Levels inU239

Abstract

Thirty-seven levels have been observed in 239 U up to an excitation energy of 1692 keV with 12-MeV deuterons and the reaction 238 U (d,p) m U. The ground-state Q value was determined as 2579d=7 keV. A germanium detector, operated as a pair spectrometer for high-energy capture gamma rays and as a totalenergy anticoincidence spectrometer for low-energy gamma rays, has been used to measure 27 high-energy transitions between 3150 and 4850 keV and 27 low-energy transitions between 490 and 900 keV. Analysis of the combined data suggests fairly definite assignments for 13 states below 373 keV. The presence of the 152-neutron energy gap is clearly indicated by the absence of states between 373 and 692 keV. From 692 keV upward, nine additional tentative assignments are made. The spectroscopic assignments are [band-head energy (keV) in parenthesis, followed by spin, parity, and (in brackets) asymptotic quantum numbers]: (ground state), f+[622] with superimposed rotational band to 11/2+; (133),}+[631] with rotational band to |+; (~173), |+[624] with rotational band to 13/2+; (692), i+[620] with rotational band to f+, and (742), §-[761] with anomalous rotational spacings to 11/2 -. A table of Cj,i values for deformation p of 0.20, 0.25, and 0.30 is presented in the Appendix for all Nilsson orbitals of interest in the actinide region.The relative intensities or signatures of the bands are found for the most part to be in good agreement with theory. Absolute magnitudes are a factor of 2 too high. This discrepancy is ascribed to Coulomb stripping effects.

Study of the level structure of239U using the thermal neutron capture reaction

“…In agreement with this we find a level at 222.2keV populated by a transition from a level at 784 keV (5/2-).This is consistent with Sheline's proposal of the I = 7/2 + 163151 band member at 219 keV [2]. Our data do not unambiguously establish this state which is therefore drawn as a dashed line in Figure 2.…”

“…[5]. This has been confirmed by the (d, p) measurement [2]. Using the Ritz combination principle we find three levels at 133, 145 and 193 keV which are populated with a total intensity of ~ 80 %.…”

“…In the (d,p) reaction [1,2] 37 levels have been observed below 1.7 MeV with a pronounced gap between 200 and 700 keV. This gap was ascribed to the particular stability associated with the semi-magic N= 152 shell.…”

“…The spin and parity assignments are based on the multipolarities obtained from the conversion electron spectrum and, when available, on the average resonance capture data, starting from the knowledge of the properties of the ground state (5/2 +) [2,5,11] and the levels at 133 keV (1/2+), 145 keV (3/2 +) and 193 keV (5/2 +) [2,4,5]. The configurations shown in the right part of the level scheme are discussed in the following section.…”

“…The study of secondary ?-rays and of conversion electrons can improve the knowledge of the level structure and configuration assignments. Earlier measurements [2,5] have suffered from insufficient sensitivity, resolution and energy precision which must be particularly high because of the large number of contaminant ?-lines arising from fission. We have, therefore, used the high-resolution spectrometers at the High Flux Reactor at Grenoble and performed additional, complementary measurements for the investigation of the nuclear levels in 239U and their decay properties.…”