Author:Author:Lototska O.VLototska O.V

11

Ionizing radiation as a factor of environment. Problem of contamination of environment by

radionuclide. Hygienic setting of ionizing radiations norms as basis of radiation

protection.

THE PLAN

Introduction

1. Sources of radiation exposure.

2. Ionizing radiation and radioactivity.

3. Radiation quantities and unit.

4. Biological manifestations of radiation exposure.

5. Principles of radiation protection.

6. The concepts of "maximum permissible dose" and "dose limit“

Conclusions

The Chernobyl accident occurred on April 26, 1986 at the Chernobyl nuclear power plant in Pripyat, Ukraine

It is regarded as the worst accident in the history of nuclear power

There are two types of radiation exposure: One is internal exposure from radioactive material taken into the body; the other is external exposure from radiation sources outside the body.

Internal exposure can continue if the radioactive material remains in the body. In contrast, external exposure will not occur again once radiation has penetrated the body, if no additional radiation reaches the body.

Components of Environmental Radiation

Naturally occurring sources

2. terrestrial radiation coming from natural radioisotopes present in the earth's crust; 30 millirem/year

3. radiation from natural radioisotopes that have been accumulated in the body as a result of the consumption of food and water and the inhalation of air containing such radioisotopes. 40 millirem/year

• cosmic radiation originating in outer space and reaching the earth's surface after reacting with, and being partially absorbed by, the earth's atmosphere;

30 millirem/year

Man-made radiation

4. radiation from other forms of radioactive

contamination

5. radiation from radioactive consumer goods and from electronic devices.

2. radiation to occupationally exposed persons

3. radiation from "fallout" from nuclear tests

1. radiation to patients from the medical uses of radiation

Radiation Source Radiation Amount (mrem/year)

Cigarette smoking (1 pack/day) 1300

Radon in homes 200

Medical x-rays and pharmaceuticals 53

Direct exposure from naturally occurring radioactivity in soil

30

Cosmic radiation 30

Continental round trip by air 5

Building materials 3.6

Examples of radiation doses from common medical procedures are:

•chest x-ray (14 x 17 inch area) - 15 mrem, •dental x-ray (3 inch diameter area) - 300 mrem, •spinal x-ray (14 x 17 inch area) - 300 mrem,

                                                          

                                                                             

Ionizing radiation and radioactivity

"Radiation" is generally defined as the process of emitting energy as waves or particles, and the energy thus radiated.

Ionizing radiations include all electromagnetic and particulate radiations that are capable of producing ions, either directly or indirectly, during their passage through matter.

Radioactivity is the property or capacity of radioactive materials to emit radiation. Radiation means particle beams carrying energy emitted from radioactive materials (radioactive isotopes). To put in an analogy, a flashlight is a radioactive material and the light from a flashlight is radiation.

What is the difference between radiation and radioactivity?What is the difference between radiation and radioactivity?

Ionizing radiations

electro magnetic radiations

Corpuscular radiations

X-r

ay

gam

ma

rays

alp

ha

par

ticl

es

bet

a p

arti

cles

(el

ectr

on

s)

pro

ton

s

Alpha radiation is simply helium nuclei, that is, each particle consists of two protons and two neutrons. Because the nuclei have no electrons, they have a +2 charge.

Beta radiation consists of electrons. They have negative charges. Because they are energetic and have no rest mass, they can be more of a potential health threat than alpha radiation.

Gamma radiation is closely related to X-rays. Like light, gamma radiation consists of photons. Gamma rays are extremely energetic and potentially dangerous.

Other types of particulate radiations include neutrons, protons and

deuterons

Protons and deuterons are usually produced in high-energy particle accelerators used in high energy physics research work and are not commonly encountered in medical applications.

Neutrons may come into more common usage in departments of radiology as the techniques of neutron radiography and radiation therapy are developed. Although neutrons do not produce ionization themselves, they may do so indirectly. They can also be absorbed by the nuclei of stable atoms to produce another isotope of that atom. If the nucleus of the new atom is unstable, the atom will be a radioactive isotope.

RADIATION QUANTITIES AND UNIT

Four of the most important quantities to Four of the most important quantities to be defined are:be defined are:

Dose equivalent (H)

Exposure (X)Exposure (X)

AAbsorbed dose (D)bsorbed dose (D)

Activity

The nuclei of atoms may be unstable as a result of too much mass, too much energy, or both. Such atoms are said to be radioactive. We can define radioactivity as a process of nuclear transformation, resulting in a new nucleus and the emission of particles and/or electromagnetic energy from the nucleus. The emitted radiation consists of particles and/or electromagnetic rays carrying a certain amount of energy.

