Radioactivity

alarm flag:
„Warning of radioactive substances or ionizing rays “

under radioactivity (of lat. radius, jet) or radioactive decay understands one the characteristic of unstable atomic nuclei to be converted spontaneously under delivery of energy. The freed energy becomes in form of ionizing radiation, particles i.e. high-energy and/or gamma radiation, delivered.

Handling or specializedlinguistically the word radioactivity is used also somewhat inaccurately for “radioactive substance”. In particular in the public discussion is frequently also the delivered radiation or even ionizing radiation from other sourcesmeant, if from radioactivity the speech is.

Table of contents

bases

with mostKinds of decay (S. down) the nuclear charge number ( ordinal number) changes - thus another chemical element develops -, with some only the mass number. Besides there are transitions, with which only the excitation state of the core changes (transition between different isomers the same nuclide). The strength of the radioactivity is described by physical dimension activity and shortened indicated in the unit Becquerel, Bq. 1 Bq stands for on the average a decay per second.

Radioactive decay is not a deterministic process.The point of decay time is absolutely coincidental. However the probability of decay per time unit is a fixed value for each nuclide, which can be described also by the radioactive half-life. The radioactive half-life is average the period, after that half of the unstable atomic nuclei of oneDisintegrated to quantity. It knows only fractions of a second, in addition, some billions years amount to. Such long-lived nuclides are for example uranium -238, Uran-235, thorium -232 and potassium -40. The more briefly the radioactive half-life, the more largely is the activity of a given substance quantity. Becomes mathematicalthe decay by the Zerfallsgesetz described.

Not only the time of the decay is coincidental, but perhaps also the kind of the decay. Can disintegrate to 212 bismuth for example with different in each case probability in three different kinds. A nuclide map shows all nuclideswith kinds and portions to the possible disintegrate and the radioactive half-lives.

An atomic nucleus is then stable and can disintegrate not further on its part, if there is no radioactive decay, which leads to an energetically lower condition. With the hydrogen is thisThe individual proton was entitled as atomic nucleus, with the helium contains the sturdy isotope to Helium-3 two protons and a neutron. With the lithium and all heavier elements at least the same as many neutrons must form as protons the core, and with heavier cores always outweighmore the neutrons. Starting from a certain mass number all atomic nuclei become unstable. By effect of particle radiation (in particular neutron radiation or neutron activation) sturdy atomic nuclei can be converted into other one, unstable atomic nuclei into nuclear reactions.

history

1896 discovered Antoine Henri Becquerelthat containing materials a radiation send uranium. This is able it to penetrate obscure materials. It determined this, when it found wrapped photographic plates in paper blackened. It stated besides that this radiation is not uniform, but differentComponents contained knows:

  1. a component with high penetrating power, those in the electrical field is not diverted (gamma radiation)
  2. a component, those in the electrical field to the positive terminal is diverted and a middle penetrating power has (beta-ray emission)
  3. a component, inelectrical field to the negative pole is diverted and a small penetrating power has (alpha radiation).

The persons substantially taken part, who researched in the area of the further clearing-up of the natural radioactivity, were Marie curie, Pierre curie and Ernest Rutherford.

kinds of decay

 Verschiedene Zerfallsarten eines Radionuklids in der Darstellung der Nuklidkarte. Senkrecht: Ordnungszahl, waagerecht: Neutronenzahl

different kinds of decay of a radionuclide in the representation of the nuclide map. Perpendicularly: Ordinal number, horizontally: Neutron number

alpha decay

is very heavy the atomic nucleus, contains thus many protons and neutrons, can the strong reciprocal effect the parent nucleus no longertogether hold and it comes to the alpha decay. The freed energy is emitted as ionic beam in the form of helium -4-Kernen with a speed of under 0,1 C. This behavior is possible despite the high Potentialbarriere due to the tunnel effect. The remainder core, alsoMentioned, the nuclear charge number reduces rückstosskern or daughter core by two with this procedure its nucleon number by four and. The alpha radiation has a particularly high harmful effect on living fabric by its ionization potential, however thereby in air a range of only fewCentimeters and paper can become completely shielded by a simple sheet. Dangerous alpha emitters are on the other hand than aerosols in air, if these are inhaled.

Example: <math> {} ^ {238} \ mathrm U \ tons {} ^ {234} \ mathrm {Th} + \ alpha </math>

beta decay

If an unfavorable relationshipfrom neutrons to protons, normally occurs beta decay exists.

Becomes with <math> \ beta^< /math> - decay converted in the core a neutron into a proton and a high-energy electron as well as an electron antineutrino emits. The nucleon number of the core does not change thereby, its ordinal numberincreases by one.

