DOSES AND SOURCES OF RADIATION EXPOSURE

DOSE CONCEPTS, QUANTITIES AND UNITS

Radiation exposure

Radiation exposure is a measure of the intensity of the radiation field For X and gamma rays, exposure is precisely defined in terms of the amount of ionization produced in air by the radiation source

Units of exposed dose The SI unit: coulombs per kilogram (C/kg) Traditional (old) unit:

Roentgen (R) 1 R = 2.58 x 10 -4 coulomb/kg

Absorbed dose (D) Energy imparted to matter from any type of radiation

D E absorbed dose, energy absorbed by material of mass ‘m’

Units of absorbed dose

The SI unit: joule/kilogram or gray (Gy) 1 Gy = 1 J/kg Traditional (old) unit: rad

(radiation absorbed dose)

1 Gy=100 rad

Variants of radiation exposure

External irradiation Internal irradiation Local irradiation Total irradiation Acute irradiation Prolonged irradiation Chronic irradiation Fractioned irradiation

Equivalent dose (H

T

) Accounts for biological effect per unit dose

radiation weighting absorbed factor ( W R )

X

dose (D) H T = W R x D

Radiation weighting factors (W

R

)

Radiation type and energy range Photons (X-rays and gamma-rays) all energies Electrons, all energies Neutrons <10 keV 10-100 keV >100 kev to 2 MeV 2-20 MeV >20 MeV Protons >20MeV Alpha-particles, fission fragments W R 1 1 5 10 20 10 5 5 20

Unit of equivalent dose The SI unit:

H T

sievert (Sv)

(Sv) = W R x D (Gy)

Traditional (old) unit:

rem

(roentgen equivalent man) H T (rem) = W R x D (rad)

1 Sv = 100 rem

Effective dose (E)

Risk related parameter, taking relative

radiosensitivity

of each organ and tissue into account E = Σ T (W T x H T ) W T H T tissue weighting factor for organ T equivalent dose received by organ or tissue T

The SI unit of effective dose:

sievert (Sv)

Tissue weighting factors (W

T

)

Organ or tissue Tissue w eighting factor (W T ) Gonads Red bone m arrow Colon Lung Stom ach Bladder Breast Liver Oesophagus Thyroid Skin Bone surface Rem ainder 0.2

0.12

0.12

0.12

0.12

0.05

0.05

0.05

0.05

0.05

0.01

0.01

0.05

Total 1.0

Collective effective dose (S)

Total radiation dose incurred by population

S = Σ i (E i x N i )

E i N i average effective dose in the population subgroup i number of individuals in subgroup i The SI unit of collective effective dose: man-sievert (man-Sv)

Conversion between units used in radiation protection Physical quantity Activity Exposure Absorbed dose Equivalent dose SI unit becquerel gray (=J/kg) sievert Non-SI unit curie (Ci) coulomb/kg roentgen ® rad rem Relationship 1 Bq=2.7x10

-11 Ci 1 Ci=3.7x10

10 Bq 1 mCi=37 MBq 1 R=2.58x10

-4 C/kg 1C/kg=3876 R 1 Gy=100 rad 1 rad=1 cGy 1 Sv=100 rem 1 rem=10 mSv

Sources and levels of radiation exposure to population

Sources of radiation exposure to people population

Background radiation

• Terrestrial radioactivity • Cosmic radiation • Internal radioactivity

Terrestrial radiation: external and internal exposure U-238 Ra-222 Th-232 Ra-220

High background areas

Cosmic radiation

Internal radioactivity Radioactivity in diet

•

potassium-40

•

lead-210

•

polonium-210

Background radiation

Air

Radon - 2 mSv Cosmic - 0.3 mSv Food - 0.4 mSv Terrestrial - 0.3 mSv

Natural background radiation doses in Europe Naturally occuring background levels of radiation can typically range from 2.0 to 4.0 mSv a year

Artificial sources of ionizing radiation

Radioactive sources Electric generators of ionizing radiation Activities using nuclear energy:



nuclear weapons



nuclear reactors

Radioactive sources

Radioactive sources are present in the sealed (normally non spreadable) and unsealed form (spreadable):

Gammagraphy

essentially uses as sources iridium-192 and sometimes cobalt-60

Neutrongraphy

californium-252 or an americium/beryllium couple. uses sources of neutrons like

Betagraphy

uses beta sources like carbon-14.

Chemical and biological radiation-treatment

uses gamma radiation sources cobalt-60 or caesium-137.

