Ionizing radiation as a environmental and occupational factor. Hygienic regulation of ionizing

radiation as a base of radiation safety

Plan 1. Radioactive contamination of the environment.

2. Hygienic characteristics of basic methods of medical usage of active material and sources of ionizing radiation.

3. Characteristic of ionizing radiation sources used in medicine

4. Conception of radiation safety, its principles.

5. Objectives and organization of medical control at work with sources of ionizing radiation.

1. Radioactive contamination of environment

• also called radiological contamination, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids or gases (including the human body), where their presence is unintended or undesirable

• Contamination may affect a person, a place, an animal, or an object such as clothing. Following an atmospheric nuclear weapon discharge or a nuclear reactor containment breach, the air, soil, people, plants, and animals in the vicinity will become contaminated by nuclear fuel and fission products.

• Cases of widespread radioactive contamination include the Rocky Flats Plant in Colorado, the Fukushima nuclear disaster, the Chernobyl disaster, and the area around the Mayak facility in Russia.

Nuclear power station

Nuclear weapon testing

The radiation warning symbol

Radioactivity• is spontaneous transformation of atoms nuclei of

chemical elements with change of their chemical nature or energy state of nucleus, accompanied by nuclear radiation

• The radioactive pollution is defined as the physical pollution of air, water and the other radioactive materials. The ability of certain materials to emit the proton, gamma rays and electrons by their nuclei is known as the radioactivity. The protons are known as the alpha particle and the electrons are also known as the beta particle. Those materials are known as the radioactive elements. The environmental radiations can be from different sources and can be natural or manmade.

The use of radiation in medicine

• It has led to major improvements in the diagnosis and treatment of human diseases. Annually, worldwide, more than 3,600 million X-ray examinations are performed, 37 million nuclear medicine procedures are carried out, and 7.5 million radiotherapy treatments are given. As the benefits for patients gain recognition, the use of radiation in medicine increases. While the development of modern health technology makes new applications safer, their inappropriate use can lead to unnecessary or unintended radiation doses, and can cause potential health hazards for patients and staff.

All methods of sources used from hygienic positions can be relatively represented by the following groups:

• 1. Radiodiagnosis.

• 2. Roentgen and gamma-ray therapy. Therapy with use of high-energy irradiations

• 3. Intracavitary. Interstitial and application therapy using of active material in closed form.

• 4. Radiotherapy and diagnostic analysis using of active material in open form.

For receiving of image or picture, following methods can be marked out:

• 1. Radioscopy- is visual observation using of strengthening screens

• 2. Radiography- is using of special (roentgen) films for receiving on image.

• 3. Photofluorography- is photographing the image on strengthening screens using of camera

• 4. Radio xerography- is formation of concealed electrostatic image on the surface of semiconductor layer of selenium plate under the action of roentgen radiation and following visible image on paper.

The level of irradiation of the personnel during radiodiagnosis depends on:

• the way of image acquisition• location of work place during investigation

(the nearer the more dangerous); • operating regime; • type of exploited equipment: • position of X-ray tube (horizontal, vertical).

2. Hygienic characteristics of basic methods of medical usage of active material and sources of

ionizing radiation

Cone-beam computed tomography

Dental radiography

3. Characteristic of ionizing radiation

sources used in medicine • In medicine open and closed sources of ionizing

radiation are used.• Closed source is radioactive source of

irradiation, arrangement of which excludes entrance of active materials in surroundings in service and deterioration conditions on which it is counted on.

• It is seen from definition that the closed source can give only irradiation and work with it is connected with the possibility of external irradiation of the personnel.

Closed sources• External irradiation is the irradiation of the body located out

of the source of radiation.

• Closed sources used in medicine can be divided into isotopic and nonisotopic sources.

• X-ray machines and accelerators of elementary particles refer to nonisotopic sources. Such sources generate irradiation occasionally only during period of their use, when the voltage is in X-ray tube and accelerator started. These machines represent danger for the personnel only during period of work.

• Radionuclide sources refer to isotope sources. These sources will permanently generate ionizing radiation because of the decay of radioactive substances.

Open source

• Open source is radionuclide source of radiation. Application of this source is connected with possible entrance of radioactive substances into environment.

• The open source gives irradiation and radioactive pollution of environment. Work of the personnel with the open source can be connected with hit of radioactive substances both inside the organism and on the surface of the body. At the same time danger may be due not only because of external irradiation but because of internal irradiation as well..

Internal irradiation

• Internal irradiation is the irradiation of the organism, systems and organs from the sources of ionizing radiation located inside of the organism.

• Radioactive danger during work with active materials and sources of ionizing radiation is determined by radiotoxicity. Radiotoxicity is determined by physical and biological characteristics of radioactive nuclides. Physical characteristics of radioactive nuclides are kind and energy of irradiation, half-value period, scheme of decay, activity, physical state of isotope etc.

• Biological characteristics are penetration way, solubility (isotope ability for transfer from environment to the organism), allocation in the organism (organotropism), and output speed (biological half-period, effective half-period).

4. Conception of radiation safety, its principles.

Radiation safety and anti radiation protection in practical work have to be built with of the following principles:

• Principle of propriety i.e. any practical activity that is accompanied by irradiation of people must not be realized if it does not bring more profit than harm to irradiated people or to society as a whole;

• Principle of optimization i.e. levels of individual doses and (or) amount of irradiated people regarding to every source of radiation have to be as much low as it can be achieved taking into account economic and social factors.

