Study of the transient-level density of excited 238Np nucleus

Absolute ρ2(U,I) values of the level-density of excited states in the second potential well are presented for 238Np nucleus produced on the (d, 2N) reaction on 238U inferred from the experimental values of the 238Np fission lifetime. Depending on the 238Np internal excitation energy U = (4.3 - 7.0) MeV, the ρ2(U,I) values are within the (106-107) MeV-1 range, which is 30 - 40 times as high as the absolute ρ1(U,I) values of the 238Np level-density of excited states under equilibrium deformation. The experimental ρ2(U,I) values are compared with the realistic level-density of the 238Np internal excited states calculated in terms of the phenomenological level-density model allowing for collective build-up effects