701 research outputs found
Self-adaptive loop for external disturbance reduction in differential measurement set-up
We present a method developed to actively compensate common-mode magnetic
disturbances on a multi-sensor device devoted to differential measurements. The
system uses a field-programmable-gated-array card, and operates in conjunction
with a high sensitivity magnetometer: compensating the common-mode of magnetic
disturbances results in a relevant reduction of the difference-mode noise. The
digital nature of the compensation system allows for using a numerical approach
aimed at automatically adapting the feedback loop filter response. A common
mode disturbance attenuation exceeding 50 dB is achieved, resulting in a final
improvement of the differential noise floor by a factor of 10 over the whole
spectral interval of interest.Comment: 7 pages, 8 figures, 26 ref
Restoring Narrow Linewidth to a Gradient-Broadened Magnetic Resonance by Inhomogeneous Dressing
We study the possibility of counteracting the line-broadening of atomic
magnetic resonances due to inhomogeneities of the static magnetic field by
means of spatially dependent magnetic dressing, driven by an alternating field
that oscillates much faster than the Larmor precession frequency. We
demonstrate that an intrinsic resonance linewidth of 25~Hz that has been
broadened up to hundreds Hz by a magnetic field gradient, can be recovered by
the application of an appropriate inhomogeneous dressing field. The findings of
our experiments may have immediate and important implications, because they
facilitate the use of atomic magnetometers as robust, high sensitivity
detectors in ultra-low-field NMR imaging.Comment: 9 pages, 7 figures, 33 refs. This is the unedited versio
Simultaneous Detection of H and D NMR Signals in a micro-Tesla Field
We present NMR spectra of remote-magnetized deuterated water, detected in an
unshielded environment by means of a differential atomic magnetometer. The
measurements are performed in a T field, while pulsed techniques are
applied -following the sample displacement- in a 100~T field, to tip both
D and H nuclei by controllable amounts. The broadband nature of the detection
system enables simultaneous detection of the two signals and accurate
evaluation of their decay times. The outcomes of the experiment demonstrate the
potential of ultra-low-field NMR spectroscopy in important applications where
the correlation between proton and deuteron spin-spin relaxation rates as a
function of external parameters contains significant information.Comment: 7 pages (letter, 4 pages) plus supplemental material as an appendix.
This document is the unedited author's version of a Submitted Work that was
subsequently accepted for publication in Journal of Phys. Chem. Lett.,
copyright American Chemical Society after peer review. To access the final
edited and published work see:
pubs.acs.org/doi/abs/10.1021/acs.jpclett.7b0285
First results from the INDRA-FAZIA apparatus on isospin diffusion in 58,64 Ni+58,64 Ni systems at Fermi energies
An investigation of the isospin equilibration process in the reactions 58;64Ni+58;64Ni at two bombarding
energies in the Fermi regime (32 MeV/nucleon and 52 MeV/nucleon) is presented. Data
have been acquired during the first experimental campaign of the coupled INDRA-FAZIA apparatus
in GANIL. Selecting from peripheral to semi-central collisions, both the neutron content of the
quasiprojectile residue and that of the light ejectiles coming from the quasiprojectile evaporation
have been used as probes of the dynamical process of isospin diffusion between projectile and target
for the asymmetric systems. The isospin transport ratio technique has been employed. The relaxation
of the initial isospin imbalance with increasing centrality has been clearly evidenced. The
isospin equilibration appears stronger for the reactions at 32 MeV/nucleon, as expected due to the
longer projectile-target interaction time than at 52 MeV/nucleon. Coherent indications of isospin
equilibration come from the quasiprojectile residue characteristics and from particles ascribed to
the quasiprojectile decay.This work was partially supported by the National Research Foundation of Korea (NRF;
Grant No. 2018R1A5A1025563) and by the Spanish Ministerio de Econom a y Empresa
(PGC2018-096994-B-C22). We acknowledge support from R egion Normandie under R eseau
d'Int er^et Normand FIDNEOS (RIN/FIDNEOS). Many thanks are due to the accelerator
sta of GANIL for delivering a very good quality beam and to the technical sta for the
