Outcome 4

Question 1

what is current mode?

Answer 1

time averaged number of ionizations/second

Question 2

what is the effect of having the gas under high pressure?

Answer 2

increase likelihood of gamma rays interacting with those gas atoms

Question 3

purpose of the dipper

Answer 3

lower the source container into the cylindrical space that is surrounded by the gas chamber

Question 4

what are the two purposes for the shielding around the cylinder?

Answer 4

1. prevent external sources of radioactivity from contributing to the measurement
2. protect surrounding area from the source being measured

Question 5

dose calibrators (can/not) distinguish between photons of different energies.

Answer 5

dose calibrators can’t distinguish between different radionuclides

Question 6

dose calibrators can measure quantities down to about ____ within +/- ____%

Answer 6

down to about 740 kBq within +/- 5%

Question 7

what happens if the activity is lower than 740 kBq?

Answer 7

it’ll be less accurate and take longer to reach a steady value

Question 8

what are characteristics dose calibrators need?

Answer 8

• good precision
• accurate
• measures a wide range of activities + variety of configurations

Question 9

constancy can be done for each source with the isotope selector buttons. t/f

Answer 9

true

Question 10

frequency of linearity qc

Answer 10

quarterly

Question 11

linearity

Answer 11

ensures that the equipment is able to measure activity over a range of different activities

Question 12

what are the two main methods to do linearity qc?

Answer 12

1. decay method
2. shield method

Question 13

decay method

Answer 13

measuring a short-lived radionuclide over a time frame (2-3 days)
- plot activity vs. time on semilogarithmic graph paper
- should be linear/match to tc-99m decay plot

Question 14

shield method

Answer 14

use of high activity source + lead sleeves (Calicheck) to mimic decay

Question 15

percent error formula

Answer 15

percent error = (corrected/expected)*100%

Question 16

what is the shield method process?

Answer 16

place source in each sleeve and measure + correct with known attenuation factor for each sleeve
- corrected values are then averaged and percent error is calculated

Question 17

formula for % error

Answer 17

% error = (actual-theoretical)/theoretical * 100

Question 18

how do you do an accuracy qc?

Answer 18

take three measurements, average and then use that as the “actual” in the % error formula

Question 19

what might cause a higher-than-expected constancy reading?

Answer 19

dipper is contaminated

Question 20

what might cause a negative background reading or a lower-than-expected constancy reading?

Answer 20

contamination originally then as it decays the levels are now in the negative range