# A Novel Method for Spectrometry Based on Imaging Systems
## 1 Introduction  
\(\gamma\)-ray spectrometry is a well-known technique in environmental radioactivity measurements. Modern application requirements need the use of brand-new detectors guaranteeing minimum weight and size, a high level of automation, multichannel and wireless connectivity. Nowadays, the most commonly used systems are easy to handle and to be carried by humans [1, 2, 3], assembled on air vehicles [4], robotic instruments [5], or dive into deep oceans aboard marine submernsels [6, 7, 8]. Facing this scenario, different types of detectors can be considered, such as scintillators (i.e., NaI:Tl) or solid-state detectors (i.e., HPGe), coupled to integrated electronic modules for data acquisition or custom-made designs to accommodate special needs. Scintillators are typically favored over solid-state detectors as mobile spectrometers since the latter traditionally require a cooling system with liquid nitrogen to operate, are generally more expensive, and are overall more sensitive in field deployment, despite the higher resolution they offer [9]. On the other hand, scintillators are sensitive to environmental conditions, especially temperature changes that may cause gain shifts during operation. Since the invention of NaI:Tl by [PERSON] in 1948, scintillators have been commonly coupled to a light-sensitive device such as the photomultiplier tube (PMT) [10]. Recentadvances in the development of semiconductor photodiodes have made silicon photomultiplier (SiPM) more suitable in some applications (i.e., when the position information is needed or in the presence of a magnetic field). These solid-state detectors are an array of many small-dimension avalanche photodiodes operated in Geiger mode. The high quantum efficiency (80-90% and therefore a better energy resolution), the low power consumption and the compact size have been promoting SiPM as the principal photodetector competitor of PMT. Furthermore, its peculiarity is to be intrinsically position sensitive (i.e., its structure is capable of localizing the position at which the centroid of light from a \(\gamma\)-ray event in the scintillator strikes the SiPM). To properly cover the entire sensitive area of the scintillator, a SiPM matrix is needed. The position information can be retained by using as many read out channels as the elements of the matrix. A further system with imaging capabilities but similar to PMTs is represented by a multi anode photomultiplier tube (MAPMT). Such systems could pave the way to finer light distribution analysis and to investigate \(\gamma\) spectrometric properties as a function of the depth of interaction (DoI). In the field of environmental radioactivity measurements, a proper choice of the scintillation material ensures the best optimization of spectrometric performances in terms of detection efficiency, time response, and energy resolution. The widely employed scintillation crystal in \(\gamma\) spectrometry is NaI:Tl. It shows a high light yield (i.e., a good energy resolution) at a reasonable cost but its slow decay time prevents high count rate sources measurements. Moreover, its hygroscopic nature requires a bulky housing which limits the realisation of compact and handled systems. The crystal showing the best properties in spectrometry applications is the LaBr\({}_{3}\):Ce. It has a strongly improved light yield and energy resolution and a fast response too, which is crucial in radioactivity measurements to spot high count rate sources. Moreover, its higher density guarantees a better detection efficiency and the possibility to realise smaller and compact detection systems. Nevertheless, this crystal is highly hygroscopic and it has a really expensive cost (i.e., about ten times higher than the NaI one) which limits its widespread use. A solution accounting for the non-hygroscopic aspect while assuring a good trade-off among energy resolution, detection efficiency, and time response could be the use of the so-called CRY018 crystal.