Gamma Ray Detection
Firstly, the gamma ray detector first has the function of a general detector, recording the energy loss of the secondary electrons in the detector; secondly it is a conversion medium that converts the incident photon energy into one or more fast electronic. The scintillator detector is mainly a radiation detector composed of scintillator, light collecting parts and photoelectric conversion devices. This traditional scintillation detector, characterized by high efficiency, high signal-to-noise ratio and fast response time, has been widely used in the research of high-energy physics, cosmic ray detection and nuclear medicine, and is an indispensable means in the field of radiation detection technology.
The ideal scintillator should have the following characteristics: high luminous efficiency, short decay time, low afterglow, high density, short radiation length, low cost, luminescence spectrum matching with the photon detector response spectrum. The length of radiation determines the absorption capacity of the scintillator to gamma photons. The wavelength of luminescence peak is the wavelength at the strongest emission spectrum of the scintillator, and the light output is the number of photons generated after the ray loses unit energy in the scintillator crystal, which directly affects the energy resolution of the detector. The decay time determines the maximum counting rate of scintillator.
The following figure shows the basic structure of the detector for the gamma ray detection. The basic detection unit in the figure is a pair of photon detectors (PMT/APD/SiPM, etc) coupled with scintillation crystals. Position readout circuit is the part of processing and calculating the output signal of the detector, which directly affects the output performance of the detector, so it is an indispensable part of the composition of the detector.
Bismuth Germanate Bi4Ge3O12 (BGO) crystal scintillator has gathered attention in terms of its high stopping power for soft gamma-rays. BGO scintillator is an attractive material for gamma ray detection because of its high detection efficiency, large photo fraction, and relatively low cost. The peak emission wavelength of BGO is – 480 nm which provides a good match to the spectral response of photomultiplier tubes. The effective atomic number of BGO is 75 and density is 7.1g/cm3 which could improve the efficiency of detecting 511 keV gamma photons by minimizing the radiation dose received by the subjects and shortening the imaging time. The radiation length of BGO is 1.12cm, which is beneficial for producing compact detector or probe parts, improving spatial resolution and saving cost.
Currently, many research institutes cooperate BGO with other scintillation crystals, which can maximize its advantages and overcome its disadvantages of low output light yield and long decay time. BGO has been primarily used as an active shield, because a large volume of a single BGO crystal is available which enable us to construct a detector with lower weight, which are essential for the developments of gamma-ray detector in space. In addition, BGO crystal has no afterglow, no dissociation surface, strong anti-irradiation ability and stable chemical properties, which is easy to process and maintain.
|BGO||Density[g/cm3]||Effective atomic number||Emission wavelength[nm]||Energy resolution [662keV gamma-rays]||Decay time[ns]|
Growing interest in the development of new scintillator materials is pushed by increasing the number of medical, industrial and scientific applications. Ce:YAG(Ce:Y3Al5O12) scintillation crystals have the advantages of high light output, fast time response, high gamma ray detection efficiency, stable physicochemical performance, good coupling between fluorescence spectrum and ordinary photosensitive devices, etc., which is very suitable for pulsed gamma ray measurement. YAG:Ce single crystal was reported in the literature as a fast oxide scintillator . The density of YAG:Ce is about 4.56 g/cm3 and its effective atomic number is 35. The emission peak is near 550nm, which is well matched with the sensitive receiving wavelength of photomultiplier tube (PMT) and silicon photodiode (PD).
The YAG:Ce crystal may be used for light charged particles and X-rays/low energy -rays, but it is not suitable for -rays above 300 keV due to its low effective atomic number and moderate density which limit the photo peak detection efficiency. Note the lower photo fraction in the spectrum measured with the YAG:Ce detector, as would be expected due to a lower effective atomic number and density of the YAG:Ce crystal. In this respect, YAG:Ce is recommended for spectrometry of X-rays and low energy -rays.
In the case of modern scintillators, the high light output, good energy resolution, high effective atomic number, fast scintillation response, chemical stability and capability of bulk crystal growth are very important parameters. LuAG:Ce single crystal has a higher density of 6.67 g/cm3 and effective atomic number is 58.9, which is advantageous in the case of high energy gamma-ray detection. High detection efficiency can be achieved by using materials with high density and high atomic number. The emission spectrum at RT is peaked around 525 nm which provides a good match to the spectral response of photomultiplier tubes.
