Resonant Detectors

The cross section of a bar is proportional to its mass, thus there are efforts to build a 100-ton spherical resonant de-teetor, with high sensitivity and omnidirectional response. The sphere must be equipped with several transducers to detect the fundamental modes the quadrupole modes and the monopole mode (not sensitive to gravitational waves). Efforts are also being devoted to developing more efficient electronics systems (transducers and amplifiers) to achieve better sensitivity. Another major improvement foreseen is the increase of the bandwidth from the current few hertz to several tens of hertz. In this way, coincident runs could allow the determination of source position. 

The forthcoming gravitational wave detectors have an initial sensitivity close to the expected level of the signals from astrophysical sources and should perform the first direct detection of waves. The research in gravitational physics involves several aspects of physics and technology, ranging from theoretical and numerical calculations to applied research in lasers and optics. Further developments in detector sensitivity should allow 

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Gershon P.D., Khilko S., Stable chelating linkage for reversible immobilization of oligohistidine tagged proteins in the BIAcore surface plasmon resonance detector, J Immun Methods 1995 183 65-76. 

The trap is loaded in a time of a few seconds, and after a preselected delay its contents are dumped into the resonator region by lowering the field of one of the pinch solenoids. The signal from the hyperfine resonance detector provides a measure of the total number of atoms N in the trap. The stored atoms decay by dipole relaxation (described below) with a rate that is proportional to the density n. From values of N and n one can find the effective volume of the trap. The effective volume depends on the field geometry and the temperature. This roundabout route is... 

J. F. Haw, T. E. Glass, D. W. Hausler, E. Motell, and H. C. Dorn, Direct coupling of a liquid chromatograph to a continuous flow hydrogen nuclear magnetic resonance detector for analysis of petroleum and synthetic fuels. And. Chem. 52 (1980), 1135-1140. 

Zhu H, White IM, Suter JD et al (2007) Integrated refractive index optical ring resonator detector for capillary electrophoresis. Anal Chem 79 930-937... 

Other detectors, such as the flame ionization detector, atomic emission detector, Eourier transform infrared spectrometer and nuclear magnetic resonance detectors, have been used in GC for the... 

The newest device to be added to the arsenal of the atomic absorption spectroscopist is the resonance detector, a photomultiplier combined with a system which responds only to the resonance line of the element for which it is designed (14), A resonance detector can replace the monochromator in an atomic absorption instrument designed to measure only one element. 

The cloud of sputtered atoms in the resonance detector fluoresces proportionately... 

If the resonance detector is well-designed, the vast majority of the magnesium atoms are unexcited. The resonance lines from the magnesium hollow cathode lamp will cause the magnesium atoms in the resonance detector to fluoresce. Some of this fluorescence will fall on a photomultiplier detector placed at right angles to the optical path. The intensity of fluorescence is proportional to the intensity of emission. Non-resonant lines from the lamp or from the flame will have no effect on the resonance detector. Therefore, a system of narrow bandwidth is produced without the requirement of a monochromator. 

The resonance detector offers a number of attractive possibilities. Instruments designed around it can inherently be made rugged, since there are no monochromator settings to drift. For single-element instruments, the absence of the monochromator may also effect a slight cost reduction. Most important, perhaps, is the potential of a lineup of reso-... 

In analytical work, a resonance instrument can produce good results, though these will be in no case better and in some cases poorer than the results from a well-designed conventional instrument. Since many elements have a number of resonance lines with diflFerent sensitivities, and the resonance detector does not distinguish between them, the sensitivities achieved with resonance detectors are often poorer than those with monochromators. Baseline drift for single beam instrumentation is likely to be comparable. The considerations affecting the signal-to-noise ratio are complex, but the upshot is that the two types of instruments are comparable in this respect also. 

The advent of the resonance detector has greatly simplified the potential problem of multi-element analysis. It is in principle possible to line up a number of resonance detectors, and, combining this with a multi-element hollow cathode lamp and a single burner, analyze a sample for a number of elements simultaneously. 

The transient magnetic resonance detector is set at a permanent position staying 300 meters away from the tunnel opening. Fig. 3 shows the detector installation project plan. 

The interpretation that some of the neutrons measured by the In resonance method have considerably higher energies does not appear very probable since Creutz found that 3 gr/cm of B4C decrease the activity of In resonance detectors to less than 1%. Particularly because of the similarity of the results obtained by Creutz and Wilson and by Fermi and Anderson, one is tempted to attribute the anomaly to the graphite. 

O Shannessy, D.J., Brigham-Burke, M., Peck, K. (1992). bnmobilization chemistries suitable for use in the BIAcore surface plasmon resonance detector. Analytical Biochemistry, 205, 132-136. 

Walsh has described a system of isolation and detection of radiation by a resonance technique. The system as used for atomic absorption is shown in Figure 6-13. Radiation from a hollow cathode source is passed through the flame sample cell into a resonance detector. The resonance detector contains an atomic vapor of the specific element under analysis. The atomic vapor in the resonance detector may be produced by cathodic sputtering or thermally. The atomic vapor in the resonance detector absorbs a portion of the... 

FIGURE 6-13. Resonance detector for atomic absorption spectroscopy. [From A. Walsh, Physical Aspects of Atomic Absorption, ASTM STP 443 (1968). Used by permission of the American Society for Testing Materials.]... 

A resonance detector is a simple device that requires no adjustment as does a conventional monochromator, and thus can be used under quite rigorous conditions. If a multielement hollow cathode source is used, resonance detectors may be aligned in series in the optical path emerging from the sample cell to provide simultaneous determination of several elements. 

The intensity of the energy emitted by the resonance detector is proportional to the intensity of the energy entering the detector from the optical path of the hollow cathode. The signal intensity from the hollow cathode is attenuated as it passes through the flame, as occurs with conventional atomic absorption instruments. The attenuated beam excites atoms in the atomic vapor of the resonance detector thus an emission signal is obtained which decreases as the concentration of the element aspirated into the flame increases. Calibration curves may be prepared in terms of absorbance units, as they are for conventional atomic absorption signals. 

The power supply to the hollow cathode source is modulated and an ac detection system is used. This arrangement prevents any radiation from the flame or resonance detector from producing an output signal. Random noise is less troublesome than in a conventional spectrophotometer. The resonance detector must, of course, produce a cloud of atomic vapor of the same element being aspirated into the flame. The hollow cathode source also must emit resonance lines of the same element. Analytical calibration curves closely parallel those obtained with conventional atomic absorption systems and sensitivities and detection limits are similar. 

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