Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved ...dark matter decay mode, n→X+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.
We report an improved measurement of the free neutron lifetime τn using the UCN τ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 × 106 surviving ultracold ...neutrons (UCNs) after storing in UCN τ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τn measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β -decay lifetime. Both techniques achieve consistent results and find a value τn = 877.75 ± 0.2 8stat + 0.22/−0.16syst s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
The ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully ...operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the design and performance of the upgraded LANL UCN source. Measurements of the cold neutron spectrum and UCN density are presented and compared to Monte Carlo predictions. The source is shown to perform as modeled. The UCN density measured at the exit of the biological shield was 184(32) UCN/cm3, a fourfold increase from the highest previously reported. The polarized UCN density stored in an external chamber was measured to be 39(7) UCN/cm3, which is sufficient to perform an experiment to search for the nonzero neutron electric dipole moment with a one-standard-deviation sensitivity of σ(dn)=3×10-27ecm.
Background
Invasive fungal infections are a major cause of morbidity and mortality among solid organ transplant (SOT) and hematopoietic cell transplant (HCT) recipients, but few data have been ...reported on the epidemiology of endemic fungal infections in these populations.
Methods
Fifteen institutions belonging to the Transplant‐Associated Infection Surveillance Network prospectively enrolled SOT and HCT recipients with histoplasmosis, blastomycosis, or coccidioidomycosis occurring between March 2001 and March 2006.
Results
A total of 70 patients (64 SOT recipients and 6 HCT recipients) had infection with an endemic mycosis, including 52 with histoplasmosis, 9 with blastomycosis, and 9 with coccidioidomycosis. The 12‐month cumulative incidence rate among SOT recipients for histoplasmosis was 0.102%. Occurrence of infection was bimodal; 28 (40%) infections occurred in the first 6 months post transplantation, and 24 (34%) occurred between 2 and 11 years post transplantation. Three patients were documented to have acquired infection from the donor organ. Seven SOT recipients with histoplasmosis and 3 with coccidioidomycosis died (16%); no HCT recipient died.
Conclusions
This 5‐year multicenter prospective surveillance study found that endemic mycoses occur uncommonly in SOT and HCT recipients, and that the period at risk extends for years after transplantation.
The atomic masses of ^{55}Sc, ^{56,58}Ti, and ^{56-59}V have been determined using the high-precision multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN's ...Radioactive Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system, which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For ^{56,58}Ti and ^{56-59}V, the mass uncertainties have been reduced down to the order of 10 keV, shedding new light on the N=34 shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species ^{58}Ti and ^{59}V. With the new precision achieved, we reveal the nonexistence of the N=34 empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap above the occupied νp_{3/2} orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell model calculations including the νd_{5/2} and νg_{9/2} orbits and compare the results with conventional shell model calculations, which exclude the νg_{9/2} and the νd_{5/2} orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at N=34.
Background Efforts to understand the properties of self-expandable metallic stents (SEMSs) through their mechanical properties have progressed. Among them, radial force (RF) is well known as an ...expanding force, but axial force (AF) has not been measured before. Correlations of these properties to clinical results are not well known. Objective We measured RF and AF of 14 different SEMSs and discussed the results in terms of clinical implications. Design Experimental study. Subjects Measurement of RF and AF of 14 different covered and uncovered SEMSs. Methods RF was measured with an RF measurement machine manufactured by Machine Solution, and AF was measured with in-house equipment. Results Measurements of RF in the process of expansion showed characteristic patterns closely related to the structures and materials of SEMSs. Results of AF measurement can be classified into 3 groups: high, medium, and low AF, depending on the type of SEMS. AF decreased with an increase of the length of stents. A plot of RF against AF revealed 3 distinguished RF/AF combinations and indicated the importance of understanding the properties by not only RF or AF individually but also by RF/AF combination. Limitations In vitro study using measurement equipment. Conclusion It was demonstrated that a combination of RF and AF is more effective than RF or AF individually in understanding the clinical implications of SEMSs. More work is needed to correlate mechanical properties with clinical results by designing model experiments.
Electroless nickel plating is an established industrial process that provides a robust and relatively low-cost coating suitable for transporting and storing ultracold neutrons (UCN). Using roughness ...measurements and UCN-storage experiments we characterized UCN guides made from polished aluminum or stainless-steel tubes plated by several vendors.
All electroless nickel platings were similarly suited for UCN storage with an average loss probability per wall bounce of 2.8 ⋅ 10-4 to 4.1 ⋅ 10-4 for energies between 90neV and 190neV, or a ratio of imaginary to real Fermi potential η of 1.7 ⋅ 10-4 to 3.3 ⋅ 10-4. Measurements at different elevations indicate that the energy dependence of UCN losses is well described by the imaginary Fermi potential. Some special considerations are required to avoid an increase in surface roughness during the plating process and hence a reduction in UCN transmission. Increased roughness had only a minor impact on storage properties.
Based on these findings we chose a vendor to plate the UCN-production vessel that will contain the superfluid-helium converter for the new TRIUMF UltraCold Advanced Neutron (TUCAN) source, achieving acceptable UCN-storage properties with η=3.5(5)⋅10-4.
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