Example: <math> {} ^ {14} _6 \ mathrm C \ tons {} ^ {14} _7 \ mathrm N + e^ + \ overline {\ nu_e} </math>

With <math> \ beta^+< /math> - decay is converted in the core a proton into a neutron and a high-energy positron and an electron neutrino is emitted. The nucleon number of theCore does not change thereby, its ordinal number is reduced around one.

Example: <math> {} ^ {13} _7 \ mathrm N \ tons {} ^ {13} _6 \ mathrm C + e^+ + \ nu_e </math>

By some meters of air or a thin layer of metal (e.g. Aluminum) can be shielded the beta-ray emission.

ThoseNeutrino radiation is very difficult to prove (and completely innocuous), since neutrinos are subject only to the weak reciprocal effect. A river of neutrinos e.g. crosses. the entire earth nearly unweakened.

electron capture, ε-decay

another possibility for the transformation of a proton ina neutron consists of it, an electron of the atomic shell into the core too „pulls”, the electron capture in such a way specified (English: electron capture, briefly EC). After the designation of the electron shell typically concerned, the K-bowl, the electron capture becomes also as no catchdesignated. The proton of the core is converted into a neutron, and emitted an electron neutrino.

With this transformation mechanism the core is subjected to the same changes as with <math> \ beta^ {+}< /math> - decay, the nucleon number remains unchanged, the ordinal number is reduced around one. Der Elektroneneinfang konkurriert daherwith <math> \ beta^ {+}< /math> - decay and is regarded also as a variant of the beta decay. There <math> \ beta^ {+}< /math> - decay the energy for the emitted positron to apply must, is not energetically applicable not for each nuclide, which disintegrates with electron capture, <math> \ beta^ {+}< /math> - decay. There the caughtElectron usually from the internal electron shell comes, in this a place free and electrons from the outside bowls will move after, whereby characteristic x-ray is emitted.

Example: <math> {} ^ {59} _ {28} \ mathrm {never} + e^ \ tons {} ^ {59} _ {27} \ mathrm {CO} + \ nu_e </math>

Double electron capture: With some cores a simple electron capture is energetically not possible, it can however by simultaneous capture of two electrons be converted. The radioactive half-lives of such transformations are typically very long and could be proven only in recent time.

Example: <math> {} ^ {124} _ {54}\ mathrm {Xe} + 2e^ \ tons {} ^ {124} _ {52} \ mathrm {width unit} + 2 \ nu_e </math>

double beta decay

with some cores is energetically not possible a simple beta decay, it can however under radiation of two electrons disintegrate. Such one disintegrates has typically for a very long timeRadioactive half-lives and were only proven in recent time. The question is still open whether with the double beta decay always two neutrinos are emitted, or whether also a neutrinoless double beta decay occurs.

Example: <math> {} ^ {96} _ {40} \ mathrm {Zr} \ tons {} ^ {96} _ {42} \ mathrm {Mo} +2 e^ + 2 \ overline {\ nu_e} </math>

gamma decay

A γ-decay (<math> \ gamma< /math> the small Greek letter is gamma) is possible, if the atomic nucleus is present after a decay in an energetically put on condition. During the transition to an energetically lower conditionthe atomic nucleus delivers energy by emission of high frequency electromagnetic radiation, so-called γ-radiation. The emission of gamma radiation does not change the neutrons - and proton number of the emitting core, it takes place only a transition between two core isomers. The designation “decay” servesthe nomenclature, is however here easy misleading, since it concerns no decay, but around a change in status in the atomic nucleus.

Example: <math> {} ^ {60m} _ {28} \ mathrm {never} \ tons {} ^ {60} _ {28} \ mathrm {never} + {\ gamma} </math>

For the screen of γ-radiation are perhaps meter-thickNecessarily, because it no certain range has concrete or Bleiplatten, but is only exponentially weakened in subject. There is therefore for each shielding material a half value thickness dependent on the gamma energy. <math> \ gamma< /math> - radiation is like light electromagnetic radiation, it is however muchmany more with high energy and lies thereby far outside of the spectrum visible for the human eye.

internal conversion

the freed energy with the transition of an atomic nucleus to an energetically lower isomer can be transferred also to an electron of the atomic shell.One calls this procedure internal conversion. Konversionselektronen are monoenergetic <contrary to> math \< beta> /math - particles.

spontaneous splitting

the spontaneous nuclear fission is a further radioactive process of transformation, which arises with particularly heavy cores. The atomic nucleus disintegrates into two or severalFragments. Usually two daughter cores equal in size and two or three neutrons develop. Examples:

<math> {} ^ {252} _ {98} \ mathrm {Cf} \ tons {} ^ {145} _ {56} \ mathrm {Ba} + {} ^ {104} _ {42} \ mathrm {Mo} + 3 {} ^ {1} _ {0} \ mathrm {n} </math> <math> {} ^ {252} _ {98} \ mathrm {Cf} \ tons {} ^ {128} _ {50} \ mathrm {SN}+ {} ^ {122} _ {48} \ mathrm {CD} + 2 {} ^ {1} _ {0} \ mathrm {n} </math>

Also the naturally occurring uranium isotopes disintegrate to a small part by spontaneous splitting.

