Kanani K. M. Lee 1,2 Gerd Steinle-Neumann 2

1. Pressure- and chemistry-dependent electron-capture-decay in crystalline solids Kanani K. M. Lee1,2 Gerd Steinle-Neumann2 1Department of Physics, New Mexico State University, Las Cruces, NM, USA. 2Bayerisches Geoinstitut – Universität Bayreuth.

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

3. 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 7Be (τ½=53 days) • 22Na (τ½=2.6 years, τ½,EC=27.7 years) • 40K (τ½=1.25 Gyr, τ½,EC =11.9 Gyr) • dependence on chemistry and pressure (decay constant λ~1/τ½)

4. Energetics of a solid Schrödinger's equation [-2+V]Ψ(r1,r2,...,rN)=EΨ(r1,r2,...,rN) Density Functional Theory (Kohn et al., 1964 ff.): electronic charge density ρis basic quantity [- 2+VKS[ρ]]ψi(ρ)= eiψi (ρ) VKS[ρ]= Vne+Vee+Vxc Static computations: • Thermal excitations (and zero point motion) neglected. • Use full periodicity of the lattice.

5. 7Be chemistry Experiments: λ[Be(OH2)42+]>λ[Be]>λ[BeO]>λ[BeF2] [Johlige et al., 1970] Our computations: λ[Be]>λ[BeO]>λ[BeCl2] 7Be pressure

6. 40K pressure

7. 22Na pressure

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

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