in different directions in magnetic fields. A third component, which could not be distracted by magnetic fields and which had a very high penetration capacity, was discovered in 1900 by Paul Villard. Rutherford coined the terms alpha, beta and gamma radiation for the three types of radiation. By 1909 it had been shown that alpha radiation consists of helium nuclei and beta radiation consists of electrons. The assumption that gamma radiation is an electromagnetic wave could only be confirmed in 1914 by Rutherford and Edward Andrade.

As early as 1903 - six years before the evidence of atomic nuclei - Rutherford and Frederick Soddy developed a hypothesis according to which radioactivity was linked to the conversion of elements. Based on this, Kasimir Fajans and Frederick Soddy formulated the so-called in 1913 radioactive displacement theorems. These describe the change in mass and atomic number during alpha and beta decay, which means that the natural decay series could be explained as a step-by-step sequence of these decay processes.

In 1933 Irène and Frédéric Joliot-Curie succeeded for the first time in artificially generating radioactive elements. By bombarding samples with α-particles, they were able to produce new isotopes that do not occur in nature due to their short half-lives. During their experiments in 1934 they discovered a new type of beta decay in which positrons are emitted instead of electrons. Since then, a distinction has been made between β+- and β-Radiation.

Types of decay

Different types of decay of a radionuclide in the representation of the nuclide map. Vertical: atomic number (proton number) Z, horizontal: neutron number N

There are three main types of decay: alpha, beta and gamma decay. (Since it was not known at the time of their discovery which phenomenon was involved, the 3 types of radiation were simply designated in the order of increasing penetration power with the first 3 letters of the Greek alphabet.) During alpha decay, they are reduced by the emission of an alpha -Particle, consisting of two protons and two neutrons, the atomic number of the atomic nucleus by 2 and the mass number by 4. During beta decay, an electron or positron is emitted from the atomic nucleus; a neutron present in the atomic nucleus transforms into a proton or vice versa. This changes the ordinal number by 1, the mass number remains the same. A gamma decay usually occurs as a direct consequence of an alpha or beta decay (exceptions are the decays of the core isomers). The mass and atomic number remain the same, but the excitation state of the nucleus changes.

Some nuclides can decay in two or more different ways (see decay channel).

A nuclide map shows as a graphic overview all stable and unstable nuclides including their possible types of decay and associated half-lives.

An atomic nucleus is then stable and cannot continue to decay without external influence if there is no type of decay that would lead to an energetically lower state. In the element hydrogen, a single proton and the deuteron are stable nuclei. In the case of helium, the stable isotope helium-3 contains two protons and one neutron, the stable helium-4 contains two protons and two neutrons. With lithium and all heavier elements, at least as many neutrons as protons have to form the nucleus in order for the nucleus to be stable, and with heavier nuclei the neutrons predominate more and more. From the mass number 209 onwards there are only unstable atomic nuclei. Due to the effect of particle radiation, especially neutron radiation (see Neutron activation), stable atomic nuclei can be converted into unstable atomic nuclei.

The types of decays alpha, beta and gamma decay were the first to be discovered and are by far the most common types of transformation. Later, other types of decay were found that could no longer be counted among these three classic types.

The large number of existing decays can be divided into three categories:

Decays with emission of nucleons
many radioactive nuclei are transformed with the emission of nucleons, i.e. protons, neutrons or even light nuclei. The most prominent example is that Alpha decay. Here, the mother core splits off a helium core. The emission of single neutrons or protons or whole carbon nuclei occurs less frequently. All decays with emission of nucleons are mediated by the strong interaction together with the electromagnetic interaction.
Beta decays
if electrons (or their antiparticles) are involved in a decay, one speaks of a beta decay. There are a number of such processes. An electron does not always have to be created as a product, as is the case with, for example Electron capture. All beta decays are processes of weak interaction.
Transition between states of one and the same nucleus
in this case no matter particles are emitted. Correspondingly, the nucleus does not change into another either; it just gives off excess energy. This can be used as a Gamma radiation become free or are given to an electron in the atomic shell (internal conversion). These are processes of electromagnetic interaction.

