Exposure Calculations (7)

Question 1

How can we calculate an exposure for x-rays?

Answer 1

• x-ray exposure curves

- x-ray exposure charts

Question 2

How can we calculate an exposure for gamma?

Answer 2

• slide-rule calculators

- gamma exposure curves

Question 3

Variables that can affect film density:

Answer 3

• spectrum of radiation
• voltage
• amperage
• time (processing and exposure)
• source-to-film distance
• specimen composition
• specimen thickness
• amount of scatter present
• type of film
• screens?
• chemical concentration

Question 4

A change in film density can be estimated based on any change in any of _______.

Answer 4

The known variables

Question 5

What are the three main factors that govern the exposure?

Answer 5

• milli-amperage (source strength)
• time
• source-to-film distance

Question 6

Milli-amperage to distance relation

Answer 6

M1 / M2

D1² / D2²
Directly Proportional

M2 = M1 x D2² / D1²

Question 7

Time to distance relation

Answer 7

T1 / T2

D1² / D2²
Directly Proportional

T2 = T1 x D2² / D1²

Question 8

Milli-amperage to time relation

Answer 8

Reciprocity Law
M1 / M2
=
T2 / T1
Inversely Proportional

Question 9

Reciprocity Law

Answer 9

Milli-amperage to time relation, an inversely proportional relationship.

• law does not apply to fluorescent screens
• less accurate when intensity is increase by 4 or more

Question 10

Describe the use of a table for solving source strength, time and distance problems:

Answer 10

mAm value is the intersection between old ffd and new ffd.

• approximated values
• round two significant digits
• accuracy within 5%