Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0$\nu \beta \beta$), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0$\nu \beta \beta$ of \ce{^{136}Xe} with projected half-life sensitivity of $1.35\times 10^{28}$~yr. To reach this sensitivity, the design goal for nEXO is $\leq$1\% energy resolution at the decay $Q$-value ($2458.07\pm 0.31$~keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163~K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay $Q$-value for the nEXO design

‘We thought if it’s going to take two years then we need to start that now’: Age, infertility risk and the timing of pregnancy in older first-time mothers

Over the past few decades, the number of women having their first babies over the age of thirty-five in most developed societies has steadily increased. Concerns have been raised over this trend amidst warnings of both the increased risk of fertility problems and health risks to mother and child. Despite this, research into the timing of pregnancy in the context of decreasing fertility has been somewhat neglected, with research typically framed in biomedical rather than social terms. However, this area merits closer attention given the contradictory nature of societal messages that simultaneously encourage women to pursue careers and enhance lifestyle, whilst warning of ‘risks’ of infertility and problems in ‘delaying’ motherhood. This article is based on a small-scale qualitative study that uses data drawn from eleven in-depth interviews with ‘older mothers’ about their transition to motherhood. The data was thematically analysed. We found that the women drew upon risk discourses around decreasing fertility and advancing maternal age, and that these discourses impacted on their decisions about the timing of their pregnancies. Some mothers felt that they started trying to conceive at ‘non-ideal’ times, owing to expectations they held about decreasing fertility. We suggest that the impact of contradictory societal messages around the timing of motherhood need to be more clearly considered for their potential effects on the timing of pregnancy and note how this topic brings the personal, and, by implication, the societal, into conflict with the (narrated) biological

Development of a 127^{127}Xe calibration source for nEXO

International audienceWe study a possible calibration technique for the nEXO experiment using a $^{127}$Xe electron capture source. nEXO is a next-generation search for neutrinoless double beta decay (0νββ) that will use a 5-tonne, monolithic liquid xenon time projection chamber (TPC). The xenon, used both as source and detection medium, will be enriched to 90% in $^{136}$Xe. To optimize the event reconstruction and energy resolution, calibrations are needed to map the position- and time-dependent detector response. The 36.3 day half-life of $^{127}$Xe and its small Q-value compared to that of $^{136}$Xe 0νββ would allow a small activity to be maintained continuously in the detector during normal operations without introducing additional backgrounds, thereby enabling in-situ calibration and monitoring of the detector response. In this work we describe a process for producing the source and preliminary experimental tests. We then use simulations to project the precision with which such a source could calibrate spatial corrections to the light and charge response of the nEXO TPC