Overview

Decay mode participating particles Daughter core
Decays with emission of nucleons
Alpha decay An alpha particle (A.=4, Z= 2) is sent. (A.−4, Z−2)
Proton emission A proton is sent out. (A.−1, Z−1)
Neutron emission A neutron is sent out. (A.−1, Z)
Double proton emission Two protons are emitted at the same time. (A.−2, Z−2)
Spontaneous split The nucleus breaks down into two or more smaller nuclei and usually 2 or 3 neutrons.
Cluster disintegration The core sends a smaller core (typically 6% to 20% of the original size) A.c, Zc out.
At A.c=4, Zc= 2 it is an alpha decay.
(A.A.c, ZZc) + (A.c,Zc)
Various beta decays
Beta-minus decay A nucleus sends out an electron and an antineutrino. (A., Z+1)
Beta plus decay Positron emission; A nucleus sends out a positron and a neutrino. (A., Z−1)
Electron capture A nucleus absorbs an electron from the atomic shell and emits a neutrino. The daughter nucleus remains in an excited, unstable state. (A., Z−1)
Double beta decay A nucleus sends out two electrons and two antineutrinos. (A., Z+2)
Double electron capture A nucleus absorbs two electrons from the atomic shell and emits two neutrinos. The daughter nucleus remains in an excited, unstable state. (A., Z−2)
Electron capture with positron emission A nucleus absorbs an electron from the atomic shell and emits a positron and two neutrinos. (A., Z−2)
Double positron emission Double positron emission; A nucleus sends out two positrons and two neutrinos. (A., Z−2)
Transitions between states of the same nucleus
Gamma decay An excited nucleus emits a high-energy photon (gamma quantum). (A., Z)
Inner conversion An excited nucleus transfers energy to a shell electron, which leaves the atom. (A., Z)

Alpha decay

Alpha decay occurs mainly in heavier and relatively low-neutron nuclides. A helium-4 nucleus, called an alpha particle in this case, leaves the mother nucleus at a speed of a few percent of the speed of light. This is possible despite the high potential barrier due to the tunnel effect. The residual nucleus, also called the recoil nucleus or daughter nucleus, has after the process a nucleon number reduced by four and a nuclear charge number reduced by two.

The general formula for alpha decay is

$ {} ^ A_Z \ mathrm {X} \ to {} ^ {A-4} _ {Z-2} \ mathrm {Y} + ^ {4} _ {2} \ mathrm {He} $
The mother nucleus X with nucleon number A and proton number Z decays with the emission of an alpha particle
in the daughter nucleus Y with a 4 reduced number of nucleons and 2 reduced number of protons.

An example of alpha decay is the decay of uranium-238 into thorium-234:

$ {} ^ {238} \ mathrm U \ to {} ^ {234} \ mathrm {Th} + \ alpha $

Beta decay

If there is an unfavorable neutrons to proton ratio, beta decay usually occurs.

β-Decay

At the β-Decay (beta-minus-decay) a neutron is converted into a proton in the nucleus and a high-energy electron and an electron antineutrino are emitted. The nucleon number of the nucleus does not change, its atomic number increases by one.

The general reaction equation for beta-minus decay is

$ {} ^ {A} _ {Z} \ mathrm {X} \ to {} ^ {A} _ {Z + 1} \ mathrm {Y} + \ mathrm {e} ^ - + \ overline \ nu_ \ mathrm {e} $
The mother nucleus X with nucleon number A and proton number Z decays with emission of an electron
and an anti-electron neutrino in the daughter nucleus Y with the same number of nucleons and increased by 1
Proton number.

An example of the β-Decay is the decay of carbon-14 into the stable isotope nitrogen-14:

$ {} ^ {14} _ {\ 6} \ mathrm C \ to {} ^ {14} _ {\ 7} \ mathrm N + e ^ - + \ overline \ nu_ \ mathrm {e} $

Through a few meters of air or z. B. a plexiglass layer can completely shield the beta radiation. The range of the radiation depends on its energy and the material used for shielding.

The neutrino radiation is very difficult to detect (and completely harmless), since neutrinos are only subject to the weak interaction. A stream of neutrinos traverses z. B. the entire earth almost unimpaired.

β+-Decay

At the β+-Decay, a proton is converted into a neutron and a high-energy positron in the nucleus and an electron-neutrino is emitted. The nucleon number of the nucleus does not change, its atomic number is reduced by one.

The general reaction equation for beta plus decay is

$ {} ^ {A} _ {Z} \ mathrm {X} \ to {} ^ {A} _ {Z-1} \ mathrm {Y} + \ mathrm {e} ^ + + \ nu_ \ mathrm {e } $
The mother nucleus X with nucleon number A and proton number Z decays with the emission of a positron
and an electron neutrino in the daughter nucleus Y with the same number of nucleons and one less number of protons.

