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Radiation Safety benefits and risks


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									                Radiation Safety
                 benefits and risks

Accidental and avoidable exposure to ionizing radiation is a risk.
Effects of ionizing radiation on life depend on types of radiation,
rates of receiving, and dosages (amounts) received.
Natural ionizing radiation include cosmic rays, X-rays and gamma
rays from space, and natural radioactivity.
Risk will be discussed in terms of types, rate of receiving, and
dosages using well defined units and quantities .

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   Early Experiences of Radiation Effects

Early workers exposed to X-rays developed dermatitis.
Uranium miners developed skin lesions.
People working with radioactivity experienced illness.
Researchers exposed to radioactivity suffered radiation sickness
at advanced age.
Manhattan project workers in Los Alamos, Oak Ridge, Hanford,
and atomic worker in the former USSR suffered anorexia, fatigue,
headache, nausea, vomiting, and diarrhea.

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    Collective Response to Radiation Risk
In 1928, the International Committee on X-ray and Radium
Protection was formed to look into the risk of radiation. It is now
called International Commission on Radiological Protection, ICRP.
In 1942, a group of health physicists had the responsibility to assess
problems and implement safe operation procedures regarding
After WW2, the (American) National Council of Radiation Protection
(NCRP) was formed in 1946.
Guidelines are given for radioactive material handling and
Today, safety committee is set up to deal with radiation risks.

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    Mission Statement of the ICRP

The International Commission on Radiological Protection,
ICRP, is an independent Registered Charity, established to
advance for the public benefit the science of radiological
protection, in particular by providing recommendations and
guidance on all aspects of protection against ionising

check with ICRP for up-to-date guidance regarding radiation

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  National Policies on Ionizing Radiation

The Environmental Health Directorate of Canada is concerned with
radiation risks. Safety Codes were prepared by the Radiation
Protection Bureau of Health Canada. The latest change was made
in October 1999.
Working with ionizing radiation must follow guidelines for the
organization and for the workers. Safe practice is more than follow
guidelines to the letter. Apply common sense to avoid as much
exposure as possible.

URL /ehp/ehd/catalogue /rpb_pubs/99ehd237.htm.

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                    Radiation Effects
Somatic effects
damages to cells passed on to succeeding cell generations.

Genetic effects
damages to genes that affect future generations.
Genes are units of hereditary information that occupy fixed
positions (locus) on a chromosome. Genes achieve their effects by
directing the synthesis of proteins.

Somatic effects and genetic effects show no immediate symptoms

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                   Somatic Effects

Damages to cell membranes, mitochondria and cell nuclei result
in abnormal cell functions, affecting their division, growth and
general heath.
Organs such as skin, lining of gastrointestinal tract, embryos,
and bone marrow, whose cells proliferate rapidly are easily
Bone marrow makes blood, and its damage leads to reduction of
blood cell counts and anemia.
Damage to germinal tissues reduces cell division, and induces

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                       Genetic Effects
Human cells contain 46 chromosomes. Germ or ovum cells contain 23.
A chromosome contains a deoxyribonucleic acid (DNA) molecule.
The double-helix DNA has two strands of phosphoric-acid and sugar linked
bases of Adenine, Guanine Cytosine or Thymine.
The A-T and G-C pairs stack on top of each other.
The DNA codon transcripts mRNA, which directs the amino-acid sequences
of protein. DNA Damages result in somatic and genetic effects.
When DNA molecules replicate (pass on to next generation), they are
sensitive to radiation damage. Joining wrong ends of broken DNA is called
Translocation, which cause mutation and deformation at birth.
Genetic effects increase frequency of mutation.
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      Genetic Effects - DNA Molecules

                                                          The double-helix
                                                          DNA has two
                                                          strands of
                                                          and sugar linked
                                                          bases of
                                                          Cytosine or
                                                          The A-T and G-C
                                                          pairs stack on
                                                          top of each other.
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   Effects -
 of DNA

                             Dose Units & Radiation Safety   10
                                       of DNA


Dose Units & Radiation Safety                          11
AL-MADA'IN, Iraq - Dozens of people are showing up every day at a
hospital near a defunct Iraqi nuclear plant, suffering from rashes, bloody
noses and other symptoms of radiation poisoning, doctors said Saturday.
The Tuwaitha nuclear facility, 12 miles south of Baghdad, was left unguarded
                             Dose Units & Radiation Safety             12
after Iraqi troops fled the area on the eve of the war. (News, Jun, 2003)
  Radiation Absorption and Dosage

           type           units             The amount of energy
                                            absorbed from exposure
        Radioactivity    Bq, Ci            to radiation is called a
                                         dose. The radiation effect
                                            measured by a dosimeter
       Exposure dose Gy, rad (R)            reflects an equivalence of
                                            certain dosage of X-rays.
         Quality factor     Q               The amounts are defined
                                            in certain units as shown
       Biological dose    Sv, rem           here.

