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Finding a Logo. One has to have a logo. To put where the ? Is. Vic is a famous guy, so it should be easy with GOOGLE IMAGE SEARCH!!!!. ?. ?. V 2 - Connection—The Light Elements--LiBeB. LiBeB Properties Rare, Fragile How are they made?. Not in stars—can’t survive T in stellar cores - PowerPoint PPT PresentationTRANSCRIPT
Viola Celebration October 29,05
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Finding a Logo
One has to have a logo. To put where the ? Is.
Vic is a famous guy, so it should be easy with
GOOGLE IMAGE SEARCH!!!!
Viola Celebration October 29,05
Viola Celebration October 29,05
Viola Celebration October 29,05
?
Viola Celebration October 29,05
V2- Connection—The Light Elements--LiBeB
LiBeB Properties
Rare, Fragile
How are they made?
Not in stars—can’t survive T in stellar cores
Spallation reactions in stellar winds at surface of T Tauri Stars?
Energies—up to 50 MeV?Aha!! We had a 50 MeV cyclotron at MSU
Viola Celebration October 29,05
p + C, N, O Ne Li Be B, Products low energy
Need only masses 6,7,9,10,11—one isotope of each mass stable on cosmic timescales.
Measure E/v2 E t2 mass
At MSU-Laumer, Davids, Panggabean, SMA, to 45 MeV
At Maryland- Roche, Clark, Mathews, Moyle, Glagola, V2, to 100 MeV
What We Measured
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Make too little 7Li, 11B => other sources: Big Bang and Supernovae?
Splat!
6Li stuff
GCR--p,
ISM target
The Results and Cosmic Ray Production
Summarized by SMA and, better, by SM Read and V2, ADNDT 31, 1984
(m
b)
12C + p
10
T Tauri flares now out as production site, cosmic rays in.
Cosmic ray production
Viola Celebration October 29,05
6,7Li Collaboration
Can synthesize 6,7Li before C,N,O made in stars is returned to the interstellar medium.
Measurements at U Maryland, IUCF, and MSU, beginning in 1975 and ending in 2001, most of them collaborative, provide quality estimates over the entire interesting range.
???
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Abundances in Metal Poor Stars and CR Nucleosynthesis
B
[Fe/H]Log (Li,Be,B)/H
10-3 0-now[Fe/H]
Be
10-3 0-now
BLi
Spite Plateau
WMAP Li
6Li
Comments and mysteries
Li mostly BB, some CR so almost constant. But too low. Stellar destruction?
6Li all CR, so should increase—doesn’t ?
B,Be increase linearly-means our classic CR picture is wrong? Many explanations, perhaps too
many explanations. Nuclear physics is almost good enough.
Viola Celebration October 29,05
Making Carbon in Stars
Triple alpha reaction--a venerable topicSaltpeter, Opik, Hoyle: 3 -> 12C in helium burning stars
Efficiency requires a double resonance process 8Be + 12C(7.65) res res
12C (g.s.) +2γ(e+e-)
New Interests—effects of 3 in: SNII (Iron core size, nucleosynthesis)AGB Stars (Carbon production and carbon stars)Limits on variation of atomic constants
How to improve (inadequate) 3 accuracy? 12% -> 5%?
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The Triple Alpha Process
Step I: 8BeResonant processForm equilibrium abundance of 8Be
Step II: 8Be + 12C(7.65)
If resonant, as for our applications:
r3 rad(7.65)e-Q/kt
rad = γ+ , Q = Q1+Q2
I
II
γ
Q1 = -92 keV
Q2= -287 keV
+8Be
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How Well Do We Know r3
γγ
rad
r3 ),exp( 3
kT
Qrad
where
γγ
rad and Q3 = Er –3M2.
Experiments 5 3 2 5 Excluded results 1 0 0 0
Each arrow a measurement
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How Well Do We Have to Know r3
Comments: Several measurements for all parametersGenerally good agreementResult is soundly based. Is it good enough? Some examples
Core collapse supernovae
Competition with following reaction 12C(γ)16O crucial
Ratio of two rates important at 10% level (Woosley et al)
At 10% level in ratio, r3 needs to be better known
Low mass AGB stars 12C produced depend strongly on r3need better
accuracy, to 5% or better.
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SNII Nucleosynthesis A=16-40
12C(γ)16O Multiplier
Pro
duct
ion
Fact
or
Heger, Woosley,
Boyes
25
M
Explosion of 25 M star
Vary rate of 12C(γ)16O
All else same
Production Factor“Same” PF for 1.2 x standard12C(γ)16O rate
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SNII--Pre-collapse Fe Core Size
Pre-supernova evolution
25 M star
Vary rate of 12C(γ)16OFe core mass changes by 0.2 M over the interesting range
Important?Naively, yes. If homologous core mass constant, need 3 x 1051 erg to dissociate extra 0.2 M to nucleons
Fe
Core
Siz
e (
Sola
r M
ass
es)
0.5
1.0
1.5
2.0
1.0 1.5 2.0 2.5 12C(γ)16O Multiplier(xBuchmann `96)
25 MHeger, Woosley, Boyes
Caveat: Is it just the ratio that counts?
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Asymptotic Giant Branch Stars
Following core H,and He burning thermal flashes in He shell induce convective currents that carry C rich material into the inter-shell region. Then tothe convective envelope.Convects to stellar surface, blown off star by strong winds.
Karakas, et al.
This 3rd dredge-upBrings 12C to stellar surface, contributes strongly to galactic nucleosynthesis
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Results-NACRE Rates (Falk Herwig and SMA)
We need to know rates better: Changes to error limits make nearly factor of 2 changes in C/O.
ResultsLow 14N(p,γ)High 3
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From seven consistent exp’tsHard to improve.
GOOD ENOUGH
Improving the Triple Alpha Reaction Rate
γγ
rad r3 ),exp( 3
kT
Qrad
where
γγ
rad and Q3 = Er –3M2.
% RATE uncertainty 2.7 9.2 6.4 1.2 (T8 = 2)
Reminder:
Q known to ± 0.2 KeV, from:
Er to ± 0.2 KeV (Nolen &
Austin (76)--incorrect in
tabulations); M to ±
0.06 eV)
GOOD ENOUGH
γ
Emphasis on and
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(e,e’)
0+ 7.65 MeV
0+ g.s.
Measuring
Using electron scattering
related to cross section for exciting 7.6 MeV state at small momentum transfer q. Use ratio of elastic and 7.6 MeV form factors, extrapolate to q=0.
Two measurementsCrannell,et al., Strehl:
=60.5 ± 3.9 eV
NEW: H. CrannellBased on analysis of all (?) extant data (unpublished):
= 52.0 ± 1.4 eV
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Measuring A hard measurement: Branch is small ~6 x 10-6
Nevertheless, the three measurements, two from BNL, one from MSU are consistent: 6.74 ± 0.62 (9.2%) New measurement: WMU,MSU
WMU Tandem, (p,p’) at 135o, 10.56 MeV (strong resonance for 7.65 state)
pairs/#-7.65
protons)Aim: ± 5% accuracy
PMPM
PM Si, 1 of 4
PMPM
PM
PMPM
PM Si, 1 of 4Side View
Top ViewPM
PM
PMPM
Plastic Scint
Liner
12C Target
BeamPM
PM
PMPM
Plastic Scint
Liner
Beam
Viola Celebration October 29,05
It was fun trying to figure out where the light elements come from and what they can tell us about the cosmos.
But did you come to East Lansing for the physics or for the Free Style Shop?
It’s Been Good to Meet Again