Lecture 22

Question 1

Dosimetry

Answer 1

Studies the quantities describing the effect of ionizing radiation on nagger and the methods of their measurement and calculation.
Eg. Radiography

Question 2

Absorbed dose

Answer 2

The energy deposited by the ionizing radiation per unit mass of the medium
PD= deltaD/deltaT

Question 3

Equivalent dose rate

Answer 3

The rate at which the equivalent rate is accumulated.
ph=deltaH/deltat
The biological effect increases

Question 4

Exposure X

Answer 4

Total charge of the ions of one polarity, produced by the radiation.

The dose exposure relationship is D=fx

Question 5

Conversion factor f

Answer 5

A measure of the energy absorption by the irradiated medium.

Depends on the energy of the quanta and the type of medium.

Question 6

Dosimetric instruments

Answer 6

Devices used to measure the dosimetric quantities.
Dosimeters are used to the measure doses and their rates whereas radiometers are used to the measure the activity of radioactive sources.

Question 7

Ionization chamber

Answer 7

The radiation ionizes the gas and a current flows in the circuit. The electric current is proportional to the exposure rate.

Question 8

Quartz fibre dosimeter

Answer 8

A small ionization chamber with no power supply so therefore it is charged by an external power source.
Ionization of the gas in the chamber reduces the charge on the electrons.

Question 9

Geiger counter

Answer 9

Each ion produces a strong electric current, the voltage between the electrode drops and the current stops.
The amplitudes of the pulses are approximately equal and do not depend on the energy of the radiation.

Question 10

Semiconductor detectors

Answer 10

The ionizing radiation increases the electrical conductance of the semiconductor material and it is used to the measure the energy distribution of the ionizing particles.

Question 11

Photographic detectors

Answer 11

Photographic films are very sensitive to radiation and so the darkening of the film depends on the absorbed dose.
However the disadvantage is that it has low accuracy.

Question 12

Natural background radiation

Answer 12

There are two types: cosmic radiation and terrestrial radiation.

CR: 300 and 400
TR: 2000 and 2400

Question 13

Compromise

Answer 13

Minimization and not elimination of the exposure

Higher exposure to a small fracture of the population can be tolerated.

Question 14

Methods of radiation protection

Answer 14

Ensure safe working conditions by the amount, time, distance and shielding.
And provide regular medical monitoring.