Physics Exam 2 Spring 2010

Front 1

what is radiation quality

Back 1

describe ability of a radiation beam to penetrate absorbing material

Front 2

how do we specify quality

Back 2

accurate method
tradiational method
other methods (PDD, Surface dose (wedge,blocks))

Front 3

accurate method

Back 3

obtain spectral distributions of energies present in radiation beam

Front 4

traditional method

Back 4

HVL.
used extensively to describe orthovoltage and diagnostic beam

Front 5

HVL used only for

Back 5

orthovoltage and diagnostic beam

Front 6

other methods which may help to describe radiation beam

Back 6

PDD, Surface dose (wedges,blocks)

Front 7

what do accelerators use to specify quality?

Back 7

peak energy is used as the descriptor;
since the beam is already highly filtered further filtration will not affect the quality (most of the time)

Front 8

what does effect quality on linac?

Back 8

45-60* wedges, flattening filter

Front 9

what does Co60 use to specify quality?

Back 9

doesn't need anything because the isotope name defines the energy of the beam....
just use the name of isotope

Front 10

what does filtration do?

Back 10

get rid of the low energy components

Front 11

what does filtration do to the beam?

Back 11

hardens by taking out soft x-rays=low energy x-rays

Front 12

what are the 2 types of filtration?

Back 12

1. inherent filtration
2. added filtration

Front 13

what is inherent filtration?

Back 13

glass envelope of tube,
exit window of housing,
oil which comes between pt. and x-ray housing

things already in place that can't be changed

Front 14

what is added filtration?

Back 14

Al, Cu, ...added between pt. and x-ray tube

Front 15

what does added filtration do?

Back 15

gets rid of photons that would not produce image but would give dose

Front 16

does filtration effect the quality of beam?

Back 16

yes

Front 17

what are the effects of filtration on a radiation beam?

Back 17

effects the intensity of the radiation beam........its decreased

makes sure low energy components of the beam are removed

Front 18

what are thoreaus filters used for?

Back 18

orthovoltage units

Front 19

which comes first for filters?

high atomic #
low attomic #

Back 19

always highest atomic # first then decrease in atomic #

Front 20

what is good geometry?

Back 20

correct method to utilize when making HVL or attenuation measurements (measure transmission through cerebend)

Front 21

what makes up good geometry?

Back 21

narrow beam to minimize scatter

detector placed far away from attenuator so that only primary photons which have not interacted w/the attenuator are detected

Front 22

what is the distance the detector should be away from the attenuator

Back 22

at least 20cm

Front 23

HVL and attenuation equations

Back 23

N=No e- ux

N=No e- (-.693)x/d(1/2)

Front 24

for a _____ beam using measuring conditions of "good" geometry the line is straight

Back 24

monoenergetic beam

not practical in real life

Front 25

filtering material for:

diagnostic region

Back 25

Al

Front 26

filtering material for:

100-150keV (orthovoltage)

Back 26

Al

Front 27

filtering material for:

150-250keV

Back 27

Cu

Front 28

filtering material for:

250keV

Back 28

Thoreaus filter

Front 29

filtering material for:

high energy megavoltage

Back 29

Pb, however the attenuation for Pb is the rage of 5-40MV first decreases (photoelectric effect) and then increases (pair production). both positive and negative contibutions are being made to teh total attenuation coeffictient.
these cancel each other out, making Pb not as sesnsitive as water or Al to spectral changes in a high energy beam

Front 30

what shape is a practical beam?

Back 30

curve

Front 31

actual beam is monoenergetic T/F?

Back 31

FALSE:
whole spectrum of energies are present tehrefort the plot is not a straight line

Front 32

what happens to the slope of the curve if absorber thickness is increased?

Back 32

decreases

because the beam is harder. requires more absorber to attenuate the same % of the beam

Front 33

what appens at heavy filtration?

Back 33

the radiation transmitted is nearly more monochromatic.

the absorption curve approaches a straight line

Front 34

what do you use to find shielding measurements?

Back 34

use 1/10th value layers to find shielding

1/2VL and 1/10VL are measured

Front 35

what is the def of Exposure

Back 35

measure of the abillity of photons to ionize AIR

Front 36

equation for Exposure?

Back 36

E-dQ/dm

dQ= total# of ions of one sign produced in air when e-'s liberated by photons in air of mass

dm= are completely stopped in air

Front 37

SI units=

Back 37

C/Kg

Front 38

traditional units

Back 38

Roentgen

Front 39

1R=? C/Kg

Back 39

2.58x10^-4C/Kg

Front 40

characteristic of Exposure

Back 40

valid only for energies of 3Mev and under
only where conditions of electronic equillibrium are met
only in air
only for photons

Front 41

def. of absorbed dose

Back 41

measure of energy imparted to a material

Front 42

equation for absorbed dose

Back 42

Dose=dE/dm

dE= mean energy imparted

Front 43

SI unit for absorbed dose

Back 43

Gray (Gy)

Front 44

1Gy=?J/Kg

Back 44

1Gy=1J/Kg

Front 45

traditional for absorbed dose

Back 45

rad

Front 46

?rad=1Gy

Back 46

1rad=.01Gy=1cGy

just remember 1rad=1cGy

Front 47

characteristic for absorbed dose

Back 47

valid for any energy
valid w/or w/out conditios of electronic equilibrium
valid for any material
valid for any type of ionizing radiation
it is a measure of biologically significant effects produced by ionizing radiation

Front 48

what does e- produce?

Back 48

hydroxi radicals

Front 49

Exposure may be converted to______?

Back 49

may be coverted to absorbed dose.

Front 50

1R of Exposure in air=?rad of absorbed dose in air

Back 50

1R=.876rad in air

Front 51

equation to convert dose in air to dose in a medium

Back 51

f med=.876x ((u en/p)med/(u en/p)air)