1. Ch6 Measurement of Ionizing Radiation

2. Introduction Chemical and Biologic effect Skin erythema dose (SED)
AD 1928 , ICRU , Roentgen
Exposure(X)

5. Free-Air ionization chamber Correction for
(a) air attenuation
(b) recombination of ions
(c) the effects of temperature, pressure, and humidity
(d) scattered photons

6. Limitations : High energy photons
Non-unique electric field and greater ion recombination

7. Thimble chambers
The inner cavity is equal to the maximum range of electrons

8. Effective of Atomic Number

9. Chamber Calibration (A) too few electrons are generated in the wall
(B) reduced because if increased attenuation of the beam in the wall

10. Practical Thimble Chambers
Condenser Chambers

11. Stem Effect

12. Farmer Chamber Condenser chamber--- lower energy beams (<=2MV)
The design of stem and excessive stem leakage create dosimetric problems

15. String Electrometer

16. Other Electrometer

17. Special chamber- Extrapolation Chamber

18. Ion Collection
Incomplete ion collection at low voltages

19. Collection Efficiency
Two voltage testing techniques
Ion recombination correction

20. Chamber Polarity effects
Compton current
Extracameral current
Environmental conditions
Exposure calibration factor(Nc):NIST
Ctp:Temperature and pressure
Cs:Recombination
Cst:Stem leakage correction