ESF Workshop on The future of stable beams in Nuclear Astrophysics, Athens, Dec. 14-15, 2007 Stable ion beams for nuclear astrophysics: Where do we stand

ESF Workshop on The future of stable beams in Nuclear Astrophysics, Athens, Dec. 14-15, 2007

Stable ion beams for nuclear astrophysics: Where do we stand ?

S. V. HarissopulosTandem Accelerator Laboratory, Institute of Nuclear Physics, NCSR “Demokritos”, Athens, GR


Nuclear Astrophysics …

studies aiming at understanding HOW

nuclear processes influence

astrophysical phenomena.


Astrophysical environments Nuclear processes

Novae, supernovae,X-ray bursts

AGB stars,supernovae II,Neutrons stars

Red giant stars, stars of the

Asymptotic branch

Big Bang(primordial nucleosynthesis)

Hydrogen burning proton-proton chain, CNO cycle, Ne-Na cycle, Mg-Al cycle

Explosive burningHot CNO cycleRapid proton capture (rp process)

Nucleosynthesis beyond ironSlow neutron captures (s-process)Rapid neutron captures (r-process) photodisintegrations and proton captures (p-

process)

Helium burning3a-process, 12C(a,γ)16OOther (a,γ) and (a,n) reactions

Reactions between the lightest elementsp, d, He, Be, Li

Advance burning stagesReactions of C, O, N, Ne, Si…

Super giant stars,Wolf-Rayet stars andPre-supernovae

Main sequence (e.g. Sun)

Cou

rtes

y: C

. An

gulo

(H

abil

itat

ion

thes

is, 2

006)


Major “stellar beams”:Major “stellar beams”: p, n, α, d, 3He, C, O ..

also γ !Targets Targets :: any nucleus (stable or unstable)

Energies :Energies : depending on the temperature of the relevant stellar environment !

(from ≈106 K up to ≈5x109 K !!!)=> cm-energies vary from 5 keV to 15

MeV

Cross between 0.1 μb and 100 mb, BUTSections :Sections : sometimes very very low … (≈ 1 fb !!!)

Typical Typical between 1 week and 1 month, beam beam however there are reactions requiring times :times : even years to be studied !!! OFTEN: DEMAND FOR VERY ACCURATE DATA (below 5%

error !!!)


Gamow peaks and windows : the astrophysically relevant energies

charged-particle induced reactions

neutron-induced reactions

3/2

0 2/bkTE

2

224

22 2

pt

G

ZZeEb

kTEkTE

E /3exp3

160

0

reactionbarrie

r(MeV)

E0

(keV)

T (K)

p + p (sun)

0.55 5.91.5×1

07

+ 12C (red giants)

300 561.5×1

08

12C + 12C (massive

stars)10.44 1500

≈ 1×109

p + 74Se (p

process)7.9 2800

≈ 3×109

Eo ≈ kT ∆En = 20 ÷ 500 keV

photon-induced

reactions

(γ,n)

(γ,α)


S factors and reaction rates: the most wanted data …

E1

nr(E) = exp(-2) S(E)

S factornon-nuclear term (s-waves only)

<v> =

0

S(E) exp dE 3/2

1/2

kT1

πμ8

12

1/2

EE

kTE G

reaction rate : reactions/sec/cm3

E0


Some typical uncertainties due to extrapolations

E0

200 %

Large uncertainties exist for many other key reactions, where the low energy limit was determined so far by beam-induced background.

CNO cycle reactions (T=2 × 107 K)

C. Angulo (Hab. thesis, 2006)

A. Aprahamian et al., Prog. Part. Nucl. Phys. 54, 535 (2005)

Uncertainties due to:

• Cosmic background

• Beam-induced bgd.

• Obsolete “tools”

Underground labs

Properly equipped high-current stable-beam labs

Inverse kinematics

Bochum data, T. Spillane et al, PRL 98, 122501 (2007)


LUNA : descending deep down to Gamow regions !

Cou

rtes

y: C

. An

gulo

(H

abil

itat

ion

thes

is, 2

006)

Sun’s center T=1.5 × 107 K

Big Bang T=0.5 × 109

K


Nucleosynthesis along the table of isotopes

39Y

28Ni

20Ca

8O

Fe

pp chain

CNO cycle

NeNa cycle

Si burning

s process r process

powered by neutrons (n,) / -

rp

proc

ess

powered by protons (p,) / +

100 yr 108 n/cm3 T=(0.1-0.4)×109 K

1 sec 1020 n/cm3 T =(1.8-3.3)×109 K

s process: M<M๏ (AGB stars, red giants...)

explosive nucleosynthesis

MgAl cycle

Novae, X-ray bursters…

up to Sn

>104 g/cm3 T(1-3)×109 K

r process: ? (supernovae, neutron stars)


Pathways for heavy-element nucleosynthesis

-

+


p-process reaction network

“seed “ abundances

s process

p-nuclei abundances

p process

reaction network

more than 20000 (,n), (,p), (,), n-, p-, -captures, -

decays, e-captures HAUSER-FESHBACH THEORY

Optical Model Potentials - Nuclear Level Densities γ-ray strength functions

(32≤Z≤83 , 36≤N≤131)

NEED FOR GLOBAL MODELS OF OMP, NLD, …


r:= <>max. / <>min.

M. Arnould and S. Goriely, Phys. Rep. 384, 1

(2003)

Impact of nuclear physics uncertainties on p-nuclei abundances

n captures

p captures

α captures

A≈100

A≈180

obtained with 14 different sets of nuclear ingredients (OMP, NLD, …) in HF calculations.

P. Demetriou et. al, Nucl. Phys. A 707, 253

(2002)


S factors and reaction rates: the most wanted data …

We also need to study

β decay properties (GT strengths, half-lives)

fission (of key importance, especially for the r process)

GDR and pygmy resonances

Nuclear masses and binding energies

Screening potentials

………..

Not only reaction rates are vital for nuclear astrophysics !


Some views …

• RIB facilities can certainly provide the tools for interesting nuclear astrophysics studies (main topic : r process). For many astrophysical questions, RIBs have to comparable to stable ones, at least in terms of intensity.

• The necessary beam-times are in most of the cases time consuming. As such, nuclear astrophysics experiments have less chances of success in PACs.

• Reaction studies in inverse kinematics can certainly provide a solution to the problem of the beam-induced background. This, however, requires certain exp. conditions, like intense beams, state-of-the art separators and target optimization and development.

• Some “old-fashioned” direct measurements like capture reactions, cannot completely be replaced by inverse kinematics studies due to beam current limitations !!!


Some views …

• Resonance physics put certain conditions to beam characteristics. A very good energy resolution is a must. Excitation function measurements require systems capable of undergoing energy changes within reasonable times. Therefore, cyclotrons and LINACs can sucessfully be used for certain applications only. VdG accelerators and especially TANDEMS are still the best tools for “standard-type” nuclear astrophysics.

• LUNA has decisively contributed to our understanding of stellar evolution. Underground labs have still a bright future.


Some views …

Indirect methodsoften model-dependent BUT very useful and

challenging

• Coulomb dissociation

• Trojan-Horse method

• Asymptotic Normalization Coefficients

need also stable beams !!!

Accelerators for nuclear astrophysics


Documents

ESF Workshop on The future of stable beams in Nuclear Astrophysics, Athens, Dec. 14-15, 2007 Stable ion beams for nuclear astrophysics: Where do we stand