Abstract
The fission probability of ^{238}Np was measured as a function of the excitation energy in the energy range of E^* = 5.4 - 6.2 MeV in order to search for transmission fission resonances. A radioactive ^{237}Np target was bombarded with deuterons of E_d = 12 MeV, whereas the energy of the protons was analyzed with a superior resolution of varDelta E = 8 keV. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory in Garching employing the ^{237}Np(d,pf) reaction. A group of fission resonances has been observed at excitation energies between E^* = 5.5 - 5.8 MeV, which could be ordered into three (superdeformed) rotational bands with a rotational parameter of hbar ^2/2varTheta = 3.507 keV, and identified as the first direct observation of transition states composing rotational bands in an odd-odd nucleus as they appear above the top of the outer fission barrier. Nuclear reaction code (talys1.95) calculations were also performed to extract the multi-humped fission barrier parameters of ^{238}Np by fitting them to the experimental data of the present (d,pf) and previous (n,f) experiments. The extracted barrier parameters also support the above interpretation of the observed resonances.
Highlights
Of the isomeric state, which has a strong quadrupole deformation (β2 ≈ 0.6 − 0.7)
We found conclusive evidence on the existence of HD bands in an odd–odd nucleus (232Pa) [19], which initiated an experimental campaign on the systematic investigation of the odd–odd actinides. 238Np is an interesting isotope regarding hyperdeformation: it is an isobar of 238U, where a hyperdeformed third minimum has already been indicated [20]
We measured the fission probability of 238Np as a function of the excitation energy in the energy range of E∗ = 5.4 − 6.2 MeV in order to search for transmission fission resonances using the (d,pf) transfer reaction on a radioactive 237Np target
Summary
Shape isomers in odd-N uranium and neptunium isotopes have not yet been observed despite the large number (n=17) of isomeric states identified in the neighboring Pu isotopes. One experiment, reported by Oberstedt and coworkers in 2007 [4], claimed the observation of the isomeric fission decay of 235U with an unexpectedly long isomeric half life of 3.6±1.8 ms, recently in a re-analysis extended to 11±3 ms [5], populated in the (n,f) reaction, which is in apparent contradiction with theoretical expectations as well as halflife systematics [6]. In this regard, 238Np is of great interest, as a good odd–odd candidate for observing an isomeric state among the Np isotopes.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
