Search forH5

Abstract

Following the suggestion that ${\mathrm{H}}^{5}$ might be stable against nucleon emission, a search was made for delayed neutrons resulting from the reaction ${\mathrm{Li}}^{7}(\ensuremath{\gamma}, 2p){\mathrm{H}}^{5}$. The targets were bombarded with a 340-MeV bremsstrahlung beam and the delayed neutrons detected in a shielded paraffin-moderated array of B${\mathrm{F}}_{3}$ counters. Counts were scaled in 14 delay channels of variable width and variable initial delay. Separated isotopes of ${\mathrm{Li}}^{7}$ and ${\mathrm{Li}}^{6}$ were used as targets. As ${\mathrm{H}}^{5}$ cannot be produced from the bombardment of ${\mathrm{Li}}^{6}$, counts observed during the bombardment of ${\mathrm{Li}}^{6}$ were used to measure the background. After background subtraction, the data fall uniformly about zero and show no apparent lifetime. Assuming a 10-msec half-life, an upper limit for the activation cross section is ${\ensuremath{\sigma}}_{A}\ensuremath{\le}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{2}$. A comparison of this with the yield expected from the extrapolation of the measured yields of the reactions ${\mathrm{B}}^{11}(\ensuremath{\gamma}, 2p){\mathrm{Li}}^{9}$ and ${\mathrm{F}}^{19}(\ensuremath{\gamma}, 2p){\mathrm{N}}^{17}$ indicates that the upper limit for the activation cross section is of the order of 1% of the expected yield. Hence it appears unlikely that ${\mathrm{H}}^{5}$ is stable against particle emission.