More Like this

1. Investigation of the electrical conduction mechanisms in P-type amorphous germanium electrical contacts for germanium detectors in searching for rare-event physics

   https://doi.org/10.1140/epjc/s10052-020-08529-z  

   Bhattarai, S.; Panth, R.; Wei, W.-Z.; Mei, H.; Mei, D.-M.; Raut, M.-S.; Acharya, P.; Wang, G.-J. (October 2020, The European Physical Journal C)

   null (Ed.)

   Abstract For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of $$2.13^{-0.05}_{+0.07}\mathrm{{A}}^\circ $$ 2 . 13 + 0.07 - 0.05 A ∘ to $$5.07^{-0.83}_{+2.58}\mathrm{{A}}^\circ $$ 5 . 07 + 2.58 - 0.83 A ∘ , depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches. 

   more » « less
2. Machine learning-powered data cleaning for LEGEND: a semi-supervised approach using affinity propagation and support vector machines

   https://doi.org/10.1088/2632-2153/adbb37  

   León, E; Li, A; Bahena_Schott, M A; Bos, B; Busch, M; Chapman, J R; Duran, G L; Gruszko, J; Henning, R; Martin, E L; et al (March 2025, Machine Learning: Science and Technology)

   Abstract Neutrinoless double-beta decay ( $0\nu \beta \beta$) is a rare nuclear process that, if observed, will provide insight into the nature of neutrinos and help explain the matter-antimatter asymmetry in the Universe. The large enriched germanium experiment for neutrinoless double-beta decay (LEGEND) will operate in two phases to search for $0\nu \beta \beta$. The first (second) stage will employ 200 (1000) kg of High-Purity Germanium (HPGe) enriched in⁷⁶Ge to achieve a half-life sensitivity of 10²⁷(10²⁸) years. In this study, we present a semi-supervised data-driven approach to remove non-physical events captured by HPGe detectors powered by a novel artificial intelligence model. We utilize affinity propagation to cluster waveform signals based on their shape and a support vector machine to classify them into different categories. We train, optimize, and test our model on data taken from a natural abundance HPGe detector installed in the Full Chain Test experimental stand at the University of North Carolina at Chapel Hill. We demonstrate that our model yields a maximum sacrifice of physics events of ${0.024}_{-0.003}^{+0.004}\mathrm{\%}$after data cleaning. Our model is being used to accelerate data cleaning development for LEGEND-200 and will serve to improve data cleaning procedures for LEGEND-1000. 

   more » « less
3. Bayesian inference of high-purity germanium detector impurities based on capacitance measurements and machine-learning accelerated capacitance calculations

   https://doi.org/10.1140/epjc/s10052-023-11509-8  

   Abt, I.; Gooch, C.; Hagemann, F.; Hauertmann, L.; Liu, X.; Schulz, O.; Schuster, M. (May 2023, The European Physical Journal C)

   Abstract The impurity density in high-purity germanium detectors is crucial to understand and simulate such detectors. However, the information about the impurities provided by the manufacturer, based on Hall effect measurements, is typically limited to a few locations and comes with a large uncertainty. As the voltage dependence of the capacitance matrix of a detector strongly depends on the impurity density distribution, capacitance measurements can provide a path to improve the knowledge on the impurities. The novel method presented here uses a machine-learned surrogate model, trained on precise GPU-accelerated capacitance calculations, to perform full Bayesian inference of impurity distribution parameters from capacitance measurements. All steps use open-source Julia software packages. Capacitances are calculated with SolidStateDetectors.jl , machine learning is done with Flux.jl and Bayesian inference performed using BAT.jl . The capacitance matrix of a detector and its dependence on the impurity density is explained and a capacitance bias-voltage scan of an n -type true-coaxial test detector is presented. The study indicates that the impurity density of the test detector also has a radial dependence. 

   more » « less
4. Impact of charge trapping on the energy resolution of Ge detectors for rare-event physics searches

   https://doi.org/10.1088/1361-6471/ab9796  

   Mei, Dongming; R Bharadwaj, Mukund; Wei, Wenzhao; Panth, Rajendra; Liu, Jing; Mei, Hao; Li, Yangyang; Acharya, Pramod; Bhattarai, Sanjay; Kooi, Kyler; et al (May 2020, Journal of Physics G: Nuclear and Particle Physics)

   Charge trapping degrades the energy resolution of germanium (Ge) detectors, which require to have increased experimental sensitivity in searching for dark matter and neutrinoless double-beta decay. We investigate the charge trapping processes utilizing nine planar detectors fabricated from USD-grown crystals with well-known net impurity levels. The charge collection efficiency as a function of charge trapping length is derived from the Shockley-Ramo theorem. Furthermore, we develop a model that correlates the energy resolution with the charge collection efficiency. This model is then applied to the experimental data. As a result, charge collection efficiency and charge trapping length are determined accordingly. Utilizing the Lax model (further developed by CDMS collaborators), the absolute impurity levels are determined for nine detectors. The knowledge of these parameters when combined with other traits such as the Fano factor serve as a reliable indicator of the intrinsic nature of charge trapping within the crystals. We demonstrate that electron trapping is more severe than hole trapping in a p-type detector and the charge collection efficiency depends on the absolute impurity level of the Ge crystal when an adequate bias voltage is applied to the detector. Negligible charge trapping is found when the absolute impurity level is less than 1.0$$\times$$10$^11/^3$ for collecting electrons and 2.0$$\times$$10$^11/^3$ for collecting holes. 

   more » « less
5. Low-energy solar neutrino detection utilizing advanced germanium detectors

   https://doi.org/10.1088/1361-6471/acc751  

   Bhattarai, S; Mei, D-M; Raut, M S (April 2023, Journal of Physics G: Nuclear and Particle Physics)

   Abstract We explore the possibility to use advanced germanium (Ge) detectors as a low-energy solar neutrino observatory by means of neutrino-nucleus elastic scattering. A Ge detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a novel technology with experimental sensitivity for detecting low-energy solar neutrinos. Ge internal charge amplification (GeICA) detectors will amplify the charge carriers induced by neutrino interacting with Ge atoms through the emission of phonons. It is those phonons that will create charge carriers through the ionization of impurities to achieve an extremely low energy threshold of ∼0.01 eV. We demonstrate the phonon absorption, excitation, and ionization probability of impurities in a Ge detector with impurity levels of 3 × 10 10 cm −3 , 9 × 10 10 cm −3 , and 2 × 10 11 cm −3 . We present the sensitivity of such a Ge experiment for detecting solar neutrinos in the low-energy region. We show that, if GeICA technology becomes available, then a new opportunity arises to observe pp and 7 Be solar neutrinos. Such a novel detector with only 1 kg of high-purity Ge will give ∼10 events per year for pp neutrinos and ∼5 events per year for 7 Be neutrinos with a detection energy threshold of 0.01 eV. 

   more » « less