The unit of measure for energy is the joule (noted J).

Another unit of measure, the eV - electronvolt, is more practical.

Activity:

The activity of a radioactive source is defined as the rate at which the isotope decays. Radioactivity may be thought of as the volume of radiation produced in a given amount of time.

The unit of measure for activity, in SI, is disintegrations per second.disintegrations per second. To honour the discoverer of radioactivity (Henri Becquerel, 1896), the unit of activity (disintegrations per second) was named the Becquerel and the notation used is Bq .

Historically, another unit was used - the Curie - noted Ci. It was named after Marie Curie, the discoverer of Radium, and other radionuclides.

One curie (or 1 Ci) is the activity of 1 gram of pure Radium. This activity is equal to 3.7x1010

disintegrations per second, or 3.7x1010 Bq.

Radiation Units

1 graygray (Gy) = 100 rad

1 sievert (SV) = 100 rem

Coloumb / kg (C/kg) =Coloumb / kg (C/kg) = roentgen (R)roentgen (R)

Quality factor is a modifying factor that is introduced to take into account the different degrees of biological effect that can result following exposure to the same absorbed doses of different types of radiation.

Type of Radiation Rad Q Factor Rem

X-Ray 1 1 1

Gamma Ray 1 1 1

Beta Particles 1 1 1

Thermal Neutrons 1 5 5

Fast Neutrons 1 10 10

Alpha Particles 1 20 20

The Q factors for several types of radiation.

Exposure X

Absorbed Dose (D )

Equivalent Dose H

Radiation type

x-rays and gamma rays

all ionizing radiations

all ionizing radiations

Media in which measured

Air Any medium Biological system

Effect measured

Ionization Deposited energy

Biological effect

Unit

SI unit

Roentgen (R)

Coloumb / kg

rad

Gray

rem

Joule / kg

Biological Effects

The biological effect of ionizing radiation

Can lead to:

The occurrence of particular health effects from exposure to ionizing radiation is a complicated

function of numerous factors including:

•Type of radiation involved.

•Size of dose received.

•Rate the dose is received.

•Part of the body exposed.

•The age of the individual.

•Biological differences.

Biologic effects of ionizing radiation

Somatic

Acute radiation sickness

Deterministiceffects

chronic radiation sickness

skin and tissue burns

alopeciaray cataract

clinical registered frustration of hemopoesis

temporary or constant sterility

Stochastic effects

Somato-stochastic Genetic

cancerogenic effect

teratogenic effect

genetic mutation

Chromosomalaberration

Ob

ject

C

har

acte

rist

ic o

f ef

fect

s

Somatic effects The early effects are normally observed within a few days or weeks of exposure; the late effects are observed after a period ranging from a few months to years.

                                                                                             

         

Relationship between Exposure Dose and Acute Radiation Effect in adult humans

A latent period supervenes after initial symptoms of malaise, loss of appetite and fatigue. The length of this period is roughly inversely proportional to the radiation dose received.The end of the latent period is followed by the onset of the illness: early lethality, destruction of bone marrow,damage to the gastrointestinal tract associated with diarrhea and hemorrhage, central nervous system symptoms, Epilation (loss of hair),dermatitis, sterility.

Pathological acute effects arise after exposure to doses hundreds of times greater than those likely to be received from environmental contamination, except in major accidents.

Deterministic effectsDeterministic effects have a clear relationship between the exposure and the effect. In addition, the magnitude of the effect is directly proportional to the size of the dose. These effects will often be evident within hours or days.

Stochastic effectsStochastic effects are those that occur by chance and consist primarily of cancer and genetic effects. Stochastic effects often show up years after exposure. As the dose to an individual increases, the probability that cancer or a genetic effect will occur also increases.

Cataracts - a clouding of the lens of the eye

Cancer is any malignant growth or tumor caused by abnormal and uncontrolled cell division.

Late effect

LeukemiaLeukemia is a cancer of the early blood-forming cells. Usually, the leukemia is a cancer of the white blood cells, but leukemia can involve other blood cell types as well. Leukemia starts in the bone marrow and then spreads to the blood.

From there it can go to the lymph nodes, spleen, liver, central nervous system (the brain and spinal cord), testes (testicles), or other organs. Leukemia is among the most likely forms of malignancy resulting from overexposure to total body radiation. Chronic lymphocytic leukemia does not appear to be related to radiation exposure.

