There are a few problems with this scenario.
With a short half-life (e.g. 260 ms), the radionuclide would decay very rapidly, so that the activiy would drop by 3 orders of magnitude in 10 half-lives (here 2600 sec < 1 hr), by 6 orders of magnitude in 20 half-lives, and by 9 orders of magnitude in 30 half-lives.
The specific energy is very low. Consider the beta energy as compared to the mass of the nucleus, and consider that the beta energy has a spectrum (the anti-neutrino shares some of the decay energy), and the most probable energy is about 1/3 of the max energy.
Beta particles are emitted in all directions. To establish a sufficient potential, a good collection system is required.
I recommend some homework on BEC -
http://en.wikipedia.org/wiki/Bose-Einstein_Condensate
The nuclear properties are not affected by the condensation of atoms.
and -
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/spinc.html#c4