An example of the β+-Decay is the breakdown of nitrogen-13 into carbon-13:

$ {} ^ {13} _ {\ 7} \ mathrm N \ to {} ^ {13} _ {\ 6} \ mathrm C + e ^ + + \ nu_e $

Electron capture

Another way of converting a proton into a neutron is to “pull” an electron from the atomic shell into the nucleus, which is known as electron capture. electron capture, EC for short), also called ε-decay. After the name of the typically affected electron shell, the K shell, electron capture is also known as K capture designated. The proton of the nucleus is converted into a neutron and an electron neutrino is emitted.

In this conversion mechanism, the nucleus is subject to the same changes as in the $ \ beta ^ {+} $ decay, the number of nucleons remains unchanged, the ordinal number is reduced by one. The electron capture therefore competes with the $ \ beta ^ {+} $ decay and is also seen as a variant of the beta decay. Since the $ \ beta ^ {+} $ decay has to generate the energy for the emitted positron, the $ \ beta ^ {+} $ decay is energetically not an option for every nuclide that decays with electron capture.Since the trapped electron mostly comes from the innermost electron shell, a space becomes free in this and electrons from the outer shells move up, with characteristic X-rays being emitted.

In general, the formula for electron capture is

$ {} ^ {A} _ {Z} \ mathrm {X} + \ mathrm {e} ^ - \ to {} ^ {A} _ {Z-1} \ mathrm {Y} + \ nu_ \ mathrm {e } $
The mother nucleus X captures an electron from the atomic shell and transforms itself with the emission of an electron neutrino
into the daughter nucleus with the same number of nucleons and one less number of protons.

An example is the decay of nickel-59 to cobalt-59:

$ {} ^ {59} _ {28} \ mathrm {Ni} + e ^ - \ to {} ^ {59} _ {27} \ mathrm {Co} + \ nu_e $

Double electron capture: With some nuclei, simple electron capture is not energetically possible, but they can be transformed by capturing two electrons at the same time. The half-lives of such conversions are typically very long and have only recently been demonstrated.

An example is the decay of xenon-124 to tellurium-124:

$ {} ^ {124} _ {\ 54} \ mathrm {Xe} + 2e ^ - \ to {} ^ {124} _ {\ 52} \ mathrm {Te} + 2 \ nu_e $

Double beta decay

With some nuclei, a simple beta decay is not energetically possible, but they can decay while emitting two electrons. Such decays typically have very long half-lives and have only recently been demonstrated.

Example: $ {} ^ {96} _ {40} \ mathrm {Zr} \ to {} ^ {96} _ {42} \ mathrm {Mon} + 2 e ^ - + 2 \ overline \ nu_ \ mathrm {e } $

So far, the question of whether two neutrinos are always emitted in a double beta decay or whether a neutrino-free double beta decay also occurs has not been answered. If the neutrinoless case could be proven, the neutrinos would have annihilated each other, which would mean that neutrinos are their own antiparticles. That would make them so-called Majorana particles.

Gamma decay

A γ decay (γ is the small Greek letter gamma) is possible if the atomic nucleus is in an energetically excited state after decay. During the transition to an energetically lower state, the atomic nucleus emits energy by emitting high-frequency electromagnetic radiation, so-called γ radiation.

The emission of gamma radiation does not change the number of neutrons and protons of the emitting nucleus, there is only a transition between two excited nuclear states or an excited nuclear state and the ground state. This usually happens immediately after a beta or alpha decay. The term gamma “decay” is somewhat misleading in this respect, but it is still a common nomenclature.

The general equation for gamma decay is

$ {} ^ {A} _ {Z} \ mathrm {X} ^ {*} \ to {} ^ {A} _ {Z} \ mathrm {X} + \ gamma $
The excited nucleus X is excited by emitting a gamma quantum. Mother and daughter core
agree

A well-known example is the emission of gamma radiation through a nickel-60 core, which (mostly) is caused by beta decay of a cobalt-60 core:

$ {} ^ {60} _ {28} \ mathrm {Ni} ^ {*} \ to {} ^ {60} _ {28} \ mathrm {Ni} + {\ gamma} $

The decay scheme of this process is shown in the graphic on the right. 60Co, an isotope with many practical uses, is a beta emitter with a half-life of 5.26 years. It decays to an excited state of nickel-60, which almost immediately (<1 ps) decays to the ground state by emitting two gamma quanta.

