We present constraints on the existence of weakly interacting massive particles (WIMPs) from an 11 kg d target exposure of the DAMIC experiment at the SNOLAB underground laboratory. The observed ...energy spectrum and spatial distribution of ionization events with electron-equivalent energies >200 eV_{ee} in the DAMIC CCDs are consistent with backgrounds from natural radioactivity. An excess of ionization events is observed above the analysis threshold of 50 eV_{ee}. While the origin of this low-energy excess requires further investigation, our data exclude spin-independent WIMP-nucleon scattering cross sections σ_{χ-n} as low as 3×10^{-41} cm^{2} for WIMPs with masses m_{χ} from 7 to 10 GeV c^{-2}. These results are the strongest constraints from a silicon target on the existence of WIMPs with m_{χ}<9 GeV c^{-2} and are directly relevant to any dark matter interpretation of the excess of nuclear-recoil events observed by the CDMS silicon experiment in 2013.
The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross section is by far the largest of all low-energy neutrino couplings. This ...mode of interaction offers new opportunities to study neutrino properties and leads to a miniaturization of detector size, with potential technological applications. We observed this process at a 6.7σ̃ confidence level, using a low-background, 14.6-kilogram CsINa scintillator exposed to the neutrino emissions from the Spallation Neutron Source at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the standard model for this process, were observed in high signal-to-background conditions. Improved constraints on nonstandard neutrino interactions with quarks are derived from this initial data set.
We study the possibility of using CsINa scintillators as an advantageous target for the detection of coherent elastic neutrino-nucleus scattering (CENNS), using the neutrino emissions from the SNS ...spallation source at Oak Ridge National Laboratory. The response of this material to low-energy nuclear recoils like those expected from this process is characterized. Backgrounds are studied using a 2kg low-background prototype crystal in a dedicated radiation shield. The conclusion is that a planned 14kg detector should measure approximately 550 CENNS events per year above a demonstrated ~7keVnr low-energy threshold, with a signal-to-background ratio sufficient for a first measurement of the CENNS cross-section. The cross-section for the Pb208(νe,e−)Bi208 reaction, of interest for future supernova neutrino detection, can be simultaneously obtained.
Electroplating was used as a purification method and produced thick (3.2–12.2 mm) copper deposits of ultra-high radiopurity. Due to the extreme thickness of these electrodeposits compared to ...traditional electroplating, characterization is necessary to prevent costly failures and ensure device reliability. The deposition rate was carefully controlled to maintain a uniform growth front and required plating for a continuous 8 months in order to produce the 12.2-mm-thick copper specimen. Tensile testing shows the electroplated copper to exhibit significant strain hardening as would be expected with face-centered cubic materials, indicating that the material is free of significant defects and voids. Testing of eight tensile samples machined according to ASTM-E8 specifications exhibited yield strengths of 95 ± 4 MPa. Hardness was measured to be 79.8 ± 5.3 HV using a 200-gf load. Microstructure and deformation showed the grains to be highly aligned with respect to the growth direction, and electron backscatter diffraction showed the development of a (110) texture.
Strain hardening in metallic multilayers is shown experimentally to be greater in trilayer films of Cu–Ni–Nb than bilayer films of Cu–Ni or Cu–Nb using both direct measurements of flow strength at ...different effective strains and an analysis of the out-of-plane deformation around nanoindentation impressions. The mechanism that accounts for increased strain hardening in the trilayer is a proposed super-threader dislocation and cross-slip mechanism, modeled using three-dimensional dislocation dynamics simulations.
PNNL has developed two low-background gamma-ray spectrometers in a new shallow underground laboratory, thereby significantly improving its ability to detect low levels of gamma-ray emitting fission ...or activation products in airborne particulate in samples from the IMS (International Monitoring System). The combination of cosmic veto panels, dry nitrogen gas to reduce radon and low background shielding results in a reduction of the background count rate by about a factor of 100 compared to detectors operating above ground at our laboratory.
