Changes In Detector Response Research Articles

Detector Calibration factor for interstitial in-vivo light dosimetry using isotropic detectors with scattering tip.

Isotropic detectors with spherical scattering tips are commonly used for in-vivo dosimetry of light fluence rate during photodynamic therapy (PDT). These detectors are typically calibrated in-air. It has been well established that the response of an isotropic detector is a function of the refractive index (n) of the surrounding medium when it is surrounded by an infinite medium of uniform n. However, there are few, if any, studies of the isotropic detector response when the detector is placed in a secondary medium, such as air, before it is placed inside the infinite uniform medium. This condition often arises when one places the isotropic detector inside an air-filled catheter which is then inserted into a turbid medium, such as tissue. We have performed theoretical and experimental studies to determine the correction factors in water (n = 1.33), which has a refractive index similar to that of tissue (n = 1.4). We found that the resulting correction factor is almost the same (within 20%) as the correction factor for the outermost medium (the water) rather than the immediate medium surrounding the isotropic detector (air). The detector correction factor is also a function of the index of refraction of the probe material. For a 1-mm diameter probe from CardioFocus, the detector correction factor varied from 1 (in air) to 1.09 (at air-water interface) to 1.49 (completely submerged in water). At the air-water interface the spherical bulb of the isotropic detector is placed half in air and half in water. For a 0.5-mm diameter probe from the same company, it varied from 1 (in air) to 1.32 (at air-water interface) to 1.87 (in water). For a 0.3-mm diameter probe from the same company, it varied from 1 (in air) to 1.32 (at air-water interface) to 1.71 (in water). We have also found that the detector response changes by less than 10% when the detector position is varied from touching the catheter wall closest to the light source, to not touching, to touching the catheter wall farthest from the light source. The calibration factors between individual isotropic detectors of the same type varied within 5% for all detector types. Thus mean correction factor can be used for each individual isotropic detector of the same type.

Measurement of the registration temperature effect in BP-1 glass

In order to determine its effect on mass measurements and charge measurements for the cosmic-ray experiments ANTIPODE and TREK, I have measured the change in detector response with temperature (the so-called registration temperature effect, or RTE) for BP-1 glass responding to relativistic gold ions and to stopping argon ions. I measure a small but finite RTE for relativistic gold, and conclude that thermal regulation is necessary for the large collector of TREK, which is being exposed outside of the Russian space station Mir. I set a small upper limit for the magnitude of RTE for stopping argon, and conclude that the thermal variations experienced by ANTIPODE in its balloon flight over Antarctica were not large enough to degrade its mass resolution; I further conclude that the thermal variations that we anticipate for the small collector of TREK, which is being exposed inside the Russian space station, will not degrade its mass resolution.

Determination of atmospheric carbonyl sulfide by isotope dilution gas chromatography/mass spectrometry

A gas chromatography/mass spectrometry (GB/MS) method for determining atmospheric carbonyl sulfide (OCS) with a precision better than 2% is reported. High precision and insensitivity to sample loss and changes in detector response were achieved by using isotopically labeled OCS as an internal standard. Tenax, Molecular Sieve 5A, Carbosieve B, and Carbosieve S were evaluated for collecting atmospheric OCS. Molecular Sieve 5A provided the best trapping and recovery efficiencies.

Si(Li) detector efficiency in standard X‐ray fluorescence geometries

AbstractSi(Li) detector efficieneres are measured up to 100 keV photon energy in typical X‐ray fluorescence geometries using 55Fe, 109Cd, 57Co and 241Am annular sources. The targets are common chemical compounds. The photopeak yield is normalized by the use of a bare CaF2(Eu) scintillator which is free of dead layer. The scintillator response is corrected for escape peak losses. The presented method permits the detection of long term changes in detector response. Discrepancies are found in published nominal detector thicknesses.

Computer Processing of LANDSAT Data for Geologic Applications: ABSTRACT

The main objectives of computer processing of LANDSAT data for geologic applications are to improve display of image data to the analyst or to facilitate evaluation of the multispectral characteristics of the data. Image enhancements involved adjustments of brightness values for individual picture elements. Image classification involves determination of the brightness values of picture elements for a particular cover type. Histograms are used to display the range and frequency of occurrence of brightness values. LANDSAT 1 and 2 data are preprocessed at Goddard End_Page 537------------------------------ Space Flight Center (GSFC) to adjust for the detector response of the Multispectral Scanner (MSS). Because illumination conditions and landscape characteristics vary considerably and detector response changes with time, the radiometric adjustments applied at GSFC are seldom perfect and detector striping remains in LANDSAT data. Therefore, adjustments are applied to minimize the effects of striping, and to adjust for bad data lines, line segments, and lost individual pixel data. Rotation of the earth under the satellite and movements of the satellite platform introduce geometric distortions in the data which must be compensated for if image data are to be correctly displayed to the data analyst. Adjustments to LANDSAT data are made to compensate for variable solar illumination and for tmospheric effects. Geometric registration of LANDSAT data involves determination of the spatial location of a pixel in the output image and determination of the new value of the pixel in the output image. End_of_Article - Last_Page 538------------

Variational Estimates of the Detector Response Change in a Fixed Source System Due to Cross-Section Perturbations

In this Note an expression is derived for estimating the change in detector response due to perturbations in a fixed source system. This expression, developed with variational theory, includes a co...