In the practical applications of Co-60 and many other radionuclides, it is very often only about this gamma radiation; the alpha or beta radiation is shielded in these cases by the housing of the radioactive preparation and only the gamma radiation penetrates to the outside.

Although the gamma radiation comes from the daughter nuclide of the alpha or beta decay, it is always linguistically assigned to the parent nuclide, so it is referred to as the "Cobalt-60 gamma emitter" etc., because the only practically usable source of this gamma radiation is a Co-60 preparation.

However, the excited state may be an isomer; that is, that it has a sufficiently long half-life to enable practical use of this gamma-ray source separately from its generation, as in the case of technetium-99:

$ {} ^ {99m} _ {43} \ mathrm {Tc} \ to {} ^ {99} _ {43} \ mathrm {Tc} + {\ gamma} $

This technetium isotope with a half-life of six hours is used in medical diagnostics.

In order to shield from γ radiation, concrete or lead plates several meters thick may be necessary, because it has no specific range in matter, but is only attenuated exponentially. There is therefore a half-value thickness that is dependent on the gamma energy for each shielding material. $ \ gamma $ radiation, like light, is electromagnetic radiation, but its quantum is much more energetic and therefore lies far outside the spectrum that is visible to the human eye.

Inner conversion

The energy released during the transition of an atomic nucleus to an energetically lower state can also be given to an electron in the atomic shell. This process is called internal conversion. In contrast to $ \ beta $ particles, conversion electrons are monoenergetic.

$ {} ^ {A} _ {Z} \ mathrm {X} ^ {*} \ to {} ^ {A} _ {Z} \ mathrm {X} + \ mathrm {e} ^ - $
The excited nucleus X is de-excited. The energy released is transferred to an electron in the atomic shell.

Radioactive decays are processes that only take place in the atomic nucleus. In the case of internal conversion, the energy released during the conversion is transferred to an electron in the atomic shell. After the decay, there is no negative charge and a positive ion remains.

Other types of decay

Spontaneous split

Spontaneous fission is another radioactive conversion process that occurs in particularly heavy nuclei. The atomic nucleus breaks up into two or more fragments. As a rule, two medium-weight daughter nuclei are created and two or three neutrons are released. A large number of different pairs of daughter nuclei are possible, but the sum of the atomic numbers and the sum of the mass numbers are always the same as those of the original nucleus. Examples:

The naturally occurring uranium isotopes also decay to a small extent through spontaneous fission.

Spontaneous nucleon emission

In the case of nuclei with a particularly high or particularly low number of neutrons, it can become spontaneous nucleon emission, so proton or neutron emission come. Atomic nuclei with a very high excess of protons can emit a proton, while atomic nuclei with a high excess of neutrons can release neutrons.

For example, helium-5 spontaneously emits a neutron:

5Hey → 4He + 1n

Boron-9, on the other hand, splits off a proton to compensate for the excess: 9B → 8Be + 1p

Cluster disintegration

Instead of individual nucleons or helium-4 nuclei, larger atomic nuclei are also emitted in very rare cases. Examples:

Two proton decay

In the case of an extreme excess of protons (such as iron-45), two-proton decay can occur, in which even two protons are emitted at the same time.

$ {} ^ {45} _ {26} \ mathrm {Fe} \ to {} ^ {43} _ {24} \ mathrm {Cr} + 2 \, {} ^ {1} _ {1} \ mathrm { p} $

Decay series

The product of a decay can be stable or, in turn, radioactive. In the latter case, a sequence of radioactive decays will take place until finally there is only one stable nuclide as the end product. This sequence of radioactive decays is called Decay series or Chain of decay.

For example, the isotope uranium-238 decays with the emission of an alpha particle into thorium-234, this then converts through beta decay into protactinium-234, which is again unstable and so on. After a total of 14 or 15 decays, this series of decays ends with the stable core lead-206. Since some nuclei can decay in different ways (see decay channel), several branches of the same decay series can start from a parent nucleus. For example, about 64% of bismuth-212 changes to polonium-212 through beta decay, and about 36% through alpha decay to thallium-208.

In this way, an originally pure sample of a radionuclide can turn into a mixture of different radionuclides over time. Long-lived nuclides accumulate more than short-lived ones.

