Nuclear Data Section
International Atomic Energy Agency
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Memo CP-D/378

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16 January 2004
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O. Schwerer

Subject: Quasi-metastable states (Reply to memo CP-C/331)
I agree to the proposal of CP-C/331 provided that a few more clarifications are introduced asfollows.
1. The LEXFOR page on Isomeric States presently gives 3 different criteria for what is a"short" half-life:"Isomeric states" must have a half-life > 0.1 seconds, except for spontaneous fission, α or pdecay, where it is > 1 milli-second. The next paragraph says that "for practical applications,a metastable state in EXFOR is defined as having a half-life of 0.1 milliseconds or longer".
With the new formalism, we can do away with this confusing situation. I propose to definethat metastable states with half-lives of 0.1 seconds or longer are coded with -M, M1 etc
while all states with shorter half-lives are coded with -L, L1 etc.
2. With these new codes we come close to the area of "ordinary partial cross sections" which
are coded not with isomeric extension in SF4 but with PAR in SF5. Therefore, theLEXFOR page on Partial Reactions should say"Partial cross sections leading to an isomeric state (with a half-life >0.1 sec) are coded with
an isomer extension in REACTION SF4. Partial cross sections for quasi-metastable states,
which are characterized by a half-life below 0.1 sec, are coded with isomer extension -L, L1,L2 etc. which link the levels with DECAY-DATA and are valid only for this particular dataset.
Partial cross sections leading to individual levels for which no half-life is given but which arecharacterized by the level energy or level number, are coded without an isomer extension in
SF4 but with PAR in SF5, and the level identification is given under the data headings E-LVL
or LVL-NUMB (or equivalent)."
3. What if both the half-life and the level energy of a quasi-metastable state are given?
I think we should have the possibility to give them both, either by• Allowing to give the level energy under LEVEL-PROP, even if neither spin nor parity
are given (this would be new); or• Giving the level energies under new data headings such as LVL-L1, LVL-L2. (It wouldbe LVL-L1 rather than E-LVL-L1 because it's not a required independent variable but
rather "additional information" much like LVL-INI and LVL-FIN.)
I prefer the first possibility:
LEVEL-PROP (39-Y-88-L1,E-LVL=0.674)
because if necessary spin and parity can be added without having too much redundance.

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