tariq al-abdullah hashemite university, jordan cairo 2009
DESCRIPTION
Problems and Issues in Nuclear Astrophysics. Tariq Al-Abdullah Hashemite University, Jordan Cairo 2009. SUMMARY. Why nuclear physics in astrophysics? Why indirect measurements of cross sections in nuclear astrophysics? The indirect teqhniques and their applicatoins! - PowerPoint PPT PresentationTRANSCRIPT
Tariq Al-Abdullah
Hashemite University, Jordan
Cairo 2009
Problems and Issues in Nuclear Astrophysics
Why nuclear physics in astrophysics?
Why indirect measurements of cross sections
in nuclear astrophysics?
The indirect teqhniques and their applicatoins!
Perspectives of the method: RIB and (part,g) reaction
Nuclear Physics Research and Education!
SUMMARY
Nucleosynthesis
1945: Gamow’s Hypothesis
“ all of today elements were made during the early BIG BANG of the Universe “
Questions:
When did it start ??
What elements are produced and can we understand the
isotopic composition ??
Do parameters of the Early Universe have an influence ??
wrong!
Big Bang Nucleosynthesis
Wrong for 3 simple reasons
oBinding energy of deuteron (2.22 MeV) is too small !!
oBinding energy of 4He is too large (28.3 MeV) !!
oThere are no stable isotopes with A=5 and A=8 !!
Deuterons are being dissociated until the Universe Has cooled down to 80 keV !!!
for further fusion the train has Long left the station !!
Universe composition:~76% H and ~23% 4He
Stellar life cycle
energy productionenergy production stability against collapsestability against collapse synthesis of “metalssynthesis of “metals””
thermonuclear thermonuclear reactionsreactions
BIRTHBIRTHgravitational contractiongravitational contraction
explosion DEATH
mixing of mixing of interstellinterstell
ar gasar gas
Interstellar gas Stars
abundance distribution
The goals of experimental Nuclear Astrophysics are:- study of the origin of the elements or
nucleosynthesis- study of the energy generation processes in stars.
Courtesy: M. Arnould
Experimental nuclear astrophysicsExperimental nuclear astrophysics
M. Smith & E. Rehm
Average Reaction rate per particle pair:
In stellar plasma the velocity of particles varies over a wide range
Assume (v) is the velocity distribution
Thermonuclear reactions in stars: general features
Reaction rate: r = N1 N2 v (v) (# reactions Volume-1 Time-
1)
R v σ(v) (v) dv
0
Thermonuclear reactions in stars: general features
<v> is a KEY quantity
Total reaction rate R12 = (1+12)-1 N1N2 <v>12
Energy production rate 12 = R12 Q12
<v> to be determined from experiments / theoretical considerations
as star evolves, T changes evaluate <v> for each temperature
energy production as star evolves - change in abundance of nuclei X
NEED ANAYLITICAL EXPRESSION FOR !
Mean lifetime of nuclei X against destruction by nuclei a
σvN
1(X)
a
a
charged particles Coulomb barrier
tunneleffect
Ekin ~ kT (keV) ECoul ~ Z1Z2 (MeV)
nuclear well
Coulomb potential
V
rr0
T ~ 15x106 K (e.g. our Sun) kT ~ 1
keV
T ~ 1010 K (Big Bang) kT ~ 1 MeV
energy available from thermal motion
exp(-2 = GAMOW factor
reactions occur by TUNNEL
EFFECT
tunneling probability P exp(-
2)
during quiescent burnings: kT << ECoul
Thermonuclear reactions in stars: charged particles
in numerical units: 2 = 31.29 Z1Z2(/E)½ in amu and Ecm in keV)
(E) = (1/E) exp(-2) S(E)
ASTROPHYSICAL FACTOR
Penetration
probability
Thermonuclear reactions in stars:Astrophysical factor
For non-resonant reactions, the cross section behaviour is dominated by the Gamow factor
Cross section can be parameterized as
Sharp drop with
energy!!!!
