A radiochemical study of f i s s i o n and s p a l l a t i o n products produced by bombardment of U 233, $35 , and U238 with 18-46 Mev helium ions has been made.As i n the case of s i m i l a r studies using isotopes of plutonium as t a r g e t s , most of the reaction c r o s s section i s taken up b y f i s s i o n . Also, t h e pronounced increase of the t o t a l cross section f o r (a,xn) reactions with increasing mass number of the t a r g e t t h a t was observed f o r plutonium t a r g e t s i s observed f o r uranium t a r g e t s .Excitation functions f o r (a,2n), (a,3n), and (a,kn) reactions a r e i nt e r p r e t e d i n terms of compound nucleus formation and f i s s i o n competition a t the various s t a g e s of t h e neutron evaporation chain. The importance of neutron binding energies on t h e competition between f i s s i o n and neutron emission i s stressed. An e x i s t i n g model f o r neutron evaporation following compound nucleus formation has been extended t o include t h e e f f e c t of f i s s i o n competition.

The beta decay of Bk 250 has been studied with a beta spectrometer. Bk 250 has two beta groups: 725±15 kev (89±1% abundant) and 1760±50 kev (11 ±1% abundant). Conversion electron lines corresponding to 42.2, 98.2, 890, 930, 990, and 1032-kev transitions were observed and their intensities measured. The information obtained from crystal spectrometer singles and coincidence measurements was combined with beta spectrometer data to construct a decay scheme for Bk 250 involving gamma vibrational levels in Cf 250 analogous to those found in Pu 238 . The beta half-life of Bk 250 is 193.3 ±0.3 minutes. The electron capture partial half-life of Bk 250 is estimated to be greater than 50 hours. The beta spectrum of Bk 249 shows an allowed or first-forbidden transition with an end-point energy of 125=b2 kev.

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