Dosimetry Lab

Question 1

Define ionizing radiation.

Answer 1

• Radiation with enough power to directly or indirectly produce ion pairs when absorbed in matter
• Corpuscular EM radiations such as X and Gamma rays

Question 2

What is the “direct effect” radiation damage?

Answer 2

Damage caused by radiation’s interaction with biologically important macromolecules such as DNA

Question 3

What is “indirect effect” radiation damage?

Answer 3

When radiation creates free radicals (-H, -OH, etc) from the water in an organism and these free radicals go on to interact with DNA, etc.

Question 4

What is “deterministic effect” radiation damage?

Typical effects?

Answer 4

Radiation with a threshold dose, above which the probability/severity of radiation damage increases abruptly and proportionally to dose.

• Typical effects are erythema and eye lens damage

Question 5

What is “stochastic effect” radiation damage?

Typical effects?

What is special about a graph of dose vs. damage probability?

Answer 5

Radiation in which the probability/severity of damage is proportional to the dose and no threshold dose is defined.

• Typical effects are genetic disorders and some cancers
• Its graph technically does not start at zero dose because of background radiation.

Question 6

What 4 factors influence radiation damage severity?

Answer 6

1. Type of radiation
2. Sensitivity of organ damaged
3. Dose received (dose rate x exposure time)
4. Timespan of received dose

Question 7

What is Absorbed Dose?

Answer 7

a simple measure of energy absorbed per unit mass

measure in gray

1 Gy = 1 Joule/kg

Question 8

What is Exposure?

Answer 8

A measure for the radiation of X and gamma rays of photon energy < 3 MeV absorbed in air

measured in Coulombs/kg

Question 9

What is equivalent dose?

Its unit?

Answer 9

A dose concept which takes into account radiation type and uses a radiation weighting factor

H_T = D_T,R ᐧ ω_R

• measured in Sieverts (J/kg)

Question 10

What is effective dose (E) ?

Its unit?

Answer 10

a dose concept that takes into account the sensitivity of the affected organ and uses a tissue weighting factor

E = H_T ᐧ ω_T

• uses Sievert (J/kg)

Question 11

What is dose rate?

Its unit(s)?

Answer 11

dose per unit time

dose rate = D/t

unit corresponds to whatever dose concept is being used

i.e. Gy/h, Sv/h

Question 12

What are the different “regions” of a current vs. voltage graph?

Answer 12

1. Recombination **Region **- where separated electron and positive ion recombine (first region of increasing current before U_sat,1)
2. **Proportional Region **- As voltage increases, primary electrons cause secondary ionization proportional to the increase (second region of increasing current)
3. **Geiger-Muller Region **- region of maximal signal production from tertiary, quaternary, etc. ionizations (flat region just after proportional region)

Question 13

How was the equivalent dose rate calculated for the dosimetry lab report?

Answer 13

1. The current of saturation (I, measured in nA) was put into the exposure rate equation X_t = I/M_gas (M_gas is the mass of air between the electrodes).
2. For M_gas, the trapezoidal area of the electrodes was first determined using **A_trapezoid = ([a + b]/2) ᐧ h **(a and b are the base and top of the trapezoid).
3. Then electrode area was multiplied by the distance between the electrodes to obtain volume.
4. This volume was then multiplied by air’s density to obtain M_gas.
5. X_t is a value in units of C/Kgᐧsec, so conversion factor ƒ₀ = 34 J/C was used to convert exposure rate to dose rate (D_t).
6. Radiation weighting factor ω_R = 1 was used in the equation H_T = D_T,R ᐧ ω_Rto determine equivalent dose rate.