Isomers of astrophysical interest in neutron-deficient nuclei at masses A = 81, 85 and 86

Abstract

Decay properties of neutron-deficient exotic nuclei close to A = 80 have been investigated at the IGISOL facility. The studied nuclei, 81 Y, 81 Sr, 81m Kr, 85 Nb, 85 Zr, 86 Mo and 86 Nb, were produced by a 32 S beam from the Jyväskylä isochronous cyclotron on 54 Fe and nat Ni targets. The internal conversion coefficient for a 190.5 keV isomeric transition in 81m Kr has been measured and the internal transition rate has been determined. The internal transition rate has been used to estimate a neutrino capture rate on 81 Br, which yields a log ft of 5.13 ± 0.09 for the reaction 81 Br(ν, e −) 81m Kr. A new isomer with a half-life of 3.3 ± 0.9 s has been observed in 85 Nb. The existence of an earlier reported isomer with a half-life of 56 s in 86 Nb has not been confirmed.

Mass measurement of neutron-deficient nuclei close to the N = Z line

“…Since in all of these cases only one state was observed, it is not possible to determine whether the measured nucleus was the ground state or the excited state. From previous decay spectroscopy ( [2] and [10]) at HIGISOL, the isomers 80m Y, 85m Zr and 85m Nb are less produced than the ground state. These production ratios support the conclusion that we have really measured the ground state masses.…”

“…At higher masses, the path will broaden and shift by about one or two units towards stable nuclei. The decay properties of several neutron-deficient nuclei near A=80 have been studied at the IGISOL facility in a series of experiments [2]. These investigations are now extended to precision mass measurements of the nuclei.…”

Three decades of research using IGISOL technique at the University of Jyväskylä

“…During 2008 a series of off-line and on-line measurements were performed to fully characterize the cryogenic ion guide, the results of which have been recently published [98]. One of the important practical consequences which was quickly verified when using cryogenic gas is that for the same vacuum pumping system a higher stopping density can be used.…”

Direct mass measurements ofSe68andY80

“…The Q p value for proton capture on 68 Se can be calculated as (12) with M(H) = 7.289 MeV [13]. The nucleus 69 Br has not been observed experimentally despite concerted efforts [9,38].…”

“…Several studies have begun to delineate the dripline in the A 60-80 mass region [5][6][7][8][9][10][11][12]. However, experimental information on masses in this region is still scarce [13], and consequently mass models or mass systematics are employed in network calculations.…”