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--- textbook:nrctextbook:chapter9 [2025-04-22 13:31]
Merja Herzig
+++ textbook:nrctextbook:chapter9 [2025-05-07 13:23] (current)
Merja Herzig
@@ Line 158: / Line 158: @@
 {{anchor:photopeak}}
 {{anchor:gamma_spectrum}}
+{{anchor:interpretation_of_gamma_spectrum}}
 ===== 9.5. Interpretation of gamma spectra =====
@@ Line 179: / Line 180: @@
 Figure IX.10. Photopeak, Compton continuum and their combination in a gamma spectra.
+{{anchor:annihilation_peak}}
 ###
-Gamma rays with energies higher than 1.022 MeV may undergo [[textbook:nrctextbook:chapter7#7.4._absorption_of_gamma_radiation|pair formation]], i.e. turn into an electron and a [[textbook:nrctextbook:chapter5#positron|positron]]. If they both lose their energy in the detector an electric pulse goes to the photopeak area. However, since the positron is not stable but annihilates after losing its kinetic energy with an electron to form two gamma rays of 0.511 MeV energy. In the case where one of these escapes the detector, a peak at Eγ - 0.511 MeV is created and correspondingly a peak at Eγ -1.022 MeV when both annihilation gamma rays escape (Figure IX.11).
+Gamma rays with energies higher than 1.022 MeV may undergo [[textbook:nrctextbook:chapter7#7.4._absorption_of_gamma_radiation|pair formation]], i.e. turn into an electron and a [[textbook:nrctextbook:chapter5#positron|positron]]. If they both lose their energy in the detector an electric pulse goes to the photopeak area. However, since the positron is not stable but [[textbook:nrctextbook:chapter5#annihilation|annihilates]] after losing its kinetic energy with an electron to form two gamma rays of 0.511 MeV energy. In the case where one of these escapes the detector, a peak at Eγ - 0.511 MeV is created and correspondingly a peak at Eγ -1.022 MeV when both annihilation gamma rays escape ([[textbook:nrctextbook:chapter9#figure_911|Figure IX.11]]).
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+{{anchor:figure_911}}
 {{:textbook:nrctextbook:gamma_spectrum_fig_9_11.png|}}
@@ Line 189: / Line 191: @@
 ###
-Still there may be additional peaks in gamma spectra. If two gamma rays simultaneously lose their energy in the detector a sum peak will be formed which is called coincidence summing. Furthermore, X-rays formed after electron capture, internal conversion and formation of Auger electrons may appear at the low energy region, but only when broad energy detector (BEGE) is used. In summary, gamma spectra are complicated, especially when several radionuclides are measured from same sample. Fortunately, there are computer programs, such as the SAMPO program, that take care of the peak analysis.
+Still there may be additional peaks in gamma spectra. If two gamma rays simultaneously lose their energy in the detector a sum peak will be formed which is called coincidence summing. Furthermore, X-rays formed after [[textbook:nrctextbook:chapter5#electron_capture|electron capture]], [[textbook:nrctextbook:chapter5#internal_conversion|internal conversion]] and [[textbook:nrctextbook:chapter5#auger_electrons|formation of Auger electrons]] may appear at the low energy region, but only when broad energy detector (BEGE) is used. In summary, gamma spectra are complicated, especially when several radionuclides are measured from same sample. Fortunately, there are computer programs, such as the SAMPO program, that take care of the peak analysis.
 ###
@@ Line 196: / Line 198: @@
 {{ :textbook:nrctextbook:substraction_of_compton_background_fig_9_12.png|}}
 ###
-From gamma spectra radioactivities are determined from net peak areas of the photopeaks. In total peaks there are background counts created by external radiation, electric noise, Compton background of the radionuclides, if any, with higher photopeak energy and from multiple Compton events of the measured radionuclide. To get the net peak area the Compton background pulses are subtracted in the way presented in Figure IX.12. In addition, the pulses coming from external sources are subtracted from net peak area based on a separate background measurement but only if there is a peak, corresponding to the measured photopeak, in the background spectrum.
+From gamma spectra radioactivities are determined from net peak areas of the [[textbook:nrctextbook:chapter9#photopeak|photopeaks]]. In total peaks there are background counts created by external radiation, electric noise, Compton background of the radionuclides, if any, with higher photopeak energy and from multiple [[textbook:nrctextbook:chapter7#7.4._absorption_of_gamma_radiation|Compton events]] of the measured [[textbook:nrctextbook:chapter4|radionuclide]]. To get the net peak area the Compton background pulses are subtracted in the way presented in Figure IX.12. In addition, the pulses coming from external sources are subtracted from net peak area based on a separate background measurement but only if there is a peak, corresponding to the measured photopeak, in the background spectrum.
 ###
 Figure IX.12. Subtraction of Compton background from gross photopeak area.
+{{anchor:sample_preparation_gamma}}
 ===== 9.7. Sample preparation for gamma spectrometric measurement =====
 ###
-Typically gamma spectrum is measured from samples without pretreatment by packing the sample into vial used in efficiency calibration. Also, the sample volume needs to correspond to a calibrated volume. Sometimes, however, pretreatment of samples is necessary. In cases where the activity concentration is so low that the activity of the target nuclide cannot be determined in a reasonable time, preconcentration is needed. For example, <sup>137</sup>Cs concentration in natural waters is usually so
+Typically gamma spectrum is measured from samples without pretreatment by packing the sample into vial used in [[textbook:nrctextbook:chapter9#efficiency_calibration|efficiency calibration]]. Also, the sample volume needs to correspond to a calibrated volume. Sometimes, however, pretreatment of samples is necessary. In cases where the [[textbook:nrctextbook:chapter6#activity_concnetration|activity concentration]] is so low that the [[textbook:nrctextbook:chapter6#activity|activity]] of the target [[textbook:nrctextbook:chapter2#nuclide|nuclide]] cannot be determined in a reasonable time, preconcentration is needed. For example, <sup>137</sup>Cs concentration in natural waters is usually so low that even measuring one-liter samples does not allow its detection in a reasonable time.  Thus <sup>137</sup>Cs is preconcentrated by evaporation into a smaller volume or is chemically separated, for example, by precipitation with ammonium phosphomolybdate. The latter method also separates efficiently <sup>137</sup>Cs from interfering radionuclides and thus gives a more accurate result.
-low that even measuring one-liter samples does not allow its detection in a reasonable time.  Thus <sup>137</sup>Cs is preconcentrated by evaporation into a smaller volume or is chemically separated, for example, by precipitation with ammonium phosphomolybdate. The latter method also separates efficiently <sup>137</sup>Cs from interfering radionuclides and thus gives a more accurate result.
 ###

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