# A Review of Requirements for Gamma Radiation Detection in Space Using CubeSats
## 3 Gamma Radiation Detection Strategy and Reference Detector  
Given the limited resources available on-board a CubeSat spacecraft, the detection strategy must be carefully designed by taking into account mission weight and size budgets, power limitations, orbital characteristics (radioactivity and temperature variation), and the gamma-ray energy range of interest.  
In this paper, we present the case of a gamma-ray detector with spectroscopic capability over a wide energy range (from 20 keV up to tens of MeV) and sub-microseconds event time stamping. The basic operations are illustrated in the flow chart reported in Figure 2.  
The reference gamma-ray detector is housed in a 1 mm thick wall aluminum box as shown in Figure 3 and fits in 1U volume of a CubeSat frame.  
For a payload fitting in 1U volume, the overall mass unit should not exceed 1.3 kg, however small deviations are possible, depending on the launch vehicle. The overall weight is in general constrained by the characteristics of the deployment mechanism.  
Figure 3: **(Left)** The outer box containing the reference detector studied in this paper. The enclosure might be either machined form solid aluminum or developed by additive manufacturing process (3D printing) and shaped to mechanically fit in the CubeSat mechanical structure. (**Right**) The schematic layout of the reference detector. Visible in the picture are the electronics, the rejection layer (VETO) for charged particle induced events, and the inner housing for the detection unit are also labeled.  
Figure 2: Schematic description of the detection concept of a gamma-ray detector operating in a CubeSat type satellite. The gamma-ray enters the payload and deposits energy in the target. The energy is in turn transformed into a flash of light that is collected from the photosensor. The signal output is read out by the front-end electronics and a charge signal generated. The processing electronics assigns a time stamp and a Attitude Determination and Control (ADC) channel to the event. The processed event is in turn sent to the On-Board Computer (OBC), a priority is assigned based on a look-up table for event categorization, and eventually made available for the transmission to ground.  
It is generally a good practice to implement redundancy features, especially for CubeSat missions where the failure rate is sensibly higher than standard space missions. When possible, it is therefore recommended to use multiple detection units rather than one single channel. The core of the gamma-ray detector presented in this paper is shown in Figure 4. It consists of a detection array of four optically independent scintillating crystals, each one of \(23\times 23\times 45\) mm\({}^{3}\) dimensions, encapsulated in an aluminum casing with overall dimensions of \(56\times 56\times 46\) mm\({}^{3}\) and equipped with a 2 mm thick quartz window for the photosensor coupling. In order to tag charged particle-induced events, a rejection layer (VETO) made out of 5 mm thick plastic scintillator tiles coupled to ASD-NUV1C-P-40 SiPM (manufactured by Advansid) has been introduced (see Figure 3 Right).