Ionizing ray

A ionizing ray is a Rayonnement which produces Ionization S in the Matière that it crosses. For the ionizing rays, there are many practical uses, but these rays are also dangerous for the human health. The two aspects are treated here.

Radiations

The man is exposed to the radiations since his appearance on ground. He, for example, is exposed to the solar radiations, i.e. with the visible Lumière coming from the Sun, which is accompanied by known invisible radiations under the name of radiations Ultraviolet S and Infrarouge S. These radiations are electromagnetic waves like are also the Ondes radio, the X-rays and the Gamma rays.

The man is also exposed to other invisible radiations which come from space and the Sun, known under the name of cosmic Rayonnement. These radiations of very great energy (waves and particles) are able to cross thick layers of rocks.

The elements Radioactif S present in our environment emit, at the time of their Désintégration S, of the radiations Alpha, Bêta and Gamma. The gamma rays are electromagnetic waves while the radiations alpha and beta are particles which are respectively a core of Hélium and a electron.

The Activity of a radioactive element, i.e. the number of disintegrations a second in a certain mass of this element, is measured in Becquerel S. Among the particulate radiations exist also the Neutron S.

Among these radiations, some are ionizing.

---- ; Note

radioactive Sources: writing and pronunciation

the radioactive sources, which thus produce ionizing rays, are Isotope S chemical private individuals of elements. To distinguish this particular isotope from the other isotopes, one indicates the number of particles (protons and neutrons) in the core before the name of the element, while exposing; on the other hand, when one speaks, one indicates the name of the element then the number of particles. Examples:

* ²⁴¹Am: Americium two hundred and forty and one;

* ¹⁴C: carbon fourteen;

* ²⁵²Cf: Californium two hundred fifty-two;

* ⁶⁰Co: Cobalt sixty;

* ¹³⁷Cs: Cesium hundred thirty-seven;

* ³H: Tritium (the term “Hydrogène three” is not used);

* ¹³¹I: Iodine hundred thirty-one;

* ¹⁹²Ir: Iridium a hundred and eighty twelve;

* ⁴⁰K: Potassium forty;

* ²²⁴ Ra: Radium two hundred and twenty-four;

* ²²⁶ Ra: Radium two hundred twenty-six;

* ²²⁰Rn: Radon two hundred and twenties;

* ²²²Rn: Radon two hundred and twenty-two;

* ⁹⁰Sr: Strontium eighty ten;

* ^99mTc: Metastable Technetium eighty nineteen ;

* ²³⁵U: Uranium two hundred thirty-five.

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Various ionizing rays

The energy radiations transfer enough from energy to the electron S of the matter to tear off them from their Atome. The atoms thus deprived of some their electrons are then positively charged. The close atoms which accommodate the electrons charge negatively.

Charged atoms positively or the negatively are called Ion S. the atoms which lost an electron became ions + (=cation) and the atoms which received this electron became ions - (=anion). The radiations able to cause of such reactions are known as ionizing.

The ionizing rays gather:

radiations of cosmic origin;
the energy waves of the electromagnetic Spectrum;

the X-rays: products by an electron beam sent on a metal target. These electrons, while interacting with the electrons of the atoms of metal, make them change energy level and emit x-rays; The electrons of the beam can also interact with the Coulomb Champ of the core of the atoms and to be deviated and braked, by emitting x-rays characteristics (radiation of braking or Bremsstrahlung)
the Gamma rays are emitted by radioactive atoms during their disintegration;

the radiations alpha, beta more and beta less (particles emitted by radioactive atoms during their disintegration);
the neutrons are not directly ionizing radiations, but since they induce radiation ionizing by the secondary particles created at the time of their interactions with the matter, they are classified among the ionizing rays.

The other radiations are called nonionizing radiations and include/understand the electromagnetic waves energy.

To be able of penetration of the ionizing rays

By their energy, the ionizing rays are penetrating, i.e. they can cross the matter. The capacity of penetration depends on the kind of radiation and the stopping power of the matter. That defines thicknesses different of materials to protect itself.

Particles alpha: helium-4 cores

Weak penetration. The particles alpha are emitted at a speed bordering the 20 km/s. Cependant being heavy and electrically charged, they are stopped very easily and quickly by the electromagnetic fields and the atoms composing the surrounding matter. A simple sheet of paper is enough to stop these particles.