Single crystal scintillators with high density and high gamma-ray absorption coefficient coupled with photo detectors are commonly used for detection of high-energy photons and particles. In the case of modern scintillators, the high light yield, good energy resolution, high effective atomic number, fast scintillation response, chemical stability and capability of large crystal growth are very important parameters. Cerium-doped Gd3(Ga, Al)5O12 (GAGG:Ce) is a promising novel scintillator for gamma-ray detectors. It is a solid, non-hygroscopic single crystal with yellowish color. It is heavy (density~6.5 g/cm3) which are commonly used for high energy gamma-ray measurements.
The emission maximum for GAGG:Ce is at around 530nm,which is typical for garnet compositions ,and suitable for silicon-based photo detectors. It is characterized by a high light output, above 40000ph/MeV and a fast decay time constant of the light pulse around of 100 ns.
|Ce GAGG||Density[g/cm3]||Emission wavelength[nm]||Energy resolution [662keV gamma-rays]||scintillationns decay[ns]||coincidence time resolution[511 keV]||light yield[ph/MeV]|
Inorganic scintillators are widely used in detection and spectroscopy of energetic photons and nuclear particles. Important requirements for the scintillators used in these applications include high light output, fast response time, high stopping power and good energy resolution.
(Lu,Y)2SiO5:Ce (LYSO:Ce) have been developed as promising scintillators for gamma ray detection due to their desirable properties such as high density, short decay time and high light output. LYSO:Ce has a density of 7.11 g/cm3 and an emission spectrum at room temperature (RT) is peaked around 420 nm. LYSO:Ce exhibits a high light yield up to about 34,000 ph/MeV.
Barium fluoride (BaF2) is an inorganic scintillation material used for the detection of gamma radiation due to its relatively high density, equivalent atomic number, radiation hardness, and high luminescence. BaF2 has a potential capacity to be used in gamma ray timing experiments due to the prompt decay emission components. BaF2 has a potential capacity to be used in gamma ray timing experiments due to the prompt decay emission components. It is known that the light output from BaF2 has three decay components: two prompt of those at approximately 195 nm and 220 nm with a decay constant around 600-800 ps and a more intense, slow component at approximately 310 nm with a decay constant around 630 ns which hinders fast timing experiments. The high density of BaF2 (4.9g/cm3) makes it well suited for gamma ray detection.
|BaF2||Density[g/cm3]||Emission wavelength[nm]||Energy resolution [662keV gamma-rays]||Decay time[ns]||Light output[ph/MeV]|
Growing interest in the development of new scintillator materials is pushed by increasing the number of medical, industrial and scientific applications. LuAG:Pr is a novel scintillation material for gamma ray detection. This scintillator shows a high stopping power, because of Lu, and fast decay and high light yield.The density of LuAG is of about 6.67 g/cm3 and its effective atomic number is of about 59. LuAG:Pr has a moderate light yield of about 19,000 photons/MeV (ph/MeV) and a very good energy resolution of 4.6%
|Pr LuAG||Density[g/cm3]||Effective atomic number||Emission wavelength[nm]||Energy resolution [662keV gamma-rays]||scintillationns decay[ns]||Light output[ph/MeV]|
As a high potential radiation detection material with excellent physical, chemical, optical and scintillation properties, thallium-doped cesium iodide (CsI:Tl) scintillators have Cesium iodide doped with thallium been used in various applications such as gamma-ray spectroscopy, medical imaging. By a high photon yield of 66,000 photons/MeV, a fast decay time of 800 ns, a high conversion efficiency and a suitable emission wavelength of 550 nm in the visible range for Si photodiodes, the classical CsI:Tl scintillators have been widely used in nuclear and medical imaging applications. CsI:Tl crystals have a cubic crystal structure with a medium density of 4.53 g/cm3 and a high atomic number (Z) of 54. They have a stronger mechanical stability with no cleavage plane and a high chemical stability of less hygroscopic nature. In case of gamma-ray detection, CsI crystal has a high stopping power by a dense packing and a high atomic number. These properties enable CsI crystals to be suitable for gamma-ray detection.
|Tl CsI||Density[g/cm3]||Emission wavelength[nm]||Energy resolution [662keV gamma-rays]||scintillationns decay[ns]||light yield[ph/MeV]|
 The design and performance of a large-volume spherical CsI(Tl) scintillation counter for gamma-ray spectroscopy
 Impact of precursor purity on optical properties and radiation detection of CsITl scintillators
 First Prototype of a Gama-Camera Based on a Single CsI(T1) Scintillator Coupled to a Silicon Drift Detector Array