Production of149gTb in deep inelastic transfer reactions: An approach to the angular momentum of fragments

Abstract

The excitation functions for deep inelastic reactions in which two to six charges are transferred from 4~ and 63Cu ions to rare earth targets have been measured using activation techniques, the observed radionuclides being 150, 151Dy and 149gTb. From the comparison of the curves relative to 149gTb and those relative to 15~ it was deduced that the low spin isomer 149gTb was produced with significant probability for low incident energies. Using data from (heavy ions, xn) reactions, it was possible to attribute this production to the deexcitation of Tb fragments formed in deep inelastic transfers with angular momenta lower than 9 h. This result is in good agreement with the angular momentum calculations performed under the hypothesis that the initial angular momentum window leading to deep inelastic reactions is situated between the critical angular momentum for fusion and that corresponding to grazing collisions. As far as Cu induced reactions are concerned, both hypothesis of rolling and sticking are consistent with the experimental data. For Ar induced reactions, the results indicate that the stage of sticking is not reached when the incident energy is lower than 200 MeV.Nuclear Reactions: 142'145Nd, 144'a48Sm, 154Gd(Ar, X)151'lS~ 149gTb E=160 280MeV; measured a(E). ~44Nd, 14SSm, 151Eu, 154Gd(Cu, X)1~1' 15~ 149gTb. E=280-420 MeV measured a(E). Enriched targets. Deduced angular momentum of Tb fragments.

Deeply inelastic transfer reactions induced by heavy ions in rare-earth targets

“…The data concerning the other systems are given in [18][19][20]. The distributions relative to a49gTb and 15~ not given here, are very similar to those of 151Dy" This is not surprising since it was shown in [30] that, for sufficiently high incident energies, the isomer ~49gTb is mainly produced through the electron capture decay of a49Dy. Thus the reactions leading to the three observed isotopes differ only by the transfer (or evaporation) of one or two neutrons.…”

“…For a given AZ, these reactions may or may not correspond to the most probable neutron transfer, i.e., to the maximum of the isotopic distribution %z (AN-x). This maximum is known from crosssection measurements [19,33,42]. In Table 3, those reactions which correspond to this maximum, within the uncertainty of _+1 neutron are labeled with the symbol m (see the exact list of theses reactions in Table 4).…”

“…AN values, associated with a given AZ, with different probabilities (these widths are probably increased by the relatively poor energy resolution of the technique). For example, for the system Fe+ 148Sm at E =364MeV, the FWHM of the E-distribution (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) can be explained by the contribution of the reaction paths in which 4p and 3 to 6n are transferred in the first reaction step, and 4 to 7 neutrons are evaporated in the second step.…”

“…the Dy nuclei can also be produced from fast decays of Ho or Er nuclei. This contribution can be estimated from isotopic distributions [18,33,42].…”