【Klose Liu】評論

閃爍偵檢器的主要結構是閃爍晶體，連接著光電倍增管，當γ-ray 入射進閃爍晶體後，因能量耗損於晶體內，讓閃爍晶體發出可見光，這些可見光經過透明的晶體，抵達光電倍增管，可見光轉換為電子訊號然後被放大，接下來這些訊號才開始進行位置以及能量的分析。當γ ray 入射進閃爍晶體後，主要會發生兩種效應，一個是光電效應，γ ray 會將能量完全給予晶體，晶體發出的光最強，另一個康普吞效應，γ ray 只有部份的能量轉移給晶體，因此發出 的光較弱，不同的發光量就會導致光電倍增管最後放大出來電子訊號的強弱

【林士豪】評論

Analysis of gamma spectra is very interesting, since it has a structure and workers must distinguish between true pulses to be analyzed and accompanying pulses from different sources of radiation. We will show the structure of the gamma spectrum on the example of cobalt-60 measured by NaI(Tl) scintillation detector and by the HPGe detector. The HPGe detector allows the separation of many closely spaced gamma lines, which is very beneficial for measuring multi-gamma emitting radioactive sources.Cobalt-60  is an artificial radioactive isotope of cobalt with a half-life of 5.2747 years. It is synthetically produced by neutron activation of cobalt-59 in nuclear reactors. Cobalt-60 is a common calibration source found in many laboratories. The gamma spectrum has two significant peaks, one at 1173.2 keV and another at 1332.5 keV. Good scintillation detectors should have adequate resolution to separate the two peaks. For HPGe detectors, these peaks are perfectly separated.As can be seen from the figure, there are two gamma ray photopeaks. Both detectors also show response at the lower energies, caused by Compton scattering, two smaller escape peaks at energies 0.511 and 1.022 MeV below the photopeak for the creation of electron-positron pairs when one or both annihilation photons escape, and a backscatter peak. Higher energies can be measured when two or more photons strike the detector almost simultaneously, appearing as sum peaks with energies up to the value of two or more photopeaks added.Figure: Caption: Comparison of NaI(Tl) and HPGe spectra for cobalt-60. Source: Radioisotopes and Radiation Methodology I, II. Soo Hyun Byun, Lecture Notes. McMaster University, Canada. Backscatter Peak A Compton backscatter peak is found when γ-rays enter the material around the detector and are scattered back into the detector. Gamma photon can interact by Compton mechanism in shield or surrounding materials and is backscattered out of a material into sensitive volume. Maximum photon energy in this interaction is ~200 keV regardless of initial photon energy. This results in a secondary peak at -200 keV.