Observation of neutronless fusion reactions in picosecond laser plasmas

The yield of $\alpha$ particles in neutronless fusion reactions ${}^{11}\mathrm{B}+p$ in plasmas produced by picosecond laser pulses with the peak intensity of $2\times {10}^{18}\mathrm{W}∕{\mathrm{cm}}^2$ has been observed. Experiments were carried out on the “Neodymium” laser facility at the pulse energy of $10–12\mathrm{J}$ and pulse duration of $1.5\mathrm{ps}$. The composite targets ${}^{11}\mathrm{B}+{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$ were used. The yield of ${10}^3$ $\alpha$ particles per pulse has been observed. The energy spectrum of $\alpha$ particles contains two maxima: at $3–4\mathrm{MeV}$ and at $6–10\mathrm{MeV}$. The first of these peaks corresponds to the secondary ${\alpha }_{12}$ particles at the decay of the intermediate first excited state of ${}^8\mathrm{Be}$, whereas the second peak demonstrates generation of ${\alpha }_1$ 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.

Figure 1

A schematic of the experimental laser setup is shown. The various aspects are as follows: T, target; M, off-axis parabolic mirror; W, the window of the vacuum chamber, LB, laser beam; VC, vacuum chamber; D1–D3, track detectors CR-39; D4–D7, scintillation detectors of $\gamma$ radiation; D8, detector of neutrons on helium counters; and D9, obscure chamber with the recording matrix.

Figure 2

Dependences of track diameters of protons and $\alpha$ particles on their energy.

Figure 3

(Color online) Total distributions of track diameters (number of tracks) for detectors covered with $11\mu \mathrm{m}$ Al. The detector area is $3{\mathrm{cm}}^2$: 1, target ${}^{11}\mathrm{B}+{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$ and 2, target ${\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$.

Figure 4

(Color online) The same as in Fig. 3, but with $22\mu \mathrm{m}$ Al. The detector area is $1.5{\mathrm{cm}}^2$: 1, target ${}^{11}\mathrm{B}+{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$ and 2, target ${\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$.

Figure 5

Oscillograph records from neutron detector D8 using helium counters (the upper part presents digital data of detector, the lower part presents analog data): (a) the target is the composite material ${}^{11}\mathrm{B}+{\left(\mathrm{C}{\mathrm{H}}_2\right)}_n$ with a thickness of $500\mu \mathrm{m}$, (b) the target is the deuterated polyethylene ${\left(\mathrm{C}{\mathrm{D}}_2\right)}_n$ with a thickness of $350\mu \mathrm{m}$.