EFFECTS
OF THICKNESS & DISTANCE
INTENSITY
OF RADIATION
ANALYSIS
B. Effect of absorber thickness
1. Correct
all of the actual counting data that you have taken by subtracting the
background rate to fill in the corrected Counts/Minute columns in
both Tables.
2. Let
Io
be the intensity (counts/minute) with zero thickness of absorber. Let I
represent the intensity for other thicknesses. Make a plot of the natural
logarithm of I, ln(I), vs. d, where d is the thickness of the aluminum absorbers in millimeters. You can
use the Excel Chart Maker if you wish to.
3. This plot should be a straight line. Find the slope of this line and enter it in cell D36 on the Worksheet.
4. Find the thickness that will reduce the intensity to one-half of its initial value and record the value in cell D38.
5. The straight line on the graph of ln(I) vs. d indicates that intensity vs. thickness follows the mathematical relationship:
where α is
the absorption constant, a measure of how well the material absorbs
radiation. With this information, answer
Question 1 on the
Worksheet.
C. Effect of source distance
1. Draw a graph of ND ( the number of counts in 5 minutes) vs. 1/d.
2. Draw a graph of ND vs. 1/d2.
3. Answer Question 2 on the Worksheet.
4 Make a modified graph of ND vs.
. Find the slope and enter it in cell D70. We are assuming that a = 12 mm following eqn (5).
5. Answer Question 3 on the Worksheet.