Dose Units & Radiation Safety 1 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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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 and applications.
Today, safety committee is set up to deal with radiation risks.
The International Commission on Radiological Protection, ICRP, is an independent Registered Charity, established to advance for the public benefit the science of radiologicalprotection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation.
From www.icrp.comcheck 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.
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.
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.
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 it’s internal.
1 Curie = 3.7e10 Bq.
These units have nothing to do with energy, type (, X-rays, neutrons, protons or particles), and effect of radiation.
Commonly used unitsMegacurieKilocurieMillicurie
MicrocurieNonocuriePicocurie
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 = 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 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) 3Fast 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
SI unit cgs unitExposure 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 Bqexposure dose X C/kg R 1 C/kg = 3876 Rabsorbed dose D Gy (J/kg) rad 1 Gy = 100 rad
=6.24 eV/gbiological 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 MonitoringDosimeters 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 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.
rad 108.0 = erg 100
rad 1
J 1
erg 10 MeV 1
J 101.6
g 1
5MeV 8-7-13
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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 NuclidesNuclides (t½ ~ 106-15 y) Radiation235, 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 rays14C (5730 y), 3T (15 y), 7Be (53 d), 10Be (2.7×106 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.
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 0.2weapon tests 0.05
consumer products 0.04airline 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 InjuriesWhole-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.
