lecture 9

Question 1

E/M radiation for photon E

Answer 1

> 100 ev starts in UV

Question 2

What is the absorbed dose

Answer 2

the measure of the amount of energy from ionizing radiation deposited in a mass of some material (delta E/delta M)

Question 3

Does the biological effect depend only on dose

Answer 3

No, it is dependent on the nature of radiation

Question 4

Old unit of Absorbed dose

Answer 4

RAD (radiation absorbed dose) = 100 ergs/g

1 erg=10^-7 J

Question 5

SI unit for absorbed dose

Answer 5

Gy (Gray)=1J/kg=10^7 erg/1000g=10000erg/g=100rad

Question 6

For what type of radiation Gy is used

Answer 6

all types of radiation and does not describe the biological effects (health effects depend on how radiation interacts with material on micro-level)

Question 7

Absorbed dose: is it a macroscopic concept

Answer 7

yes, it is not related to microdosimetry

Question 8

Is energy delivered by radiation is continuous and uniform?

Answer 8

No, it is delivered not uniformly through the entire mass

Question 9

Why do we care about secondary electrons?

Answer 9

They produce additional ionization and excitation until the energies fall below the threshold for further interaction

Question 10

What paradox illustrated irradiation of viruses

Answer 10

both sensitive and highly resistant, some of them were killed at low dose. On average they tolerated very large doses: actually receiving a dose is not equal to the dose delivered, bioeffects can be very different at the same dose. Random statistical hit.

Question 11

How many J in ev

Answer 11

1.6*10^(-19)

Question 12

Absorbed energy depends on

Answer 12

number of particles traversing the mass and energy that they deposit in tissue

Question 13

Main problems with the absorbed dose concept

Answer 13

neglects the density of energy absorbed per unit mass in a point in the medium,
on a small scale (micrometer) the energy distribution is non-uniform,
energy is localized near tracks,
E transfer takes place in discrete amounts,
statistical quantity gives a global value (large enough that statistical fluctuations are not significant)

Question 14

The biological effect is related to the dose

Answer 14

deposition at micro-level (cell, DNA), depends on nature nad E of particles

Question 15

Can we use exposure for neutrons?

Answer 15

No, only for gamma and x-rays.

Question 16

What affects the absorbed dose?

Answer 16

type and E of Radiation, depth and elementary composition of the material.

Question 17

How do we characterize dose from X-ray fields?

Answer 17

exposure

Question 18

What is exposure/ what unit is used?

Answer 18

amount of E transferred from the X-ray field to a unit mass of AIR. 1 [X] unit = 1C/kg air = 34 Gy/air (production of single ion pair = 34 ev)

Question 19

Charge of single ion?

Answer 19

1.6*10^(-19) C

Question 20

What unit is used for exposure (non SI)

Answer 20

R = quantity of gamma radiation that produces ions carrying one SC (3*10^9 C) per cm^3 at T=0C, and P = 760mm. [R] = 1 [sc/cm^3]

Question 21

convert 1 X unit to R

Answer 21

1 X = 3881 R

1R = 2.58*10^-4 X

Question 22

Dose to air from 1R

Answer 22

1R= 0.877 rad = 87.7 erg/g air = 8.7 *10^-4 Gy

Question 23

Formula and units for exposure rate

Answer 23

dX/dt = Fluence rate ([photones/(cm^28s) * E (Mev) 1.610^(-13) J/Mev* mu (air/cm)]/density of air34) [C/kgs]

Question 24

Formula and units for dose rate

Answer 24

dD/dt = Fluence rate ([photones/(cm^28s) * E (Mev) 1.610^(-13) J/Mev* mu (/cm)]/density of medium*1) [Gy/s]

Question 25

The formula for a point source of gamma rays Dose rate

Answer 25

dD/dt = E fluence rate* mass E abs coefficient (cm^2/g)= CE(mu.en/rho)/4Pir^2), where C is activity

Question 26

Dose rate from exposure rate can be found as

Answer 26

34Xrate mu/density if medium divided on mu/density of air

Question 27

Dose for a beam of photons

Answer 27

D = mu.en/rho * photon fluence (/cm^2) * E

Question 28

Two reactions of tissue with neutrons

Answer 28

capture (thermal) and scattering (higher E)

Question 29

Dose from thermal neutrons formula

Answer 29

D=fluence (/cm^2)*atom density (/cm^3) reaction cross sectionE /tissue density

Question 30

name major neutron capture reactions is tissue

Answer 30

14N(n, p)14c, 1H(n, gama)2H

Question 31

name 4 principal tissue components

Answer 31

H, O, C N

Question 32

Average E lost by fast neutron

Answer 32

4MmE/2(m+M)^2

Question 33

first collision dose

Answer 33

represent the abs dose when mean free path&raquo_space; target size;

D delivered by individual neutron;

Question 34

formula and units for first collision dose

Answer 34

D=atom densityscattering cross sectionAverage E lost by fast neutron/density;
[Gy*cm^2]

Question 35

What is KERMA

Answer 35

(for indirectly ionizing radiation - no charge) the measure of all the E transferred from the uncharged particle (gamma, neutron to primary ionizing particle (e, photo e, Compton e, scattered nuclei and etc) per unit mass

Question 36

Provide examples of radionuclides with specific metabolic pathways?

Answer 36

I- thyroid
Ra, Sr -bone,
3H - water in body,
Cs- throughout the whole body

Question 37

Range of alpha particle

Answer 37

short, E deposited locally

Question 38

Rate of E absorption per gram tissue for alpha particle

Answer 38

dD/dx = AE [Mev/g*s]

Question 39

Dose formula for alpha particle

Answer 39

D= fluence * mu.rho *E absorbed

Question 40

Formula for KERMA

Answer 40

D= fluence * mu.rho *E transferred

Question 41

10 MEV photon penetration in 100 g tissue

Answer 41

single interaction produces beta - and beta + with 4.5 MEV each, that dissipate all E through Brems giving us Kerma os 2*4.5Mev / 0.1kg