Particles beta less: electrons

Average penetration. The electron emitted having a negligible mass, according to the theory of relativity, it has a speed close to that of the light (approximately 290.000 km/s). However, electrically charged, it will be stopped by the surrounding matter and electromagnetic fields. An aluminum foil of a few millimetres can stop the electrons. A screen of one centimetre plexiglass stops all the particles beta lower than 2 MeV.

Particles beta more: positrons

The penetration is similar to that of the electrons. But at the end of sound Parcours, a Positron is destroyed with an electron met on its passage by forming two photons gamma, which brings back the problem to the case of the gamma ray.

X-radiations and gamma

Very large penetration, function of the energy of the radiation: several hundred meters in the air. A strong thickness of Concrete or Plomb makes it possible to be protected some.

Neutrons

The neutron not being charged, it does not produce ionizations while crossing the matter. The free neutrons thus do not form an ionizing ray, but by causing nuclear fissions, they can generate ionizing rays.

The free Neutron S are especially present in the nuclear reactors; they are emitted, for example, during the fission of atoms of Uranium 235. They are indirectly ionizing because it is their capture by the cores or their interaction with those which generates gamma rays and/or various particles. The neutrons are also present at altitudes of flight of the planes long mail and subsonic: they take part in 30% of the amount received by the sailing personnel.

Penetration dependant on their energy. A strong thickness of concrete, water or Paraffine stops the neutrons.

The amount: energy absorptive by the matter

When a radiation penetrates the matter, it interacts with it and transfers to him from energy. The absorptive Dose by the matter characterizes this transfer of energy. The unit of amount absorptive by the matter is the Gray (Gy) which is equivalent to a Joule absorptive per kilogram of matter.

Clinical demonstrations of the lesions

Types of effects

The effects of the ionizing rays include one vast range of reactions very different from/to each other in their relation amount-effect, their demonstrations clinical, their succession in the corresponding time and forecasts. By convenience, one often subdivides the effects in two main categories:

effects Hereditary S, or genetic effects which appear at the descendants of the exposed people; and
effects Somatique S, which appears at the exposed people themselves. The latter include/understand the acute effects, which appear shortly after the irradiation, and the long-term effects (or differed), which can appear months, years or even of the decades later.

Acute effects

The acute effects of the ionizing rays result especially of impoverishment in cells capable of reproduction in irradiated fabrics and appear only in presence of enough important amounts to destroy much of these cells. It is for this reason which one considers that these effects are of nature not Stochastique or deterministic.

It is not the same mutagen and cancerogenic effects of the radiations, considered like stochastic phenomena resulting from molecular deteriorations random of individual cells, of which the frequency grows according linear to the amount.

The acute lesions, which were current in the first workers exposed to the ionizing rays and the first patients subjected to treatments of Radiotherapy, practically have missing in consequence of the improvement of the security measures and of methods of treatment. Nevertheless, majority of the treated patients by irradiation nowadays still certain lesions undergo in healthy fabrics. Moreover, serious accidents continue to occur. Indeed, the few 285 declared accidents (Tchernobyl not included/understood) occurred in the nuclear plants the different ones countries between 1945 and 1987 caused the irradiation of more than 1.350 people, of which 33 were mortally reached. With him only, the accident of Tchernobyl has released sufficient radioactive substances to require evacuation of tens of thousands of people and animals of the surrounding area. Moreover, more than 200 firemen and members of emergency teams were reached evil of the rays and 31 died about it (Scientific committee of the United Nations for the study of the effects of ionizing rays (UNSCEAR), 1988).

One cannot predict with certainty the long-term effects of released radioactive substances, but the estimate of the risks of effects cancerogenic based on models of relation amount-effect without threshold gives rise to think that the population northern hemisphere could record, consequently accident, 30.000 deaths additional per cancer with the course from the 70 next years, though the number of additional cancers recorded in each country will be probably too much small to be detectable on an epidemiologic basis (United States Department off Energy (USDOE), 1987).

