4. 1- Cosmic Radiation
• These are highly energetic radiations
bombarding the earth from outer
space. The primary cosmic incident on
the earth consists of mixture of
protons (87%), alpha particles (11%),
and a trace of heavier nuclei (1%) and
electron (1%). The energies of these
particles range between 108- 1020 eV
(origin ununderstood).
• The annual cosmic ray dose at sea
level is between26 and 27 mrems. The
dose rate increases with altitude.
4
5. 2- Terrestrial Radiation
• Terrestrial radiation
• There are approximately 340 naturally occurring nuclides
found on the earth, of these, about 70 are radioactive.
Natural radio nuclides are divided into two groups,
depending upon their origin:
• Primordial radio nuclides are those that have been since
earth was formed, The most common primordial nuclides
are 238U (T1/2 = 1.4 × 109 yrs), 235U (T1/2 = 7.8 × 108 yrs),
232Th (T1/2 = 1.4 × 10 10 yrs), 87Rb (T1/2 = 4.8 × 1010 yrs)
and 40K (T1/2 = 1.3 × 10 9 yrs). Some of these radio nuclides
have greater biological significance.
• Cosmogenic radio nuclides are those which are
continuously being produced by the action of cosmic rays.
C 14 (T1/2 = 5730 yrs.) is formed primarily by interaction of
thermalized neutrons with nitrogen in the atmosphere .
5
6. A- External Terrestrial Exposure
• External exposure to terrestrial radioactivity originates with the y
-rays emitted following the decay of uranium, thorium, and their
daughter products. (Fig. Lamarsh 9.7)
• These radionuclides are widely, but unevenly, distributed about
the world. In the United States, for instance, there are three
broad areas of differing terrestrial gamma ray levels. The
Colorado Plateau lies atop geological formations rich in uranium
and radium.; as a result, this region tends to have a much higher
radiation level (90 mrem/yr).
• There are also locations in the world, particularly in Brazil and
India, where the presence of thorium-bearing monozite sands
leads to radiation levels that are especially high (up to 3mR/hr).
The population averaged annual external terrestrial dose in the
United States is 26 mrems.
6
8. B- Internal Terrestrial Exposure
• The principal source of internal Terrestrial radiation
exposure is from primordial 40K. This nuclide decays
both by –ve ß-decay to 40Ca and by +decay to 40Ar.
There is about 0.0157g of 40K from a total of 130g of
potassium in an average person weighing 70kg. The
total activity of the 40K in the body is therefore
approximately 0.11µCi.
• The heavy primordial nuclides and their daughters
enter the body by ingetion of drinking water or food
stuffs. Heavy radionuclides also enter the body as
the result of inhalation of 222Rn (T1/2 = 3.8 days)
and its daughter products especially 210Pb (T1/2 = 21
yrs).
• 222Rn is the immediate daughter of the decay of
226Ra and it is therefore produced in radium bearing
rocks, soil and construction materials.
8
9. http://physics.isu.edu/radinf/natural.htm
The common radionuclides in food are (40K), (226Ra) and (238U) and the associated progeny. Here is
a table of some of the common foods and their levels of 40K and 226Ra.
Food
40K
pCi/kg
226Ra
pCi/kg
Banana 3,520 1
Brazil Nuts 5,600 1,000-7,000
Carrot 3,400 0.6-2
White Potatoes 3,400 1-2.5
Red Meat 3,000 0.5
Lima Bean
raw
4,640 2-5
Drinking water --- 0-0.17
9
10. 3- Man-made radiation sources
(that result in an exposure to members of the public):
• Medical Exposures
• Fallout
• Nuclear Power
• Building materials
• Air Travel
• Televisions
• Tobacco
• Other Man-made Sources
(mnemonic MFNBATTO)
10
12. http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/UnderstandingRadiationTopics/Dos
eComparisonsForIonisingRadiation/
Source of Exposure Dose
Dental X-ray 0.005 mSv
135g bag of Brazil nuts 0.005 mSv
Chest X-ray 0.02 mSv
Transatlantic flight 0.07 mSv
Nuclear power station worker average annual
occupational exposure 0.18 mSv
UK annual average radon dose 1.3 mSv
CT scan of the head 1.4 mSv
UK average annual radiation dose 2.7 mSv
USA average annual radiation dose 6.2 mSv
CT scan of the chest 6.6 mSv
Average annual radon dose to people in
Cornwall 7.8 mSv
Whole body CT scan 10 mSv
Annual exposure limit for nuclear industry
employees 20 mSv
Level at which changes in blood cells can be
readily observed 100 mSv
Acute radiation effects including nausea and a
reduction in white blood cell count 1000 mSv
Dose of radiation which would kill about half of
those receiving it in a month 5000 mSv
12
13. Medical exposures
By far, the most significant source of man-made
radiation exposure to the public is from
medical
procedures, such as:
1. Medical & dental diagnostic radiology
2. Clinical nuclear medicine
3. Radiation therapy
4. Occupational exposure of medical & dental
personnel
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14. Fallout
• Fallout from a nuclear weapon consists of fission fragments
and neutron activation products in weapon debris that
become attached to dust and water particles in the
atmosphere.
• The larger of these particles soon come to earth near the
site of the detonation.
• The smaller ones may remain aloft in the upper
atmosphere for five years or more. In time, they become
distributed more or less uniformly around the world, and
contribute to the general level of environmental radiation.
• The long-term exposure from fallout is mostly internal,
from fission products ingested.
