Gamma Energy Flashcards
What is mono-energetic γ-radiation?
γ-radiation, which has photons of equal E
What is dual isotope labeling?
Why are 2 isotopes used?
investigation of a physiological process by 2 γ-emitting isotopes of different photon E
What is a integral discriminator?
device that
- lets through pulses of amplitude higher than a certain level, the discriminator level
- blocks those of smaller amplitude
What is a differential discriminator?
device that
- lets through pulsed for which the amplitude is between 2 DD levels, the channel
- blocks those of the amplitude outside the channel
⇒ used to make size distribution of pulses
What is a photopeak?
On what does its width depend on?
γ-photon absorbed by photoeffect in the scintillator
→ light flash intensity dependent on photon E
→ amplitude of voltage pulse generated by PMT proportional to photon E
⇒ sorted by DD → histogram with photopeak
width depends on: type of detector
What is a Compton range?
Why do we achieve a broad Compton range instead of a narrow line like in photopeaks?
similar to photopeak, but wider range with lower peaks generated by Compton scatter
→ wider spread amplitude range due to partial E transfer
How can the position of the photopeak in the pulse rate vs. voltage graph be shifted?
increased anode voltage → increased dynode voltage → enlarged secondary-electron multiplying factor → pulses of higher amplitude → photopeak shifted to the right
How can the height of the graph in the pulse rate vs. voltage graph be shifted?
increased activity (decay rate) → more γ-photons absorbed → more pulses → amplitude of graph increased
What did we calculate in the gamma energy lab and how? Give the formula.
gamma energy of one isotope determined by using the ratio of the photopeaks and the gamma energy of the second isotope.
E1 = E2 * Uphoto 1/Uphoto 2