QUADRUPOLE DEFORMED AND OCTUPOLE COLLECTIVE BANDS IN RA-228

Spins and parities for collective states in Ra-228 have been determine d from conversion electron measurements with a mini-orange beta spectr ometer. The fast-timing beta gamma gamma(t) method has been used to me asure lifetimes of T-1/2 = 550(20) ps and 181(3) ps for the 2(1)(+) an d 4(1)(+) members of the K = 0(+) band, and T-1/2 less than or equal t o 7 ps and less than or equal to 6 ps for the 1(1)(-) and 3(1)(-) memb ers of the K = 0(-) band, respectively. The quadrupole moments, Q(0), deduced from the B(E2;2(1)(+) --> 0(1)(+)) and B(E2;4(1)(+) -->2(1)(+) ) rates are in good agreement with the previously measured value and t he systematics of the region. However, the B(EI) rates of greater than or equal to 4 x 10(-4) e(2) fm(2), which represent the first B(E1) me asurements for this nucleus, are at least 25 times larger than the val ue previously suggested for Ra-228. The new results are consistent wit h the B(E1) rates recently measured for the neighbouring Ra-227 and re veal octupole correlations in Ra-228. (C) 1998 Elsevier Science B.V.