A direct measurement of the helicity dependence of the total photoabsorption cross section on the proton was carried out at MAMI (Mainz) in the energy range 200 < Eγ < 800 MeV. The experiment used a 4π detection system, a circularly polarized tagged photon beam and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability γ0 determined from the data are 226±5(stat) ± 12(sys) µb and -187±8(stat) ± 10(sys) 10 −6 fm 4 , respectively, for 200 < Eγ < 800 MeV. PACS number(s): 13.60. Le, 13.60.Hb, 25.20.Lj
The helicity dependence of the single pion photoproduction on the proton has been measured in the energy range from 200 to 450 MeV for the first time. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a frozen-spin target. The data obtained provide new information for multipole analyses of pion photoproduction and determine the main contributions to the Gerasimov-Drell-Hearn sum rule and the forward spin polarizability gamma(0).
To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.
45, 304 (1973). The thermodynamic functions given for KCN and NaCN in thls paper are incorrect. (1 5) An attempt to use silver vaporized under identical conditions, Including using the same effuslon cell, to check our values of ku, kD, and kT failed because there is no reliable means to estimate the relatlve cross sections, e.g., uA,+uW In fact, comparison of our KCN and Ag data suggests that uA,+(gM x uD i= uT) = 5.0 f 0.2 at 20 eV.This large ratio is understandable on the basis that fragmentation to Kt Is much more probable than forming the ions we monitored. Table I data clearly support this idea. (16) D. 0. Welch, 0.The behavior of polymeric iron phthalocyanine catalysts during the cathodic reduction of oxygen in sulfuric acid was studied by labeling central iron atoms with 5?Fe. Moreover, in order to get an insight into the interaction between iron polyphthalocyanines and carbon supports, Mossbauer spectroscopic investigations have been undertaken. The experiments showed that iron polyphthalocyanine electrocatalysts, which are built in carbon-teflon electrodes, could be classified in (a) phthalocyanine molecules with low stability and large quadrupole splitting which have only a low influence on the electrochemical operation of the electrode and (b) phthalocyanine molecules with high stability and low quadrupole splitting which are decisive in electrocatalysis.In agreement with the mechanism of long-life electrocatalytic operation and deactivation, derived from these experiments, carbon-teflon cathodes with polymeric iron polyphthalocyanine catalysts could be constructed which are characterized by a high stability during continuous operation in 6 N HzS04 up to 3000 h.
Experimental Section1. Electrochemical Measurements. The electrocatalytic properties of polymeric iron phthalocyanines that are being discussed in this paper have been tested in teflon-bonded porous electrodes. For details of synthesis see, e.g., ref 22
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