•Two new low-background gamma detectors in shallow underground laboratory at PNNL•The detectors are designed for use with the International Monitoring System•Gamma-ray background about a factor of 100 lower than our surface gamma detectors•Detection limits are about a factor of 10 lower than surface gamma detectors
Shear deformation has been highlighted in multiple research efforts for its ability to impart novel microstructures that demonstrate improvements in mechanical properties. When used to process and ...densify powdered material, these shear-based consolidation techniques are commonly referred to as friction consolidation (FC). In this paper, the microstructural evolution from compacted Cu and Ni powders to a consolidated Cu0.5Ni0.5 alloy is examined. Various stages of porosity reduction and deformation are shown. Deformation was observed to accumulate preferentially in the more ductile material early in the process, leading to the formation of a tortuous microstructural zone. Porosity reduction was extensive, decreasing from ~65% in the pre-compacted state to ~1% in the fully consolidated alloy. The final consolidated alloy showed a ~2× hardness improvement over the unalloyed, compacted material. Unique aspects of this work include demonstration of FC processing to produce an equiaxed, sub-micrometer grain size in samples within a 0.5 to 2 min processing time. The results point to future opportunities to implement shear deformation during powder densification to expand the range of property outcomes in bulk materials.
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•Friction Stir Consolidation (FSC) of Cu and Ni powder was performed.•A tortuous microstructural intermediate zone was observed as porosity decreased.•The intermediate microstructure was caused by shear and pressure gradients.•Shear and pressure gradients generate thermal, chemical and structural zones.•Onset of the intermediate zone coincided with dynamic recrystallization of Cu.•Viscosity differences following Cu recrystallization produced the tortuous zone.
Specific environmental applications can benefit from dual tritium and radiocarbon measurements in a single compound. Assuming typical environmental levels, it is often the low tritium activity ...relative to the higher radiocarbon activity that limits the dual measurement. In this paper, we explore the parameter space for a combined tritium and radiocarbon measurement using a natural methane sample mixed with an argon fill gas in low-background proportional counters of a specific design. We present an optimized methane percentage, detector fill pressure, and analysis energy windows to maximize measurement sensitivity while minimizing count time. The final optimized method uses a 9-atm fill of P35 (35% methane, 65% argon), and a tritium analysis window from 1.5 to 10.3keV, which stops short of the tritium beta decay endpoint energy of 18.6keV. This method optimizes tritium-counting efficiency while minimizing radiocarbon beta-decay interference.
•Use of a single compound (methane) for dual tritium and radiocarbon measurements.•Optimized analysis window for simultaneous tritium and radiocarbon measurement.•Allows for optimization of tritium counting in the presence of radiocarbon.
Over the past several years, the Pacific Northwest National Laboratory (PNNL) has developed an ultra-low-background proportional counter (ULBPC) technology. The resulting detector is the product of ...an effort to produce a low-background, physically robust gas proportional counter for applications like radon emanation measurements, groundwater tritium, and
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Ar. In order to fully take advantage of the inherent low-background properties designed into the ULBPC, a comparably low-background dedicated counting system is required. An ultra-low-background counting system (ULBCS) was recently built in the new shallow underground laboratory at PNNL. With a design depth of 30 m water-equivalent, the shallow underground laboratory provides approximately 100× fewer fast neutrons and 6× fewer muons than a surface location. The ULBCS itself provides additional shielding in the form of active anti-cosmic veto (via 2-in-thick plastic scintillator paddles) and passive borated poly (1 in.), lead (6 in.), and copper (~3 in.) shielding. This work will provide details on PNNL’s new shallow underground laboratory, examine the motivation for the design of the counting system, and provide results from the characterization of the ULBCS, including initial detector background.
The C-4 dark matter experiment Bonicalzi, R.M.; Collar, J.I.; Colaresi, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2013, Letnik:
712
Journal Article
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We describe the experimental design of C-4, an expansion of the CoGeNT dark matter search to four identical detectors each approximately three times the mass of the p-type point contact germanium ...diode presently taking data at the Soudan Underground Laboratory. Expected reductions of radioactive backgrounds and energy threshold are discussed, including an estimate of the additional sensitivity to low-mass dark matter candidates to be obtained with this search.
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