C.A. Quarles

Bremsstrahlung: an experimentalist’s personal perspective on the postmodern era

Abstract In this brief review I will discuss the recent experimental work on the doubly differential cross section, i.e. the photon energy and angular distribution, for electron bremsstrahlung from thin solid film and gas targets. Since the beginning of the modern era in the study of bremsstrahlung with the publication of the 1971 paper by Tseng and Pratt, Professor Pratt has been the dominant influence in bremsstrahlung research. Most, if not all, experimental research during the modern era has been motivated by the interest in comparing data with the theory of Pratt and his coworkers. As bremsstrahlung research has moved into its postmodern era, new experiments with increasing precision are concentrating on determining under what conditions ordinary bremsstrahlung theory needs to be supplemented by a contribution from polarization bremsstrahlung. Efforts to improve the comparison of thin-target experiment with theory have also led to new experimental and modeling work on bremsstrahlung from thick solid targets. Thick-target bremsstrahlung is interesting in its own right, but we also want to understand it better since it is the ever-present background in the thin-target experiments and the limiting factor in the effort to distinguish the polarization contribution to the total bremsstrahlung spectrum. Professor Pratt ushered in the modern era in bremsstrahlung research and has recently guided the transition into the postmodern era. It can be expected that he will continue to have a formative influence on the developments of bremsstrahlung research into the foreseeable future.

Possible new well-logging tool using positron Doppler broadening to detect total organic carbon (TOC) in hydrocarbon source rocks

Abstract The use of well-logging tools has proven to be a cheap, effective method of formation evaluation in potential petroleum basins. One of the few remaining unanswered questions of economic importance is the amount of organic matter available to produce oil and gas in source rocks. Using Doppler broadening spectroscopy, we measured the S -parameter along the length of a shaly source rock with known TOC values. The S -parameter was observed to correlate well with the geochemically derived organic carbon weight percent values.

Positron Spectroscopy Investigation of Normal Brain Section and Brain Section with Glioma Derived from a Rat Glioma Model

The application of positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS) to the study of animal or human tissue has only recently been reported [G. Liu, et al. phys. stat. sol

Application of Positron Doppler Broadening Spectroscopy to the Measurement of the Uniformity of Composite Materials

The uniformity of rubber‐carbon black composite materials has been investigated with positron Doppler Broadening Spectroscopy (DBS). The number of grams of carbon black (CB) mixed into one hundred grams of rubber, phr, is used to characterize a sample. A typical concentration for rubber in tires is 50 phr. The S parameter measured by DBS has been found to depend on the phr of the sample as well as the type of rubber and carbon black. The variation in carbon black concentration within a surface area of about 5 mm diameter can be measured by moving a standard Na‐22 or Ge‐68 positron source over an extended sample. The precision of the concentration measurement depends on the dwell time at a point on the sample. The time required to determine uniformity over an extended sample can be reduced by running with much higher counting rate than is typical in DBS and correcting for the systematic variation of S parameter with counting rate. Variation in CB concentration with mixing time at the level of about 0.5% has been observed.The uniformity of rubber‐carbon black composite materials has been investigated with positron Doppler Broadening Spectroscopy (DBS). The number of grams of carbon black (CB) mixed into one hundred grams of rubber, phr, is used to characterize a sample. A typical concentration for rubber in tires is 50 phr. The S parameter measured by DBS has been found to depend on the phr of the sample as well as the type of rubber and carbon black. The variation in carbon black concentration within a surface area of about 5 mm diameter can be measured by moving a standard Na‐22 or Ge‐68 positron source over an extended sample. The precision of the concentration measurement depends on the dwell time at a point on the sample. The time required to determine uniformity over an extended sample can be reduced by running with much higher counting rate than is typical in DBS and correcting for the systematic variation of S parameter with counting rate. Variation in CB concentration with mixing time at the level of about 0.5% ha...

Positron Study of Carbon Black Parameters: Structure and Surface Area

Carbon black (CB) is essentially carbon in the form of extremely fine particle aggregates (100-200nm) having an amorphous molecular structure. Oil absorption or compressed dibutyl phthalate (CDBP) and iodine adsorption or nitrogen surface area (N2SA) are parameters commonly used to describe CB morphology or structure and the surface area of CB available for reaction with rubber. We have used both positron lifetime and Doppler broadening spectroscopy to study these two parameters for a variety of rubber CB composite samples. The o-Ps pickoff lifetime depends only on the type of rubber and is independent of CDBP and N2SA. However, the o-Ps lifetime intensity, I3, and the S parameter decrease with both CDBP and N2SA.