Investigation of photon-photon angular correlations in atomic mercury

Abstract

By application of the time differential coincidence technique developed in nuclear spectroscopy, for the first time the angular correlation of light quanta of atomic decays was observed. The experiments were carried out with the 73S1-63P1-61So-cascade of mercury excited by electron impact at energies of 50 eV. The two transitions of 4358 and 2536 A were selected by interference filters and detected by photomultipliers. Time differential coincidence spectra were measured at the two angular positions 0=90 ° and 0=180 °. It was found that the excitation of the 73S1-state by the electron beam leads to no alignment. Therefore the usual γ-γ angular correlation theory is applicable. Perturbations occur by static interaction with external magnetic fields and by free hyperfine interaction in the odd isotopes of mercury. The interaction frequencies of the free hyperfine interaction are in all cases too high to be resolved. Measurements were performed using mercury of natural abundances, with and without external magnetic fields. First of all the spin rotation in the magnetic field of the earth (690 mG) was observed, giving for theg-factor of the 63P1-state $$g(Hg, 6^3 P_1 ) = 1.35 \pm 0.10.$$ This value is in agreement with the more precise values determined by other techniques. Shielding of the earth's field gave a nearly unattenuated angular correlation, with an integral attenuation factor of $$G_2 = 0.98 \pm 0.06.$$ The value of the angular correlation coefficientA2. $$A_2 = - 0.188 \pm 0.009,$$ is in good agreement with the expected average value for the natural isotope mixture $$\overline {A_2^{theor} } = - 0.196.$$ A third measurement in an external magnetic field of 5.6 G showed several complete spin rotations. A nice fit was possible by using the superposition of all six participating cascades in the hyperfine level schemes of the different isotopes. The theoretical anisotropies,g F -values, and intensities were inserted according to natural isotope abundances.