# ^α-decay

^α-decay

Consider the following decay

As a nucleus decays due to internal force of repulsion, there is no net external force on it, hence in any nuclear reaction linear momentum must be conserved.

Before disintegration, the nucleus can be assumed to be at rest, so the total momentum was zero. After disintegration let it be mava & mD vD for  alpha particle & daughter nuclei respectively. To conserve linear momentum the total vector momentum must still be zero i.e.  mava + mDvD = 0 or mava = -mDvD

i.e. momentum of a particle must be equal & opposite to that of daughter’s nucleus.

In magnitude, mava = mDvD

As mass of alpha particle is much lighter than thorium, thus the lighter α particle carries off most of the energy in the form its KE (about 98% of the total KE).

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