Fluke Biomedical 07-611 - Manual (Page 18)

Nuclear Associates Radiographic and Mammographic Focal Spot Measurement Products
Operators Manual
2-12
5. For the Star Test Pattern, the formula and data
presented yield the equivalent homogeneous
focal spot size, not the actual size.
2.4 Procedure - Half-Value Layer Measurements
1. Place the focal spot test stand on the tabletop. Adjust the leveling screws so that the base is raised
1" (2.5 cm) above tabletop.
2. Place a sheet of lead under the base.
3. Adjust the stand so that the top is located at one-half of source-to-tabletop distance, e.g., for a 40"
source-to-table-top distance adjust the stand to 20".
4. Place both the large and small adaptors in the top of the stand.
5. Collimate the x-ray beam to the top aperture of stand.
6. Place the ionization chamber on the base just above the aperture (Figure 2-11).
7. Select the technique factors that will produce about 300 mR at 80 kVp.
8. Make an exposure without added aluminum and record the result.
9. Add 2 mm of type 1100 aluminum.
9. Make an exposure and record the result.
10. Repeat steps 9 and 10, adding an additional 1 mm of aluminum each time until the exposure
reading is approximately 100 mR.
12. For data analysis, potential problems, and acceptance limits, See Reference 2 on page 2-12.