continuous support
Nuclear symmetry energy at work in heavy ion reactions: new results from the INDRA-FAZIA apparatus
The recently coupled INDRA-FAZIA apparatus offers unique opportunities to investigate heavy ion collisions at Fermi energies by combining the optimal identification capabilities of FAZIA and the large angular coverage of INDRA. We present a selection of the results of the analysis of the first experimental campaign performed with INDRA-FAZIA, in which the four reactions Ni-58,Ni-64+Ni-58,Ni-64 have been studied at two different beam energies (32 and 52 MeV/nucleon) in the intermediate energy regime. The present work is focused on the isospin diffusion effects in semiperipheral and peripheral collisions. A stronger isospin equilibration is found at 32 MeV/nucleon than at 52 MeV/nucleon, as expected due to a shorter projectile-target interaction time in the latter cas
Sub-millimetric ultra-low-field MRI detected in situ by a dressed atomic magnetometer
Magnetic Resonance Imaging (MRI) is universally acknowledged as an excellent
tool to extract detailed spatial information with minimally invasive
measurements. Efforts toward ultra-low-field (ULF) MRI are made to simplify the
scanners and to reduce artefacts and incompatibilities. Optical Atomic
Magnetometers (OAMs) are among the sensitive magnetic detectors eligible for
ULF operation, however they are not compatible with the strong field gradients
used in MRI. We show that a magnetic-dressing technique restores the OAMs
operability despite the gradient, and we demonstrate sub-millimetric resolution
MRI with a compact experimental setup based on an in situ detection. The
proof-of-concept experiment produces unidimensional imaging of remotely
magnetized samples with a dual sensor, but the approach is suited to be adapted
for 3-D imaging of samples magnetized in loco. An extension to multi-sensor
architectures is also possible.Comment: 5 pages, 3 figures, 36 refs, 3 pages supplemental material (+ 3refs).
Accepted for publication in Appl.Phys.Let
Spin dynamic response to a time dependent field
The dynamic response of a parametric system constituted by a spin precessing
in a time dependent magnetic field is studied by means of a perturbative
approach that unveils unexpected features, and is then experimentally
validated. The first-order analysis puts in evidence different regimes: beside
a tailorable low-pass-filter behaviour, a band-pass response with interesting
potential applications emerges. Extending the analysis to the second
perturbation order permits to study the response to generically oriented fields
and to characterize several non-linear features in the behaviour of such kind
of systems.Comment: 13 pages, 7 figures, 52 references. Accepted for publication in
Applied Physics
Electromagnetic induction imaging with a scanning radio-frequency atomic magnetometer
We demonstrate electromagnetic induction imaging with an unshielded, portable
radio-frequency atomic magnetometer scanning over the target object. This
configuration satisfies standard requirements in typical applications, from
security screening to medical imaging. The ability to scan the magnetometer
over the object relies on the miniaturization of the sensor head and on the
active compensation of the ambient magnetic field. Additionally, a procedure is
implemented to extract high-quality images from the recorded spatial dependent
magnetic resonance. The procedure is shown to be effective in suppressing the
detrimental effects of the spatial variation of the magnetic environment.Comment: Lette
Fast, cheap, and scalable magnetic tracker with an array of magnetoresistors
We present the hardware of a cheap multi-sensor magnetometric setup where a
relatively large set of magnetic field components is measured in several
positions by calibrated magnetoresistive detectors. The setup is developed with
the scope of mapping the (inhomogeneous) field generated by a known magnetic
source, which is measured as superimposed to the (homogeneous) geomagnetic
field. The final goal is to use the data produced by this hardware to
reconstruct position and orientation of the magnetic source with respect to the
sensor frame, simultaneously with the orientation of the frame with respect to
the environmental field. Possible applications of the setup are shortly
discussed, together with a synthetic description of the data elaboration and
analysis.Comment: 10 pages, 7 figures, 30 ref
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