The TRACER instrument ("Transition Radiation Array for Cosmic Energetic Radiation") has been developed for direct measurements of the heavier primary cosmic-ray nuclei at high energies. The instrument had a successful long-duration balloon flight in Antarctica in 2003. The detector system and measurement process are described, details of the data analysis are discussed, and the individual energy spectra of the elements O, Ne, Mg, Si, S, Ar, Ca, and Fe (nuclear charge Z=8 to 26) are presented. The large geometric factor of TRACER and the use of a transition radiation detector make it possible to determine the spectra up to energies in excess of 10 14 eV per particle. A power-law fit to the individual energy spectra above 20 GeV per amu exhibits nearly the same spectral index (∼ 2.65 ± 0.05) for all elements, without noticeable dependence on the elemental charge Z.
The General AntiParticle Spectrometer experiment (GAPS) is foreseen to carry out a dark matter search using low-energy cosmic ray antideuterons at stratospheric altitudes with a novel detection approach. A prototype flight from Taiki, Japan was carried out in June 2012 to prove the performance of the GAPS instrument subsystems (Lithium-drifted Silicon tracker and time-of-flight) and the thermal cooling concept as well as to measure background levels. The flight was a success and the stable flight operation of the GAPS detector concept was proven. During the flight about $10^6$ charged particle triggers were recorded, extensive X-ray calibrations of the individual tracker modules were performed by using an onboard X-ray tube, and the background level of atmospheric and cosmic X-rays was measured. The behavior of the tracker performance as a function of temperature was investigated. The tracks of charged particle events were reconstructed and used to study the tracking resolution, the detection efficiency of the tracker, and coherent X-ray backgrounds. A timing calibration of the time-of-flight subsystem was performed to measure the particle velocity. The flux as a function of flight altitude and as a function of velocity was extracted taking into account systematic instrumental effects. The developed analysis techniques will form the basis for future flights.Comment: accepted for publication by Astroparticle Physics: 33 pages, 36 figure
We present systematic measurements of longitudinal relaxation rates (1/T 1 ) of spin polarization in the ground state of the nitrogen-vacancy (NV − ) color center in synthetic diamond as a function of NV − concentration and magnetic field B. NV − centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV − center concentrations. Values of (1/T 1 ) were measured for each spot as a function of B. and small ensembles 8-12 and single nuclear spins 13 , study magnetic resonance on a molecular scale, measure electric fields, strain and temperature, detect low concentrations of paramagnetic molecules and ions, and image magnetic field distributions of physical or biological systems. These applications are made possible by the unique properties of the NV − center level structure, shown in Fig. 1, which allows manipulation of the ground-state spin state by optical fields and microwaves and measurement of the interactions of the ground-state spin with the local environment by monitoring the fluorescence intensity. Understanding spin relaxation processes is important in optimizing these techniques. Previous measurements of the dependence of longitudinal relaxation rate (1/T 1 ) of magnetic field have shown enhanced rates near B = 0 G, B = 595 G (Refs.14-17 ), and B = 514 G (Refs. ( 15,18 ). The enhancements at zero field and B = 595 G have been linked to interactions with NV centers whose orientation makes their energies degenerate at these fields, while the enhancement at B = 514 G is related to interactions with substitutional nitrogen (P1 centers). Previous work has also shown that the 1/T 1 rate depends on NV concentration 17 . In this paper we describe systematic measurements of the longitudinal relaxation rates of ensembles of NV − centers created with different, controlled radiation doses on a single diamond crystal, achieved through irradiation with a transmission electron microscope (TEM). This method of preparing NV − centers is more convenient for many laboratories than irradiation in accelerators and also could facilitate
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