Can Solar 6Li Really Be
Explained by Galactic Cosmic
Rays?
Tijana Prodanović
University of Novi Sad, Serbia
Brian D. Fields
University of Illinois at Urbana-Champaign
July 5th, 2007
30th ICRC, Merida, Mexico
Outline






Standard 6Li origin: Galactic Cosmic-Ray (GCR)
nucleosynthesis
New observations indicate new 6Li source
CR interactions: Li & gamma-rays connected
Use extragalactic gamma-ray background
(EGRB) to constrain GCR made 6Li
EGRB allows only ~50% of solar 6Li to be
made by GCRs!
New source? MW higher CR flux? Low-energy
CR component?
Tijana Prodanovic
30th ICRC, Mexico
July, 5th 2007
How Well Do We Understand 6Li?
 7Li
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origin: cosmic rays + BBN
But 6Li only made by cosmic rays via
6




Li and spallation p,   CNO 6 Li
fusion
Standard assumption: 6LiSolar made by Galactic CRs
But new observations indicate a 6LiSolar plateau?
New source of 6Li needed?
Asplund et al.(2006)
Tijana Prodanovic
30th ICRC, Mexico
July, 5th 2007
Cosmic-Ray Interactions

Hadronic cosmic-ray interaction production
of
 Pionic
Gamma Rays
p  p   0  
 Lithium
   6 Li
p,   CNO6 Li
6Li
Tijana Prodanovic
& pionic gamma-rays
connected!
30th ICRC, Mexico
July, 5th 2007
Li--ray Connection
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Any cosmic-ray source produces both gammarays and lithium
Connected essentially with ratio of reaction rates
(Fields and Prodanović 2005)

1

Li
y ,ism y ,cr  

 Li
abundance: local CR fluence
 Diffuse extragalactic   : CR fluence across Universe

Use gamma rays to constrain Li!
Tijana Prodanovic
30th ICRC, Mexico
July, 5th 2007
Galactic CRs and

6Li
: Results
Prodanović & Fields (2006)
Pionic gamma-ray fraction
 Normalized
to the Milky Way (blue)
 ~30% of the total EGRB (normal gal.)
 6Li
production channels included
 fusion
    6 Li
O  H11 B  H 6 Li
 2-step reactions, eg. p,   CNO 6 Li
 spallation
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Account for astration
Gamma rays allow for only ~50% of 6Li to be
produced by GCRs!
Tijana Prodanovic
30th ICRC, Mexico
July, 5th 2007
Implications & Conclusions
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Only ~ 50% of solar 6Li can be explained by
GCRs without overproducing gamma-rays
Need new important 6Li source
observations in halo stars: 6Li plateau? But at
10% level of solar (Asplund et al. 2006)
 Recent

Milky Way GCR flux higher than the cosmic
mean?
 Implications

for star-formation rate
Low-energy CR component?
 Energetics
Tijana Prodanovic
and LiBeB ratio constraints
30th ICRC, Mexico
July, 5th 2007
Thank You!
Tijana Prodanovic
30th ICRC, Mexico
July, 5th 2007