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1.
Rev Sci Instrum ; 89(7): 073303, 2018 Jul.
Article in English | MEDLINE | ID: mdl-30068099

ABSTRACT

In this work, two compact, permanent magnet, electron spectrometers have been built to measure the electron beam energy at the Dual Axis Radiographic Hydrodynamic Test facility. Using H- and OH- anions, the spectrometers were calibrated at the Special Technologies Laboratory in Santa Barbara, California (USA). The spectrometers were mounted on a custom drift tube that allows the magnet assemblies to be translated, which increases the path length of the electrons traveling through the magnetic field and therefore increases the upper bound of the measurable electron kinetic energy. The measurable range of electron kinetic energies is between 2.8 MeV-4.1 MeV for the first spectrometer and 14.1 MeV-21.1 MeV for the second spectrometer, with an overall measurement uncertainty of 0.32%.

2.
Rev Sci Instrum ; 87(11): 11D830, 2016 Nov.
Article in English | MEDLINE | ID: mdl-27910305

ABSTRACT

The neutron imaging diagnostic at the National Ignition Facility has been operating since 2011 generating neutron images of deuterium-tritium (DT) implosions at peak compression. The current design features a scintillating fiber array, which allows for high imaging resolution to discern small-scale structure within the implosion. In recent years, it has become clear that additional neutron imaging systems need to be constructed in order to provide 3D reconstructions of the DT source and these additional views need to be on a shorter line of sight. As a result, there has been increased effort to identify new image collection techniques that improve upon imaging resolution for these next generation neutron imaging systems, such as monolithic deuterated scintillators. This work details measurements performed at the Weapons Neutron Research Facility at Los Alamos National Laboratory that compares the radiographic abilities of the fiber scintillator with a monolithic scintillator, which may be featured in a future short line of sight neutron imaging systems.

3.
Solid State Nucl Magn Reson ; 61-62: 35-8, 2014.
Article in English | MEDLINE | ID: mdl-24882748

ABSTRACT

We demonstrate a dramatic increase in the signal-to-noise ratio (SNR) of a nuclear quadrupole resonance (NQR) signal by using a polarization enhancement technique. By first applying a static magnetic field to pre-polarize one spin subsystem of a material, and then allowing that net polarization to be transferred to the quadrupole subsystem, we increased the SNR of a sample of ammonium nitrate by one-order of magnitude.


Subject(s)
Magnetic Resonance Spectroscopy/methods , Explosive Agents/analysis
4.
J Magn Reson ; 199(2): 188-91, 2009 Aug.
Article in English | MEDLINE | ID: mdl-19435672

ABSTRACT

Conventionally implemented MRI is performed in a strong magnetic field, typically >1T. The high fields, however, can lead to many limitations. To overcome these limitations, ultra-low field (ULF) [or microtesla] MRI systems have been proposed and implemented. To-date such systems rely on low-Tc Superconducting Quantum Interference Devices (SQUIDs) leading to the requirement of cryogens. In this letter, we report ULF-MRI obtained with a non-cryogenic atomic magnetometer. This demonstration creates opportunities for developing inexpensive and widely applicable MRI scanners.


Subject(s)
Image Enhancement/instrumentation , Magnetic Resonance Imaging/instrumentation , Magnetics/instrumentation , Equipment Design , Equipment Failure Analysis , Phantoms, Imaging
5.
J Magn Reson ; 175(1): 103-13, 2005 Jul.
Article in English | MEDLINE | ID: mdl-15869890

ABSTRACT

Growing interest in magnetic resonance imaging (MRI) at ultra-low magnetic fields (ULF, approximately muT fields) has been motivated by several advantages over its counterparts at higher magnetic fields. These include narrow line widths, the possibility of novel imaging schemes, reduced imaging artifacts from susceptibility variations within a sample, and reduced system cost and complexity. In addition, ULF NMR/MRI with superconducting quantum interference devices is compatible with simultaneous measurements of biomagnetic signals, a capability conventional systems cannot offer. Acquisition of MRI at ULF must, however, account for concomitant gradients that would otherwise result in severe image distortions. In this paper, we introduce the general theoretical framework that describes concomitant gradients, explain why such gradients are more problematic at low field, and present possible approaches to correct for these unavoidable gradients in the context of a non-slice-selective MRI protocol.


Subject(s)
Algorithms , Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Magnetic Resonance Imaging/methods , Models, Biological , Models, Chemical , Computer Simulation , Electromagnetic Fields , Spin Labels
6.
Phys Med Biol ; 49(10): 2117-28, 2004 May 21.
Article in English | MEDLINE | ID: mdl-15214546

ABSTRACT

Perhaps the greatest impediment to acquiring high-quality magnetoencephalography (MEG) recordings is the ubiquitous ambient magnetic field noise. We have designed and built a whole-head MEG system using a helmet-like superconducting imaging surface (SIS) surrounding the array of superconducting quantum interference device (SQUID) magnetometers used to measure the MEG signal. We previously demonstrated that the SIS passively shields the SQUID array from ambient magnetic field noise, independent of frequency, by 25-60 dB depending on sensor location. SQUID 'reference sensors' located on the outside of the SIS helmet measure ambient magnetic fields in very close proximity to the MEG magnetometers while being nearly perfectly shielded from all sources in the brain. The fact that the reference sensors measure no brain signal yet are located in close proximity to the MEG sensors enables very accurate estimation and subtraction of the ambient field noise contribution to the MEG sensors using an adaptive algorithm. We have demonstrated total ambient noise reduction factors in excess of 10(6) (> 120 dB). The residual noise for most MEG SQUID channels is at or near the intrinsic SQUID noise floor, typically 2-3 fT Hz-1/2. We are recording MEG signals with greater signal-to-noise than equivalent EEG measurements.


Subject(s)
Brain/pathology , Brain/physiology , Magnetoencephalography/methods , Artifacts , Head , Humans , Magnetics , Models, Statistical , Reproducibility of Results , Time Factors
7.
Neurol Clin Neurophysiol ; 2004: 12, 2004 Nov 30.
Article in English | MEDLINE | ID: mdl-16012616

ABSTRACT

We have obtained 1H NMR spectra simultaneously with high temporal resolution biomagnetic signals such as the magnetocardiogram (MCG) and magnetomyogram (MMG). The NMR spectra are acquired at measurement fields of 2-50 microT, with corresponding proton Larmor frequencies of 80-2000 Hz. Our measurements demonstrate a method suitable for MR imaging with concurrent measurement of biomagnetic signals that can provide sub-millisecond temporal resolution. The narrow line widths, reduction in susceptibility noise and enhanced spectral resolution at ultra low fields provide a new and extremely sensitive measurement method that may enable direct imaging of biological currents by detecting the phase or frequency shifts produced by magnetic fields arising from those currents. The results of our simultaneous measurements of NMR with MCG and MMG are compared to results from a current phantom to investigate the exciting potential of direct MRI of bioelectric currents.


Subject(s)
Electrocardiography/methods , Electromagnetic Fields , Electromyography/methods , Magnetic Resonance Spectroscopy/methods , Female , Humans , Male
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