A. R. Arends

Data reduction methodology for perturbed angular correlation experiments

Data reduction schemes currently used for time differential perturbed angular correlation measurements are evaluated in terms of (i) their relative effectiveness in eliminating irrelevant variables, including single counter efficiencies and spectrum time shifts; and (ii) their effectiveness in putting data in a form that can easily be fitted by theoretical correlation functions. It is pointed out that erroneous conclusions may be derived from improperly reduced data, but that properly analyzed experiments performed at four angles allow a good determination of both the time-dependent and time-independent parts of the correlation function. Correction of data for accidentals, source self-absorption and spectrum livetime differences are discussed.

DATING PEAT WITH U/TH DISEQUILIBRIUM - SOME GEOCHEMICAL CONSIDERATIONS

Abstract The applicability of the U/Th disequilibrium dating method (UTD) for peat is investigated. Dating is performed by measurements of the U and Th isotopes in the bulk material of the sample as well as in different fractions. Due to the complex geochemistry of U and Th in organic matter, dating peat by UTD is not a simple and straightforward method. It may appear from our results that the number of cases in which the method is applicable is limited because post-formation contamination with Th may occur. However, one interesting case, the Tenaghi Phillippon core from Greece, seems to fulfill the requirement that little or no environmental Th has entered the system after formation. Results obtained from this core agree well with 14 C data. Evidence is found for the theory that complexation of actinides with humic and fulvic acids limits the mobility of U and Th. The data can be explained assuming that ion exchange is the dominant process in the accumulation of U and Th by peats.

ELECTRIC-FIELD GRADIENTS IN DILUTE ALLOYS OF CU, AG AND AU

In this paper we present perturbed angular correlation (PAC) measurements on100Rh and111Cd in a number of dilute alloys of Cu, Ag and Au. We discuss the electric field gradient (EFG) values derived from these and other experiments in the framework of a theory of the EFG at nearest neighbours of point defects in metals, essentially based on the screening of a point charge in a free electron gas. We include in our discussion the EFG due to a neighbour monovacancy for a number of fcc metals.

MAGNETIC HYPERFINE FIELDS OF ZR IN NICKEL AND IRON MEASURED BY THE DPAD METHOD

The magnetic hyperfine fields of Zr in nickel and iron were measured by the DPAD method. Using the 8+ isomeric states in90Zr and88Zr these fields were found to beHhf(ZrNi)=−4.65(10) T andHhf(ZrFe)=−27.4(4) T, respectively.

CRITICAL-BEHAVIOR IN RADIATION DAMAGED SYSTEMS

Perturbed angular distribution (PAD) measurements of Bleck et al. of the critical behavior of63NiNi,66CuNi, and67ZnNi have been reanalyzed, and shown to be insufficiently asymptotic to permit deduction of meaningful critical exponents. Via experiments on implanted111InNi, done with and without annealing of radiation damage, and by comparison to diffused111InNi, it is suggested that unannealed radiation damage can produce serious systematic errors in critical exponents.