Reference materials for PCDD and PCDF analysis: production and verification of the contents of twelve congeners in iso-octane reference solutions

Summary The Community Bureau of Reference (BCR) of the Commission of the European Communities has produced standard solutions of PCDDs and PCDFs (dirty dozen) to guarantee proper calibration and traceability of results in the certification of these compounds in matrix materials. The purity of each individual isomer has been evaluated on the initial crystals using several analytical methods. Solvents have been checked for impurities. The entire procedure of preparation of the twelve solutions has been performed under strict metrological conditions and will be published elsewhere. All results and the preparation procedure followed are described. The solutions are not certified, but may be obtained from BCR together with an analytical report.     

Symmetric and asymmetric yields in the photofission of232Th,235U,238U and239Pu

Measurements are presented for the mass and energy distributions of fragments from the photofission of²³²Th,²³⁵U,²³⁸U and²³⁹Pu. The experiments were performed for bremsstrahlung endpoint energies between 15 and 55 MeV, using silicon surface barrier detectors. The results are discussed with respect to the competition between the symmetric and asymmetric fission modes.     

In-beam γ-ray spectroscopy of the neutron deficient 100Ag

Conversion coefficients and conversion ratios of someγ-transitions in²⁰¹Tl and²⁰³Tl were measured by means of simultaneous spectroscopy ofγ-quanta and conversion electrons employing intensity calibrated semiconductor detectors. The experiments aimed at a precision as high as possible within the limits of the experimental methode used. Theγ-transitions were of the typeM 1(+E2). From the measured values the penetration parameters of the internal conversion for theM 1 components (λ) together with the multipol mixing ratios (δ²) were deduced. The necessary theoretical coefficients were taken from the tables of Hager and Seltzer. The results are for the ?-forbidden 331 keV transition in²⁰¹Tl,λ=+4.0±1.0,δ ²=1.78±0.16; for the ?-allowed 361 keV transition in²⁰¹Tl,λ=+0.5±0.5,δ ²=0.02±0.02; for the ?-forbidden 279 keV transition in²⁰³Tl,λ=+ 5.71±0.45,δ ²=1.55±0.08.