Definitely less catastrophic, but much more that failures of nuclear plants, accidents caused by medical sources and industrial of gamma rays also made deaths and casualties. Thus in 1987 an apparatus of radiotherapy, containing a source of cesium 137, abandoned in a closed down private clinic, in Goiânia (Goiás), in Brazil, involved the contamination and the irradiation of tens of noninformed people, of which four died in the six weeks which followed the accident.

A complete examination of the lesions caused by the radiations ionizing the framework of this article would exceed. However, account held of the general interest of information on the acute reactions of the most radiosensitive fabrics, it is useful to present one of them short description in the following paragraphs.

Ds the effects acute one finds: - the erythema or " blow of soleil" - Necroses acute: exposure of particles Beta of weak energy - acute ulceration: for 20 Gy in acute exposure

Skin

The cells of the basal layer of the skin are particularly radiosensitive. Consequently, a fast exposure skin with an amount of 6 Sv or more causes an erythema (redness) of the affected zone, which appears in general in day which follows, usually lasts a few hours, then is follow-up, two to four weeks later, by one or more waves of a deeper erythema and more prolonged, like by a depilation (loss of hairs or hair). If the amount exceeds 10 to 20 Sv, phlyctene, necrose and ulceration appear in both to four weeks, then are followed by a fibrosis of derm and of the subjacent vascular system, which can carry out to the atrophy and with a second wave of ulcerations a few months or a few years later (CIPR, 1984).

Osseous marrow and lymphoid bodies

The lymphocytes are also very radiosensitive: an amount from 2 to 3 Sv received quickly by all it body can kill some sufficiently in a few hours to make to fall peripheral lymphocytary numeration and to compromise immune reactions. Also radiosensitive, hematopoietic cells of osseous marrow can sufficiently decrease of number under the effect of an amount comparable to cause a granulocytopénie and a thrombocytopenia in the three to five weeks which follow. These reductions numerations of granulocytes and plates can be enough serious after a strong irradiation to cause a hemorrhage or an infection mortal.

Intestine

Original cells of the epithelial coating of the intestine hail are extremely radiosensitive. An acute exposure to 10 Sv can reduce the number sufficiently of it to strip them intestinal villosities in a few days. The denudation of an important surface of the mucous membrane often cause a fulminant syndrome dysentériforme being able quickly to evolve to the death of the victim.

Gonades

The mature spermatozoa can survive strong amounts (100 Sv) of ionizing rays, but spermatogonies are so radiosensitive that an amount of 0,15 Sv applied quickly to the two testicles is enough to cause oligospermy and that an amount from 2 to 4 Sv can involve one permanent sterility. The ovocytes are also strongly radiosensitive: the fast exposure of the two ovaries to an amount from 1,5 to 2 Sv can cause a temporary sterility, being able to become permanent if the amount increases, according to the age of the woman at the time of the exposure. At the transitory Man sterility Pr 0,5 sievert; final 3,5 to 6 Among women sterility for 2,5 to 6 sievert There are no consequences genetics, since one is in a state of sterility

Respiratory tracts

The lungs are not strongly radiosensitive, but a fast exposure to an amount from 6 to 10 Sv can cause, one to three months later, an acute pneumonia in the exposed zone. If an important volume of pulmonary fabric is affected, the victim can suffer from respiratory insufficiency in following weeks as well as pulmonary fibrosis and of pulmonary heart a few months or a few years later.

Crystalline lens

Cells of the former epithelium of the crystalline lens, which continue to divide during all the life, are relatively radiosensitive. Consequently, a fast exposure of the crystalline lens to an amount exceeding 1 Sv can lead in a few months to formation of a microscopic posterior polar opacity. Of even, an amount from 2 to 3 Sv received in once in a short lapse time or an amount from 5,5 to 14 Sv accumulated over one period of a few months can cause a serious cataract.

Other fabrics

By comparison with fabrics mentioned above, the other fabrics of the organization are in general definitely less radiosensitive. However, the embryo constitutes an important exception in this respect, as we note it further. It is necessary also to announce that the radiosensitivity of a fabric increases if it is in phase of rapid growth.

X-ray lesions due to a total-body radiation

The fast exposure of an important part of the body to an amount exceeding 1 Gy can cause the syndrome of acute radioexposition. This syndrome comprises various phases:

an initial prodromic phase characterized by symptoms such as faintnesses, anorexia, nauseas and vomiting;
one latency period;
a second phase (principal) of disease; and finally
either the re-establishment, or death.

