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The observation of gravitational waves is hindered by the presence of transient noise (glitches). We study data from the third observing run of the Advanced LIGO detectors, and identify new glitch classes. Using training sets assembled by monitoring of the state of the detector, and by citizen-science volunteers, we update the Gravity Spy machine-learning algorithm for glitch classification. We find that a new glitch class linked to ground motion at the detector sites is especially prevalent, and identify two subclasses of this linked to different types of ground motion. Reclassification of data based on the updated model finds that 27 % of all transient noise at LIGO Livingston belongs to the new glitch class, making it the most frequent source of transient noise at that site. Our results demonstrate both how glitch classification can reveal potential improvements to gravitational-wave detectors, and how, given an appropriate framework, citizen-science volunteers may make discoveries in large data sets., 26 pages, 10 figures

GRI+ (Gamma-Ray Imager) is a cart-based Compton camera developed at the University of Liverpool. The system comprises three electrically-cooled semiconductor detectors; two planar double-sided strip detectors (Si(Li) and HPGe) and an HPGe coaxial detector. The mobile cart houses the necessary components for data acquisition and analysis, providing complete functionality for imaging gamma-ray sources in an industrial setting. This paper reports on the operation of the system and the methods used to improve intrinsic system performance. The processing chain for extracting information pertaining to gamma-ray interactions has been developed and the imaging performance is characterised using an analytical reconstruction code. The obtainable Angular Resolution Measure (ARM) from a Cs-137 point source placed 10.5 cm from the front of the Si(Li) cryostat was determined to be 4.12∘ after the application of data processing techniques. The system energy resolution, which is key to isotope identification and image quality, was calculated to be less than 0.5% at 1332.5 keV.

Transition quadrupole moments, Qt, of two ultrahigh-spin, collective structures in 154Er have been measured for the first time using the Doppler Shift Attenuation Method (DSAM). Data were acquired at the ATLAS accelerator facility of Argonne National Laboratory, using the Gammasphere detector array. A thick, gold-backed 110Pd foil was bombarded by a beam of 48Ti ions at 215 MeV. The Qt for each band was determined from the Doppler shift of gamma rays emitted by the resulting recoil nuclei. The extracted transition quadrupole moments are significantly different in magnitude, suggesting the two structures in 154Er represent distinct exotic nuclear shapes, namely axial superdeformed (SD) with Qt ≈ 20 eb, and triaxial strongly deformed (TSD) with Qt ≈ 11 eb. Indeed, the results calibrate the quadrupole moments of TSD bands recently measured in light erbium nuclei, 157,158Er.

A new collective band with high dynamic moment of inertia in 158Er at spins beyond band termination has been found in addition to the two previously reported ones. The measured transition quadrupole moments (Qt) of these three bands are very similar. These three bands have been suggested to possess a triaxial strongly deformed shape, based on comparisons with calculations using the cranked Nilsson-Strutinsky model and with tilted axis cranking calculations using the Skyrme-Hartree-Fock model. In addition, three collective bands with similar high dynamic moments of inertia, tentatively assigned to 157Ho, have been observed. Thus, it is suggested that all these structures share a common underlying character and that they are most likely associated with triaxial strongly deformed minima which are predicted to be close to the yrast line at spin 50 – 70.