Determine the exact half-life of the 29/2+ isomer in 197Au

Determine the precise half-life of the I^π = 29/2^+ metastable state at E_x = 2102 keV in ^197Au through a future long-timescale decay measurement, thereby establishing whether its B(E4) transition probability is enhanced, suppressed, or close to the single-particle estimate.

Background

The newly identified Iπ = 29/2+ state in 197Au has only a lower-limit half-life, T_1/2 > 10 s, because the available beam-off measurements did not determine its decay curve over a sufficiently long interval. This limit yields only upper bounds on the reduced transition probabilities: B(E2) < 6.2 × 10-9 W.u. and B(E4) < 107 W.u.

An exact half-life would permit a direct determination of the E4 transition strength and would clarify whether the competing E4 branch has enhanced, suppressed, or approximately single-particle character. The measurement is also intended to constrain the structural interpretation of the unusual coexistence of shape- and spin-related hindrance in 197Au.

References

A future measurement of T_{1/2}(29/2{+}) would affirm whether the B(E4) probability is enhanced, suppressed or close to the single-particle estimate.

— Singular observation of shape and spin hindrance in metastable nuclear decay of $^{197}$Au  (2610.25915 - Tandel et al., 19 Oct 2026) in Discussion of transition probabilities; Summary

An inspection of the data collected when the beam was switched off suggests a half-life longer than several minutes; however, a precise value could not be determined, therefore, a T_{1/2} > 10 s lower limit has been adopted.

— Singular observation of shape and spin hindrance in metastable nuclear decay of $^{197}$Au  (2610.25915 - Tandel et al., 19 Oct 2026) in Experimental results describing the 2102-keV state