mid sem exam week 1-4

what are the two effects of radiation

deterministic effect, stochastic effect

what is tthe meaning of deterministic effect

same input always produces exact same output

what is stochastic effect

random and the probability increases with dose, severity is not affected by magnitude of dose, no threshold

what is relative risk (RR)

ratio of disease incidence in exposed population vs general population

what is excess relative risk (ERR)

RR-1 (relative risk)

what is the origin of radiation for xray

decaying atom in atomic state

what is the origin of radiation for gamma

decaying atom in nuclear state

what is pair production

photon spontaneously creates an electron-positron pair

what are the types of ionising radiation

particulate and electromagnetic

what interaction is involved with ionising radiation with matter

transfer of energy from the radiation to atomic electron/nuclei

what is LET

linear energy transfer

what is LET for electrons and beta particles

primarily atomic electrons, large changes in direction, may cause ionisation

what is LET for photons (xray and gamma)

primarily photoelectric effect, compton scatter: ionisation and excitation

what is the unit for dose

gray/ sievert

what is absorbed dose

the energy imparted by the ionising radiation per unit mass of matter

what is equivalent dose

for the same absorbed dose, the biological effects of IR depend on the type and energy, of the radiation

what is effective dose

apply a tissue weighting factor to the equivalent dose, which will give us the effective dose

what is tissue weighting factor

it represents the relative contribution of that organ or tissue to the total detriment (cause harm) due to effects resulting from uniform irradiation of the whole body

what is the desirable uniform equivalent dose over the whole body to effective dose

same

what dose exposure measure

number of photons

what is the unit for exposure

C kg^-1

what are the classes of ionising radiation exposures

external radiation exposure, internal radiation exposure

what is external radiation exposure

stops when the source is turned off or when a person moves away from the source

what is internal radiation exposure

an intake of a radionuclide commits to the person receiving a dose for a period of time which depends on the effective half-life of the radionuclides

what is committed equivalent dose

the equivalent dose which an organ of tissue is committed to receive from the intake of radioactive materal

what is committed effective dose

the effective dose which a person is committed to receive from the intake of radioactive material

what is collective dose and the unit

the sum of all individual effective doses for a group, man-sieverts

what are the 3 principles of radiation protection

justification, optimisation, limitation

what is considered in optimisation in radiation protection

the magnitude of dose, the number of people exposed, the likelihood that potential exposures will be kept

what is the public limit for dose

1 mSv/year

what are the types of exposures

planned exposure, emergency exposure, existing exposure

what are the categories of exposures

occupational, medical, public

what is the dose limit for occupational

20 mSv/year

what does film badges include

silver halide film

what are some examples of personal dosimeters

film badges, thermoluminescent dosimeters (TLDs), optically stimulated luminescence devices, pocket electronic dosimeters

how do TLDs work

radiation traps electrons in crystal defects. heating releases electrons → light emitted → dose proportional

what is in TLDs

LiF or CaSO₄:Dy

what are the 3-4 chips in TLD badges estimate

shallow dose, eye dose, deep dose

what is the minimum measurable dose for TLD

• ~10–20 µSv (diagnostic energies)

  • ~70 µSv (megavoltage therapy)

how are TLD reused

annealed at 400°C

what are the 3 key principles for protection from external radiation

time, distance, shielding

what is the dose rate from gamma sources

• T = k‑factor (µSv/h at 1 m per MBq)

• A = activity (MBq)

• d = distance (m)

what is the shielding calculation for Narrow beam

what is the shielding calculations for broad beam

B: build up factor

what does structural shielding protect against

primary beam, scattered radiation, leakage radiation

what is the weekly dose equation

• Workload (W) — mA·min/week

• Use factor (U) — fraction of time beam points at barrier

• Occupancy factor (T) — fraction of time area is occupied

• Distance (d) — from tube to barrier

• Transmission factor (K) — from lead attenuation graphs

Design dose limits used

what is the key differences between therapists and radiographers in shielding calculations

therapists uses Monitor units (MU), annual dose used instead of weekly dose

what is the thickness of lead equivalence for personal protection

0.25-1mm