Professor Jocelyn Monroe

Abstract:

Dark matter elastic scattering off nuclei can result in the excitation and ionization of the recoiling atom through the so-called Migdal effect. The energy deposition from the ionization electron adds to the energy deposited by the recoiling nuclear system and allows for the detection of interactions of sub-GeV/c^{2} mass dark matter. We present new constraints for sub-GeV/c^{2} dark matter using the dual-phase liquid argon time projection chamber of the DarkSide-50 experiment with an exposure of (12 306±184)  kg d. The analysis is based on the ionization signal alone and significantly enhances the sensitivity of DarkSide-50, enabling sensitivity to dark matter with masses down to 40  MeV/c^{2}. Furthermore, it sets the most stringent upper limit on the spin independent dark matter nucleon cross section for masses below 3.6  GeV/c^{2}.

Abstract:

The World Health Organisation (WHO) presents an upper limit for lead in drinking water of 10 parts per billion ppb. Typically, to reach this level of sensitivity, expensive metrology is required. To increase the sensitivity range of low-cost devices, this paper explores the prospects of using a volume reduction technique of a boiled water sample doped with Lead-210 (210 Pb), as a means to increase the solute’s concentration. 210Pb is a radioactive lead isotope and its concentration in a water sample can be measured with e.g. High Purity Germanium (HPGe) detectors at the Boulby Underground Germanium Suite. Concentrations close to the WHO limit have not been examined. This paper presents a measurement of the volume reduction technique retaining 99±(9)% of 210Pb starting from a concentration of 1.9×10−6 ppb before reduction and resulting in 2.63×10−4 ppb after reduction. This work also applies the volume reduction technique to London tap water and reports the radioassay results from gamma counting in HPGe detectors. Among other radio-isotopes, 40K, 210Pb, 131I and 177Lu were identified at measured concentrations of 2.83×103 ppb, 2.55×10−7 ppb, 5.06×10−10 ppb and 5.84×10−10 ppb in the London tap water sample. This technique retained 90±50% of 40K. Stable lead was inferred from the same water sample at a measured concentration of 0.012 ppb, prior to reduction

Abstract:

Isotope identification is a recurrent problem in γ spectroscopy with high-purity germanium detectors. In this work, new strategies are introduced to facilitate this type of analysis. Five criteria are used to identify the parent isotopes making a query on a large database of γ lines from a multitude of isotopes producing an output list whose entries are sorted so that the γ lines with the highest chance of being present in a sample are placed at the top. A metric to evaluate the performance of the different criteria is introduced and used to compare them. Two of the criteria are found to be superior than the others: one based on fuzzy logic and another that makes use of the γ relative emission probabilities. A program called histoGe implements these criteria using an SQLite database containing the γ lines of isotopes which was parsed from WWW Table of Radioactive Isotopes. histoGe is Free Software and is provided along with the database so they can be used to analyze spectra obtained with generic γ -ray detectors.

Abstract:

The DEAP-3600 experiment searches for dark matter via the interactions of WIMPs with a liquid argon target. The experiment is located at SNOLAB in Sudbury, Ontario, 2 km underground to shield the detector from cosmic rays. The detector consists of an acrylic sphere with an inner diameter of ∼170 cm containing ∼3300 kg of liquid argon. Liquid argon is chosen as a target due to its ability to reject electromagnetic backgrounds by examining its scintillation pulse shape. The argon volume is instrumented with 255 PMTs which are connected to the vessel via acrylic light guides. As liquid argon scintillates at a wavelength of 128 nm, its scintillation light needs to be shifted to a wavelength into a region where the PMTs are more sensitive; this is done by coating the inside of the acrylic vessel with TPB wavelength shifter, which re-emits the argon scintillation light at a wavelength of 420 nm. This talk will describe the current status of the experiment and some recent analyses performed by the collaboration. The status of planned upgrades to the detector and the plans for the future of the experiment will also be detailed.

Abstract:

In this article, the affiliation ’Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad de México, México’ for D. J. Marín-Lámbarri was missing. Affiliations 3 and 5 have been corrected: 3 Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Ciudad de México, 04510, México 5 Instituto de Física, Universidad Nacional Autónoma de México, Ciudad de México, 01000, México The original article has been revised.