DETERMINATION OF MsTh$sub 1$ BY MsTh$sub 2$ /cap beta/ PARTICLES IN PRESENCE OF Rd-226

The separation and determination of MsTh/sub 1/(Ra/sup 228/) with barium sulfate in porous crucibles are described, and a correcting system for determining MsTh, in presence of Rd/sup 226/ is given. The beta particle method of MsTh/sub 1/ determination is much more efficient than the radiothorium increase method and can be used for determining MsTh quantities 10/sup -5/ g/g in specimens weighing 15 g. (R.V.J.)