Potassium in the deep Earth: Radioactivity under pressure
Download
1 / 46

Radioactive decay of K- behavior under pressure - PowerPoint PPT Presentation


  • 334 Views
  • Updated On :

Potassium in the deep Earth: Radioactivity under pressure. Kanani K. M. Lee. DOANOW, March 23-25, 2007. [email protected] http://www.physics.nmsu.edu/~kanani. Earth’s Deep Interior. Lamb & Sington (1994). Heat  Dynamics. SOURCES Primordial: accretion differentiation

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Radioactive decay of K- behavior under pressure' - HarrisCezar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Slide1 l.jpg

Potassium in the deep Earth: Radioactivity under pressure

Kanani K. M. Lee

DOANOW, March 23-25, 2007

[email protected]

http://www.physics.nmsu.edu/~kanani


Slide2 l.jpg

Earth’s Deep Interior

Lamb & Sington (1994)


Slide3 l.jpg

Heat  Dynamics

  • SOURCES

  • Primordial:

    • accretion

    • differentiation

  • Radioactivity:

    • K, U, Th

www.gridclub.com/fact_gadget/ 1001/earth/earth/99.html


Slide4 l.jpg

  • What we “know”:

    • Chondritic K/U ratio ~8 x 104 (Wasserburg et al., 1964)

    • Terrestrial K/U ratio ~1 x 104

  • 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?!?


Slide5 l.jpg

Fe-K alloying at high P/T

Diamond-Anvil Cell experiments

Ab-initio QM calculations

Lee & Jeanloz, GRL, 2003; Lee et al., GRL, 2004


Slide6 l.jpg

Very HOT early Earth.

  • Long-lived magma ocean?

  • Core-Mantle boundary reactions?

Heat  Dynamics

  • Up to 20% of the Earth’s power generated from 40K decay in the core!!

    • Geodynamo

    • Mantle convection

www.gridclub.com/fact_gadget/ 1001/earth/earth/99.html


Earth s current p t conditions l.jpg
Earth’s current P/T conditions

300 K

~2000 K

~3000 K ?

~6000 K ?

or greater?


Slide8 l.jpg

 radioactive decay schemes

- decay

+ decay

e- capture


Slide9 l.jpg

A bit of Electron Capture History

  • 1947: Electron capture decay of 7Be predicted to be affected by extra-nuclear environments: Segré, Daudel

  • Late 1940’s-1950’s: lots of theory, measurements on chemical environment effect on 7Be decay

  • 1963: first pressure-dependent measurement on 7Be decay (Gogarty et al., ONR)

  • 1970’s: more theory (40K, e.g., Bukowinski, 1976), another P measurement (7Be, Hensley et al., 1973)

  • 2000’s: more theory, another P measurement (Liu et al., 2000)


Slide10 l.jpg

e.g., Bukowinski, 1979

EC decay is dependent on pressure, temperature, chemistry, ionization, etc.


Slide11 l.jpg

Electron orbitals

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


Slide12 l.jpg

5d

4d

3d

6s

5s

4s

3s

2s

1s

5p

4p

3p

2p

Energy

Relative energies of atomic orbitals


Slide13 l.jpg

Computational Method

  • Structures fully relaxed using VASP

  • All-electron method, full potential (LAPW), Wien2k

  • Both GGA and LDA approximations to many-body interactions VXC

  • Energy convergence to ~1 meV/atom

In collaboration with Gerd Steinle-Neumann, BGI


Slide14 l.jpg

7Be

  • 1/2 ~ 53.3 days

  • 100% electron capture decay

  • = 0.478 MeV

    Be, BeO, BeCl2


Slide15 l.jpg

7Be under pressure


Slide16 l.jpg

7Be

Prediction: ~0.1 days decrease in 1/2 at 50 GPa for

Be, BeO in hcp structure and BeCl2 in orth structure


Slide17 l.jpg

Heat  Dynamics

  • SOURCES

  • Primordial:

    • accretion

    • differentiation

  • Radioactivity:

    • K, U, Th

www.gridclub.com/fact_gadget/ 1001/earth/earth/99.html


Slide18 l.jpg

40K long-lived radioactive decay

Electron capture

- decay

t1/2,total~1.25 billion years!!!

