Changes induced by perturbed aerosol conditions in moderately deep mixed-phase convective clouds
(cloud top height ∼ 5 km)
developing along sea-breeze convergence
lines are investigated with ...high-resolution numerical model simulations. The
simulations utilise the newly developed Cloud–AeroSol Interacting Microphysics (CASIM) module for
the Unified Model (UM), which allows for the representation of the two-way interaction between cloud and
aerosol fields. Simulations are evaluated against observations collected during the COnvective
Precipitation Experiment (COPE) field campaign over the southwestern peninsula of the UK in 2013.
The simulations compare favourably with observed thermodynamic profiles, cloud base cloud droplet
number concentrations (CDNC), cloud depth, and radar reflectivity statistics. Including the
modification of aerosol fields by cloud microphysical processes improves the correspondence with
observed CDNC values and spatial variability, but reduces the agreement with observations for
average cloud size and cloud top height. Accumulated precipitation is suppressed for higher-aerosol conditions before clouds become organised
along the sea-breeze convergence lines. Changes in precipitation are smaller in simulations with
aerosol processing. The precipitation suppression is due to less efficient precipitation production
by warm-phase microphysics, consistent with parcel model predictions. In contrast, after convective cells organise along the sea-breeze convergence zone, accumulated
precipitation increases with aerosol concentrations. Condensate production increases with the
aerosol concentrations due to higher vertical velocities in the convective cores and higher cloud
top heights. However, for the highest-aerosol scenarios, no further increase in the condensate
production occurs, as clouds grow into an upper-level stable layer. In these cases, the reduced
precipitation efficiency (PE) dominates the precipitation response and no further precipitation
enhancement occurs. Previous studies of deep convective clouds have related larger vertical
velocities under high-aerosol conditions to enhanced latent heating from freezing.
In the presented simulations changes in latent heating above the 0∘C are negligible, but latent
heating from condensation increases with aerosol concentrations. It is hypothesised that this
increase is related to changes in the cloud field structure reducing the mixing of environmental air
into the convective core. The precipitation response of the deeper mixed-phase clouds along well-established convergence lines
can be the opposite of predictions from parcel models. This occurs when clouds interact with a
pre-existing thermodynamic environment and cloud field structural changes occur that are not
captured by simple parcel model approaches.
We present new experimental constraints on the WIMP-nucleon spin-dependent elastic cross sections using data from the first science run of ZEPLIN-III, a two-phase xenon experiment searching for ...galactic dark matter weakly interacting massive particles based at the Boulby mine. Analysis of approximately 450 kg x days fiducial exposure allow us to place a 90%-confidence upper limit on the pure WIMP-neutron cross section of sigma(n)=1.9x10(-2) pb at 55 GeV/c(2) WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn charge-dependent nucleon-nucleon potential were used for the odd-neutron isotopes 129Xe and 131Xe. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction could be much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of approximately 2.
The Boulby Underground Germanium Suite (BUGS) comprises three low-background, high-purity germanium detectors operating in the Boulby Underground Laboratory, located 1.1 km underground in the ...north-east of England, UK. BUGS utilises three types of detector to facilitate a high-sensitivity, high-throughput radio-assay programme to support the development of rare-event search experiments. A Broad Energy Germanium (BEGe) detector delivers sensitivity to low-energy gamma-rays such as those emitted by 210Pb and 234Th. A Small Anode Germanium (SAGe) well-type detector is employed for efficient screening of small samples. Finally, a standard p-type coaxial detector provides fast screening of standard samples. This paper presents the steps used to characterise the performance of these detectors for a variety of sample geometries, including the corrections applied to account for cascade summing effects. For low-density materials, BUGS is able to radio-assay to specific activities down to 3.6mBqkg−1 for 234Th and 6.6mBqkg−1 for 210Pb both of which have uncovered some significant equilibrium breaks in the 238U chain. In denser materials, where gamma-ray self-absorption increases, sensitivity is demonstrated to specific activities of 0.9mBqkg−1 for 226Ra, 1.1mBqkg−1 for 228Ra, 0.3mBqkg−1 for 224Ra, and 8.6mBqkg−1 for 40K with all upper limits at a 90% confidence level. These meet the requirements of most screening campaigns presently under way for rare-event search experiments, such as the LUX-ZEPLIN (LZ) dark matter experiment. We also highlight the ability of the BEGe detector to probe the X-ray fluorescence region which can be important to identify the presence of radioisotopes associated with neutron production; this is of particular relevance in experiments sensitive to nuclear recoils.
We present limits on the WIMP–nucleon cross section for inelastic dark matter from a reanalysis of the 2008 run of ZEPLIN-III. Cuts, notably on scintillation pulse shape and ...scintillation-to-ionisation ratio, give a net exposure of 63kgday in the range 20–80keV nuclear recoil energy, in which 6 events are observed. Upper limits on signal rate are derived from the maximum empty patch in the data. Under standard halo assumptions a small region of parameter space consistent, at 99% CL, with causing the 1.17tonyr DAMA modulation signal is allowed at 90% CL: it is in the mass range 45–60GeVc−2 with a minimum CL of 87%, again derived from the maximum patch. This is the tightest constraint yet presented using xenon, a target nucleus whose similarity to iodine mitigiates systematic error from the assumed halo.
