🚀 go-pugleaf

Tim Josling <tej_at_melbpc.org.au_rubbish@nospam.com> wrote in
news:en9m6v$djp$1@possum.melbpc.org.au: 

> Greg Locock wrote:
>> 
>> I'm sorry, you are right. Alpha and beta decay are distinct from 
>> fission.
>> 
>> Regards
>> 
>> Greg Locock
> 
> Alpha decay is not really fundamentally different from fission. With 
> alpha decay, as with other forms of fission, the nucleus splits into
> two parts. It is just that with alpha decay one part consists of two
> protons and two neutrons ie an alpha particle. With other forms of
> fission, the two parts consist of quite large nuclei, often of roughly
> similar size. 
> 
> With alpha decay the mechanism of decay is thought to be quantum 
> tunnelling - the "alpha particle" gets close to the edge of the
> nucleus and tunnels through the potential barrier. Having escaped, it
> is driven away at high speed by eletric repulsion.
> 
> With the more usual forms of fission, the large nucleus is unstable, a
> bit like a large drop of water. Either spontaneously or as a result of
> being hit by a neutron, it breaks up into two parts.
> 
> Beta decay is indeed another thing altogether, governed by the weak
> force. 


Yes, I had gently wondered whether the alpha decay of a small nucleus 
was really any different to fission. Still, CRC (my only handy 
reference) reckons that fission implies splitting into roughly equal 
parts, so in most cases alpha decay does not fit that definition. Either 
way Bill's definition is much closer to accepted practice than mine.

Cheers

Greg