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Register a new userA Background-Free Direction-Sensitive Neutron Detector2 A Background-Free Direction-Sensitive Neutron Detector
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We show data from a new type of detector that can be used to determine neutron flux, energy distribution, and direction of neutron motion for both fast and thermal neutrons. Many neutron detectors are plagued by large backgrounds from x-rays and gamma rays, and most current neutron detectors lack single-event energy sensitivity or any information on neutron directionality. Even the best detectors are limited by cosmic ray neutron backgrounds. All applications (neutron scattering and radiography, measurements of solar and cosmic ray neutron flux, measurements of neutron interaction cross sections, monitoring of neutrons at nuclear facilities, oil exploration, and searches for fissile weapons of mass destruction) will benefit from the improved neutron detection sensitivity and improved measurements of neutron properties made possible by this detector. The detector is free of backgrounds from x-rays, gamma rays, beta particles, relativistic singely charged particles and cosmic ray neutrons. It is sensitive to thermal neutrons, fission neutrons, and high energy neutrons, with detection features distinctive for each energy range. It is capable of determining the location of a source of fission neutrons based on characteristics of elastic scattering of neutrons by helium nuclei. The detector we have constructed could identify one gram of reactor grade plutonium, one meter away, with less than one minute of observation time.
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The known direction of motion of dark matter particles relative to the Earth may be a key for their unambiguous identification even in the presence of backgrounds. We describe a prototype detector that is able to reconstruct direction vectors of weakly interacting massive particles that may the dominant constituent of the dark matter in our galaxy. The detector uses a low-density gas (CF4) in a 10liter time-projection chamber with mesh-based electrodes and optical and charge readout. Initial results confirm good performance in the reconstruction of direction angle and sense (head-tail) for low-momentum nuclear recoils.
NEWAGE is a direction-sensitive dark matter search using a low-pressure gaseous time projection chamber. A low alpha-ray emission rate micro pixel chamber had been developed in order to reduce background for dark matter search. We conducted the dark matter search at the Kamioka Observatory in 2018. The total live time was 107.6 days corresponding to an exposure of 1.1 kg${cdot}$days. Two events remained in the energy region of 50-60 keV which was consistent with 2.5 events of the expected background. A directional analysis was carried out and no significant forward-backward asymmetry derived from the WIMP-nucleus elastic scatterings was found. Thus a 90% confidence level upper limit on Spin-Dependent WIMP-proton cross section of 50 pb for a WIMP mass of 100 GeV/c2 was derived. This limit is the most stringent yet obtained from direction-sensitive dark matter search experiments.
In this paper, the detection efficiency of a large area neutron sensitive microchannel plate detector has been evaluated. A 6LiF/ZnS detector was employed as the benchmark detector, the TOF spectra of these two detectors were simultaneously measured and the energy spectra were then deduced to calculate the detection efficiency curve of the nMCP detector. Tests show the detection [email protected] meV thermal neutron is 34% for this nMCP detector.
Extremely radiation hard sensors are needed in particle physics experiments to instrument the region near the beam pipe. Examples are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial diamond sensors are widely used. In this paper single crystal sapphire sensors are considered as a promising alternative. Industrially grown sapphire wafers are available in large sizes, are of low cost and, like diamond sensors, can be operated without cooling. Here we present results of an irradiation study done with sapphire sensors in a high intensity low energy electron beam. Then, a multichannel direction-sensitive sapphire detector stack is described. It comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness, metallized on both sides, and apposed to form a stack. Each second metal layer is supplied with a bias voltage, and the layers in between are connected to charge-sensitive preamplifiers. The performance of the detector was studied in a 5 GeV electron beam. The charge collection efficiency measured as a function of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The signal size obtained from electrons crossing the stack at this voltage is about 22000 e, where e is the unit charge. The signal size is measured as a function of the hit position, showing variations of up to 20 % in the direction perpendicular to the beam and to the electric field. The measurement of the signal size as a function of the coordinate parallel to the electric field confirms the prediction that mainly electrons contribute to the signal. Also evidence for the presence of a polarisation field was observed.
Nanometer-thin rare-earth-transition metal (RE-TM) alloys with precisely controlled compositions and out-of-plane magnetic anisotropy are currently in the focus for ultrafast magnetophotonic applications. However, achieving lateral nanoscale dimensions, crucial for potential device downscaling, while maintaining designable optomagnetic functionality and out-of-plane magnetic anisotropy is extremely challenging. Here we integrate nanosized Tb$_{18}$Co$_{82}$ ferrimagnetic alloys, having strong out-of-plane magnetic anisotropy, within a gold plasmonic nanoantenna array to design micrometer-scale a magnetophotonic crystal that exhibit abrupt and narrow magneto-optical spectral features that are both magnetic field and light incidence direction controlled. The narrow Fano-type resonance arises through the interference of the individual nanoantennas surface plasmons and a Rayleigh anomaly of the whole nanoantenna array, in both optical and magneto-optical spectra, which we demonstrate and explain using Maxwell-theory simulations. This robust magnetophotonic crystal opens the way for conceptually new high-resolution light incidence direction sensors, as well as for building blocks for plasmon-assisted all-optical magnetization switching in ferrimagnetic RE-TM alloys.
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