ydrogen Burning in Stars-II ydrogen in induced reaction have lowest oulomb barrier highest reaction rate Reaction chain with lowest Z elements are the -chains -chains limited by weak interaction based -reaction Take over of hydrogen burning at higher Z elements cycles governed by electromagnetic and strong interaction based reaction cross sections. burning stars are the stars on the uer art of the Main Sequence in the R Diagram!
ydrogen Burning in Massive Stars
The main cycle e 0 8 6 6 8 0 -- --2 --3 --4
Reactions in the cycles -: 2 3 S 2 =3 0-3 MeV-barn 3 ν 3 3 4 4 5 S 4 =2 0-3 MeV-barn 5 ν 5 5 α 2 S 5α = 0 2 MeV-barn -2: 5 6 S 5 =5 0-2 MeV-barn 6 7 7 ν 7 7 α 4-3: 7 8 8 ν 8 8 α 5-4
etwork for cycle 5 5 5 5 5 4 4 5 5 5 3 3 4 4 4 3 3 3 3 3 2 2 3 3 3 5 5 2 2 2 α α d d d d d d
time [s] Reaction network of onversion of the initial to 4 e 2 6 to 4
etwork for higher order s [ ] [ ] 8 8 9 9 9 9 8 8 8 8 8 8 7 7 8 8 8 8 8 5 5 5 5 5 5 4 4 5 5 5 7 7 3 3 4 4 4 7 7 7 7 7 7 6 6 7 7 7 9 9 5 5 6 6 6 α α α α α α α d d d d d d d d d leakage -II mod. -I -III -IV
mass fraction X etwork simulations at low temerature conditions of 0 7 K time [s]
etwork simulation for ydrogen burning at 3 0 7 K mass fraction X time [s]
Resonance measurements Reaction rates in cycle reactions have considerable cross section contributions from low energy resonances. Resonance cross section is determined by Breit-Wigner function strong energy deendence of cross section!!! 2 2 tan 2 tan 2 2 0 2 0 max 0 0 0 2 0 2 2 2 M m M M m M d R R tot R ex in ε ω π ε ω π ε σ ω π σ = Γ Γ = = Γ Γ Γ = D if the energy deendence of ε Γ in/ex is negligible over wih Γ of resonance and if «Γ!!! if» Γ ield measurement gives resonance strength!
Resonant Reaction Rate σv =.540 3/ 2.605 T9 ω [ MeV ] µ T 9 e R [ MeV ] ω = 2π M 2 M ε m max n exact measurement of the resonance energy R and the thick-target yield max rovides the necessary information for calculating the resonant reaction rate σν!
Thick target ield urve ield /2 R δ beam resolution
Limitation of Thick Target Technique 9 Be 0 B; R =.07 MeV; Γ=4keV wih of yield curve reresents energy loss of articles in target rule for thick target yield alication: 5 Γ
Problems in cycle? 4 5 is the slowest reaction in the cycle Therefore 4 enrichment during burning! Tyical question: are there missing Resonances near the threshold? These could enhance the reaction rate by orders of magnitude and turn 4 5 into a fast rocess.
The low energy range of 4 5 data oints? Gamow Range
ew Resonance? Infinite thick target measurement TUL 200 o confirming evidence in U data 2002
4 5 0 6 0 5 0 4 Gamma yield at cm =200 kev Q = 36 I = 400 µ t = day 0 3 0 2 0 0 0 0-0 -2 background σ in Gran Sasso Lab 50 70 90 0 30 50 70 90 beam kev
Imact of seculated resonance! Reaction Rate [cm3/moles].0000.00-05.00-0.00-5 new resonance? res. acceted rate 0 0.05 0. 0.5 0.2 Temerature [GK]
The hot cycle mode X σν 3 4 3 3 X σν 7 8 e 7 7
ot cycle network [ ] 5 5 5 5 5 4 4 5 5 5 4 4 4 4 4 3 3 4 4 4 2 2 3 3 3 3 3 5 5 2 2 2 = α α d d d d d d slowest reactions become decays of 4 5
Imact on energy generation ε 26 MeV/00s =260 kev/s
Summary hydrogen burning ydrogen burning oerates mainly through the -chains for low mass stars the cycles for massive stars hydrogen induced reactions on higher Z nuclei are unlikely due to oulomb-barrier high T required ucleosynthesis consequences are of only minor relevance for galactic abundance distribution but creates the basis for the stellar evolution and the subsequent roduction of massive nuclei!