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Viola Celebration October 29,05

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Finding a Logo

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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


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


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


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.

???


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.


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%?


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


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


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.


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


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?


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


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


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


(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


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


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

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