Radiation Safety benefits and risks

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Radiation Safetybenefits 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
radioactivity. After WW2, the (American)
National Council of Radiation Protection (NCRP)
was formed in 1946. Guidelines are given for
radioactive material handling and
applications. 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 radiation. From www.icrp.com 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
hc-sc.gc.ca /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 effectsdamages 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
damaged. 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 sterility.
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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
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.
http//www.accessexcellence.org/AB/GG/dna_molecule
.html
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Genetic Effects - Replication of DNA
http//www.accessexcellence.org/AB/GG/possible.htm
l
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Transcription of DNA
http//www.accessexcellence.org/AB/GG/protein_synt
hesis.html
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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 after Iraqi troops fled the area on the
eve of the war. (News, Jun, 2003)
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Radiation Absorption and Dosage
The amount of energy absorbed from exposure to
radiation is called a dose. The radiation effect
measured by a dosimeter reflects an equivalence
of certain dosage of X-rays. The amounts are
defined in certain units as shown here.
type units ? Radioactivity Bq, Ci
? ? ? Exposure dose Gy, rad (R)
Quality factor Q Biological dose
Sv, rem
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Units for Radiation Source (review)
The SI unit for radioactivity is Bq (1 becquerel
1 dps). The decay is not necessary all
absorbed unless its internal. 1 Curie 3.7e10
Bq. These units have nothing to do with energy,
type (a, b, g, X-rays, neutrons, protons or
particles), and effect of radiation.
Commonly used units Megacurie Kilocurie Millicurie
Microcurie Nonocurie Picocurie these modifiers
are also 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 ?-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 organ. 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 Units
Quality factor (Q) or (rbe) of various
radiations. Radiation Q or rbe X-,
?- and ? rays 1 Thermal neutrons (n) 3 Fast
n, ?, and protons 10 Recoil nuclei 20
The factor reflecting the relative harmfulness of
various types of radiation is called the quality
factor (Q) or relative biological effectiveness
(rbe)
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
(QGy) 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)forearms
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 reaction 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 ? particle is absorbed by 1 gram of
water, estimate the dosage in rad and rem.
The Q factor is 10 for ? 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 23
5, 238U, 232Th and their off springs ?, ?,
? 144Nd, 147, 148, 149Sm, 152Gd, 186Os, 190,
192Pt ? (?) 40K, 87Rb, 115In, 123Te, 138La,
176Lu, 187Re, 210Bi etc. ?, ?, EC (?) Nuclides
produced by cosmic rays 14C (5730 y), 3T (15
y), 7Be (53 d), 10Be (2.7106 y) ?
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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 Type mSv natural
occurring sources 0.8 medical procedures
(X-rays) 0.8 others 0.2 weapon
tests 0.05 consumer products 0.04 airline
travel 0.005 Total 1.9
Low-dose exposures in addition to natural
background radiation have delayed somatic and
genetic effects.
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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.