The principal phase of the disease generally takes one of the following forms, according to the prevalent localization of the X-ray lesions:

hematologic form;
gastro-intestinal form;
cerebral form; or
pulmonary form.

Localized X-ray lesions

Contrary to the clinical demonstrations, in general fast and spectacular, of the syndrome of radioexposition acute rising from the exposure of all the body, reaction to a very localized irradiation, produced by a source external or a radionuclide deposited inside the organization, tends to appear slowly with few symptoms or external signs, unless the volume of irradiated fabrics or that the amount are not relatively important.

Effects according to the radionuclides

Certain radionuclides, like tritium (³ H), carbon-14 (¹⁴C) and cesium 137 (¹³⁷Cs), tend to be distributed in all the organization, producing a total-body radiation, while other radionuclides are fixed rather in particular bodies, causing very localized lesions. Radium and strontium 90 (⁹⁰Sr), for example, are fixed primarily in the bones, causing osseous lesions especially, while radioactive iodine concentrates in the thyroid gland, which is thus the first attack.

The exposure of the Man to the radiations

To assess with their right value the risks related to the ionizing rays, it is necessary to look at the natural exposure of the man to which it was always subjected. All the living organisms there are adapted and seem able to correct, until a certain degree, the damage due to the irradiation.

In France, the annual exposure of the man to the ionizing rays is from approximately two millisieverts. In addition to this natural Radioactivity, we are exposed to radiations coming from artificial sources. These radiations are of the same type as those emitted by natural sources and their effects on living matter are, with equal amount, identical. They are primarily medical or dental radiographies.

Only 1,5% come from other sources like the repercussions of the air tests of the nuclear weapons and the repercussions from the accident of Tchernobyl, but their effect perhaps very worsened when the contamination is internal, following absorption of radionuclides in food. Certain mushrooms in particular, of which the truffle of the stag ( Elaphomyces granulatus ) strongly bioaccumulant the Cesium 137 repercussions of Tchernobyl, in particular since the years 2000, because its zone of prospection is approximately with - 20 cm under the level of the ground, and the cesium migrating at a rate of 1cm per annum approximately, it was necessary twenty year so that it reaches this zone. This mushroom particularly required and is consumed by the Sanglier S, which one showed in 2005 in Germany (in the Land of the Rhineland-Palatinat) that they presented an increasing contamination (12% among 1400 wild boars) were radioactive audelà standards authorized for the food and marketing in only one Land, just in the East of Luxembourg, and the wild boars taken more in the west were touched, which corresponds to the zones where it rained at the time of the passage of the cloud of Tchernobyl.

Modes of exposure to the radiations

According to the way in which the radiations reach the organization, one distinguishes two modes from exposure: external or intern.

the external exposure of the man to the radiations causes an external irradiation. It takes place when this one is exposed with radiation sources which are external for him (radioactive substances in the form of cloud or of deposit on the ground, sources of industrial or medical use…).

The external exposure can relate to all the organization or a part only of this one. It ceases as soon as one is not any more on the trajectory of the radiations (case for example of a radiography of the thorax).

the internal exposure (contamination interns) is possible when radioactive substances are inside the organization. Those cause an internal-source irradiation. They could penetrate by inhalation, ingestion, wound of the skin, and are distributed then in the organization. One speaks then about internal contamination. This one ceases only when the radioactive substances disappeared from the organization after a more or less long time by natural elimination and radioactive decrease or treatment.

One speaks since 2006 about:

- external exposure remotely (irradiation)

- external exposure to the contact (external contamination)

- exposure interns (contamination interns)

See also Irradiation and radioactive Contamination.

The radioactive decrease is the following one:

for the Iodine 131 (¹³¹I): 8 days;
for the Carbon 14 (¹⁴C): 5.700 years;
for the Potassium 40 (⁴⁰K): 1,3 billion years.

All the radioelements are not eliminated naturally (urines…) at the same speed. Some can accumulate in specific bodies (bone, liver…) before being evacuated body.

