Discovery of a Nuclear Isomer inFe65with PenningTrap Mass Spectrometry

Abstract

A new long-lived isomeric state in (65)Fe has been discovered with Penning trap mass spectrometry and high-precision mass measurements of the neutron-rich isotopes (63-65)Fe and (64-66)Co have been performed with the Low-Energy Beam and Ion Trap Facility at the NSCL. For the new isomer in (65)Fe an excitation energy of 402(5) keV has been determined from the measured mass difference between the isomeric and ground states. The mass uncertainties of all isotopes have been reduced by a factor of 10-100 compared to previous results. In the case of (64)Co the previous mass value was found to deviate by about 5 standard deviations from the new measurement.

β−decay of65Mn to65Fe

“…If the 215.8-keV line feeds a level at 393.7(2) keV, then one defines a new level at 609.5 keV deexcited by the 215.8-keV transition, and then all four coincident lines deexcite levels already assigned to the level scheme based on other γ γ coincidences. The 393.7-keV level is identified as the isomeric level at 402(10) keV reported in [22]. Thus the energy of the β-decaying isomer is precisely determined at 393.7(2) keV.…”

“…A second isomer in 65 Fe was identified using Penning trap mass spectrometry. The excitation energy of this β − decaying state was measured at 402(10) keV [22,23]. Precise γ -spectroscopic studies established that the two β-decaying states in 65 Fe populate two sets of mutually independent level schemes in 65 Co [24].…”

Low-energy structure of2766Co39and2768CoLiddick1, Abromeit2, Ayres3 et al. 2012Phys. Rev. C285291View full textAdd to dashboardCite

“…The systematics of the E(2 + 1 ) states in both Fe and Cr isotopes do not display a peak at N = 40 [11,12] but monotonically decrease in energy starting at N = 36 and N = 32, respectively. Positive parity isomeric states attributed to the neutron g 9/2 single-particle orbital are known in 59 Cr [13] and 65,67 Fe [14][15][16]. Within the odd-odd 58,60,62 Mn isotopes, the energy of the negative parity band heads resulting from the coupling of the πf 7/2 and νg 9/2 single particle states consistently drops as N = 40 is approached [17].…”

Shape coexistence alongN=40

“…The ground states in both 65 Fe and 67 Fe are attributed to filling the K = 1/2 − level, suggesting small changes occur to the energy separation between the νp 1/2 and νf 5/2 single-particle states between N = 39 and N = 41. Further, based on half-life considerations for the unobserved isomeric level in 67 Fe, an assignment of 9/2 + [29] was excluded in favor of a 5/2 + spin and parity due to the K = 5/2 + level of the neutron g 9/2 single-particle state [11].…”