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  Units for Radiation Source (review)

The SI unit for radioactivity is Bq
(1 becquerel = 1 dps).                           Commonly used units
The decay is not necessary all                       Megacurie
absorbed unless it’s internal.                        Kilocurie
1 Curie = 3.7e10 Bq.                                 Microcurie
These units have nothing to do                       Nonocurie
with energy, type (a, b, g, X-                       Picocurie
rays, neutrons, protons or                         these modifiers are also
particles), and effect of radiation.                 used for other units.

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Dose Units - roentgen, rad, and gray
Amounts of absorbed energy are not the same as exposed.
The amount of radiation energy absorbed is called a dose.
A roentgen ( R) is a dose of X- or g-rays that produce 1 esu charge
(negative and positive each or 2.1e9 ion pairs) in 1.0 L.
        1 R = 352.1e9
           = 7.35e10 eV (*1.6x10-12 erg/eV)
           = 0.12 erg    (per 0.00123 g air)
           = 1 rad       (100 erg per g of any substance)
        1 Gy = 1 J / kg (1 J per kg of any substance is a gray, Gy)
             = 1e7 erg / kg = 100(100 erg/g)
             ~ 100 rad

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Integral Dose Used in Radiation Therapy

  Total energy absorbed by an organ called integral dose is
  gram-rad or g-rad or g-Gy total dosage received by an
      g-Gy = dose * mass of the organ
  Accumulated dose is the dose received over a period,
  but g-Gy is the total dose received in a single time.

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 The Quality Factor Q and Dosage

The factor reflecting the            Quality factor (Q) or (rbe) of
relative harmfulness of                  various radiations.
various types of radiation
is called the quality factor                  Radiation      Q or rbe
(Q) or relative biological             X-, g- and b rays     1
                                   Thermal neutrons (n)      3
effectiveness (rbe)
                                  Fast n, a, and protons     10
                                             Recoil nuclei   20

           Biological dose = Q * exposure dose

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Exposure and Biological Dosage
                                type             units

                            Radioactivity       Bq, Ci
             

                          Exposure dose Gy, rad (R)

                             Quality factor        Q

                            Biological dose   Sv, rem

                 SI unit cgs unit
 Exposure unit 1 Gy = 100 rad (=100 R)
 Biological dose 1 Sv = 100 rem (= Qrad)

 Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent man
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 Summary of Units for Radioactive Dosage

      Quantity Symbol         SI unit   cgs unit      Conversion factor
  radioactivity   A            Bq           Ci        1 Ci = 3.7e10 Bq
exposure dose     X          C/kg           R         1 C/kg = 3876 R
absorbed dose     D         Gy (J/kg)      rad        1 Gy = 100 rad
                                                       =6.24 eV/g
biological dose   H        Sv (Q*Gy)      rem         1 Sv = 100 rem

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                Exposure Limit

 Maximum permissible dosage of workers in radiation zone

              Max. accumulated           Max. dose/13 wk
                     mSv                        mSv

Whole body        50(age-18)                       30

Hands and                                      250 (750/y)

                 1 Sv = 1000 mSv = 100 rem

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    Dosimeters for Dosage Monitoring
Dosimeters are devices to measure exposed doses.
Film-badges, electroscopes, ionization chambers, biological and
chemical dosimeters have been used for radiation monitors.
Plants, cells, bacteria, and viruses reacting to radiation are biological
dosimeter candidates.
Ferrous sulfate, FeSO4, solution is a chemical dosimeter due to the
        4 Fe2+ + energy + O2  4 Fe3+(brown) + 2 O2-
Some glasses and crystals serve as solid state dosimeters.
Shelf life, linearity, stability, usage simplicity, easy-to-read, dose-rate
and equal responses to various radiation are some considerations.
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   Chemical 3-dimensional Dosimeter

Ferrous ions, Fe2+, are oxidized by ionizing radiation, and convert to
ferric ions, Fe3+, which complexes with xylenol orange dye to give an
orange compound.
When the sample is prepared in a gel form, it serves as a 3-
dimensional dosimeter, because the complexes are localized in the
gel. These dosimeters are useful for planning radiation medical
treatments such as radiation cancer treatment.

