133 research outputs found
Ultrasensitive 3He magnetometer for measurements of high magnetic fields
We describe a 3He magnetometer capable to measure high magnetic fields (B >
0.1 Tesla) with a relative accuracy of better than 10^-12. Our approach is
based on the measurement of the free induction decay of gaseous, nuclear spin
polarized 3He following a resonant radio frequency pulse excitation. The
measurement sensitivity can be attributed to the long coherent spin precession
time T2* being of order minutes which is achieved for spherical sample cells in
the regime of motional narrowing where the disturbing influence of field
inhomogeneities is strongly suppressed. The 3He gas is spin polarized in-situ
using a new, non-standard variant of the metastability exchange optical
pumping. We show that miniaturization helps to increase T2* further and that
the measurement sensitivity is not significantly affected by temporal field
fluctuations of order 10^-4.Comment: 27 pages, 7 figure
Возможности применения лазерной сварки для низкоуглеродистой промышленной стали X80
Объектом исследования является стали категории прочности Х80 после контролируемой продольной прокатки с окончанием прокатки в (?+?) – области и последующим ускоренным охлаждением.
Цель работы – изучить микроструктуру промышленной трубной стали категории прочности Х80 после термомеханической обработки, а также особенности формирования структур в зоне сварного соединения стали Х80 под воздействием лазерной сварки и оценить механические свойства полученных сварных соединений.
Значимость работы заключается в изучении новой технологии создания сварных соединений для газо- и нефтепроводов работающих в условиях низких температур.The object of research is steel of strength category X80 after controlled longitudinal rolling with the end of rolling in the (? + ?) region and subsequent accelerated cooling.
The purpose of the work – is to study the microstructure of industrial pipe steel of strength category X80 after thermomechanical processing, as well as the features of the formation of structures in the weld zone of steel X80 under the influence of laser welding and to evaluate the mechanical properties of the welded joints.
The significance of the work consists in the study of a new technology for creating welded joints in gas and oil pipelines working in difficult climatic conditions
Precise Measurement of Magnetic Field Gradients from Free Spin Precession Signals of He and Xe Magnetometers
We report on precise measurements of magnetic field gradients extracted from
transverse relaxation rates of precessing spin samples. The experimental
approach is based on the free precession of gaseous, nuclear spin polarized
He and Xe atoms in a spherical cell inside a magnetic guiding field
of about 400 nT using LT SQUIDs as low-noise magnetic flux detectors. The
transverse relaxation rates of both spin species are simultaneously monitored
as magnetic field gradients are varied. For transverse relaxation times
reaching 100 h, the residual longitudinal field gradient across the spin sample
could be deduced to be pT/cm. The method takes
advantage of the high signal-to-noise ratio with which the decaying spin
precession signal can be monitored that finally leads to the exceptional
accuracy to determine magnetic field gradients at the sub pT/cm scale
Optimized Continuous Application of Hyperpolarized Xenon to Liquids
International audienceIn recent years, NMR with hyperpolarized (HP) xenon inside functionalized host structures (e.g. cryptophanes) have become a potential candidate for the direct observation of metabolic processes (i.e. molecular imaging). A critical issue for real applications is the dissolution of the HP-gas in the liquid which contains the host. In this work, we present recent developments for an improved and controlled dissolution of HP-Xe in liquids using hollow fiber membranes and different compressor systems. The designed apparatus consists of a compressor and a membrane unit. The compressor provides HP-129 Xe continuously at small adjustable pressures and in a polarization-preserving way. The membrane unit enables a molecular solution of the HP-gas in aqueous liquids, avoiding the formation of bubbles or even foams. Two different types of compressors were tested in terms of function and useful materials. Special emphasis was put on a systematic reduction of transfer losses in the gas and liquid phase. In order to optimize the system parameters, several physical models were developed to describe the transport and the losses of nuclear polarization. Finally, the successful implementation was demonstrated in several experiments. HP-Xe was dissolved in an aqueous cryptophane-A-(OCH 2 COOH) 6 solution, and stable Xe signals could be measured over 35 min, only limited by the size of the gas reservoir. Such long and stable Version 6 21.10.2019 BN experimental conditions enabled the study of chemical exchange of xenon between cryptophane and water environments even for a time-consuming 2D NMR-experiment. The good signal stability over the measurement time allowed an exact determination of the residence time of the Xe-atom inside the cryptophane, resulting in an average residence time of 42.9 ± 3.3 ms
SPECT: A spin-flip loaded magnetic ultracold neutron trap for a determination of the neutron lifetime
The confinement of ultracold neutrons (UCNs) in a three dimensional magnetic
field gradient trap allows for a measurement of the free neutron lifetime with
superior control over spurious loss channels and can provide a large kinetic
energy acceptance to enhance statistical sensitivity. In this paper, we present
the first successful implementation of a pulsed spin-flip based loading scheme
for a three-dimensional magnetic UCN trap. The measurements with the
SPECT experiment were performed at the pulsed UCN source of the research
reactor TRIGA Mainz. We report on detailed investigations of major systematic
effects influencing the neutron storage time, statistically limited by the size
of the recorded data set. The extracted neutron storage time constant of is compatible with, but not to be interpreted as, a
measurement of the free neutron lifetime.Comment: 15 pages, 19 figure
- …