radiation protection questions for week 2

Question 1

define TLD

Answer 1

Thermoluminescent dosimeter

Question 2

define Use Factor

Answer 2

percentage of time during which the x-ray tube is on and directed toward a particular protective barrier

Question 3

define Diagnostic protective x-ray tube housing

Answer 3

Protective shielding in the x-ray tube housing designed to reduce leakage radiation to less than 100mr/hr at 1 m

Question 4

define glow curve

Answer 4

The graphically displayed response of a TLD as a function of temperature

Question 5

define primary protective barrier

Answer 5

Barrier designed to shield against primary radiation. The image-intensifier assembly serves as a primary protective barrier. Secondary protective barriers are designed to shield areas from secondary radiation and are always less thick than primary barriers

Question 6

define x-ray linearity

Answer 6

Radiation intensity is proportional to the mA station selected

Question 7

define secondary radiation

Answer 7

Leakage radiation; scatter radiation

Question 8

define occupancy factor

Answer 8

Level of occupancy of an area adjacent to x-ray rooms. The concept of the relative time that a protected area is occupied

Question 9

define Geiger-Muller region

Answer 9

voltage plateau over which the Geiger counter detector operates

Question 10

define resolving time

Answer 10

Applies to Geiger counter and scintillation detector. The minimum time between two interactions allowing both interactions to be detected

Question 11

What do audible and visible signals indicate on the radiographic control console?

Answer 11

That the x-ray beam is energized and at what technique

Question 12

List as many devices used for radiation protection on radiographic equipment as you can

Answer 12

Protective drapes, Bucky slot cover, 5 minute reset timer, exposure switch that fastens to the console, dead-man switch, collimator, filter, tube housing, 6 ft cord on mobile unit

Question 13

What is the result if the x-ray beam and the film are not properly aligned?

Answer 13

Misalignment causes unintended tissue to be irradiated, and intended tissue to be missed

Question 14

What filtration is used for mammography equipment operated below 30 kVp

Answer 14

50mr/hr

Question 15

How are reproducibility and linearity different when the intensity of the x-ray beam is measured?

Answer 15

Reproducibility- requires constant radiation intensity for multiple exposures at a fixed technique
Linearity- implies proportional radiation exposure at adjacent mA stations

Question 16

What characteristics of fluoroscopic equipment are designed for radiation protection

Answer 16

protective curtain on the image-intensifier tower
Bucky slot cover
5 minute reset timer.

Question 17

How can filtration be measured it=f the amount of inherent and added filtration is unknown?

Answer 17

Experimentally determine the half-value layer and check to see that it exceeds the minimum HVL’s published by the NCRP

Question 18

Name the three types of radiation exposure that are of concern when protective barriers are designed

Answer 18

Primary radiation, leakage radiation, and scatter radiation

Question 19

List 4 factors that are taken into consideration when a barrier for a radiographic room is designed

Answer 19

Use factor,
occupancy factor,
distance, 
dose limit, 
kVp

Question 20

What is the difference between a controlled area and an uncontrolled area?

Answer 20

Controlled areas- are those primarily occupied by radiology personnel and patients. Normally, workers who enter a controlled area would be provided with an occupational radiation monitor
An uncontrolled area can be occupied by anyone; therefore, the maximum exposure rate allowed is based on the recommended dose limit for the public

Question 21

What are the units of workload for an x-ray examination room?

Answer 21

mA min/wk

Question 22

Explain the use factor (U) as it relates to a protective barrier in an x-ray examination room

Answer 22

use factor of a room helps determine whether a given wall or the ceiling is a primary or secondary protective barrier and therefore what protective design is necessary

Question 23

Why is the use factor for secondary barriers always 1?

Answer 23

Secondary radiation, leakage, and scatter are continuously present when an x-ray tube is energized

Question 24

Name the three gas-filled dosimeters

Answer 24

Ionization chamber, proportional counter, Geiger-Mueller counter

Question 25

Discuss the properties of TLD that make it suitable for personnel monitoring

Answer 25

Sensitive, accurate, nonfading with time, unaffected by temperature and humidity, absorption characteristics equivalent to human tissue, reusable

Question 26

Which modality of diagnostic imaging uses scintillation detection as a radiation detection process?

Answer 26

Nuclear medicine and CT

Question 27

What are the 2 most widely used scintillation phosphors?

Answer 27

Sodium iodide (NaI), and cadmium tungstate (CdWO4).

Question 28

A photomultiplier has 9 dynodes, each of which has a gain of 2.2 What is the overall tube gain?

Answer 28

Gain = (2.2)9 = 1207.5