In MsgID<tGMkj.75466$KC3.51549@newsfe6-gui.ntli.net> on Sun, 20 Jan 2008
18:46:49 GMT, in uk.net.news.management, 'John Briggs' wrote:

[..]

>> Isomeric states? Sorry about the timewarp, even family disasters don't
>> stop me catching up *eventually* ;)
>>
>> The meaning I know for isomer would be something like 'same components
>> different structure' How can that work for an atom? Different physical
>> structure within the nucleus?
>
>It's an analogy, of course. Same atomic number, same mass number - different 
>energy state, and hence different radioactive properties. The nucleus is 
>excited to a metastable state, which is regarded as the upper isomer. In 
>this case, both the upper isomer and lower isomer are radioactive - which 
>makes the concept of a 'ground state' a trifle moot. Very short-lived 
>metastable states tend to get ignored, so the definition is a bit arbitrary.

Only halfway understand that, maybe by excitation you mean in a similar
way to the leaps involved in fluorescence. Thanks for the search terms if
something 'excites' me up to 'auto-investigation' level..

>
>> Sorry, curiousity's a powerful force, with quite a long range..
>> Beats attraction to topic by an order of magnitude or two :)
>
>A bit like gravity compared to the electromagnetic force, I suppose...

S'what I was thinking of.. As per nuclei IIRC.

Dave J.


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Dave J. wrote:
> In MsgID<tGMkj.75466$KC3.51549@newsfe6-gui.ntli.net> on Sun, 20 Jan
> 2008 18:46:49 GMT, in uk.net.news.management, 'John Briggs' wrote:
>
> [..]
>
>>> Isomeric states? Sorry about the timewarp, even family disasters
>>> don't stop me catching up *eventually* ;)
>>>
>>> The meaning I know for isomer would be something like 'same
>>> components different structure' How can that work for an atom?
>>> Different physical structure within the nucleus?
>>
>> It's an analogy, of course. Same atomic number, same mass number -
>> different energy state, and hence different radioactive properties.
>> The nucleus is excited to a metastable state, which is regarded as
>> the upper isomer. In this case, both the upper isomer and lower
>> isomer are radioactive - which makes the concept of a 'ground state'
>> a trifle moot. Very short-lived metastable states tend to get
>> ignored, so the definition is a bit arbitrary.
>
> Only halfway understand that, maybe by excitation you mean in a
> similar way to the leaps involved in fluorescence. Thanks for the
> search terms if something 'excites' me up to 'auto-investigation'
> level..

The same sort of thing - they are atomic energy levels, rather than nuclear 
in this case.

>>> Sorry, curiousity's a powerful force, with quite a long range..
>>> Beats attraction to topic by an order of magnitude or two :)
>>
>> A bit like gravity compared to the electromagnetic force, I
>> suppose...
>
> S'what I was thinking of.. As per nuclei IIRC.

Well, on that scale there are the strong and weak nuclear forces: which are 
incredibly short-range.
-- 
John Briggs