<math> {} ^ {235} _ {92} \ mathrm {U} \ tons {} ^ {142} _ {56} \ mathrm {Ba} + {} ^ {90} _ {36} \ mathrm {Kr} + 3 {} ^ {1} _ {0} \ mathrm {n} </math> <math> {} ^ {238} _ {92} \ mathrm {U} \ tons {} ^ {140} _ {54} \ mathrm {Xe} + {} ^ {96} _ {38} \ mathrm {SR} + 2 {} ^ {1} _ {0} \ mathrm {n} </math>
<math> {} ^ {235} _ {92} \ mathrm {U} \ tons {} ^ {135} _ {53} \ mathrm {I} + {} ^ {98} _ {39} \ mathrm {Y} + 2 {} ^ {1} _ {0} \ mathrm {n} </math> <math> {} ^ {238} _ {92} \ mathrm {U} \ tons {} ^ {133} _ {51} \ mathrm{Self-service} + {} ^ {102} _ {41} \ mathrm {Nb} + 3 {} ^ {1} _ {0} \ mathrm {n} </math>

special kinds of decay

with very short-lived, artificially produced nuclides occur still further kinds of decay, those usually among the radioactivity to be ranked, physically however likewise do not run:

Work on []

Spontaneous nucleon emission

with cores with particularly high or particularly small neutron number can come it to spontaneous nucleon emission, thus proton or neutron emission. Atomic nuclei with very high proton surplus can deliver a proton, atomic nuclei with high Neutronenüberschuss can neutrons deliver.

5He → 4 He + 1 n

9 B → 8 + 1 p

cluster decay

place of individual nucleons or Helium-4-Kerne are emitted in very rare cases also larger atomic nuclei. Examples:

<math> {} ^ {247} _ {97} \ mathrm {UC} \ tons {} ^ {235} _ {91} \ mathrm{Pa} + {} ^ {12} _ {6} \ mathrm {C} </math> <math> {} ^ {247} _ {97} \ mathrm {UC} \ tons {} ^ {199} _ {77} \ mathrm {IR} + {} ^ {48} _ {20} \ mathrm {approx.} </math> <math> {} ^ {248} _ {98} \ mathrm {Cf} \ tons {} ^ {232} _ {90} \ mathrm {Th} + {} ^ {16} _ {8} \ mathrm {O} </math>

two-proton decay

with extreme proton surplus (like for examplewith 45 iron) can occur the two-proton decay, with which even two protons are radiated at the same time.

45 Fe → 43 CR + 2 1 p

sizes and units

activity

SI-UNIT old person units
activity Becquerel curie
Dose Gray wheel
equivalent dose Sievert rem

as activity one designates the number of decay events per time unit, which arises in a sample of a radioactive or radioactively contaminated material.

Becquerel Bq
1 Bq = 1 decay per second. SI-UNIT for the activity.
Curie Ci
became outdated to unit of radioactive activity.
1 Ci = 37 GBq = 3,7 · 10 10 Bq


  • the following sizes and units generally refer to ionizing radiation, from radioactive or other sources:

absorbed dose

as absorbed dose (short ) One designates dose from an illuminated object, e.g. Body fabric, over a load period area absorbed measure-specific energy quantity. It depends on the intensity of the irradiation, the absorption capacity of the illuminated material for the given kind of radiation and - energy and geometrical factors.

Gray Gy
(SI - unit of the absorbed dose). The Gray replaces the old designation “wheel” (“radiation absorbed box”).
1 Gray = 1 J/kg = 100 rad;
Wheel
radiation absorbed box; old unit of the absorbed dose, replaced by Gray (Gy).
1 rad = 0.01 Gray.

ion dose

the ion dose is expressed a measure for the strength of the ionization, by the set free charge per kilogram of the illuminated material.

C/kg (coulomb per kilogram)
SI-UNIT of the ion dose
Roentgen R
old unit of the ion dose, replaced by Coulomb/kg. 1 R = 2,58 · 10 -4 C/kg.

equivalent dose

the equivalent dose is a measure for the strength of the biological effect a certain dose. Equal large equivalent doses are thus independentof the kind of jet in their effect on humans comparably.