For each radioactive element, one defines, in addition to his radioactive Half-life, a biological Half-life, time with the end of which half of the activity of a radioactive substance was eliminated from the organization, by natural ways.

The natural exposure

The ionizing rays which we receive from natural sources have of the various origins and are divided into three principal types:

Cosmic radiations

One calls cosmic radiation a flow of particles (mainly of the protons) equipped with one very high energy, about GeV. It is of solar or galactic origin. These protons of high energy enter in collision with the cores of the atoms of the atmosphere and fragments themselves create equipped with an energy high (protons, neutrons, muons, neutrinos, mesons,….).

The flow of equivalent of amount due to the cosmic radiations is on average of 0,3 mSv/an with sea level. But it varies considerably according to altitude and from the latitude (see the table below).

Variation of the flow of equivalent of amount absorptive (mSv/an) according to altitude and of the latitude.

That has as a consequence that certain populations undergo an exposure more important than the average. The table below gives the equivalent of amount received by the populations of cities located in altitude.

Flow of equivalent of amount of the cosmic radiations in areas high altitude.

Radioactive elements contained in the ground

We are exposed to the radiations due to the radioelements present in the Earth's crust. There exists about fifty natural radioelements whose majority belong to the 3 natural families of the Thorium, of the Uranium and the Actinium.

It is the Thorium which exists in the largest quantity (10 ppm on average). One finds then the Uranium (2 to 3 ppm), then the Actinium.

Another radioelement contributes significantly, it is the ⁴⁰K, natural isotope of the Potassium (0,01167%). Its concentration is about 100 to 1000 Bq/Kg of ground.

The rate dose absorptive average due to the whole of these Isotopes is approximately 0,3 mSv/an in France. It varies however largely according to the composition of the ground. The equivalent of amount received in Brittany or the Vosges east from 2 to 3 times superior with that received in the Paris basin. In certain areas, like the State of Kerala on the South-western coast of the India, it reaches even 30 mSv/an.

Let us note that it is this natural radioactivity of the ground which is the origin of the Géothermie.

Natural radioactive elements that we absorb while breathing or by nourishing us

Gas emanations of certain products resulting from the disintegration of the Uranium contained in the ground such as the Radon, or the Potassium of the food of which we retain a part in our organization (element of which we maintain a stock of permanently approximately 165 G per anybody) cause at each one among us, on average, an irradiation of 1,55 millisievert per annum. The independent source of natural irradiation is the Radon 222, radioactive natural gas. It represents approximately a third of the received irradiation and increases in the granitic areas.

All the natural families have in their chain an isotope of radon (²²²Rn generated by the ²²⁶Ra, and the ²²⁰Rn called also Thoron, generated by the ²²⁴Ra). These gases emanate from the ground, water and construction materials. The median values of the concentrations were estimated at 2 Bq/m in the open air and 20 Bq/m in dwellings for most important of them: the ²²²Rn. These solid gases and their descendants irradiate lungs.

The Potassium being an important component of our constitution and vital to the good performance of our cells (approximately 165 G/nobody), the isotope ⁴⁰K of this element contributes to a constant activity interior from approximately 5000 Bq, to which come to be added a similar share which had with the activity of the whole of the others unstable Isotopes of our body.

Example: Radioactivity of various natural environments

Rainwater: 0,3 to 1 Bq/L
Water of river: 0,07 Bq/L (²²⁶Ra and descendants); 0,07 Bq/L (⁴⁰K); 11 Bq/L (³ H)
Sea water: 14 Bq/L (⁴⁰K primarily)
mineral Water: 1 to 2 Bq/L (²²⁶Ra, ²²²Rn)
Milk: 60 Bq/L
sedimentary Ground: 400 Bq/kg
granitic Ground: 8.000 Bq/kg
Human body: 8.000 - 10.000 Bq (of which 5.000 due to the ⁴⁰K)

The following table summarizes the contribution of the various components of the natural radioactivity. It is necessary however to remember that they are suitable median values for important variations in function of altitude, the latitude and the composition of the basement.

The artificial exposure

For each inhabitant, the average annual exposure to the artificial sources of irradiation is from approximately 1 millisievert. Those are mainly the medical irradiations and the industrial applications of the radiations.

