Total-body PET (TB-PET) scanners, with axial lengths exceeding 1 meter, provide significantly higher sensitivity than conventional PET scanners due to their greater acceptance of gamma pairs. ...However, this increased sensitivity often comes from gamma rays detected at oblique angles, leading to substantial multiple scattering along the patient's body. Additionally, the cost of TB-PET scanners scales with their extended detector length, often costing 5 to 10 times more than conventional scanners. Therefore, optimizing TB-PET performance requires crystals that enhance energy resolution and control costs. Cesium iodide (CsI), though historically less favored for PET due to its lower stopping power and light yield compared to crystals like LYSO, shows remarkable improvement when operated at cryogenic temperatures (\(\sim\)100 K). Under these conditions, CsI light yield rises dramatically to about 100 photons/keV, providing excellent energy resolution and good coincidence time resolution at a lower cost - typically 3 to 5 times cheaper than other crystals at parity of radiation length. In our study, cryogenic CsI crystals achieved an energy resolution better than 7% FWHM at 511 keV and a coincidence time resolution of less than 2 ns. These results demonstrate the potential of cryogenic CsI as a cost-effective, high-performance material for TB-PET scanners.
The NEXT-White detector, a high-pressure gaseous xenon time projection chamber, demonstrated the excellence of this technology for future neutrinoless double beta decay searches using photomultiplier ...tubes (PMTs) to measure energy and silicon photomultipliers (SiPMs) to extract topology information. This analysis uses \(^{83m}\text{Kr}\) data from the NEXT-White detector to measure and understand the energy resolution that can be obtained with the SiPMs, rather than with PMTs. The energy resolution obtained of (10.9 \(\pm\) 0.6) \(\%\), full-width half-maximum, is slightly larger than predicted based on the photon statistics resulting from very low light detection coverage of the SiPM plane in the NEXT-White detector. The difference in the predicted and measured resolution is attributed to poor corrections, which are expected to be improved with larger statistics. Furthermore, the noise of the SiPMs is shown to not be a dominant factor in the energy resolution and may be negligible when noise subtraction is applied appropriately, for high-energy events or larger SiPM coverage detectors. These results, which are extrapolated to estimate the response of large coverage SiPM planes, are promising for the development of future, SiPM-only, readout planes that can offer imaging and achieve similar energy resolution to that previously demonstrated with PMTs.
The imaging of individual Ba\(^{2+}\) ions in high pressure xenon gas is one possible way to attain background-free sensitivity to neutrinoless double beta decay and hence establish the Majorana ...nature of the neutrino. In this paper we demonstrate selective single Ba\(^{2+}\) ion imaging inside a high-pressure xenon gas environment. Ba\(^{2+}\) ions chelated with molecular chemosensors are resolved at the gas-solid interface using a diffraction-limited imaging system with scan area of 1\(\times\)1~cm\(^2\) located inside 10~bar of xenon gas. This new form of microscopy represents an important enabling step in the development of barium tagging for neutrinoless double beta decay searches in \(^{136}\)Xe, as well as a new tool for studying the photophysics of fluorescent molecules and chemosensors at the solid-gas interface.
NEXT-100 is currently being constructed at the Laboratorio Subterráneo de Canfranc in the Spanish Pyrenees and will search for neutrinoless double beta decay using a high-pressure gaseous time ...projection chamber (TPC) with 100 kg of xenon. Charge amplification is carried out via electroluminescence (EL) which is the process of accelerating electrons in a high electric field region causing secondary scintillation of the medium proportional to the initial charge. The NEXT-100 EL and cathode regions are made from tensioned hexagonal meshes of 1 m diameter. This paper describes the design, characterization, and installation of these parts for NEXT-100. Simulations of the electric field are performed to model the drift and amplification of ionization electrons produced in the detector under various EL region alignments and rotations. Measurements of the electrostatic breakdown voltage in air characterize performance under high voltage conditions and identify breakdown points. The electrostatic deflection of the mesh is quantified and fit to a first-principles mechanical model. Measurements were performed with both a standalone test EL region and with the NEXT-100 EL region before its installation in the detector. Finally, we describe the parts as installed in NEXT-100, following their deployment in Summer 2023.
Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers ...typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from \(^{83\mathrm{m}}\)Kr calibration electron captures (\(E\sim45\)keV), the position of origin of low-energy events is determined to \(2~\)cm precision with bias \(< 1\)mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E\(\geq\)1.5MeV), yielding a precision of 3cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Q\(_{\beta\beta}\) in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.
The NEXT experiment aims at the sensitive search of the neutrinoless double beta decay in \(^{136}\)Xe, using high-pressure gas electroluminescent time projection chambers. The NEXT-White detector is ...the first radiopure demonstrator of this technology, operated in the Laboratorio Subterráneo de Canfranc. Achieving an energy resolution of 1% FWHM at 2.6 MeV and further background rejection by means of the topology of the reconstructed tracks, NEXT-White has been exploited beyond its original goals in order to perform a neutrinoless double beta decay search. The analysis considers the combination of 271.6 days of \(^{136}\)Xe-enriched data and 208.9 days of \(^{136}\)Xe-depleted data. A detailed background modeling and measurement has been developed, ensuring the time stability of the radiogenic and cosmogenic contributions across both data samples. Limits to the neutrinoless mode are obtained in two alternative analyses: a background-model-dependent approach and a novel direct background-subtraction technique, offering results with small dependence on the background model assumptions. With a fiducial mass of only 3.50\(\pm\)0.01 kg of \(^{136}\)Xe-enriched xenon, 90% C.L. lower limits to the neutrinoless double beta decay are found in the T\(_{1/2}^{0\nu}>5.5\times10^{23}-1.3\times10^{24}\) yr range, depending on the method. The presented techniques stand as a proof-of-concept for the searches to be implemented with larger NEXT detectors.
The search for neutrinoless double beta decay (\(0\nu\beta\beta\)) remains one of the most compelling experimental avenues for the discovery in the neutrino sector. Electroluminescent gas-phase time ...projection chambers are well suited to \(0\nu\beta\beta\) searches due to their intrinsically precise energy resolution and topological event identification capabilities. Scalability to ton- and multi-ton masses requires readout of large-area electroluminescent regions with fine spatial resolution, low radiogenic backgrounds, and a scalable data acquisition system. This paper presents a detector prototype that records event topology in an electroluminescent xenon gas TPC via VUV image-intensified cameras. This enables an extendable readout of large tracking planes with commercial devices that reside almost entirely outside of the active medium.Following further development in intermediate scale demonstrators, this technique may represent a novel and enlargeable method for topological event imaging in \(0\nu\beta\beta\).
