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Dose Units & Radiation Safety 1

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 andapplications.

Today, safety committee is set up to deal with radiation risks.
http://www.icrp.org/http://www.icrp.org/

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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 effectsdamages 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 resultin 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 EffectsHuman 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 ofAdenine, Guanine Cytosine orThymine.

TheA-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 calledTranslocation, which cause mutation and deformation at birth.

Genetic effects increase frequency of mutation.

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Genetic Effects - DNA Molecules

The double-helixDNA has two

strands of

phosphoric-acid

and sugar linked

bases of

Adenine,

Guanine

Cytosine or

Thymine.

TheA-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 -

Replicationof DNA

http://www.accessexcellenc

e.org/AB/GG/possible.html

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Transcription

of DNA

http://www.accessexcellence.org/

AB/GG/protein_synthesis.html

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AL-MADA'IN, Iraq - Dozens of people are showing up every day at ahospital near a defunct Iraqi nuclear plant, suffering from rashes, bloodynoses and other symptoms of radiation poisoning, doctors said Saturday.

The Tuwaitha nuclear facility, 12 miles south of Baghdad, was left unguardedafter 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 dosimeterreflects an equivalence of

certain dosage of X-rays.

The amounts are defined

in certain units as shownhere.

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 decayis 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 orparticles), 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- org-rays that produce 1 esu charge

(negative and positive each or 2.1e9 ion pairs) in 1.0 L.

1 R = 352.1e9

= 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 org-rad org-Gy total dosage received by an

organ.

g-Gy = dose * mass of the organAccumulated 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 FactorQ and Dosage

Units

Quality factor (Q) or (rbe) of

various radiations.

Radiation Qorrbe

X-, g- and b rays 1Thermal neutrons (n) 3

Fast n, a, and protons 10

Recoil nuclei 20

The factor reflecting the

relative harmfulness of

various types of radiation

is called the quality factor(Q) orrelative biological

effectiveness (rbe)

Biological dose = Q* exposure dose

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Exposure and Biological Dosage

SI unit cgs unit

Exposure unit 1 Gy = 100 rad (=100 R)Biological dose 1 Sv = 100 rem (= Qrad)

Gy: gray, Sv: sievert, R: roentgen, rem: roentgen equivalent man

type units

Radioactivity Bq, Ci

Exposure dose Gy, rad (R)

Quality factor Q

Biological dose Sv, rem

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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)

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

dosimetercandidates.

Ferrous sulfate, FeSO4, solution is a chemical dosimeterdue 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 a particle is absorbed by 1 gram of water,estimate the dosage in rad and rem.

The Q factor is 10 fora 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.

rad108.0=

erg100

rad1

J1

erg10

MeV1

J101.6

g1

5MeV 8-7-13

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Natural Radiation Sources

Cosmic rays consist of high-energy protons, helium ions, heaviernuclei, 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 (t ~ 106-15 y) Radiation

235, 238U, 232Th and their off springs a, b, g144Nd, 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 rays14C (5730 y), 3T (15 y), 7Be (53 d), 10Be (2.7106 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

Type mSv

natural occurring sources 0.8medical procedures (X-rays) 0.8

others 0.2

weapon tests 0.05

consumer products 0.04airline travel 0.005

Total 1.9

Low-dose exposures in

addition to natural

background radiationhave delayed somatic

and genetic effects.

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High-dosage Exposures

Symptoms develop shortly in high-dosage exposures.

1 Sv or lowerdose 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 shockdue 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, anddiarrhea. 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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