Genetic effects

Most geneticists believe that the majority of such mutations in man are undesirable or harmful.In addition to point mutations, genetic damage can arise through chromosomal aberrations.

If the information that is jumbled is in a germ cell that subsequently is fertilized, then the new individual may carry a genetic defect, or a mutation. Such a mutation is often called a point mutation, since it results from damage to one point on a gene.

Nonstochastic (Acute) EffectsNonstochastic effects have a clear relationship between the exposure and the effect. In addition, the magnitude of the effect is directly proportional to the size of the dose. Nonstochastic effects typically result when very large dosages of radiation are received in a short amount of time. These effects will often be evident within hours or days. Examples of nonstochastic effects include erythema (skin reddening), skin and tissue burns, cataract formation, sterility, radiation sickness and death.

the particular organs or tissues that are critical because of the damage they may suffer is the essential simplifying step. For example, in the case of radioisotopes of iodine, the critical organ is the thyroid, since the concentration of such isotopes in it, and therefore the dose received, is far greater than for any other organ.

Critical organs

For general irradiation of the whole body, the critical organs and tissues arethe gonads (fertility, hereditary effects), the haematopoietic organs, the bone marrow (leukemia),the eye (cataracts).

PRINCIPLES OF RADIATION PROTECTION

External Radiation of a TumorRods for Internal Radiation

Shortening the time of exposure, increasing distance from a radiation source and shielding are the basic countermeasures (or protective measures) to reduce doses from external exposure.

The physical protection against external radiation is based on the following three principles:•distance from the source of radiation (distance), •limitation of the time of irradiation (time), •absorption of radiation (shielding).

To reduce doses from intake of radioactive substances, the following basic countermeasures can be considered:

shortening time of exposure to contaminants;preventing surface contamination;preventing inhalation of radioactive materials in air;preventing ingestion of contaminated foodstuffs and drinking water.

The picture above demonstrates how image hold techniques can be useful in decreasing radiation exposure to the patient during dynamic fluoroscopic imaging procedures. The high resolution of modern monitors allows the physician to make observations not easily seen with archaic imaging equipment. It can be seen in this picture that an ERCP procedure is being done; this imaging department uses two monitors in their fluoro room, one for dynamic imaging the other for last image hold.

The duration of exposure during fluoroscopy can be minimized by the fluoroscopist by using image hold technique, intermittent beam on-off imaging, and avoiding long static imaging.

Area "A" is smaller and the radiation is more concentrated than in an equal area "A1" which is some distance from "A." Each square A1 is the same size as "A" but only 1/4 the number of photons occupies it because of the divergence of the radiation with increasing distance.

I1/l2 =(D2/D1)2

Distance is the most effective means of radiation protection

The use of shielding as a cardinal principle of radiation protection

Secondary barriers are designed for protection from scatter radiation.

                                                     

                                                          

This picture demonstrates the protective curtain to be at least 0.25 mm Pb equivalency. It should not be routinely removed for fluoroscopic procedures (white arrow).

mobile shields

The curtain will protect the technologist and radiologist from a significant amount of scatter radiation.

Thyroid shields used to help reduce exposure to the thyroid gland during fluoroscopy exams. Lead aprons used to protect from scatter radiation can protect up to 80% of the active blood forming organs in the body.

Lead gloves are used to protect the worker when a potential for exposure to the hands may occur.

Shielding requirements according to NCRP recommendation are:

• Lead aprons - 0.5 mm lead equivalency • Lead gloves, protective curtain, thyroid

shield – 0.25 mm lead equivalency • Thyroid shields – 0.25 mm lead

equivalency

Protection from radiation : Avoid unusual exposure to radiation.

Protective devices such as gloves, goggles and lead sheets must be used by persons working in radiology department.

Workers must wear a film badge which shows accumulated exposure to radiation since last time the instrument was charged.

Regular medical check- up.

Standards laid down by International Commission on Radiological Protection (ICRP), International Atomic Energy Agency (IAEA) and W.H.O. must be followed.

                                                    

        

This picture is of a canister used to transport radioisotopes for PET imaging, and the syringe holder for protection during dose administration.

Some radiology departments equip their exterior room door with a light indicator (right & left picture) to warn nursing, patient transport, and others, that the room is energized, and no one should enter the room at this time.

                                                    

       

Radiation dosimeters are important for people working with radioactive isotopes, as in analytical research laboratories, in nuclear medical applications, in medical X-ray imaging, in nuclear power-stations or in non-destructive testing of materials by ionizing radiation. They need to known their received radiation dose and need to be warned when threshold values become exceeded.