De Broglie wavelengh
t
S(E) is a sort of linearization of the cross section where all non-nuclear effects have been taken
out
exp 2E
Maxwell-Boltzmann velocity distribution
Quiescent stellar burning scenarios:non-relativistic, non-degenerate gas in thermodynamic equilibrium at temperature T
= reduced massv = relative velocity
Pro
bab
ilit
y (
E)
EnergykT
(E) E
(E) exp(-E/kT)
Thermonuclear reactions in stars: general features
kTE
exp2kTμv
expΦ(v)2
dE E kTE
exp σ(E)(kT)
1πμ8
σv0
3/2
1/2
1212
Reaction rate:
1 2
3 2 1 20
8 1( )exp
E bS E dE
KT EKT
Thermonuclear reactions in stars: Gamow window
E0
Gives the energy dependence
MAXIMUM reaction rate:
Gamow peak
tunnelling throughCoulomb barrier exp(- )
Maxwell-Boltzmanndistribution exp(-E/kT)
rela
tive p
rob
ab
ilit
y
energykT E0
/GE E
( )0
df E
dE
varies smoothly with energy
only small energy range contributes
to reaction rate
OK to set S(E) ~ S(E0) =
const.
221 eZZ
2b
E0 < E0
T ~ 106 – 108 K E0 ~ 100 keV << Ecoul tunnel effect
10-20 barn < < 10-9 barn
average interaction time ~ <v>-1 ~ 109 y
unstable species DO NOT play a significant role
Scenario of quiescent burning stages of stellar evolution
FEATURES
PROBLEMS
10-20 b < < 10-9 b poor signal-to-noise ratio major experimental challenge extrapolation procedure required
REQUIREMENTS
poor signal-to-noise ratio long measurements ultra pure targets high beam intensities high detection efficiency
Experimental approach: generalities
measure measure (E)(E) over a wide range of energies, over a wide range of energies,
EXTREXTRAPOLATEAPOLATE down to Gamow energy region down to Gamow energy region
around Earound E00
Experimental procedureExperimental procedure
LOGSCALE
E0EEcoulcoul
Coulomb barrier
(E)(E)
non-resonant
resonance
direct measurements
extrapolation needed !
many orders of magnitude
C.M. Energy
Experimental approach: extrapolation
DANGER IN EXTRAPOLATION: large uncertainties!
Even using the S(E)-factor, extrapolation is not a piece of cake!!!
Experimental approach: extrapolation II
Er
non resonant process
interaction energy E
direct measurement
0
S(E)
(LINEARSCALE)
-Er
sub-threshold resonance
low-energy tail of broad resonance
Extr
apol
atio
n
EEXPERIMENTAL SOLUTIONXPERIMENTAL SOLUTION
IMPROVEMENTS TO INCREASE THE NUMBER OF DETECTED PARTICLES
New accelerator with high beam intensity
Gas target
4 detectors
IMPROVEMENTS TO REDUCE THE BACKGROUND
Use of laboratory with natural shield reduce (cosmic) background
example: LUNA facility in Italy
Experimental approach: avoiding extrapolation
IDEA: To avoid extrapolation it is necessary to measure
Cros sections in the Gamow region
The ELECTRON SCREENING
A NEW PROBLEM ARISE
BUT…
at astrophysical energies
Experimental approach: new problem
WHY IS THIS A PROBLEM?
It is a problem because electron screening in STARS
and in LABORATORIES is not the same!
To avoid extrapolation experimental techniques were improved
to perform measurement at very low energiesAfter improving measurements at very low energies,
electron screening effects
were discovered
To extract the To extract the
bare astrophysical Sbare astrophysical Sbb(E)(E) –factor–factor
from from direct (shielded) measurementsdirect (shielded) measurements
extrapolation were performed at higher energextrapolation were performed at higher energiesies
EXTRAPOLATION IS BACK AGAIN
Is there any way out ?
INDIRECT METHODS
Asymptotic Normalisation Coefficients (ANC) method (radiative capture reactions).
Trojan Horse Method (thermonuclear reactions induced by light particles)
Coulomb Dissociation method (radiative capture reactions).
In order to solve some of the problem cited above (low cross sections, electron screening) some indirect approaches were proposed such as:
Direct Capture Reactions for charges particles:
The binding energy of the captured particle is low. The capture occurs through the tail of the overlap function. The Amplitude of the tail is given by the ANCs.