Radioactive sources in medicine

In medicine there are three uses for non-sealed radioactive nuclides:

Biological analyses:

radio-markers have been replaced progressively by non-radioactive markers.

Medical imaging:

nuclear medicine department use radio-pharmaceuticals for diagnostics, which are ingested by the patient to obtain an image of the tissue or organ while it is functioning.

Therapy: radio-pharmaceuticals can constitute the treatment itself, for example iodine 131 for the treatment of thyroid cancer.

Electric generators of ionizing radiation

The industrial applications of electric generators of ionizing radiation are neighbors of radioactive sources.

 

Medical applications comprise radio-diagnostics and radiotherapy: Medical radio diagnostics is man’s largest source of exposure to ionizing radiation. It uses standard radiography equipment and X-scanners.

The electric generators used in radiotherapy are electron accelerators of medium energy (20 million volts) which enable a beam of electrons or X-rays to be obtained.

In the research sector the large accelerators and scientific instruments are used to study the fine structure of matter.

Effective doses from medical exposure Effective dose (mSv) Equivalent period of natural radiation Radiography Chest Pelvis 0.02

1.0

IVP 4.6

Barium studies 9.0

CT (Chest, Abdomen) 8.0

Nuclear Medicine Thyroid imaging 1.0

3 days 6 months 2.5 years 4.5 years 4 years 6 months Bone imaging 3.6

1.8 years

Nuclear weapons

Nuclear weapons can function by two very different modes – nuclear fission or nuclear fusion:

Fission arms

employ the principle of an uncontrolled chain reaction, i.e. each fission reaction leads to several further fission reactions

Fusion arms (thermonuclear)

amount of energy use the fact that the union of deuterium and tritium to form a single nucleus of helium liberates a very large

Summary number of explosions of nuclear weapons from 1945 to 1998

Country Years USA Russia France Great Britain China India Pakistan 1945 – 1992 1949 – 1991 1960 – 1997 1950 – 1960 1964 – 1996 1974, 1998 1998 Number of explosions 1030 716 210 44 45 6 5

Summary number of nuclear explosions in atmosphere 193 142 10,6 5,2 5 % 33,6 45,6 USA Russia 45 France 22 China 21 Britain

Nuclear explosions in atmosphere in various years 90 80 70 60 50 40 30 20 10 0

Ecological consequences of nuclear explosions and radiation accident

Nuclear explosions in atmospheres Chernobyl accident, 1986 Summary activity, x 10 16 Bq 181 060 Contamination areas, km 2 510 x 10 16 185 250 x 10 6 River Techa accident, 1950 Kyshtym accident, 1957 Wind scale accident, 1957 Lake Karachay accident, 1967 10,2 7,4 1,1 0,003 2 x 10 2 23 x 10 3 3 x 10 2 2 x 10 2

Effective doses received during various types of work ‘Non-coal’ mining 16.3 milisieverts

Comparison of radiation doses from any sources 0.1 mSv:

Atlantic dental X-ray or return flight across

1 mSv:

average yearly dose from natural radiation excluding radon

20 mSv:

In many countries, the highest allowable yearly dose for people working with radioactivity

A few 100 mSv/year:

lower limit for deterministic effects from prolonged exposure

1000 to few 1000 mSv:

thresholds for different deterministic effects at acute exposures

10 000 mSv:

will kill most people and higher animals after acute exposure

Dose limits recomended by ICRP (1991)

whole body

Occupational exposure 50 mSv maximum in any 1 year Public exposure 5 mSv in any 5 consecutive years 100 mSv in 5 years Working figure 20 mSv per year Working figure 1 mSv per year

Dose limits recomended by ICRP (1991)

tissues

Annual doses to tissues Occupational Public Lens of the eye Skin (1 cm 2 ) Hands and feet or individual organ 150 mSv 500 mSv 500 mSv 15 mSv 50 mSv

Modalities of irradiation and risk of radiation exposure

Risk due to radiation exposure

External exposure

The risks associated with external exposure depend on the type of incident radiation:

Alpha radiation

does not present any risk by external exposure

Beta radiation

can be hazard at the site of exposure on the skin and deep derma

Neutrons

radiation entail the same risks as gamma

Gamma radiation

reaches the skin, the derma and all deep tissues

The San Salvador accident in February 1989

Three employees at an industrial sterilization plant in San Salvador were using a very significant Co-60 source of 600 TBq (more than 15,000 Ci). They were seriously irradiated due to obsolete plant and their not being aware of the risks. As a result of their position and the time they spent near the source, the whole body exposure doses they received have been estimated at 8 Gy, 4 Gy and 3 Gy, respectively. Vomiting appeared less than two hours after exposure. The three victims were referred to the nearest hospital because they felt very tired and could not stop vomiting. They did not present any other sign of acute exposure. Although they had mentioned their work in a plant using ionizing radiation, they were diagnosed as having food poisoning. Acute irradiation syndrome was only recognized three days later when another patient presented with erythema, skin burns, nausea and vomiting and told them that there had been a technical accident at an irradiation plant.

