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• Natural background radiation
- Construction materials (55 %)- Radiation of the soil (26 %)- Cosmic radiation (17%)- Food (2%)
Sources of radiation 1Radiation we live with
Sources of radiation 2Radiation we live with
Food Radioactive levels (Bq/kg)Daily intake
(g/d)
Ra-226 Th-228 Pb-210 K-40
Rice 150 0.126 0.267
0.133
62.4
Wheat
270
0.296
0.270
0.133
142.2
Pulses
60
0.233
0.093
0.115
397.0
Other Vegetables
70
0.126
0.167
--
135.2
Leafy Vegetables
15
0.267
0.326
--89.1
Milk 90-- -- -- 38.1
Composite Diet 1370 0.067 0.089 0.063 65.0
• Artificial– the X-ray tubes– reactors and cyclotrons
- Could have detrimental effects- Optimal function – radiation safety
Sources of the radiation 4
Decay of radionuclides
Mother nuclide Daughter nuclide+ particles+ energy (e.g.photon)
Type of decay
Half life
Decay processes
Alpha decaye.g. 224Ra
A
Z XA-4
Z-2Y + alpha + E4
2
Beta decaye.g. 14C, 99Mo
X Y + e + Ev + EßAZ
AZ+1
0-1
Positron decaye.g. 11C, 18F X Y + e + Ev + Eß+
AZ
AZ-1 +1
0
Electron capturee.g. 111In, 125I
X + e- Y* Y + gammaA A AZ Z-1 Z-1
• Ionising– Particule radiation (Energia MeV)
• alfa (α) 2-10 • beta (β) 0,01-50• protons (p) 1-10• neutrons (n) 0,02-30• ions 1-50
– Electromagnetic radiation• X-rays 0,005-0,5• gamma-radiation (γ) 0,005-50
Sources of radiation 2
• Non ionising radiation– Electromagnetic
• optical (light)• high frequency• low frequency
– Sound• infrasound• ultrasound
Sources of radiation 3
Biological effects of the radiation 1
• Physical phase (10-18-10-16 s)– Direct effects (ionisation and excitation)– Indirect effects
• H2O radiolysis• Free radicals
• Chemical phase (10-16-1 s)– DNA– Molecule fragmentation
• Biological phase (sec-years)– Stochastic effects– Deterministic effects
Risc assessmentInternational Commission on Radiological Protection (ICRP)
– For radiation workers: 4,0 x (10-
2/Sv)– For population: 5,0 x (10-2/Sv)
• 20 mSv: 8 x 10-4 = 1/1250• 1 mSv/y: 5 x 10-5 = 1/20000
Radiation doses 1
• Absorbed dose• Equivalent dose• Effective dose• Personal dose equivalent• Committed equivalent dose• Committed effective dose• Collective dose
Radiation doses 2• Absorbed dose
D = d ε /dmunite: J/ kg; gray (Gy)
• Equivalent doseH T,R = wR DT,R
unite: J/ kg; sievert (Si); wR=1 (photons)
• Effective doseE = Σ wT HT = Σ wT Σ wR DT,R
T T Runite: J/ kg; ievert (Sv)
Radiation doses 3
Commited dose– long lived radionuclides
137-Cs (30 year), 90-Sr (28.5 year)- we intake them with food, water, air
• 137-Cs (K biological analog)accumulates in soft tissues
• 90-Sr (Ca biological analog)accumulates in bones
Dose limits96/29/EURATOM• for the Professional radiation workers:Effective dose:100 mSv/ 5 consecutive years; 50 mSv/any year
Organ doses:Eyes: 150 mSv/ year (equivalent dose)Hands: 500 mSv/ year (equivalent dose)
Dose limits96/29/EURATOM• for the PublicEffective dose:1 mSv/ 1 year
Organ doses:Eyes: 15 mSv/ year (equivalent dose)Hands: 50 mSv/ year (equivalent dose)
Detection of the radiation
• Gas detectors– Ionisation chambers– Proportional counters– Geiger-Müller counters
• Scintillation detectors (SPECT, PET, CT)
• X-ray films
Scintillation detectors
• Higher counting rates (fast resolving times)• Gamma radiation (proportionality)• Sodium iodine crystals (Tl activated)
– Gamma camera, SPECT, well counter• BGO, LSO (PET)• Semiconductors (dosimeter, camera?)
Radiation safety in NM
• As low as reasonably achievable (ALARA)• Reducing radiation exposure:
– time– distance– shilding
Figure 2. Schematic illustrates the inverse-square law
Brateman L Radiographics 1999;19:1037-1055
©1999 by Radiological Society of North America
• Shilding– 0,5 mm Pb
• 70 kV energy X-rays penetration: 0,36%• 100 kV energy X-reay penetration: 3,2%
– Pb glass• 30%-70%
Rules for working safely with unsealed radionuclide sources
• Always work in areas designed for handling radionuclides.
• To open sealed bottles use a well-designed hood or glove box.
• Work areas should be covered, to catch any spills and to prevent the spread of contamination.
• Plan all procedures in advance.• Do not eat, drink or smoke in areas where unsealed
radionuclides are being used or stored.• Wear protective clothing and surgical gloves while
working
Radioactive material decontamination procedures
• Place absorbent material over the spill to keep it from spreading.
• Notify others in the area and limit access to the spill area.
• Monitor personnel for contamination and, if necessary, decontaminate immediately.
• Label the boundaries of the spill area.• Dispose all cleanup materials as radioactive waste.