A Measurement of the Interaction of Neutrons With $^{\mathrm{7}}$Be at Cosmological Energies

We exposed the 4.4 GBq electroplated $^{\mathrm{7}}$Be target prepared at the Paul Scherrer Institute in Switzerland to the high neutrons flux of 5x10$^{\mathrm{10}}$ /sec/cm$^{\mathrm{2}}$ generated by the LiLiT at the Soreq Applied Research Accelerator Facility (SARAF) in Israel. The so produced quasi-Maxwelian neutron spectrum with an equivalent kT $=$ 49.2 keV simulate directly BBN conditions with T$=$ 700 - 500 MK (kT $=$ 60 - 43 keV), allowing the first measurement at Big Bang energies. The measured alpha-particles emanating from all possible $^{\mathrm{8}}$Be states populated in the $^{\mathrm{7}}$Be(n,$\alpha )$ and $^{\mathrm{7}}$Be(n,$\gamma \alpha )$ reaction, detected with a CR39 plastic track detectors, will be shown and discussed.