Properties of the5−state at 839 keV inLu176and the

Abstract

The s-process branching at mass number A = 176 depends on the coupling between the high-K ground state and a low-lying low-K isomer in 176 Lu. This coupling is based on electromagnetic transitions via intermediate states at higher energies. The properties of the lowest experimentally confirmed intermediate state at 839 keV are reviewed, and the transition rate between low-K and high-K states under stellar conditions is calculated on the basis of new experimental data for the 839 keV state. Properties of further candidates for intermediate states are briefly analyzed. It is found that the coupling between the high-K ground state and the low-K isomer in 176 Lu is at least one order of magnitude stronger than previously assumed leading to crucial consequences for the interpretation of the 176 Lu/ 176 Hf pair as an s-process thermometer.

Modification of nuclear transitions in stellar plasma by electronic processes:Kisomers inLu176andGosselin1, Morel2, Mohr3 2010Phys. Rev. CSelf Cite130160View full textAdd to dashboardCite

“…This value is in the experimental limits 10 ps ≤ τ ≤ 433 ps for the lifetime of the 839 keV state because this state predominantly (branching > ∼ 80 %) decays by the 839 → 0 transition. In agreement with the theoretical arguments in [47] and the experimental photoactivation yields [25,26] (see discussion in [5] where τ ≈ 12 ps is suggested with an uncertainty of about a factor of two) we use a value close to the upper experimental limit of the width (or lower limit of the lifetime).…”

“…Such IMS have been detected experimentally by high-resolution γ-ray spectroscopy for 176 Lu [12][13][14][15][16], and an indirect proof for the existence of IMS was obtained from various photoactivation studies [17][18][19][20][21][22][23][24][25][26]. A review of the results for 176 Lu is given in [5]. For 180 Ta only indirect evidence for the existence of IMS was derived from photoactivation [27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”

“…The s-process nucleosynthesis of 176 Lu and 176 Hf and the interpretation of the 176 Hf/ 176 Lu ratio as s-process thermometer are discussed in several recent papers (see [4][5][6], and references therein). The open question on the nucleosynthetic origin of 180 Ta in various processes (s-process, r-process, p-process or γ-process, ν-process) and the survival probability of the 9…”

Nucleosynthesis ofNb92and the relevance of the low-lying isomer at 135.5 keV

“…For the transition from the 7 + ground state to the 2 + isomer the integrated cross section via the 4 + IMS is I * σ = 133 eV fm 2 with an uncertainty of about 20 % which is given by the 16 % uncertainty of the lifetime of the IMS and the 13 % uncertainty of the branching ratio. Values of the same order of magnitude have been obtained for integrated cross sections in the neighboring odd-odd nucleus 108 Ag [26], whereas this result is about a factor of 20 − 100 larger than the lowest experimentally known IMSs in the heavy odd-odd nuclei 176 Lu [27] and 180 Ta [28,29] which are located at slightly higher excitation energies. The lowest IMS candidate in 180 Ta is located at a similar excitation energy as the 4 + IMS in 92 Nb; its integrated cross section is almost six orders of magnitude smaller [24].…”

Nuclear Excitation Processes in Astrophysical Plasmas

“…(Gallino et al, 1998). Under these conditions dramatic variations of isomer production and destruction rates can be expected (Ward & Fowler, 1980;Mohr et al 2007;Gintautas et al, 2009;Mohr et al, 2009;Hayakawa et al, 2010). It has to be noted that the stellar transition rates may exceed the experimentally accessible ground state contribution (Belic et al, 2002;Mohr et al, 2007b;Rauscher et al, 2011) by orders of magnitude.…”