Given T,
The probability of any particle attaining vboom is pv. If radioactive decay is the result of particles colliding at vboom, then the portion of particles decaying away at any one time is,
dNdt=−pv.N --- (*)
where N is the number of particles.
N(t)=Noe−pvt
where No is the number of particles at time t=0. Consider,
12No=Noe−pvt1/2
t1/2=ln(2)pv
Half life can be calculated from a graph of Probability, p vs Velocity, v. Unfortunately such plots are often illustrative. The velocities profile of free particles in a solid has never been done.
Note: Expression (*) requires that pv=NvN where Nv is the number of particles with velocity equals to vboom and N is the total number of particles; that the probability of a particle having vboom is the fraction of particles having vboom.