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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.

Abstract:

The γ-ray flux inside La Quaalude mine, the selected site for the construction of the underground laboratory LABChico in Mexico, is reported for energies below 3 MeV. Data were recorded with a 0.669 kg thallium-activated sodium iodide (NaI) crystal detector deployed for 3.6 hr. The detector response was calculated via Monte Carlo simulations with GEANT4 and validated against point-like calibration sources, and the γ-ray spectrum was extracted using an unfolding technique. The γ-ray flux above 250 keV and below 3 MeV is 0.1768 γ/cm²/s. The two most intense γ-rays in the natural radioactive background, ⁴⁰K and ²⁰⁸Tl, were identified. The flux measured for these isotopes is 0.0363 ± 0.0020 γ/cm²/s and 0.0016 ± 0.0005 γ/cm²/s, respectively. A γ-ray spectrometry analysis of rock samples showed 674.0 ± 2.0 Bq/kg, 24.0 ± 0.1 Bq/kg, and 17.7 ± 0.2 Bq/kg, of ⁴⁰K, ²³²Th, and ²³⁸U, respectively. These results are compared with deep underground facilities such as SURF, SNOLAB, Boulby, Modane, and Gran Sasso, with differences observed mainly due to the rock composition. Geotechnical studies of the mine and its rock composition are also reported.

Abstract:

In the article, the Non-Relativistic Effective Field Theory (NREFT) rate calculations were determined using the wimpy_nreft software [1], which was updated on September 29, 2021, to include a previously missing (q/mN)2 factor in the implementation. This update affects the results related to the O3 operator that now scales as (q/mN)4 instead of (q/mN)2. The corrections to Figs. 2, 6, 9, 10, and 11 are presented below. The couplings to O3 constrained by this analysis are higher than those reported in the article. Additionally: (i) In Sec. V A, operator O3 is suppressed at low recoil energies, exhibiting now a peak around 50 keV (Fig. 2). (ii) The third paragraph in Sec. V B should read as follows: “The operator O3 is proportional to (q/mN)4, while O11 goes as (q/mN)2. O3 is described by the F'' multipole operator [discussed in Eqs. (9) and (10)], while O11 is described by M. Since the former operator is related to spin-orbit coupling, it couples to the two unpaired neutrons and proton holes in 40 Ar , rather than to all 40 nucleons. This leads to a suppression of ~10 2 in addition to the extra q2 suppression.” (iii) In Sec. V F, the statement “Operators that introduce a factor of q2 to the DM response function, such as O3, O5, and O11 change the shape of the recoil energy spectrum, compared to O1” should read “Operators that introduce a factor of q2 or q4 to the DM response function, such as O3, O5, and O11 change the shape of the recoil energy spectrum, compared to O1.” (iv) The sentence in Sec. VI “Constraints on operators proportional to v? are weaker than those proportional to q, which are weaker than those proportional to neither” should read “Constraints on operators proportional to vn? are weaker than those proportional to q raised to the same power, which in turn are weaker than constant couplings.” (v) In Sec. VI, exclusion curves on O3 and data to reproduce its recoil energy spectra were uploaded to a new Zenodo version [2]. (Figure Presented).