Radiation physics and radiation protection

University of SzegedDepartment of Nuclear Medicine

Radiation doses to the population 1

Radiation doses to the population 2

• 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

Sources of radiation 3Radiation we live with

• Artificial– the X-ray tubes– reactors and cyclotrons

- Could have detrimental effects- Optimal function – radiation safety

Sources of the radiation 4

CTX ray emission inall directions

X ray tube

collimators

Cyclotrons

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

Decay scheme of 14C

Principal decay scheme of 99Mo

Decay scheme of 18F

• Ionising radiation

• Non ionising radiation

• 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

Path of heavy charged particle in matter

excitation

ionization

close approach

Principal photon interactions in matter

Positron annihilation

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

Stochastic effects 1

• cancer induction• genetic effects

– No threshold dose!

Stochastic effects 2Risk models

Deterministic effects 1

Absorbed dose

Effect

Threshold dose

Deterministic effects 2

• Dermatitis

• Cataracta

• Acute radiation sickness

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

We live with1-3 mSv

Could be lethal4000 mSv

Radiation

Border?

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

Gas-filled detectors

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?)

Scintillation detectors

Gamma Camera Detector

SPECT

PET

Personal Dosimeters

• X-ray films• TLD dosimeters• Electronic dosimeters• Optical dosimeters

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

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%

International Atomic Energy Agency (IAEA)

• IBSS 115 (1966) standards

mSv

Year

Changes in Dose Limit (ICRP) (Safe levels)

0

100

200

300

400

500

1931 1947 1977 1990

PET

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.