Observed reduction of α-decay rate under compression and correlation to decay Q-value

The observation of uranium in the extremely metal-poor stars and Uranium/Thorium cosmochronometry play important roles to date r-process events in early Galaxy [1]. So, it is important to study possible changes of α-decay rate under compression inside the stars [2]. Lattice compression of α-emitting radioactive atom is a way to study the effect of pressure.

Density functional calculations indicate that the pressure on the implanted ²¹¹At ions ( α-emitter; half-life ≈ 7.2 hours) in Pd (lattice constant=3.9Å) would reduce Q-value of α-decay by ~70 eV compared to that in Pb (lattice constant=4.9Å) without any measurable change of electron density at ²¹¹At nucleus, thus decreasing α-decay rate in Pd by ~0.08%. We produced ²¹¹At by ²⁰⁹Bi(⁴He,2n)²¹¹At reaction at VECC, Kolkata and implanted them in Pb and Pd foils. ²¹¹At decays by α-emission ( α-line: 5869.5 keV) and EC followed by prompt α-decays. The emitted α-particles from Pb and Pd catcher foils were counted by a PIPS detector in an evacuated chamber along with a 250Hz pulser to correct for the dead time of Data Acquisition System. Experimentally, the quantity [(λ_EC ∼λ_α)/λ_α]×100% for ²¹¹At implanted in Pb and Pd was measured by monitoring the ratio of the sum of prompt α-decay lines followed by EC to 5869 keV α-line with time and found to be higher in Pd by (0.064 ± 0.019)%, providing first definitive observation of the reduction of λ_α under compression and correlation to Q-value reduction.



[1] H. Schatz et al., ApJ 579, 626 (2002).

[2] F. Belloni, Eur. Phys. J. A52, 32 (2016).