Excited states of the odd-odd nucleus ${}^{158}\mathrm{Eu}$ from the ($d,\alpha$) reaction

Excited states in the ${}^{158}\mathrm{Eu}$ nucleus have been determined with the ${}^{160}\mathrm{Gd}(d,\alpha ){}^{158}\mathrm{Eu}$ reaction, studied at an incident energy of 18.0 MeV with the Munich tandem and Q3D spectrograph. More than 50 excited states have been determined up to 1.6 MeV excitation, some of them corresponding to states previously observed in the ${\beta }^{-}$ decay of ${}^{158}\mathrm{Sm}$. The number of levels found in this nucleus at low excitation energies follows the systematic trend of the level densities in the other isotopes with mass 152–156.

Figure 1

Graph of the energy loss versus the rest energy (both in arbitrary units) of the reaction products that reach the focal plane detector, showing the good separation of the $\alpha$ particles.

Figure 2

Spectra measured at ${10}^{\circ }$ with the same magnetic settings of the spectrograph for (a) our reaction, and (b) the reaction used for energy calibration, ${}^{111}\mathrm{Cd}(d,\alpha ){}^{109}\mathrm{Ag}$. In spectrum (b) the peaks are labeled both with the ENSDF adopted energies [6] (in red italics) and those assigned with the calibration curve, respectively. In spectrum (a) the peaks are labeled with the excitation energies of the states in ${}^{158}\mathrm{Eu}$, as found with the calibration curve (see text and Table 1). The spectrum in (a) was obtained in 19 h of measurement with a beam of about 0.5 $\mu \mathrm{A}$. For comparison, the spectrum in (b) was produced in 100 min under similar conditions.

Figure 3

The gaspan program fits to the spectrum of Fig. 1. The peaks are labeled with the level energy in keV (see Table 1). A residue spectrum with two standard deviations statistical limit is shown below each graph. The six graphs correspond to the six groups of levels displayed in Table 1.

Figure 4

The experimental $a$ parameter of the BSFG model level densities [11] (black triangles) and the simplified level density of levels up to 0.35 MeV excitation (circles and dotted line).