Formation and occurrence of radioactivity

From a physical point of view, the distinction between natural and artificial radioactivity is arbitrary. However, there are considerable differences in the isotopic composition and in the half-lives of the artificially produced or natural isotopes.

Natural radioactivity

As far as we know today, only the lightest nuclides were initially formed when the universe was formed, mainly hydrogen and helium nuclei, and lithium and beryllium on a comparatively small scale. All heavier nuclides originate from complex superimpositions of fusion processes as they take place in the stars (nucleosynthesis). Such nuclides, which were already present in the material from which the earth was formed and which are still present today due to their long half-life, are referred to as primordial Nuclides. They include B. Potassium-40, which is always contained in the human body, and uranium, which is important as a nuclear fuel. Other radionuclides arise indirectly as decay products of the radioactive decay series that are constantly being reproduced, for example radon, a gas that escapes everywhere from the earth. These nuclides are known as radiogenic. Further, so-called cosmogenic Radionuclides are continuously generated in the atmosphere through nuclear reactions with cosmic rays. One of them is z. B. Carbon-14, which, like potassium, enters all organisms through metabolism.

The radiation from the ubiquitous natural radionuclides is known as terrestrial radiation.

Artificial radioactivity

Radionuclides are inevitably formed during nuclear fission, for example when generating energy in nuclear reactors. The unwanted isotopes are colloquially referred to as radioactive waste. In addition to fission products, these are also products of neutron capture. Fission products are also formed in nuclear weapon explosions and were released into the atmosphere during weapon tests.

Purposely, for medical, technical or research purposes, radionuclides are produced by neutron capture in research reactors. Some fission products generated in nuclear reactors are also made usable in this way. However, the product nuclides from nuclear fission and neutron capture are always neutron-rich and therefore mostly beta-minus emitters. Beta-plus radiating nuclides, which are used, for example, for positron emission tomography, have to be produced using particle accelerators (mostly cyclotrons).

Sizes and units of measure

activity

Activity is the number of decay events per unit of time that occur in a sample of a radioactive or radioactively contaminated substance. The activity is usually given in the SI unit Becquerel (Bq), one Becquerel corresponds to one decay per second.

Radiation dose

The quantities and units of measurement relating to the effects of ionizing radiation (from radioactive or other sources) include:

Radioactivity measuring devices

In nuclear physics there is a large number of detectors for the detection and measurement of the most diverse particle beams, each of which is suitable for the investigation of certain types of radiation. A well-known example is the Geiger counter. Ionization chambers and cloud chambers can be used to detect alpha, beta and gamma radiation, scintillation counters (coupled with photomultipliers) and semiconductor detectors are used to detect beta and gamma rays. For radiation protection, various dosimeters are used to measure radiation exposure.

The very first measurement that gave a quantitative statement about the radiation was carried out by Pierre Curie and Marie Curie with the help of an electroscope. However, this did not directly measure the radiation, but the decrease in an electrical charge due to the conductivity of the air caused by the ionization.

Applications

Technical application

Radionuclide batteries are used in space travel for power supply and radionuclide heating elements for heating. Beyond Jupiter's orbit, the radiation from the distant sun is no longer sufficient[2]in order to cover the energy requirements of the probes with solar cells of practicable size. Strong radiation belts such as those surrounding Jupiter can also make the use of solar cells impossible. In the USSR, very powerful radionuclide batteries were used 90Strontium fill used to power lighthouses and radio beacons in the Arctic Circle.

Important applications that exploit the radioactivity of substances are the age determination of objects and material testing.

In archeology, art history, geology and paleoclimatology measurements of the concentration of radioactive isotopes are used to determine the age, e.g. B. radiocarbon dating (radiocarbon dating).

A technical application is the thickness measurement and material testing by means of radiography. A material is irradiated with gamma rays and a counter determines the average density with a known layer thickness or, conversely, the layer thickness with a known density based on the penetrating rays and the law of absorption. The radiation can also create an image on an X-ray film behind the material layer. Radiographic testing is used in this form for materials.

Radiometric level measurements in large containers with bulk material or granules are also carried out with gamma radiation from one container wall to the other.

Further applications are element analysis (see gamma spectroscopy) and precision measurements in chemical analysis (see Mössbauer effect). Furthermore, lightning rods with tips made of radioactive material were occasionally installed, although their effectiveness could never be proven.

Medical application

The use of unsealed radioactive substances on humans is the subject of nuclear medicine.

