Performance of different photocathode materials in a liquid argon purity monitor

Purity monitor devices are increasingly used in liquid noble gas time projection chambers to measure the lifetime of drifting electrons. Purity monitors work by emitting electrons from a photocathode material via the photoelectric effect. The electrons are then drifted towards an anode by means of an applied electric drift field. By measuring the difference in charge between the cathode and the anode, one can extract the lifetime of the drifting electrons in the medium. For the first time, we test the performance of different photocathode materials—silver, titanium, and aluminium—and compare them to gold, which is the standard photocathode material used for purity monitors. Titanium and aluminium were found to have a worse performance than gold in vacuum, whereas silver showed a signal of the same order of magnitude as gold. Further tests in liquid argon were carried out on silver and gold with the conclusion that the signal produced by silver is about three times stronger than that of gold

Performance of Hamamatsu 64-anode photomultipliers for use with wavelength--shifting optical fibres

Hamamatsu R5900-00-M64 and R7600-00-M64 photomultiplier tubes will be used with wavelength--shifting optical fibres to read out scintillator strips in the MINOS near detector. We report on measurements of the gain, efficiency, linearity, crosstalk, and dark noise of 232 of these PMTs, of which 219 met MINOS requirements.Comment: 15 pages, 12 figures. Accepted by Nucl. Inst. Meth.

Selective Phosphorylation of Conjugated α-Enones at the Carbonyl Group, Catalyzed by Cyclohexylamine

Reaction of dialkyl phosphites with benzalacetophenone (chalcone) and benzalacetone in the presence of cyclohexylamine as a catalyst is a convenient preparative method for selective phosphorylation of conjugated α, β-unsaturated carbonyl compounds at the carbonyl group. The kinetics of cyclohexylamine-catalyzed addition of dialkyl phosphites to cis- and trans-chalcones is studied, and factors are revealed that influence the reactivity of addends in this reaction

Complex temperatures zeroes of partition function in spin-glass models

An approximate method is proposed for investigating complex-temperature properties of real-dimensional spin-glass models. The method uses the complex-temperature data of the ferromagnetic model on the same lattice. The universality line in the complex-temperature space is obtained.Comment: latex, corrected some misprint

Competition between glassiness and order in a multi-spin glass

A mean-field multi-spin interaction spin glass model is analyzed in the presence of a ferromagnetic coupling. The static and dynamical phase diagrams contain four phases (paramagnet, spin glass, ordinary ferromagnet and glassy ferromagnet) and exhibit reentrant behavior. The glassy ferromagnet phase has anomalous dynamical properties. The results are consistent with a nonequilibrium thermodynamics that has been proposed for glasses.Comment: revised version, 4 pages Revtex, 2 eps-figures. Phys. Rev. E, Rapid Communication, to appea

RADIOSURGICAL TREATMENT OF BENIGN SMALL EYELID TUMORS

Aim of the study – to evaluate the long-term results of the radiosurgical method using microsurgical techniques for the treatment of small benign eyelid tumors. Material and methods. In Ocular Oncology Centre of Helmholtz Moscow Research Institute of Eye Diseases for the period from 2012 to 2018 year 248 patients were examined and treated (108 children aged 12 ± 1.2 years and 140 adults aged 46 ± 8.1 years) with benign eyelid tumors: pigmented (nevus), vascular (capillary hemangiomas), epithelial (follicular keratosis, keratopapilloma). The Surgitron EMC radiosurgery device was used as surgical aids. All patients used microsurgical technique. The longitudinal size of the tumors was 3.4 ± 0.5 mm, transverse – 6 ± 0.8 mm. All patients after surgical treatment underwent histopathological study. The observation period is on average 6 ± 1.4 years. Results. In 133 (53.6 %) of 248 patients, nevi were detected, in 76 (30.7 %) – keratopapilloma and inverted follicular keratosis, in 39 (15.7 %) – capillary hemangioma. Various modifications of radiosurgical treatment were used depending on the location of the tumor, its size, the degree of activity using different modes and powers from 1 to 4 Wt. Intraoperative complications were not noted. The early postoperative period was accompanied by the presence of signs of mild inflammation, which was stopped by local therapy. The formation of a tender scar was observed on average after 7 ± 2 days. Two cases (0.8 %) of recurrence of keratopapilloma were noted 2 years after the first operation. Tumors were removed by radio excision. Conclusion. Benign eyelid tumors, especially of melanocytic origin, are subject to obligatory dynamic observation, and if minimal signs of their progression are detected, their surgical removal is indicated. Radiosurgical treatment using microsurgical techniques is the method of choice in the treatment of small benign eyelid tumors and depends on the size of the tumor, its localization and the nature of the tumor process. The use of the radiosurgical method with obligatory microsurgical technique for treating benign tumors of small sizes with the observance of the rules of radicalness and antiblasticity allows maintaining visual functions with simultaneous surgical treatment, providing normal anatomical and topographic correlations of the anterior segment of the eye and high quality of life of the patient

Low-background gamma spectroscopy at the Boulby Underground Laboratory

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 210 Pb and 234 Th. 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 234 Th and 6.6mBqkg −1 for 210 Pb both of which have uncovered some significant equilibrium breaks in the 238 U chain. In denser materials, where gamma-ray self-absorption increases, sensitivity is demonstrated to specific activities of 0.9mBqkg −1 for 226 Ra, 1.1mBqkg −1 for 228 Ra, 0.3mBqkg −1 for 224 Ra, and 8.6mBqkg −1 for 40 K 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

Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in $^{208}$Tl and $^{214}$Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 $m^2$ of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in $^{208}$Tl. After more than one year of background measurement, a surface activity of the scintillators of $\mathcal{A}$($^{208}$Tl) $=$ 1.5 $\mu$Bq/m$^2$ is reported here. Given this level of background, a larger BiPo detector having 12 m$^2$ of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of $\mathcal{A}$($^{208}$Tl) $<$ 2 $\mu$Bq/kg (90% C.L.) with a six month measurement.Comment: 24 pages, submitted to N.I.M.