Observation of neutronless fusion reactions in picosecond laser plasmas

The yield of $\ensuremath{\alpha}$ particles in neutronless fusion reactions $^{11}\mathrm{B}+p$ in plasmas produced by picosecond laser pulses with the peak intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ has been observed. Experiments were carried out on the ``Neodymium'' laser facility at the pulse energy of $10--12\phantom{\rule{0.3em}{0ex}}\mathrm{J}$ and pulse duration of $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. The composite targets $^{11}\mathrm{B}+{(\mathrm{C}{\mathrm{H}}_{2})}_{n}$ were used. The yield of ${10}^{3}$ $\ensuremath{\alpha}$ particles per pulse has been observed. The energy spectrum of $\ensuremath{\alpha}$ particles contains two maxima: at $3--4\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and at $6--10\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The first of these peaks corresponds to the secondary ${\ensuremath{\alpha}}_{12}$ particles at the decay of the intermediate first excited state of $^{8}\mathrm{Be}$, whereas the second peak demonstrates generation of ${\ensuremath{\alpha}}_{1}$ particles in the reaction $^{11}\mathrm{B}+p$ with the production of this excited state. Simultaneous measurements of neutrons result in zero yield, which proves the observation of neutronless fusion reactions in our experiments.