Difference between revisions of "Basics about Efficiency Calibration of Gamma Detectors"
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The sources are measured and then we can calculate the counting efficiency: If the source activity | The sources are measured and then we can calculate the counting efficiency: If the source activity | ||
is A, the number of counts obtained with a given detector is R, then the counting efficiency is given | is A, the number of counts obtained with a given detector is R, then the counting efficiency is given | ||
− | by: | + | by:<br> |
<math>\epsilon=\frac{R}{A}</math><br> | <math>\epsilon=\frac{R}{A}</math><br> | ||
− | To calibrate a | + | To calibrate a <math>\gamma</math> detector we must also take into consideration that a <math>\gamma</math> ray will not necessarily be |
emitted every time the source disintegrate. The frequency <math>\gamma</math> rays are emitted can be found in tables | emitted every time the source disintegrate. The frequency <math>\gamma</math> rays are emitted can be found in tables | ||
− | and is given as the | + | and is given as the <math>\gamma</math> intensity, usually symbolised with I<sub><math>\gamma</math></sub>. The formula we use to calculate the |
− | efficiency then looks like this: | + | efficiency then looks like this:<br> |
+ | <math>\epsilon=\frac{R_{E}}{A\cdotI_{\gamma}}</math><br> | ||
+ | Notice that we have indexed the <math>\epsilon</math> and R with an E to indicate that these are energy dependant. Since | ||
+ | all the absorbation processes for <math>\gamma</math> radiation is strongly dependent on the <math>\gamma</math>-ray energy, the detector | ||
+ | efficiency will also be dependent on energy. Thus, to calibrate a <math>\gamma</math> detector we must use a range of | ||
+ | sources with energies that cover the range of energy we are planing to measure in. The efficiency | ||
+ | calibration will then look like something in Figure 1. The most common range to measure <math>\gamma</math> radiation | ||
+ | in is from about 50 keV and up to about 1-2 MeV. From Figure 1 we can se that the range between | ||
+ | about 200 keV and up to 2 MeV is nearly linear in double-logarithmic scale. Below 200-250 keV | ||
+ | this is not true. |
Revision as of 09:53, 27 June 2012
In this exercise you are to do an efficiency calibration of a Ge-detector. The efficiency to any
detector is dependent on quantities such as the
To calibrate a detector we must also take into consideration that a ray will not necessarily be
emitted every time the source disintegrate. The frequency rays are emitted can be found in tables
and is given as the intensity, usually symbolised with I . The formula we use to calculate the
efficiency then looks like this:
Notice that we have indexed the and R with an E to indicate that these are energy dependant. Since
all the absorbation processes for radiation is strongly dependent on the -ray energy, the detector
efficiency will also be dependent on energy. Thus, to calibrate a detector we must use a range of
sources with energies that cover the range of energy we are planing to measure in. The efficiency
calibration will then look like something in Figure 1. The most common range to measure radiation
in is from about 50 keV and up to about 1-2 MeV. From Figure 1 we can se that the range between
about 200 keV and up to 2 MeV is nearly linear in double-logarithmic scale. Below 200-250 keV
this is not true.