• Principle of unexceeding i.e. inadmissibility of exceeding of maximum permissible individual doses of radiation from sources of ionizing radiation.

Categories of irradiated people (by NRSU):

• Category A (personnel) – the persons that permanently works directly with sources of ionizing radiation.

• Category B (personnel) – the persons that do not work directly with the source of ionizing radiation but because of location of their work place in premises and in industry can receive additional irradiation.

• Category C – whole population.

Limits of doses Category of irradiated persons

Аab Bа Cа

Dle (limit of effective dose) 20c 2 1

Limits of equivalent dose of external irradiation

DLlenz (For crystalline lens)150 15 15

DLskin (for skin) 500 50 50

DLextrim (for hands and feet) 500 50 -

Limits of irradiation dose (mZv/year)Comments:

distribution of irradiation dose during official year is not regulated;there are limitations for women of childbearing age (under 45) and for

expectant mothers for any consistent 5 years work on average but not more than 50mZv per

single year

Principles of protection at work with closed and open sources of ionizing radiation

• Ionizing radiation possesses high activity (biological one). Its effect appears on every level: molecular, cellular, tissular, organ and organism. Taking into account the danger irradiation of organism it is necessary to use effective protection of the personnel and patients in case of RS and SIR use.

• At work with sources of ionizing radiation it is necessary to use principles and methods for protection of the personnel. There are 4 principles used for the external irradiation protection:

• Protection by time• Protection by distance• Protection by quantity or activity• Shielding

• Protection by time is based on decreasing of contact time with ionizing radiation. Dose is directly proportional to the time of influence. Practical realization of this principle is professional development, decreasing of work time duration.

• Protection by distance is based on increasing distance from the source of radiation. There is inversely proportional dependence between the dose and distance squared i.e. the larger distance squared the fewer doses. Therefore the increase of distance in 2 times leads to decrease of dose in 4 times, the increase of distance in 4 times decreases the dose of irradiation in 16 times etc. Protection by distance is realized by using of remote control, remote instruments, master-slave devices etc.

• Dose of irradiation is proportional to dose rate and therefore to activity. Decrease of the dose rate (activity of substance) decreases the dose of irradiation. Therefore that is on what principle of protection by quantity or activity it is based

• Protection by shields is based on ability of materials to absorb ionizing radiation owing to interaction with atoms and molecules of environment and to transmission of energy to them. That’s why it is necessary to select right shield (screen) material according to the kind of radiation in order to exclude by-effects, and to determine right effective sickness of screen according to energy of radiation. The most effective one is triple shielding: shielding of source, shielding of the organism and installation of shield between the source and the worker.

The protection from open sources consists of two principles:

• to exclude the hit of radioactive substances in the environment;

• to exclude the hit of radioactive substance inside the organism.

To exclude the hit of radioactive substance

inside the organism by maintenance of regulations of work with radioactive nuclides, by use of personal protective equipment, by effective ventilation and deactivation.

Source of ionizing radiation

Activity

Exposure dose its quantitative characteristic of radiation which

based on ability of radiation to ionizedair

Irradiation of human organism

Absorbed dose(quantity of energy of IR that was absorbed

by unit of mass ofmedium (Gray, Gy)

Equivalent dose (dose of any kind of

ionizing radiation thatcauses the same

biological effects as standard (sample) roentgen radiation

with energy 200 KeV )

Effective dose (sum of equivalent doses that were

received by separate organs and tissues during radiation,

multiplied by tissue weighting factor: for gonads – 0.20, for red

bone marrow, lungs, stomach- 0.12, for other organs and tissues – 0.05 )

Radiation dose units

Radioactivity

Absorded dose

Equivalent dose

Exposure

Common Units

Curie (Ci) rad rem roentgen (R)

Si units becquerel (Bq)

gray (Gy)

sievert (Sv)

coulomb/kilogram (C/kg)

Radiation effects of human irradiation

Determinate Stochastic

Acute radiation disease

Chronic radiation disease

Local radiation injury

Somato - stochastic Genetic

Shortening average life

Increase of common sickness rate

Malignant neoplasms

Dominant genetic mutation

Inherited carcinogenesis

Chromosomal aberration

Measures of radiation safety Collective measures are:• Organizational-legislative – measures that provide correct work

organization with closed and open sources of ionizing radiation, observance of radiation safety State regulations – NRSU-97, BSRU-2001.

• Technological measures provide using of radionuclide's with low toxicity in technological process which do not form aerosols and radioactive gases.

• Technical-and-engineering measures provide automation, mechanization of work processes, capsulation of manufacturing equipment, use of protective constructions made of proper materials depending on kind and energy of radiation.

• Planning measures provide observance of regulations of radiation establishments allocation and principles of premises planning. Allocation of establishments is realized according to the kind of source, its activity and in case of work with open source – class of work.

• Hygienic and sanitary measures include preventive and current sanitary inspection of radiological objects.

Individual protective measures include observance of personal protection rules, use of personal protective equipment: working clothes, protective footwear, goggles, gloves and other equipment.