1. 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
In this short talk I will show you how and why the standard picture of origin of 6Li where 6Li is made in GCR interactions might be in trouble.
July 5th, 2007
30th ICRC, Merida, Mexico

2. 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

3. How Well Do We Understand 6Li?
7Li origin: cosmic rays + BBN
But 6Li only made by cosmic rays via
fusion and spallation
Standard assumption: 6LiSolar made by Galactic CRs
But new observations indicate a 6LiSolar plateau?
Intro: the reson for this was the Li7 problem, but we wanted to test our connection on something we thought we know- Li6, but as you’ll see it turned out that there is a li6 problem as well.
Theoretical suggestion: from decaying DM.
Plot: curves- different chemical evolution models (dotted- Brian)
New source of 6Li needed?
Asplund et al.(2006)
Tijana Prodanovic
30th ICRC, Mexico

4. Cosmic-Ray Interactions
Hadronic cosmic-ray interaction production of
Pionic Gamma Rays
Lithium
CRs also make 9Be, 10B (make 11B too but, it is also made in core collapse SNs through neutrino process)
6Li & pionic gamma-rays
connected!
Tijana Prodanovic
30th ICRC, Mexico

5. Li-g-ray Connection
Any cosmic-ray source produces both gamma-rays and lithium
Connected essentially with ratio of reaction rates (Fields and Prodanović 2005)
Li abundance: local CR fluence
Diffuse extragalactic : CR fluence across Universe
Use gamma rays to constrain Li!
Since we use gamma rays to probe lithium, let me first tell you how they are related.
Emphasize: EXTRAGALACTIC i.e. looking at what CRs do not in our Galaxy but in ALL galaxies together
Tijana Prodanovic
30th ICRC, Mexico

6. 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
spallation
2-step reactions, eg.
Account for astration
Gamma rays allow for only ~50% of 6Li to be produced by GCRs!
Tijana Prodanovic
30th ICRC, Mexico

7. Implications & Conclusions
Only ~ 50% of solar 6Li can be explained by GCRs without overproducing gamma-rays
Need new important 6Li source
Recent observations in halo stars: 6Li plateau? But at 10% level of solar (Asplund et al. 2006)
Milky Way GCR flux higher than the cosmic mean?
Implications for star-formation rate
Low-energy CR component?
Energetics and LiBeB ratio constraints
Low-E CRs created in superbubbles! High enrichement with C and O, but week shocks. McCall- observe more 3H+ than expected but 3H+ created by CRs
Transition: “…but I will now show you that even diffuse gammas from MW are not well understood, and I will show you how we will be able to improve on that”
Tijana Prodanovic
30th ICRC, Mexico

8. Thank You!
Tijana Prodanovic
30th ICRC, Mexico