title: Energy splitting of the ground-state doublet in the nucleus 229Th.
abstract: The energy splitting of the 229Th ground-state doublet is measured to be 7.6+/-0.5 eV, significantly greater than earlier measurements. Gamma rays produced following the alpha decay of 233U (105 muCi) were counted in the NASA/electron beam ion trap x-ray microcalorimeter spectrometer with an experimental energy resolution of 26 eV (FWHM). A difference technique was applied to the gamma-ray decay of the 71.82 keV level that populates both members of the doublet. A positive correction amounting to 0.6 eV was made for the unobserved interband decay of the 29.19 keV state (29.19-->0 keV).
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: B R
authors.initials: BR
authors.lastname: Beck
authors.forename: J A
authors.initials: JA
authors.lastname: Becker
authors.forename: P
authors.initials: P
authors.lastname: Beiersdorfer
authors.forename: G V
authors.initials: GV
authors.lastname: Brown
authors.forename: K J
authors.initials: KJ
authors.lastname: Moody
authors.forename: J B
authors.initials: JB
authors.lastname: Wilhelmy
authors.forename: F S
authors.initials: FS
authors.lastname: Porter
authors.forename: C A
authors.initials: CA
authors.lastname: Kilbourne
authors.forename: R L
authors.initials: RL
authors.lastname: Kelley