Kanani K. M. Lee 1,2 Gerd Steinle-Neumann 2 1 Department of Physics, New Mexico State University, Las Cruces, NM, USA. 2 Bayerisches Geoinstitut – Universität Bayreuth. Pressure- and chemistry-dependent electron-capture-decay in crystalline solids

Radioactive decay  Dating of rocks ( 235 U, 238 U, 232 Th, 40 K, 87 Rb)  Heat  dynamics ( 235 U, 238 U, 232 Th, 40 K)  Mostly α decay (U, Th)  40 K decays by β + (89%) and electron capture (11%) (emission of γ ray)  Other electron capture isotopes: 7 Be, 22 Na, 26 Al, 53 Mn β -, there is also β +

Radioactive decay Radioactive decay nuclear process, hence independent on environment:  true for α and β processes (on fundamental grounds but also measured)  electron capture ~ charge density at nucleus  here 7 Be (τ ½ =53 days) 22 Na (τ ½ =2.6 years, τ ½,EC =27.7 years) 40 K (τ ½ =1.25 Gyr, τ ½,EC =11.9 Gyr)  dependence on chemistry and pressure (decay constant λ~1/τ ½ )

Energetics of a solid Schrödinger's equation [-  2 +V]Ψ(r 1,r 2,...,r N )=EΨ(r 1,r 2,...,r N ) Density Functional Theory (Kohn et al., 1964 ff.): electronic charge density ρ is basic quantity [-  2 +V KS [ρ]]ψ i (ρ)= e i ψ i (ρ) V KS [ρ]= V ne +V ee +V xc Static computations:  Thermal excitations (and zero point motion) neglected.  Use full periodicity of the lattice.

7 Be chemistry Experiments: λ[Be(OH 2 ) 4 2+ ]>λ[Be]>λ[BeO]>λ[BeF 2 ] [Johlige et al., 1970] Our computations: λ[Be]>λ[BeO]>λ[BeCl 2 ] 7 Be pressure

40 K pressure

22 Na pressure

Conclusions Using first principles computations for the electronic charge density of electron capture isotopes we  reproduce the chemical dependence of λ for 7 Be in various chemical forms  can not confirm the strong P dependence of λ for 7 Be  find small P dependence of λ for 22 Na and 40 K  see transition in electronic state (s  d) for 22 Na and 40 K Changes in λ for alkalines are small, are they measurable (γ rays)? 22 Na: ~32 billion decays/day 40 K: ~40 decays/day 22 Na available from ORNL as Na(OH) gel

Background measurements Empty DAC at GEANIE facility at LANL 1275 keV 22 Na 611 keV 137 Cs 1461 keV 40 K 2615 keV 232 Th  208 Tl  …