The nuclear plants, the plants reprocessing, the repercussions of the old atmospheric nuclear tests and Tchernobyl, etc, expose each man on average to 0,002 millisievert per annum.

Medical irradiations

They are mainly the medical and dental Radiographie S which cause an external irradiation near to 1 millisievert per annum (average in France).

The rise of the radiodiagnosis was one of the crucial factors of medical progress during the 20th century. The equivalents of amount delivered by the various types of examinations vary considerably according to the depth of the studied bodies and the dimension of the segment of the organization concerned. Beside the classical devices appeared gradually more sophisticated apparatuses (scanner S) which, associated with computers, allow to carry out images crosses from there (Tomographie S) of the organization.

Amounts delivered during the most current examinations in radiodiagnosis

The external Radiothérapie is one of the basic salaries of cancers. One generally uses radiations of high energy emitted by sources of radioactive Cobalt ⁶⁰Co or by accelerators. In certain treatments known as of curiethérapie, a radioactive body is placed, either with the immediate contact of fabrics to be irradiated, or established in the form of radioactive needles (Iridium, Césium). The classically managed amounts high (40 to 80 Gy) and are spaced in time to make it possible healthy fabrics to regenerate itself. The techniques of final establishment of radioactive grains (Iodine, palladium) are expanding.

The nuclear medicine uses radioactive isotopes for the exploration of the human organism. It consists in injecting a radioactive isotope which is fixed in the part to explore and to carry out an image using a camera with scintillation (Scintigraphie).

The isotopes used are the Iode ¹³¹I for the functional exploration of thyroid and especially the Technétium ^99mTc whose interest is its short period (T = 6,02 H) what minimizes the equivalents of administered dose. It can be obtained starting from Molybdène ^99mMo by an apparatus with elution.

The functional exploration of bodies such as the brain uses the Tomographie with emission of positons. The isotope used is often the Fluor (¹⁸F, of period 2:00) injected under a form related to a sucre : the cerebral activity consumes glucose and the most active zones at the time of a task Cognitive will be visualized by a Gamma camera.

Equivalent of amount after injection of ^99mTc for various explorations

Industrial methods of measurement

Because of their strong interaction and penetration depth their with the matter, the radiation ionizing are used to take measurements.

; Gammagraphy

It is a technique of industrial radiography using a source of gamma rays. It consists in placing the part to be radiographed between the radiation source and a photographic film contained in a flexible or rigid cassette. After a duration depending on the nature and the thickness of radiographed material, the film is developed and reveals the defects possibly existing inside the part. The fields of application are numerous (boiler making, foundry, industry oil, naval construction and aeronautics).

Radioelements used:

* ⁶⁰Co: transmitter gamma of energies of 1,17 and 1,33 MeV (15% of the apparatuses)

* ¹⁹²Ir: transmitter gamma of energies ranging between 200 and 600 keV (80% of the apparatuses)

Types of apparatuses

* the portable devices are most widespread. They contain sources from 2 to 5 TBq of ¹⁹²Ir. They were at the origin of several accidents (blocking of the source in position of irradiation, loss of the source).

* the fixtures equipped with source of ⁶⁰Co several hundreds of TBq are reserved for the control strong thicknesses. They are generally installed in casemates of shooting.

; Radiograph X

Its principle is the same one as for gammagraphy, the source of photons being replaced by a Générateur x-rays. The potential differences used go from 50 keV to several MeV. This type of technology for example is used for the inspection of the luggage in the airports.

; Neutron beam photography

It can be carried out thanks to a neutron beam resulting from an engine, an accelerator of ions or a source of ²⁵²Cf (transmitting of neutrons). It is used for the control of hydrogenated materials.

; Spectrometry and diffractometry

to see the articles Spectrometry of x-ray fluorescence , Diffractometry of x-rays .

; Gauges

the principle of the gauges is based on the law of the attenuation of the radiations (Loi of Beer-Lambert)

* Jauges of level: they indicate the presence or the absence of material on the horizontal way of the beam (source and detector placed on both sides of material). The sources used are transmitters beta or gamma according to the thickness and the density of material to be measured. They are used for the control of the tanks of liquids, of the silos (sand, grains, cement…)

* Thickness gauges: If the material is of constant density, the intensity of the signal received by the detector will be function thickness of this one. They are used for measurement uninterrupted products in sheets: papers, fabrics, rubber,….