Decay energy and concentration  relevant to the Earth


Slide19 l.jpg

40K long-lived radioactive decay

Electron capture

Decay is dependent on pressure, temperature, chemistry, ionization, etc.


Slide20 l.jpg

s  d electronic transition in K

Transition metals

With pressure a

4s  3d

electronic transition makes K, an alkali metal, more like a transition metal (Bukowinski, 1976)


Slide21 l.jpg

5d

4d

3d

6s

5s

4s

3s

2s

1s

5p

4p

3p

2p

Energy

Relative energies of atomic orbitals


Slide22 l.jpg

5d

4d

3d

6s

5s

4s

3s

2s

1s

5p

4p

3p

2p

Energy

K

Relative energies of atomic orbitals


Slide23 l.jpg

5d

4d

3d

6s

5s

4s

3s

2s

1s

5p

4p

3p

2p

Energy

K

Relative energies of atomic orbitals


Slide24 l.jpg

40K

1/2,total ~ 1.25 Gyr

1/2,EC ~ 11.9 Gyr

1/2,- ~ 1.4 Gyr

~11% electron capture decay

 = 1.461 MeV

K, K2O, KCl


Slide25 l.jpg

40K under pressure


Slide26 l.jpg

sd

electronic

transition

40K under pressure

fcc K


Slide27 l.jpg

40K under pressure

start of sd electronic transition:

~1% of electrons are in d orbital

fcc K


Slide28 l.jpg

40K

Prediction: ~3 Myr decrease in 1/2,ec at 25 GPa for K and

~0.6 Myr decrease for K2O and KCl

sd transition matters!


Slide29 l.jpg

Are these changes measurable?

7Be: Yes! ~40 billion decays/min

40K: Probably not. ~40 decays/day



Slide31 l.jpg

Comparable EC system: 22Na

1/2,total ~ 2.6 yr

1/2,EC ~ 27.7 yr

1/2,- ~ 2.8 yr

~9.4% electron capture decay

 = 1.275 MeV

Na, Na2O, NaCl

~32 billion decays/day!!


Slide32 l.jpg

22Na under pressure


Slide33 l.jpg

22Na under pressure


Slide34 l.jpg

sd

electronic

transition!?!

22Na under pressure


Slide35 l.jpg

22Na under pressure

start of sd electronic transition:

~2% of electrons are in d orbital


Slide36 l.jpg

Are these changes measurable?

7Be: Yes! ~40 billion decays/min

22Na: Yes! ~32 billion decays/day

40K: Probably not. ~40 decays/day


Slide37 l.jpg

Pressure

DIAMOND ANVIL CELL

  • Strength

  • Transparency

Diamond


Slide38 l.jpg

measurements under high P

Ge

detector

Ge

detector


Slide39 l.jpg

measurements under high P

Ge

detector

Ge

detector


Slide40 l.jpg

1-day background  spectra

of empty diamond cell


Slide41 l.jpg

511 keV e+ emission

1275 keV 22Na -ray emission: 3+ billion counts per day!!!

1-day expected  spectra


Slide42 l.jpg

511 keV e+ emission

1275 keV 22Na -ray emission: 3+ billion counts per day!!!

661 keV: 137Cs

1461 keV: 40K

2615 keV: 232Th208Tl


Slide43 l.jpg

Conclusions

  • Pressure and chemistry DO have an effect on electron capture radioactive decay, although small

    • 7Be 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


Slide44 l.jpg

Funded by:

Alexander von Humboldt Foundation

Bayerisches Geoinstitut (Bayreuth)

CDAC (Department of Energy)


Slide45 l.jpg

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)


ad