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HK: Physik der Hadronen und Kerne

HK 16: Kernphysik/Spektroskopie II

HK 16.4: Vortrag

Dienstag, 18. März 2003, 16:45–17:00, A

Search for a new Shape Isomer in ²³⁹U^* — •C. Alvarez¹, P.G. Thirolf¹, D. Habs¹, H.J. Maier¹, T. Morgan¹, W. Schwerdtfeger¹, and R.S. Simon² — ¹Ludwig-Maximilians-Universität München — ²GSI, Darmstadt

Experimental evidence exists from ²³⁸U(n,f) studies for the existence of a so far unobserved shape isomer in ²³⁹U with an unusually low ground state excitation energy of E_II=1.700 MeV [1] and a halflife of t_1/2>250 ns. The γ back decay of this potential shape isomer into the first minimum should be observable by in-beam γ-ray spectroscopy [2]. In a first experiment at the Garching Tandem accelerator prompt and delayed γ-rays following the ²³⁸U(d,p) reaction with a pulsed deuteron beam (E_d= 11 MeV, pulse distance 1.6 µs) were detected in coincidence with protons. At the neutron separation energy a much larger transmission through the inner barrier is observed than expected from the parameters of the top of the barrier, resulting in a good isomer population. The goal was to study the population cross section and the halflife of the potential shape isomer, using a large, radially segmented cylindrical NaI detector prior to future high-resolution studies with the MINIBALL spectrometer. First experimental results will be presented.
[1] S. Oberstedt et al., Nucl. Phys. A636 (1998) 129
[2] P.G. Thirolf and D. Habs, Prog. Part. Nucl. Phys. 49 (2002) 325
^* Supported by the DFG and Maier-Leibnitz-Laboratorium, Garching