; Applications resting on the principle of ionization of the gases

* Elimination of static electricity: The use of sources of ²⁴¹Am (transmitting gamma), in the form of ribbons placed at the end of the production machine tools of papers, plastics, synthetic fibers, etc with a few millimetres of material allows while making the air neighbouring conducting, to remove the accumulation of static electricity.

* Smoke detector: Two ionization chambers are laid out in series: one being used as witness, the other, latticed, in contact with the ambient air. In each one of these rooms, a small source of some KBq of ²⁴¹Am gives rise to a constant current. So particles of smoke penetrate in the opened room, they involve a variation of the current which starts an alarm signal. There are in France 3 million and half of smoke detectors based on this principle.

* Tracer radioactive industrialists: The principle of the tracing is the marking of some individuals of a population allows the study of the total behavior of this population. The radioactive tracers are particularly powerful because they mark the elementary entity that is the atom and allow a detection facile.
Exemples use:

** Marking of a liquid or a gas by a transmitter gamma allowing the leakage survey on drains

** Marking of a part of engine allowing thanks to the measurement of the radioactivity of the lubricating oil to evaluate the wear of the components.

Destruction of germs by irradiation

Radioconservation of the foodstuffs

Currently in full rise, the radioconservation of the foodstuffs uses the radiation gamma of the ⁶⁰Co or the accelerated electrons. It induces, of course, no radioactivity within food. It causes:

Increase in the shelf life of food by the deceleration of maturation, germination, by reduction of the number of micro-organisms responsible for deteriorations,
Elimination of the harmful insects in the stored food products (dried cereals, flours, fruits, fish).
the bacterial cleansing by destruction of pathogenic micro-organisms (poultries, eggs).

The amounts used are about 10 ² with 10⁴ Gy.

Sterilization

The radiosterilization of the medico-surgical material by gamma ray (25 kGy) can be carried out on the material already placed in its final packing.

Electrical production

The nuclear plants constitute only one element of the electrical production. This one comprises three stages:

preparation of combustible matter,
operation of the power stations,
reprocessing of fuel.

; Preparation of the fuel

It is done in several stages:

* extraction of the uranium ore,

* concentration and refining,

* transformation in order to obtain uranium salts (Uranous salt, Nitrate of uranyl),

* enrichment in ²³⁵U by gas diffusion after transformation into Uranium hexafluoride gas,

* manufacture of combustible matter.

These operations are done in controlled medium and do not involve normally an exposure for the people, except accident. For the workers, the most critical phase is the extraction of the ore which involves an internal exposure by inhalation of dust and ²²²Rn.

; Operation of the Fission product nuclear plants

*: The Nuclear fission, true explosion of the core, gives rise to:

** of the fragments of fission (generally 2),

** of the neutrons (2 or 3),

** of energy (200 MeV on average).

the fission products are for the majority radioactive, transmitting beta or gamma.

* Produced activation: The action of the neutrons on cladding materials of fuel, the impurities of the coolants and the various elements of structure gives, birth with radioactive products of activation of various nature and period. An engine functions in closed circuit, but the fluid of the primary education circuit is contaminated by the products of activation and the escaped fission products of the metal sheaths containing the uranium and of which some can become defective. The purgings, drainings and maintenance actions produce gas effluents (rare gases, iodize) and liquids which are dispersed in the environment directly or after treatment, but in any event in a strictly controlled way.

; Reprocessing of fuel

Each year part of fuel is withdrawn from the heart of the engine and reprocessed after one period of decrease of several years. This reprocessing is intended to reduce volume, to recover reusable matters (Plutonium, Uranium 235). With this intention, the sheaths are sheared, the fuel dissolves in the nitric acid then treated by various solvents. These operations release a certain quantity of gas and liquid effluents.

Conclusion

To conclude, it seems interesting to present a synthetic view of the independent sources of exposure of the man with the corresponding equivalents of amount. One should not lose sight of the fact that they are median values and that certain groups of individuals (workers of nuclear energy, populations living in certain areas etc) are exposed to more important equivalents of amount.

general Inventory of engagements of amount (mSv/an) for an average individual.

References

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