A
bstract
We present an experimental study of single electron emission in ZEPLIN-III, a two-phase xenon experiment built to search for dark matter WIMPs, and discuss appli-cations enabled by the ...excellent signal-to-noise ratio achieved in detecting this signature. Firstly, we demonstrate a practical method for precise measurement of the free electron lifetime in liquid xenon during normal operation of these detectors. Then, using a realistic detector response model and backgrounds, we assess the feasibility of deploying such an instrument for measuring coherent neutrino-nucleus elastic scattering using the ionisation channel in the few-electron regime. We conclude that it should be possible to measure this elusive neutrino signature above an ionisation threshold of ~3 electrons both at a stopped pion source and at a nuclear reactor. Detectable signal rates are larger in the reactor case, but the triggered measurement and harder recoil energy spectrum afforded by the accelerator source enable lower overall background and fiducialisation of the active volume.
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.
210
Pb 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
210
Pb 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,
40
K,
210
Pb,
131
I and
177
Lu were identified at measured concentrations of
2.83
×
10
3
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
40
K. Stable lead was inferred from the same water sample at a measured concentration of 0.012 ppb, prior to reduction.
► We propose a 3-stage DM and Iˆ1/2 observatory based on multi-ton LXe and LAr detectors. ► This work is a quantitative study of the topics in Astropart. Phys. 31 (2009) 63–74. ► WIMP cross-sections ...and masses could be measured with sensitivity of 10-47cm2. ► 0ν2β decay could be observed for 136Xe with sensitivity to half-lives 10E27–10E28y. ► The pp solar ν spectrum, and ν flux from a Galactic SN, could also be measured.
We study a three stage dark matter and neutrino observatory based on multi-ton two-phase liquid Xe and Ar detectors with sufficiently low backgrounds to be sensitive to WIMP dark matter interaction cross sections down to 10-47cm2, and to provide both identification and two independent measurements of the WIMP mass through the use of the two target elements in a 5:1 mass ratio, giving an expected similarity of event numbers. The same detection systems will also allow measurement of the pp solar neutrino spectrum, the neutrino flux and temperature from a Galactic supernova, and neutrinoless double beta decay of 136Xe to the lifetime level of 1027–1028y corresponding to the Majorana mass predicted from current neutrino oscillation data. The proposed scheme would be operated in three Generic stages G2, G3, G4, beginning with fiducial masses 1-ton Xe+5-ton Ar (G2), progressing to 10-ton Xe+50-ton Ar (G3) then, dependent on results and performance of the latter, expandable to 100-ton Xe+500-ton Ar (G4). This method of scale-up offers the advantage of utilizing the Ar vessel and ancillary systems of one stage for the Xe detector of the succeeding stage, requiring only one new detector vessel at each stage. Simulations show the feasibility of reducing or rejecting all external and internal background levels to a level <1 events per year for each succeeding mass level, by utilizing an increasing outer thickness of target material as self-shielding. The system would, with increasing mass scale, become increasingly sensitive to annual signal modulation, the agreement of Xe and Ar results confirming the Galactic origin of the signal. Dark matter sensitivities for spin-dependent and inelastic interactions are also included, and we conclude with a discussion of possible further gains from the use of Xe/Ar mixtures.
► We examine backgrounds from radioactivity in the ZEPLIN-III dark matter experiment. ► Electron recoil rates are predicted accurately by Monte Carlo simulation. ► Nuclear recoil rates from neutron ...scattering are also presented. ► We analyse rare background topologies which can affect the sensitivity of direct WIMP searches.
We examine electron and nuclear recoil backgrounds from radioactivity in the ZEPLIN-III dark matter experiment at Boulby. The rate of low-energy electron recoils in the liquid xenon WIMP target is 0.75±0.05 events/kg/day/keV, which represents a 20-fold improvement over the rate observed during the first science run. Energy and spatial distributions agree with those predicted by component-level Monte Carlo simulations propagating the effects of the radiological contamination measured for materials employed in the experiment. Neutron elastic scattering is predicted to yield 3.05±0.5 nuclear recoils with energy 5–50keV per year, which translates to an expectation of 0.4 events in a 1yr dataset in anti-coincidence with the veto detector for realistic signal acceptance. Less obvious background sources are discussed, especially in the context of future experiments. These include contamination of scintillation pulses with Cherenkov light from Compton electrons and from β activity internal to photomultipliers, which can increase the size and lower the apparent time constant of the scintillation response. Another challenge is posed by multiple-scatter γ-rays with one or more vertices in regions that yield no ionisation. If the discrimination power achieved in the first run can be replicated, ZEPLIN-III should reach a sensitivity of ∼1×10−8pb·yr to the scalar WIMP–nucleon elastic cross-section, as originally conceived.
Summary
We examined whether men with anabolic‐steroid‐induced hypogonadism (ASIH) seeking testosterone supplementation therapy (TST) regretted their decision to use anabolic‐androgenic steroids (AAS) ...and what their reasons were for this regret. An anonymous, prospective survey was distributed to 382 men seeking follow‐up treatment for hypogonadism. Prior AAS use was confirmed by self‐report, and men were categorised based upon whether they regretted (R) or did not regret (NR) their use of AAS. The average patient age was 40 ± 0.9 years (n = 79) and 15.2% expressed regret over AAS use. No demographic differences were identified between those who regretted AAS use (n = 12) and those who did not (n = 67). Regret was not related to ASIH diagnosis or to AAS‐related side effects like increased aggression, mood disorders, erectile dysfunction, acne, fluid retention or dyslipidemia. Those who regretted AAS use were significantly more likely to have not comprehended the negative impact on future fertility (P < 0.030). Actual fertility issues were comparable in men who regretted AAS use (16.7%) and those who did not (13%). A total of 15.2% of men regretted using AAS. A lack of awareness regarding the negative long‐term effects on fertility was the primary factor related to regret of AAS use in men with ASIH.
PDF