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        A Dosage Evaluation Example
    A 5-MeV a particle is absorbed by 1 gram of water,
    estimate the dosage in rad and rem.

         5MeV 1.6 10 -13 J 10 7 erg 1 rad
                                           = 8.0 10 -8 rad
          1g    1 MeV         1 J 100 erg

The Q factor is 10 for a particle, and thus the dose is 8e-7 rem or
8e-9 Sv.

If the a particle is absorbed by a of 10-9 g cell, then the dose is 109 times
higher (0.8 Gy, 8 Sv), exceeded lethal dose for most living beings.
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           Natural Radiation Sources
  Cosmic rays consist of high-energy protons, helium ions, heavier
  nuclei, and some electrons. They cause nuclear reactions
  generating secondary electrons and radioactivity.
  The terrestrial radiation sources are natural radioactive nuclides.

                 Some Natural Occurring Radioactive Nuclides
Nuclides (t½ ~ 106-15 y)                                   Radiation
235, 238U, 232Th and their off springs                     a, b, g
144Nd, 147, 148, 149Sm, 152Gd, 186Os, 190, 192Pt           a (g)
40K, 87Rb, 115In, 123Te, 138La, 176Lu, 187Re, 210Bi etc.   b+, b, EC (g)
Nuclides produced by cosmic rays
14C (5730 y), 3T (15 y), 7Be (53 d), 10Be (2.7×106 y)      b

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         Artificial Radiation Sources
X-rays are generated by stopping fast moving electrons. A chest X-
ray exam is exposed to less than 0.01 Sv, more if multiple images
are taken.
Accelerators generate high-speed electrons, atomic nuclei, high-
energy particles, and synchrotron radiation.
Nuclear explosions leave radioactive fission products.
Nuclear reactors are sources of ionizing radiation.
Leakage of radioactive nuclides contaminates environment.
Nuclear-waste areas are sources of radiation.
Uranium mining tailings are more radioactive than natural sources.
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            Low-dosage Exposures

                                   Background annual exposure
Low-dose exposures in
addition to natural                                     Type mSv
background radiation               natural occurring sources     0.8
have delayed somatic             medical procedures (X-rays)     0.8
and genetic effects.                                   others    0.2
                                               weapon tests      0.05
                                          consumer products      0.04
                                                airline travel   0.005
                                                         Total   1.9

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           High-dosage Exposures

Symptoms develop shortly in high-dosage exposures.
1 Sv or lower dose exposure has little immediate symptoms.
1-2 Sv exposures cause nausea and occasional vomiting in a few
days. Victims survive when infection is medicated.
2-4 Sv exposures cause anorexia, fatigue, nausea and vomiting,
diarrhea, low chance to survive.
4-5 Sv, lethal dose (LD50), absorption lead to disorientation and shock
due to injury to central nervous and cardiovascular systems.

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                   Radiation Injuries
Whole-body radiation victims mostly suffer from injuries to the
hemopoietic, gastrointestinal (GI), and central nervous (CN) systems.
Injuries to the hemopoietic system lead to bone morrow syndromes
with low red and white cells and platelet counts.
The GI syndromes are anorexia, fatigue, nausea, vomiting, and
diarrhea. GI system failures weakens body defence.
Damages to the isolated and non-renewable CN system show ataxia
(loss of motion control), disorientation, apathy, depression, prostration
(exhaustion), convulsions, and shock.
Organs such as skin, gonads, and eyes are sensitive to radiation.

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                      A Summary
Early experiences led to the discoveries of radiation effects.
Radiation causes delayed somatic and genetic effects due to
damages to cells and the DNA molecules.
Quantities of radiation, absorbed or exposed doses, and
biological effective doses must be expressed in units.
Exposure limits for workers are guidelines, and limits for the
general public are 100th of those for workers.
Some principles of dosimeters have also been discussed.
Understanding radiation sickness symptoms and injuries leads
to a peaceful mind.

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