Interactions of Ionizing Radiation

Question 1

Inverse Sq Law

Answer 1

I/I = (r1/R2)^2

Question 2

Attenuation definition

Answer 2

Reduction in # photons (dN) is proportional to the # incident photons (N) and thickness of the adsorber (dx). mu is attn coeff.

Question 3

Attenuation coefficient

Answer 3

dN = -μNdx

Question 4

Intensity

Answer 4

I(x) = Io × e-(μx)

Question 5

Linear attenuation coefficient (μ) depends on ____ and _____.

Answer 5

density and beam energy

The larger the μ the more the beam will be attenuated.

Question 6

μ for water __ μ for ice __ μ for steam

what if this was mass attenuation μ/ρ

Answer 6

> and >

For mass attenuation, = and =

Question 7

HVL equation

Answer 7

HVL = ln2/μ = 0.693/μ

Question 8

HVL in monoenergetic beams vs polyenergetic beams

Answer 8

monoenergetic HVL1 = HVL2

polyenergetic HVL1

Question 9

Coherent scattering collision

Answer 9

photon in photon out.

low energy photon reacts with an orbital e- and the e- sends off that same photon at a small angle

Question 10

Is energy transferred in coherent scatter?

Answer 10

No, elastic

Question 11

Photoelectric effect collision

Answer 11

Photon in, E- out.

1) Low energy photon transfers all of its energy to an orbital e- in an inner shell (K, L, M, N), ejecting the e- (“photoelectron”) with energy = energy of bombarding photon 2) –the result is that the photon is absorbed/ceases to exist and its energy is transferred to the ejected atomic electron; no scattered photon
3) Once the photoelectron is ejected, characteristic X-ray or emission or Auger electron emission will follow (from energy released as outer shell electron falls to fill the vacancy)

Question 12

Probability that a photon will undergo a photoelectric interaction with relation to E and Z

Answer 12

(1/E^3)

Z^3

Question 13

Compton Effect / Incoherent scatter

Answer 13

photon in, e- out along with scattered photon.

Question 14

When does compton occur?

Answer 14

When photon E is so high it can’t give up all of its energy to an electron.

Question 15

When does compton occur? (E and Z)

Answer 15

When photon E is so high it can’t give up all of its energy to an electron.
Relatively independent of Z

Question 16

Compton scattering: angle of emitted e-?
E of photon with max energy transfer?
E of photon with grazing hit?
90 degree photon E?

Answer 16

0-90 Degrees
When 0, photon backscatters with minimum energy 0.255 MeV and there is max energy transfer.
With grazing hit, e- scatters at 90, the photon keeps going at 0 degrees with negligible energy transfer.
with 90-degree photon scatter, the max photon energy is 0.511 MeV independent of if incident photon E was high. (e- angle depends on energy of incident photon and rest energy of e-)

Question 17

What is Photonuclear disintegration? (And why is it important?)

Answer 17

High-energy photon interacts with nucleus, totally disrupting the nucleus, with emission of one or more nucleons
- can produce unwanted neutrons

Question 18

what interaction will occur at .01 MeV?

Answer 18

95% photoelectric

Question 19

what interaction will occur at .025 MeV?

Answer 19

50/50 photoelectric/compton

Question 20

what interaction will occur at 0.1 MeV?

Answer 20

100% compton

Question 21

what interaction will occur at 24 MeV?

Answer 21

50/50 compton/pair production

Question 22

what interaction will occur at 100 MeV?

Answer 22

84% Pair production

Question 23

Pair Production probability of happening?

Answer 23

proportional to Z^2

High E

Question 24

Pair production initial interaction

Answer 24

High E photon interacts with a nucleus and converts ALL E to an electron - positron pair. 1.02 MeV is used to make the pair, the rest goes to kinetic energy.

Question 25

Pair production subsequent reaction

Answer 25

positron hits another electron producing two photons with E = 0.511 MeV in opposite directions

Question 26

Electron nucleus reactions

Answer 26

Deflections (elastic)
Radiative loss (ineleastic) aka bremsstrahlung

Question 27

Bremsstrahlung

Answer 27

E- reacts with a nucleus inelastically, losing some k energy