Radiation Protection Standards.

The concept of "tolerance dose"

Exposure Limits Concern over the biological effect of ionizing

radiation began shortly after the discovery of X-rays in 1895. Over the years, numerous recommendations regarding occupational exposure limits have been developed by the International Commission on Radiological Protection (ICRP) and other radiation protection groups. In general, the guidelines established for radiation exposure have had two principle objectives:

1) to prevent acute exposure; and2) to limit chronic exposure to "acceptable" levels.

MAXIMUM PERMISSIBLE DOSES AND DOSE LIMITS'

Organ or tissue Maximum permissible dose for adults exposed in the course of their work

Dose limits for members of the public (average for groups of individuals)

Whole body (in case of uniform irradiation),

5 rem in a year 0.5 rem in a year

Skin, bone and thyroid 30 rem in a year 3 rem in a year3

Other single organs 15 rem in a year 1.5 rem in a year

Hands and forearms; feet and ankles

75 rem in a year 7.5 rem in a year

The shallow-dose equivalent is the external dose to the skin of the whole-body or extremities from an external source of ionizing radiation. This value is the dose equivalent at a tissue depth of 0.007 cm averaged over and area of 10 cm2.The lens dose equivalent is the dose equivalent to the lens of the eye from an external source of ionizing radiation. This value is the dose equivalent at a tissue depth of 0.3 cm.The deep-dose equivalent is the whole-body dose from an external source of ionizing radiation. This value is the dose equivalent at a tissue depth of 1 cm.The total effective dose equivalent is the dose equivalent to the whole-body.

Declared Pregnant Workers and Minors

Because of the increased health risks to the rapidly developing embryo and fetus, pregnant women can receive no more than 0.5 rem during the entire gestation period. This is 10% of the dose limit that normally applies to radiation workers. Persons under the age of 18 years are also limited to 0.5rem/year.

Non-radiation Workers and the Public

The dose limit to non-radiation workers and members of the public are two percent of the annual occupational dose limit. Therefore, a non-radiation worker can receive a whole body dose of no more that 0.1 rem/year from industrial ionizing radiation. This exposure would be in addition to the 0.3 rem/year from natural background radiation and the 0.05 rem/year from man-made sources such as medical x-rays.

According to " Norms of radiating safety of According to " Norms of radiating safety of Ukraine " all population divided on three categoriesUkraine " all population divided on three categories

C - all other population

A - persons from among the personnel which constantly or temporarily work directly with sources of ionization radiations;

BB - - persons from among the personnel which directly do not work with sources ionization radiations, but in connection with an arrangement of workplaces in rooms and on industrial platforms of objects with radio-nuclear technologies may receive an additional irradiation;

Categories of population

Maximum permissible dose for groups of critical organs

1 group 1 group 1 group

A 5 15 30

B 0,5 1,5 3,0

C

RADIATION MONITORING DEVICES

Human beings cannot detect the presence of ionizing radiation with any of their five senses, and therefore one or another kind of instrument must be used for this purpose. Radiation detection instruments should be able to measure both the type (qualitative) and amount (quantitative) of radiation exposure. The operation of such instruments is usually based on their response to charged particles that are produced as radiation interacts with and ionizes matter through which it is passing. In general, radiation detection and measuring instruments can be divided into two categories, depending upon whether they are used for personnel monitoring or area survey purposes.

Survey Meters for determine the presence and intensity of radiation

Safety Controls Since X-ray and gamma radiation are not detectable by the human senses and the resulting damage to the body is not immediately apparent, a variety of safety controls are used to limit exposure. The two basic types of radiation safety controls used to provide a safe working environment are engineered and administrative controls. Engineered controls include shielding, interlocks, alarms, warning signals, and material containment. Administrative controls include postings, procedures, dosimetry, and training.

Radiation Detectors

Instruments used for radiation measurement fall into two broad categories:   - rate measuring instruments and   - personal dose measuring instruments.

Dose measuring instruments are those that measure the total amount of exposure received during a measuring period. The dose measuring instruments, or dosimeters, that are commonly used in industrial radiography are small devices which are designed to be worn by an individual to measure the exposure received by the individual.

Direct Read Pocket Dosimeter

Digital Electronic Dosimeter

Audible Alarm Rate Meters and Digital Electronic Dosimeters

Film Badges

Thermoluminescent Dosimeter

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