14
15. Fallout
• Fallout is the residual radiation hazard from a
nuclear explosion, so called because it "falls
out" of the atmosphere after the explosion. It
commonly refers to the radioactive dust
created when a nuclear weapon explodes.
This radioactive dust, consisting of hot
particles, is a kind of radioactive
contamination. It can lead to the
contamination of ground and the animal food
chain.
15
16. Nuclear Power
• The increasing use of nuclear power will lead to a small, but increasing, radiation
dose to the general public. This dose is due not only to radiation released from
power plants themselves, but also from uranium mines, mills and fabrication
plants, and fuel-reprocessing facilities. In any case, the population-averaged dose
in the United States was less than 1 mrem/year in 1980.
• The occupational dose to workers in the commercial nuclear industry is computed
from industry data submitted to and published by the US Nuclear Regulatory
Commission.
• http://www.world-nuclear.org/info/Safety-and-Security/Radiation-and-
Health/Nuclear-Radiation-and-Health-Effects/
• The average annual radiation dose to employees at uranium mines (in addition to
natural background) is around 2 mSv (ranging up to 10 mSv). Natural background
radiation is about 2 mSv. In most mines, keeping doses to such low levels is
achieved with straightforward ventilation techniques coupled with rigorously
enforced procedures for hygiene.
• Occupational doses in the US nuclear energy industry – conversion, enrichment,
fuel fabrication and reactor operation – average less than 3 mSv/yr.
16
17. Building materials
• The building material used for house building influences the radiation
dose of human beings due to natural radioactive substances. The radiation
within buildings made of bricks or concrete is higher than in buildings
made of wood or some type of pre-assembled units since this building
material contains less natural radioactive substances.
17
18. Air travels
• People travelling in aircraft may be exposed to more
ionising radiation because the earth’s atmosphere
provides less protection from cosmic radiation at the
typical altitudes of commercial aircraft. Exposure also
increases the further that the flight path is away
from the equator. Therefore, the radiation dose will
vary between different flights depending on origin,
destination, route, flight level pattern and solar
activity at the time. Aircrew and frequent flyers get
the most additional exposure because of the extra
time they spend at high altitudes.
18
19. Air Travel
– At high altitudes cosmic rays dose is much higher
• Aircrafts at altitudes 9–15 km receive higher dose
• High energy particulate dose rate can be measured by CR-
39 made windows
19
21. Television
• Some television sets and computer screens contain a cathode
ray tube (CRT), which bounces electrons off the screen to
create an image. The interaction between the electrons and
the screen can potentially create low-level x-rays. CRT displays
using vacuum tube high voltage rectifiers or regulators also
generate x-rays.
• http://www.fda.gov/Radiation-EmittingProducts/
• With the adoption of Federal regulation, the individual dose rate has
fallen over the past decade, and the average annual dose to the
gonads of viewers is now between 0.2 and 1 .5 mrems. (see Table 9.11)
• The flat panel TVs incorporating Liquid Crystal Displays (LCD) or Plasma
displays are not capable of emitting x-radiation. As such these products
and are not subject to the FDA standard and do not pose a public health
hazard.
21
22. Tobacco
• 222Rn diffuses from the earth to the atmosphere, where it decays into
210Pb, which subsequently falls to the earth attached to dust or moisture
particles. If these particles fall onto leafy vegetables or pasture grasses,
the 210Pb may enter directly into the food chain.
• If the particles fall onto broadleaf tobacco plants, the 210Pb and its
daughter 210Po may be incorporated into commercial smoking materials.
Measurements show that there are on the order of 10 to 20 pCi of both
210Pb and 210Po in an average pack of cigarettes.
• The annual local dose to this tissue for an average cigarette smoker ( 1 .5
packs per day) is estimated to be as high as 8 rems (80 mSv) and
proportionately higher for heavy smokers. Many researchers believe that
this radiation is the origin of the high incidence of lung cancer among
smokers.
22
24. 24
OBJECTIVES OF RADIATION PROTECTION
24
PREVENTION of deterministic
effect
LIMITING the probability of
stochastic effect
25. Lamarsh-9.8 Standard of Radiation
Protection
In 1928 , in response to the growing recognition
of the hazard of radiation, the second
congress of Radiology establish the
International Commission on Radiological
Protection (ICRP) to set standards of
permissible exposure to radiation.
25
26. Standard of Radiation Protection
• ICRP (International Commission of
Radiological protection)
• NCRP (National Council on Radiation
protection & Measurements)
• FRC (Federal Radiation Council)
• EPA (Environmental Protection Agency)
• RPGs (Radiation Protection Guides)
• MPD (Maximum Permissible Dose)
26
27. Ground Rules For Radiation Exposure
1. Any exposure to radiation may be harmful,
however if any compensatory benefit is realized,
then deliberate exposure will must be justified.
2. All exposure to radiation should be kept “ as low as
reasonably achievable” (ALARA).
3. Radiation doses to individuals should not exceed
certain recommended values which are known as
maximum permissible doses (MPDs).
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28. Assumptions of Standards Setting Bodies
a) There is a linear dose-effect relationship for all
radiation effects from zero to high dose levels (in
the ranges of several hundred rads)
b) There is no threshold radiation dose above which
an effect may occur, but below which it does not.
c) Low doses delivered to an organ are additive, no
matter at what rate or at what intervals they may
be delivered.
d) There is no biological recovery from radiation
effects at low doses.
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