Posted: April 10th, 2015

X-ray Laboratory

X-ray Laboratory

Include answers to the following questions

Using the combo.jpg image (see below) and steps similar to those in the section above, determine the transmitted light intensity for the thickest steps of brass and aluminium step wedges, the lead sample and the thick and thin copper samples. Note that the background is not the same for each of these, so separate background readings will need to be taken.

1.    What assumption do we need to make about the background light illuminating the film?
2.    When measuring the transmitted intensity of the lead sample why do we need to be careful about what region is chosen?
3.    What technology could be used in order to obtain a more accurate image of the x-ray film instead of taking a photo as was done in this case?

(B) X-ray transmission changes due to different metal samples
The last section of Part A of this laboratory class investigates an x-ray film taken of a number of different metal samples (see photo given at the end of this document). In this section the theoretical changes in the x-ray transmission of these different samples will be calculated.
• The first thing that needs to be done is to measure the thickness of the various samples using the vernier calipers provided.

1.    Is one measurement of thickness sufficient?
2.    Discuss how the design of the step wedges may affect measurements of thickness, and how you have measured the individual thicknesses of each of the steps.
3.    What is the accuracy of the vernier calipers used?

The x-ray attenuation coefficient of a material varies as a function of energy. Therefore the x-ray energy needs to be known in order to determine the level of attenuation. Assume x-rays of 70 kVp have been used. In general it is the mass attenuation coefficients of a material that are usually reported.

1.    Why is the mass attenuation coefficient a useful way to represent attenuation?

Use the attenuation coefficient data provided in the NIST database in subsequent calculations.
http://www.nist.gov/pml/data/xraycoef/index.cfm

Include an answer to the following
You will note that the NIST database doesn’t provide values for 70 keV x-rays,
2.    Explain in your report how you can estimate the mass attenuation coefficient at 70 keV from the values provided.