Calibration of Cherenkov detectors for monoenergetic photon imaging in active interrogation applications

Abstract

Active interrogation of cargo containers using monoenergetic photons offers a rapid and low-dose approach to search for shielded special nuclear materials. Cherenkov detectors can be used for imaging of the cargo provided that gamma ray energies used in interrogation are well resolved, as the case in 11 B(d,nγ) 12 C reaction resulting in 4.4 MeV and 15.1 MeV photons. While an array of Cherenkov threshold detectors reduces low energy background from scatter while providing the ability of high contrast transmission imaging, thus confirming the presence of high-Z materials, these detectors require a special approach to energy calibration due to the lack of resolution. In this paper, we discuss the utility of Cherenkov detectors for active interrogation with monoenergetic photons as well as the results of computational and experimental studies of their energy calibration. The results of the studies with sources emitting monoenergetic photons as well as complex gamma ray spectrum sources, for example 232 Th, show that calibration is possible as long as the energies of photons of interest are distinct.

Uncovering Special Nuclear Materials by Low-energy Nuclear Reaction Imaging

“…We employed a LaBr scintillation detector to measure the spectrum of photons generated by the 11 B(d,nγ) 12 C reaction ( Fig. 1b ) and an array of Cherenkov detectors based on quartz 18 to measure the energy-dependent opacity of objects of different areal density and elemental composition. Both types of detectors exhibit spectroscopic capability, and while the Cherenkov detectors have only crude energy resolution, it is sufficient for measurements when the gamma rays have large energy separation.…”

“…Figure 2a demonstrates energy-dependent transmission measurement of several objects composed of different materials with the same aerial density (see Supplementary Table 1 for the details on objects measured). Since spectral analysis with Cherenkov detectors is not a common practice due to lack of resolved peaks, custom energy calibration methods using spectral shoulders and inflection points were developed 18 specifically for this type of application. In this work the faux-peaks are integrated within bounds illustrated with shaded areas in Fig.…”

“…During the analysis, the detector configuration was taken into account in order to compare the signal among different designs. Energy calibration methodology was developed specifically for Cherenkov detectors 18 .…”

“…The data analysis was carried out using the open-source data analysis suite ROOT 24 . Digital data processing is based on standard methods of waveform baseline subtraction, and pulse area integration, which were previously described 18 21 for photon and neutron detectors, respectively.…”

Assessment of image reconstruction algorithm coupled with fine-resolution array of Cherenkov detectors

“…Demand for fine-resolution imaging in high-dose applications, including high-energy physics, medical physics, and nuclear security place a number of requirements on detection systems: withstand potential radiation damage, operate with short decay time, and function with high background present 1 , 2 . Typically, scintillators are used in imaging applications because of their energy resolution capabilities, especially in active interrogation space 3 , 4 .…”