Structure of 51Cr via 48Ti( 4He, nγ) and 51V(p, nγ) prompt γ-ray spectrometry

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The level structure of 51Cr has been studied in some detail via prompt γ-ray energy and intensity measurements utilizing a NaI(Tl)-Ge(Li) anti-Compton spectrometer and a 511-γ-511 escape peak spectrometer via the 51V(p, nγ) reaction with proton energies in the range 2.6–6.0 MeV and via the 48Ti( 4He, nγ) reaction with t4He ++ energies in the range 12.0–15.0 MeV. Many of the γ-rays associated with levels in 51Cr were identified with the ( 4He, nγ) or the (p, nγ) reaction by means of nγ coincidence measurements employing an organic phosphor as the fast neutron detector and a Ge(Li) γ-ray detector. Characterization of many levels populated in the (p, nγ) reaction was achieved by means of thresholds for individual γ-rays obtained from measurement of excitation functions of individual γ-rays and from the γγ coincidence relationships established in on-beam γγ coincidence measurements in the 51V(p, nγ) reaction at E p = 5.0 MeV employing a NaI(Tl) and a Ge(Li) detector. It was thus established that 39 levels in 51Cr are populated in these reactions. The levels at 2255.7, 2385.6, 2767.1 and 3001.6 or 3004.1 keV which were observed in these experiments have not been reported previously. The rest of the levels studied in this work have been studied previously by means of (d, p), (p, d) and ( n th , γ) reactions. With the exception of the first six levels, the levels reported here have not been reported previously in the (p, nγ) or the ( 4He, nγ) reactions. For the levels below 2704 keV in 51Cr branching ratios for deexcitation of these levels by γ-decay were obtained by averaging the measured angular correlation of each γ-ray about the beam direction. The new γ-ray information from the present study was used in conjunction with the results of previously reported (d, p) reaction studies to make definite J π assignments to many stripping levels in 51Cr and to place limits to the J π values for many levels which were reported earlier to exhibit proton angular distribution patterns from the (d, p) reaction non-characteristic of a stripping reaction. In this work a number of γ-rays were assigned to deexcite levels in 51V that are populated via the 51V(p, p'γ) and 48Ti( 4He, pγ) reactions and which were found to compete to a small extent with the (p, nγ) and (4He, nγ) reactions. A tentative decay scheme for the deexcitation of levels in 51V is offered. The level structure of 51Cr and of 51V is compared with previously reported results of the Coriolis coupling model for the f 7 2 . shell and good qualitative agreement in the level ordering is found.