  Experimental observation of 159Tb(n,2n) reaction product was performed with
application of the activation technique. Tb specimen of natural composition was
irradiated with (d,d) neutrons of 5.39 and 7 MeV energy at the AMANDE neutron
generating facility. Several instrumental spectra of Tb specimen were measured
with HPGe spectrometer in 1.5 years after last irradiation. An unexpected 944.2
keV {\gamma}-ray peak was observed. Other {\gamma}-ray lines of 158Tb were
identified as well. A bonded dineutron emission with the binding energy (Bdn)
within limitations 1.3 MeV < Bdn < 2.8 MeV is evidenced by the energy of
incident neutrons and by 158Tb presence in output channel. The specific nuclear
properties of 158Tb as deformed nucleus were then discussed to explain a bonded
dineutron formation with certain half-lives based on theoretical assumptions
and corresponding calculations, using standard parameters for this mass region.
