Collective properties of Cr

The mean lifetimes of levels below 3 MeV excitation in ⁴⁹Cr were measured using the reaction ⁴⁹Ti(, nγ)⁴⁹Cr. The Doppler-shift attenuation method was used in a neutron-gamma coincidence measurement. The lifetime of the first excited state was determined with the recoil distance method. The results are : 272 keV, 19±5 ps; 1085 keV, 260±90 fs; 1563 keV, 590₋₁₂₀⁺³⁰⁰ fs; 1704 keV, > 5.5 ps; 1742 keV, > 4 ps; 1982 keV, > 6.5 ps; 2169 keV, > 4.5 ps; 2433 keV, > 6 ps; 2504 keV, < 12 fs; 2614 keV, 65 ±20 fs. The lifetimes of the second and third excited states in combination with known multipole mixing ratios gave evidence for spin assignments of for the 1085 keV level and for the 1563 keV level. The energies and spins of the four lowest levels as well as the B(M1) and B(E2) values of their γ-decays are in good agreement with calculations based on the strong coupling model and suggest that these levels are strongly collective. Dipole transitions of the higher levels to the ground and first excited states are highly retarded.