For a Transfer reaction (X+A→Y+B):• The DWBA amplitude:
• The Asymptotic behavior of the radial overlap function:
• The Asymptotic normalization of the bound-state wave function:
• For r > RN, the radial dependences are the same
0 2 4 6 8 10 12 140.0
0.2
0.4
0.6
0.8
1.0
rh ,
r (
fm-1
/2)
r (fm)
12C+n-->13C
E0
p
A
Y
B (A+p)
X (Y+P)( ) ( )
, , , ,( ) ( ) ( )B Xf A p A p Y p Y p iM E I r V I r
, 1 2( ), ,
2( )
NB
r Rl BB sp B
A p A p
W rI r C
r
, 1 2, , ,
2( )
NB
B B B B B
r Rl B
n l j l j
W rr b
r
, ,( ) ( )BA p A pI r S r 2 2C = Sb
Asymptotic Normalization Coefficients (ANCS)
Peripheral Transfer Reaction (X+A→Y+B):
The reaction cross section:
In terms of the ANCs:
Procedure to extract the ANCs:
B B X X B B X X
B B X X
DWBAAal j yal j l j l j
l j l j
dS S
d
2 2
2 2B B X X
B B X X
DWBAB XAal j Yal j
Aal j Yal j
dC C
d b b
A
Y
B(A+a)
X (Y+a)
a
C2(B)
C2(X)
Elastic Scattering
ExperimentalAngular Distribution
Double FoldingWood-Saxon
OMPs
Transfer Reaction
DWBAcalculation
Comparison
Spectroscopic factors
ExperimentalAngular Distribution
ANCs
Elastic Scattering
ExperimentalAngular Distribution
Double FoldingWood-Saxon
OMPs
Transfer Reaction
DWBAcalculation
Comparison
Spectroscopic factors
ExperimentalAngular Distribution
ANCs
Extracting the ANCS
Ne-Na cycle
12C 13C
13N 15N
15O
14N
17O
17F
16O
19F18F
18O14O
19Ne18Ne
13O
11C
12N
8B
7Be
9C 10C
10B
11N
11B9B
8Be
20Ne 22Ne21Ne
9Be
23Na
17Ne
16F15F
22Na21Na20Na
24Al23Al 25Al
24Mg23Mg22Mg21Mg20Mg
19Na
(p,γ)(p,α)(β+ ν)
= studied at TAMU
CNO, HCNO
25Si24Si 26Si
June 2008
Comp with direct meas: 16O(3He,d)17F vs. 16O(p,)17F
Gagliardi e.a. PRC 1999 vs. Morlock e.a. PRL 1997
7Be(p,)8B (solar neutrinos probl.):
p-transfer: S17(0)=18.2±1.7 eVbBreakup: S17(0)=18.7±1.9 eVbDirect meas: S17(0)=20.8±1.4
eVb
Experiments using the ANCS
ANC’s measured by stable beams
• 9Be + p 10B [9Be(3He,d)10B;9Be(10B,9Be)10B]• 7Li + n 8Li [12C(7Li,8Li)13C]• 13C + p 14N [13C(3He,d)14N;13C(14N,13C)14N]• 14N + p 15O [14N(3He,d)15O]• 16O + p 17F [16O(3He,d)17F]• 20Ne + p 21Na [20Ne(3He,d)21Na]
beams 10 MeV/u
ANC’s measured by radioactive (rare isotope) beams
• 7Be + p 8B [10B(7Be,8B)9Be] [14N(7Be,8B)13C]
• 11C + p 12N [14N(11C,12N)13C] • 13N + p 14O [14N(13N,14O)13C] • 17F + p 18Ne [14N(17F,18Ne)13C]
beams 10 - 12 MeV/u
ANC’s measured by stable beams (mirror symmetry)
7Be + p 8B [13C(7Li,8Li)12C]
22Mg + p 23Al [13C(22Ne,23Ne)12C]**
17F + p 18Ne [13C(17O,18O)12C]**
** T. Al-Abdullah, PhD Thesis
Rare Isotope Accelerators
Why RIA ??
How are the heavy elements created?
How do nuclear properties influence the stars?
What is the structure of atomic nuclei?
How do complex systems get properties from their
constituents?
How can complex many-body systems display
regularities?
Which new symmetries characterize exotic nuclei?
What are the fundamental symmetries of nature?
Radioactive Nuclei in Supernovae
International Prespectives
The international effort to study the science of rare
isotopes is highly complementary.
RIA will be the first and only facility that will have the
capability to meet the challenge of understanding the origin
of the elements.
RIA will attract the brightest minds, new generations of
the highest-caliber students and the future nuclear
scientists.
RIA will provide many new isotopes that can be used to
specific diagnostic and therapeutic applications. RIA: Connecting Nuclei with the Universe
Research and Education
Well organized Institute
People Quality Instruments Funding Support
Thank you