Scintigraphy is mostly used in nuclear medicine diagnostics. Small amounts of a γ-emitting substance (tracer) are used (“applied”) to the patient, for example injected into a vein or inhaled. The radiation emanating from the tracer is registered outside the body by a gamma camera based on scintillation detectors and produces a two-dimensional image. Modern further developments of the method allow three-dimensional representations by means of computed tomography (Single Photon Emission Computed Tomography, SPECT); Another imaging method in nuclear medicine that also provides three-dimensional images is positron emission tomography (PET). Certain laboratory tests can also be carried out with radioactive substances, for example the radioimmunoassay.

Pure or predominantly β-emitters are used in nuclear medicine therapy. The most common areas of application are radioiodine therapy for benign and malignant diseases of the thyroid gland, radiosynoviorthesis for certain joint diseases and radionuclide treatment for pain relief in bone metastases.

Dangerousness

With regard to the danger posed by radioactivity, a distinction must be made between various risks:

  • Radiation exposure as a long-range effect (see alsoDose conversion factor)
  • Contamination (contamination) with radioactive material, which under certain circumstances can lead to long-term irradiation, e.g. B. with contamination of the skin
  • Incorporation (uptake) of radioactive substances into the body through inhalation (inhalation) or eating / drinking (Ingestion).

These terms are often confused in reporting and the public. Accordingly, for example, the term “irradiated” is incorrectly used instead contaminated used; radiation means - analogously to combustion - Significant damage or injury caused by radiation.

It is not the radioactivity per se, but the ionizing radiation emitted by it that is responsible for the sometimes dangerous biological effect.

Warning symbols

(1) New warning sign directly on dangerous radioactive emitters

Because the radiation warning sign used so far (, also Trefoil called, in Unicode at code position U + 2622) was often not recognized as a warning of strong radioactive emitters, fatal accidents have occurred, especially in developing countries, because people removed a strongly radiating nuclide from its shielding (for example the Goiânia Accident in Brazil in 1987). Therefore, on February 15, 2007, the IAEA announced that radiators of radiation categories 1, 2 and 3[3] a new, more conspicuous warning sign is to be affixed. With the help of more meaningful symbols, this warns of the deadly danger of radioactive radiation and prompts people to flee. Only the old symbol should still be attached to the container itself, since it shields the radiation to such an extent that it does not pose any immediate danger. Standardization as ISO standard 21482 the new warning sign for dangerous radiation sources should be introduced as quickly as possible and internationally binding. In Germany, the warning label has neither been adopted in a national standard nor included in the accident prevention regulations. It is also not included in the draft of the new version of DIN 4844-2, which regulates warning signs. In Austria it is standardized in OENORM ISO 21482.

The labeling should not be changed for weak radiation sources.[4] The development of symbols to warn posterity about radioactive dangers is the subject of atomic semiotics.

See also

literature

  • Werner Stolz: Radioactivity. Basics, measurement, applications. 5th edition. Teubner, Wiesbaden 2005, ISBN 3-519-53022-8.
  • Bogdan Povh, K. Rith, C. Scholz, Zetsche: Particles and nuclei. An introduction to the physical concepts. 7th edition. Springer, Berlin / Heidelberg 2006, ISBN 978-3540366850.
  • Klaus Bethge, Gertrud Walter, Bernhard Wiedemann: Nuclear physics. 2nd Edition. Springer, Berlin / Heidelberg 2001, ISBN 3-540-41444-4.
  • Hanno Krieger: Basics of radiation physics and radiation protection. 2nd Edition. Teubner, Wiesbaden 2007, ISBN 978-3835101999
  • IAEA Safety Glossary. Terminology Used in Nuclear Safety and Radiation Protection. IAEA Publications, Vienna 2007, ISBN 92-0-100707-8.
  • Michael G. Stabin: Radiation Protection and Dosimetry. An Introduction to Health Physics. Springer, 2007, ISBN 978-0387499826.
  • Glenn Knoll: Radiation Detection and Measurement. 3. Edition. Wiley & Sons, New York 2007, ISBN 978-0471073383.

Web links

Individual evidence

  1. ↑ Interactive nuclide map
  2. ↑ Bernd Leitenberger: The radioisotope elements on board space probes. Retrieved March 24, 2011.
  3. ^ New Symbol Launched to Warn Public About Radiation Dangers
  4. ↑ Flash Video of the IAEA