Isomerism transition

An isomeric transition , also known as isomeric transition or isomeric conversion , is the spontaneous transition of an atomic nucleus from a metastable excited state to a less highly excited state or to the ground state . The energy difference is usually given off as gamma radiation . If the gamma emission is "forbidden" due to a large angular momentum difference between the two states, i. H. is unlikely, the release through internal conversion is also observed , especially in the case of heavy atomic nuclei . With transition energies well above 1022 keV (total rest energy of an electron-positron pair), inner pairing also occurs, especially with light nuclides .

Nuclear isomers are identified in the formula symbol after the mass number with the lower case letter m (for metastable), often followed by a number (if there are several of these states).

Examples with half-lives T _1/2 :

${\displaystyle {}_{\ 73}^{180m}\mathrm {Ta} \;\;{\xrightarrow {\mathrm {IT} }}\;\;{}_{\ 73}^{180}\mathrm {Ta} +\gamma \ \ }$ with T _1/2 > 1.2 · 10 ¹⁵ a

${\displaystyle {}\;_{\ 43}^{\ 99m}\mathrm {Tc} \;\;{\xrightarrow {\mathrm {IT} }}\;\;{}_{\ 43}^{\ 99}\mathrm {Tc} +\gamma \ \ }$  with T _1/2 = 6 h

${\displaystyle {}\;_{\ 27}^{\ 60m}\mathrm {Co} \;\;{\xrightarrow {\mathrm {IT} }}\;\;{}_{\ 27}^{\ 60}\mathrm {Co} +\gamma \ \ }$  with T _1/2 = 10.5 min

${\displaystyle {}\;\;_{\ 38}^{\ 86m}\mathrm {Sr} \;\;{\xrightarrow {\mathrm {IT} }}\;\;\;{}_{\ 38}^{\ 86}\mathrm {Sr} +\gamma \ \ }$  with T _1/2 = 0.45 µs

The isomeric transition is often abbreviated to IT ( Isomeric Transition ) as the type of “decay” .

literature

• Povh, Rith, Scholz, Zetsche: Particles and Cores . Springer, 4th edition 1997, ISBN 3-540-61737-X
• Hans Bucka : Nucleonenphysik , Walter de Gruyter, Berlin / New York 1981, ISBN 3-11-008404-X

References and comments

1. ↑ Hans Bucka : Nukleonenphysik , Walter de Gruyter, 1981, p. 392ff
2. ↑ https://people.nscl.msu.edu/~witek/Classes/PHY802/EMdecay.pdf
3. ↑ DK Jha, Radioactivity And Radioactive Decay , Chapter 4.5, pp. 146ff