The equivalent dose arises as a result of multiplication of the absorbed dose (Gray) with a quality factor, the so-called. Relative biological effectiveness, which of the kind of radiation and - energy depends.

For <math> \ beta< /math> - and <math> \ gamma< /math> - radiation is the quality factor 1, i.e. 1 sports association = 1 Gy. For <math> \ alpha< /math> - radiation is it 20, which considers the increased reciprocal effect when penetrating fabric.

Sievert sports association
1 sports association = 1 J/kg. SI-UNIT of the equivalent dose; the old designation solves rem (X-ray equivalent one) off.
rem
X-ray equivalent one; old unit of the equivalent dose, replaced by Sievert (sports association)
to 1 rem = 0.01 J/kg = 0.01 sports association

applications

technical application

isotopic batteries apply frequently in space travel. In former timesused one it also for the enterprise of cardiac pacemakers. In isotopic batteries warmth, which develops during the absorption of the radiation of a radionuclide, is used technically. The temperature difference to the environment is converted here by a thermocouple into electricity (efficiency ≈5%). Hereat the most frequent <math> \ alpha< /math> are used - emitters, particularly plutonium -238.

Another technical application is the thickness measurement and material testing by means of radiography. Here a material (with gamma-rays) is illuminated and a counter determined due to the penetrating jets and the law of absorption the middleDensity (with well-known layer thickness) or the layer thickness with well-known density. The radiation can produce also on a radiographic film behind the material layer a picture. In this form the X-ray inspection is used with materials.

With clocks and other radioactive sources of light those becomesbright characteristic „luminescence “, which would add through by radioactive substances (tritium, in former times radium or promethium) to zinc sulfide crystals is reached, used.

Also lightning conductors with radioactive material were manufactured, whose effectiveness could be however never proven (Radioactive lightning conductor).

medical application

in the nuclear medicine one finds the Szintigraphie. Small quantities of a radioactive substance are injected into the body (usually <math> \ gamma< /math> - emitters). This material radiates then from the body, thus one becomesInvestigation possible. The jets are caught by a detector and represented by means of a gamma camera or a Computertomographen figurativy.

For each organ there are special radioactive connections. Thus one injects for example radioactive iodine, which deposits itself in the thyroid,in order to be able to examine it. (Due to the radiation dose this method today only to tumor the fight applied).

Further picture-giving procedures, which use radioactivity, are positron emission tomography (PET) and the single photon emission Computed Tomography (SPECT).

A further field of deployment is the radionuclide treatment to the Schmerzlinderung with Knochenmetastasen. Here within diseased bone ranges of the Metastase a radionuclide is enriched, which has a schmerzlindernde effect. These methods have also a certain risk, since also healthy fabric can be destroyed, which to an immune attenuationor malfunction of the marrow to lead can.

biological effect

humans knows ionizing radiation whether from radioactive or other sources, to notice not directly. For an effective radiation protection while handling radioactive materials therefore special care is and if necessary.the use of measuring instruments (dosimeters) necessarily.

Regarding the danger of radioactivity two different risks must be differentiated: 1. the radiation dose , 2. the contamination (pollution) with radioactive material, which can perhaps lead to for a long time continuous irradiation, in particulare.g. with contamination of the skin of persons or admission (incorporation) of radioactive substance into the body by inhalation (inhalation) or meal/drinking (Ingestion).

These two terms are often confounded in reporting and public. Becomes accordinglyfor example the term “radioactively contaminated” wrongly instead of contaminated uses; Radioactive contamination means - similar to the burn - a substantial damage or injury caused by irradiation.

The radiation dose for organisms is measured as effective dose or equivalent dose in the unit Sievert (S. above).Therein the different injurious character of math <\> alpha /math< ->, math< \> beta /math< -> becomes and <math> \ gamma< /math> - jets as well as the different sensitivity of individual fabrics considers.

Directly observable (acute) radiation effects (radiation sickness) arise with humans only with very high short term equivalent doses starting from 0,5 sports association. Also substantially smaller doseslead however with a certain probability to long-term sequences (cancer or hereditary damage).

natural radiation dose

each humans is exposed to natural radiation dose. A small part of it goes on constantly existing radionuclides in the own body back (with the adult approximately 8000Bq, mainly Kohlenstoff-14 and Kalium-40). The remaining, outside natural radiation dose comes approximately to the half from radon withdrawing from the ground and its decay products, besides also from Kalium-40 (in building materials) and unites other nuclides. Radon is as the secondarymost frequent cause for Cancer of the lungs designated in Germany.

see also

radiation risk

material

 

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