Potassium in the deep Earth: Radioactivity under pressure Kanani K. M. Lee DOANOW, March 23-25,

Lamb & Sington (1994) Earth’s Deep Interior

1001/earth/earth/99.html Heat  Dynamics SOURCES Primordial: accretion differentiation Radioactivity: K, U, Th

26 Al  26 Mg0.72 Myr 53 Mn  53 Cr3.7 Myr ‘Short’-lived EC isotopes Timing Heating Heterogeneity

What we “know”: Chondritic K/U ratio ~8 x 10 4 (Wasserburg et al., 1964) Terrestrial K/U ratio ~1 x 10 4 What we don’t know: Why is there a discrepancy in the K/U ratios? K lost to space during accretion?!? K incorporated in the deep Earth during accretion?!?

Lee & Jeanloz, GRL, 2003; Lee et al., GRL, 2004 Fe-K alloying at high P/T Diamond-Anvil Cell experiments Ab-initio QM calculations

1001/earth/earth/99.html Heat  Dynamics Up to 20% of the Earth’s power generated from 40 K decay in the core!! Geodynamo Mantle convection Long-lived magma ocean? Core-Mantle boundary reactions? Very HOT early Earth.

Earth’s current P/T conditions 300 K ~2000 K ~3000 K ? ~6000 K ? or greater?

 - decay  + decay e - capture  radioactive decay schemes

1947: Electron capture decay of 7 Be predicted to be affected by extra-nuclear environments: Segré, Daudel Late 1940’s-1950’s: lots of theory, measurements on chemical environment effect on 7 Be decay 1963: first pressure-dependent measurement on 7 Be decay (Gogarty et al., ONR) 1970’s: more theory ( 40 K, e.g., Bukowinski, 1976), another P measurement ( 7 Be, Hensley et al., 1973) 2000’s: more theory, another P measurement (Liu et al., 2000) A bit of Electron Capture History

EC decay is dependent on pressure, temperature, chemistry, ionization, etc. e.g., Bukowinski, 1979

Electron orbitals cougar.slvhs.slv.k12.ca.us/.../firstsemass.html

6s 5s 4s 3s 2s 1s 5p 4p 3p 2p 5d 4d 3d Energy Relative energies of atomic orbitals

In collaboration with Gerd Steinle-Neumann, BGI Structures fully relaxed using VASP All-electron method, full potential (LAPW), Wien2k Both GGA and LDA approximations to many-body interactions V XC Energy convergence to ~1 meV/atom Computational Method

 1/2 ~ 53.3 days 100% electron capture decay  = MeV Be, BeO, BeCl 2 7 Be

7 Be under pressure

Prediction: ~0.1 days decrease in  1/2 at 50 GPa for Be, BeO in hcp structure and BeCl 2 in orth structure 7 Be

1001/earth/earth/99.html Heat  Dynamics SOURCES Primordial: accretion differentiation Radioactivity: K, U, Th

  total ~1.25 billion years!!! Decay energy and concentration  relevant to the Earth 40 K long-lived radioactive decay Electron capture  - decay

40 K long-lived radioactive decay Electron capture Decay is dependent on pressure, temperature, chemistry, ionization, etc.

With pressure a 4s  3d electronic transition makes K, an alkali metal, more like a transition metal (Bukowinski, 1976) Transition metals s  d electronic transition in K

6s 5s 4s 3s 2s 1s 5p 4p 3p 2p 5d 4d 3d Energy Relative energies of atomic orbitals

6s 5s 4s 3s 2s 1s 5p 4p 3p 2p 5d 4d 3d Relative energies of atomic orbitals K Energy

6s 5s 4s 3s 2s 1s 5p 4p 3p 2p 5d 4d 3d Relative energies of atomic orbitals K Energy

 1/2,total ~ 1.25 Gyr  1/2,EC ~ 11.9 Gyr  1/2,  - ~ 1.4 Gyr ~11% electron capture decay  = MeV K, K 2 O, KCl 40 K

40 K under pressure

s  d electronic transition fcc K

40 K under pressure fcc K start of s  d electronic transition: ~1% of electrons are in d orbital

40 K Prediction: ~3 Myr decrease in  1/2,ec at 25 GPa for K and ~0.6 Myr decrease for K 2 O and KCl s  d transition matters!

Are these changes measurable? 7 Be: Yes! ~40 billion decays/min 40 K: Probably not. ~40 decays/day

Periodic Table of Elements

Comparable EC system: 22 Na  1/2,total ~ 2.6 yr  1/2,EC ~ 27.7 yr  1/2,  - ~ 2.8 yr ~9.4% electron capture decay  = MeV Na, Na 2 O, NaCl ~32 billion decays/day!!

22 Na under pressure

s  d electronic transition!?!

22 Na under pressure start of s  d electronic transition: ~2% of electrons are in d orbital

Are these changes measurable? 7 Be: Yes! ~40 billion decays/min 22 Na: Yes! ~32 billion decays/day 40 K: Probably not. ~40 decays/day

DIAMOND ANVIL CELL Diamond Strength Transparency Pressure

Ge  detector Ge  detector  measurements under high P

Ge  detector Ge  detector  measurements under high P

1-day background  spectra of empty diamond cell

511 keV e + emission 1275 keV 22 Na  -ray emission: 3+ billion counts per day!!! 1-day expected  spectra

511 keV e + emission 1275 keV 22 Na  -ray emission: 3+ billion counts per day!!! 661 keV: 137 Cs 1461 keV: 40 K 2615 keV: 232 Th  208 Tl 

Pressure and chemistry DO have an effect on electron capture radioactive decay, although small 7 Be predictions are compatible with previous experiments, although lower Na and K as pure metals are predicted to show more P-dependence than respective simple oxides and chlorides Pressure, chemical environment effects are measurable for longer-lived isotope systems Conclusions

Funded by: Alexander von Humboldt Foundation Bayerisches Geoinstitut (Bayreuth) CDAC (Department of Energy)

Special thanks to: Gerd Steinle-Neumann (BGI) Sofia Akber-Knutson (UCSD) Ron Nelson (LANL) Bob Rundberg (LANL) Boris Kiefer (NMSU) Allen Knutson (UCSD) David Dolejs (BGI) Innokenty Kantor (BGI) Artem Oganov (ETH)