Up to this point in time, we have used a gain setting of 1.0, which gives us a range of 1-1000 keV. However, we sometimes perform studies with radionuclides having a keV gamma peak of greater than 1000 keV, such as 59Iron, which has peaks at 1.095 meV and1.292 meV. Additionally, many instruments cannot be accurately calibrated in the lower ranges under 100 keV. Therefore, an adjustment in gain can be made to accommodate the above-mentioned exceptions.Gain settings will vary from instrument to instrument. Some equipment, such as thyroid uptake probes, have the following gain settings: 0.1, 0.2, 0.5, 1.0, and 2.0. When the gain is on 1.0, the keV range represents 1-1000 keV. If the gain is changed to 2.0, the range becomes 1-2000 keV, and when the gain is changed to 0.5, the keV range becomes 0-500 keV. Of course, when the gain is changed, all other settings must be changed. For example, with a 1.0 gain, 662 on the potentiometer represents 662 keV, providing the high voltage has been properly adjusted. But when the gain is changed to 2.0, 662 on the potentiometer stands for 1324 keV (662 X 2). Likewise, if the gain is changed to 0.5, 662 on the potentiometer represents 331 keV (662 X 0.5). Other types of equipment will have gain settings such as 1,2, 4, 8, and 16. A gain of 4 on such a piece of equipment may represent the same keV range as 1.0 on the uptake probe.It is imperative to read the operator’s manual before using any piece of equipment, as gain settings will vary according to the manufacturer. In addition, increasing gain setting does not necessarily represent an increase in the keV range. On some pieces of equipment, an increase in the setting may result in a decrease in the keV range. For example, increasing the gain setting from 1.0 to 2.0 increases the range from 1-1000 keV to 1-2000 keV: this type of gain is known as inverse gain. On other pieces of equipment, an increase in a gain of 4 to 8, for example may represent a decrease in the keV range from 1-1000 to 1-500 keV; this represents true gain. Again, you must read the operator’s manual before attempting to correctly set and use new pieces of equipment.
2Section 1:The gain settings on your piece of equipment rare 0.1, 0.2, 0.5, 1.0 and 2.0. Assume 1.0 represents a keV range of 1-1000 and 0.5 represents a range of 1-500. Assume you will be working with independent windowsConvert the following LL and UL settings with a gain of 1.0 to LL and UL settings with a gain of 0.5: (10 points)New LLNew UL1.LL = 138UL = 1742.LL = 230UL = 2503.LL = 310UL = 3804.LL = 420UL = 4605.LL = 510UL = 590Convert the same LL and UL settings in question 1-5 above to LL and UL settings with a gain of 2.0: (10 points)New LLNew UL6.7.8.9.10.11.(1 point) Is this example above representative of inverse or true gain?____________ (Hint: When the gain is turned up, which way did the spectrum move?)The gain settings on your piece of equipment are 2, 4, 8, 16 and 32. The gain setting of 8 represents a range of 1-1000 keV. This piece of equipment has true gain. Convert the following settings as seen on gain of 8 to those on the gain settings as designated below.(30 Points)24Gain8163212.700-76013.670-75014.600-68015.240-32016.120-200For questions 12-16 above, name the isotope which would be counted in each window. Assume the isotope peak is midway between the LL and UL on the appropriate gain setting: (10points)
3Use a“Table of radionuclides” to identify the isotope.17. Isotope counted in window #12 ______18. Isotope counted in window #13 ______19. Isotope counted in window #14 ______20. Isotope counted in window #15 ______21. Isotope counted in window #16 ______The gain settings on your piece of equipment are 0.5, 1.0, and 2.0. Assume that 1.0 represents a keV range of 1-1000 keV and 2.0 represents a range of 1-500 keV. Assume you will be working with independent windows.Convert the following LL and UL settings with a gain of 1.0 to LL and UL settings with a gain of 0.5. (10 points)New LLNew UL22.LL = 80UL = 11023.LL = 130UL = 19024.LL = 260UL = 30025.LL = 480UL = 55026.LL = 560UL = 630Convert the same LL and UL settings in questions 22-26 above to LL and UL settings with a gain of 2.0. (10 points)New LLNew UL27.28.29.30.31.32.Is the example above representative of inverse gain or true gain? (1 point)____
