Lecture 6. Quantities and Units

Question 1

What is Fluence Rate?

Answer 1

The number of particles or photons crossing the plane per unit area exposed per unit time

Question 2

Formula for fluence rate:

Answer 2

Question 3

What is Exposure?

Answer 3

A measure of ionization in AIR caused by ionizing radiation from X-rays and Gamma rays

NB: SI unit of exposure is coulomb/kilogram
Exposure only applies to photons!!

Question 4

Formula for Exposure

Answer 4

Question 5

What is the common unit of measurement for exposure?

Answer 5

Roentgen

NB: 1 C/kg = 3876 R

Question 6

What device is used to measure exposure?

Answer 6

Ion chamber

Question 7

What is Absorbed Dose?

Answer 7

A measure of the amount of energy deposited in matter by radiation

Question 8

Formula for Absorbed Dose

Answer 8

Question 9

What is the SI unit for absorbed dose?

Answer 9

Gray (Gy)

NB: Non-SI unit is the rad (used by Americans)
1 rad = 1 cGy

Question 10

What is Absorbed Dose Rate?

Answer 10

The mean energy imparted by ionizing radiation per unit mass of matter per unit time

NB: SI unit is Gy/s or cGy/min

Question 11

What is Linear Energy Transfer (LET)?

Answer 11

Linear energy transfer (LET) quantifies energy deposition by charged particles per unit distance travelled in a material, influencing radiation effects, ionization, and biological damage, with higher LET causing greater localized energy deposition

Question 12

List different types of radiation from low LET to high LET

Answer 12

1. X-rays, Gamma rays, Electrons (less than 3.5)
2. Thermal neutrons (about 5)
3. Neutrons between 0.1 and 2 MeV (greater than 53)
4. Alpha particles (about 175)

Question 13

List the radiation weighting factors for the different types of radiation

Answer 13

1. Photons 1
2. Electrons 1
3. Protons 2
4. Alpha 20

Question 14

Summary of Quantities

Answer 14