External contamination

The risks linked to external exposure of the skin differ according to the type of radiation:

alpha emitting radio-elements

any risk do not by external contamination, a priori present beta emitting radio-elements because they entail exposure which is almost exclusively of the skin, do present a special risk

gamma emitting radio-elements

problems pose the same by external contamination as in external exposure, external contamination by a

neutron emitting radio element

is impossible.

External contamination reveals a secondary potential risk of internal contamination by inhalation, ingestion or breaking and penetration of the skin.

People involved in the Chernobyl accident in 1986 The Chernobyl accident, 26 April 1986, involved the very serious irradiation and contamination of a number of people working in the power station and those who immediately intervened, it provides a good example of external contamination. More than 200 patients were hospitalized in the hours following the catastrophe. Before this massive flood of victims, the initial efforts to manage the situation were limited to treatment of the symptoms a full assessment of lesions, treatment of traumatic lesions and summary external decontamination. The latter fact was revealed to be particularly damaging as all the patients had external contamination by fission products, such as Cs-137, Sr-90, or I-131, all of them being beta and some gamma emitters. Beta emitters on the skin caused severe radiological burns with complex development. It is estimated that 5 of the 28 premature deaths following the accident were attributable in part to radiological burns. These 5 deaths, and perhaps others, could doubtless have been avoided if good external decontamination of all the exposed subjects had been carried out in the shortest time.

Internal contamination

When radioactive nuclides enter an organism it is still called

internal exposure inhalation and wounds

.

. Incorporation can occur via different pathways: respiratory, digestive, transcutaneous or through breaking and penetration of the skin. The most frequent points of entry are by In internal contamination the radio-elements are in contact with living cells. This position does not much alter the risk induced by beta or X radiation. By contrast, the is major here.

risk associated with alpha radiation

, which did not exist for the other modes of exposure, The presence of radio-elements in an organism is not always pathological, a certain number of atoms, of which the organism is constructed, are radio-elements (example: K-40).

Paints for luminous watch faces

In the 1920s and 1930s the clock making industry used radium 226 and 228 in radio-luminescent paint for watches. At this time, the risk from alpha emitting radio-elements was almost unknown.

The workers who painted the luminous faces had the bad habit of tapering their brushes with their lips. Every time they did this they ingested several becquerels of radium. The fact that radium and calcium are chemical homologues, resulted in rare bone cancers appearing starting from the 20s, in the form of carcinoma of the sinus of the face. An epidemiological enquiry demonstrated the link between exposure to radium and the risk of bone cancer in 2,403 workers, whose ingestion of quantities of radium could be evaluated. 64 were suffering from osteosarcoma whereas 2 cases of this type of cancer would have been expected statistically.

Common risks

Approximately 1 in 10,000 will die from – Working one year in a safe industry – Receiving 50 mSv whole body – Smoking 10 packs of cigarettes – Living with a smoker for 15 years – Drinking 50 bottles of wine – Taking a 1,000 mile bike ride – Traveling 30,000 miles by car – 10,000 hours flying time

Summary of lecture

•

Becquerel (Bq), coulomb per kilogram (C/kg), gray (Gy) and sievert (Sv) are part of International System of Units

•

(SI) Absorbed dose of radiation in SI units is expressed in

•

gray (Gy) Ability of some types of radiation to cause more significant levels of biological damage taken into account with radiation weighting factor used to determine

•

equivalent dose, expressed in sieverts (Sv) Effective dose, expressed in sieverts (Sv), is based upon the estimates of the relative risk of stochastic effects from the irradiation of the different tissues

•

Natural sources of radiation is made 85 % of effective doses received people from various sources of radiation

Lecture is ended

THANKS FOR ATTENTION

In lecture materials of the International Atomic Energy Agency (IAEA), kindly given by doctor Elena Buglova, were used