Investigation of excited states of 7Li by means of thermal neutron capture

Capture of unpolarized thermal neutrons has been used to gain information on the ⁷Li level scheme. Two reactions have been investigated. Firstly, a study has been made of the decay scheme of ⁷Li through the ⁶Li(n, γ)⁷Li reaction. Three γ-transitions were observed and placed. The binding energy value of this reaction turned out to be Q = 7251.02(9) keV. Secondly, investigation of radiation from excited Li produced by the ¹⁰B(n,α)⁷Li reaction, made it possible to deduce a more precise lifetime of the 478 keV level of ⁷Li; namely τ = 102 ± 5 fs. This value is compared with existing data; it agrees with previous less accurate independent values and an average could be made in order to reduce the error further. As a byproduct the analysis of the peak shape of the 478 keV transition offered a new method for estimating the size of boron grains embedded in other materials.