Transcript Slide 1

Physics LOI for NEDA
R. Wadsworth University of York , G. de Angelis INFN LNL
Istanbul 19 june 2009
Defining the Physics
• Nuclear Astrophysics
– Element abundances in the Inhomogeneous Bib Bang
Model (Weizmann, Soreq, GANIL, York collaboration)
– Isospin effects on the symmetry energy and stellar
collaps
• Nuclear Reactions
– Level densities of neutron rich nuclei (Naples,
Bordeaux, Debrecen, LNL, Florence collaboration)
– Fission dynamics of neutron-rich intermediate fissility
systems
• Nuclear Structure
– Probe of the T=0 correlations in N=Z nuclei: The
structure of 92Pd
– Coulomb Energy Differences in isobaric multiplets:
T=0 versus T=1 states
– Coulomb Energy Differences and Nuclear Shapes
– Low-lying collective modes in proton rich nuclei
Reaction Paths in Nuclear Astrophysics
rapid proton capture,
Nuclear Astrophysics :
Element abundances in the Inhomogeneous Bib Bang Model
(Weizmann, Soreq, GANIL, York collaboration)
Letter of Intent for the proposed “Neutron Wall” at SPIRAL-II
Measurement of the 8Li(a,n) 11B Reaction
Michael Hass
for the
Weizmann-Soreq-GANIL-York collaboration
We propose to study the 4He(8Li,n)11B reaction using 8Li beams at SPIRAL-II. The R&D
efforts to produce unsurpassed intense beams of 8Li at SPIRAL-II may result
in 8Li very well becoming one of the first radioactive beams to be used at
SPIRAL-II. This fact, together with the unique performance of the proposed
neutron wall and of other ancillary charge-particle detectors will provide an
ideal experimental setup for such studies. The data thus obtained should clarify
the poorly known cross section for this reaction, which is important for several scenarios
in the field of explosive nucleo-synthesis.
Michael Hass - 8Li(a,n)11B
Fig. 1 Experimental data
available in the literature
Fig. 2 States in 12B that are in the region of
interest for cosmological (and stellar)
environment(s) at temperatures of ~ 1 GK
Michael Hass - 8Li(a,n)11B
11B
Expected Yields for a BeO target:
SARAF (40 MeV, 2 mA): 8∙1012 [6He/sec]
SPIRAL2 (40 MeV, 5 mA): 2∙1013 [6He/sec]
Expected Yields for a BN target:
SARAF (40 MeV, 2 mA): 2∙1012 [8Li/sec]
SPIRAL2 (40 MeV, 5 mA): 5∙1012 [8Li/sec]
Under current R&D:
• Diffusion and effusion in the material
• Ionization and extraction
• Choice of ion source
Michael Hass - 8Li(a,n)11B
Neutron (energy) + charge particle detections
Issues for consideration
• 8Li@SPIRALII
The present scheme
uses the 11B(n,a)8Li reaction with
secondary neutrons from the initial
5 mA, 40 MeV d beam with a porous
BN target.
Post-acceleration. Energy degrader.
• The neutron wall
• Charge particle (11B) detection
Fig. 3 The proposed experimental setup.
Michael Hass - 8Li(a,n)11B
Isospin effects on the symmetry energy and stellar collaps
(Naples, Debrecen, LNL, Florence collaboration)
Why is it important to study the symmetry energy ?
•
•
•
•
Esym=bsym(T)(N-Z)2/A
As a part of the nuclear Equation Of State it may influence the
mechanism of Supernova explosion
General theoretical agreement on its temperature dependence
(LRT+QRPA vs. large scale SMMC)
Possible consequences of T dependence of Esym on core-collapse
Supernova events
Effects enhanced by the instrinsic isospin dependence of Esym
Fusion-evaporation reactions: Esym affects the particle B.E.
SYMMETRY ENERGY
Framework: Dynamical Shell
Model
Hartree-Fock
Coupling single particle states
to suface vibrations
Nucleon effective mass
mw(T) 0 < T < 3 MeV - 98Mo, 64Zn, 64Ni
-LRT – QRPA
Decrease of the effective mass  Increase of Esym
Esym(T)= bsym(T) x (N-Z)2/A
bsym(T)=bsym(0)+(h2ko2m/6mk)[mw(T)-1 – mw(0)-1]
mk mw
m 
m

mw(T)=m + [mw(0) – m]exp(-T/To)
Isospin effects on the symmetry energy
Study with RIB’s from SPIRAL2
105Zr
+ 4He  109Mo
109Mo
Ex=16 MeV
1n channel
The isospin effects are larger than those due to the change of level density parameter
a from A/8 to A/10. A strong sensitivity on isospin is also expected for the ER yields.
(Same observables and experimental setup)
Neutron energy and multiplicity information + Charged particle
information + gamma ray information
Nuclear Reaction Mechanisms:
Evaporative neutron emission as a probe for the level
density of hot neutron-rich compound nuclei (Naples,
Bordeaux, Debrecen, LNL, Florence collaboration)
Neutron energy and multiplicity information + Charged
particle information + gamma ray information
Why is it important to study the level
density ?
Level density is a basic ingredient for x-section calculations
Astrophysical processes
“Astrophysical Reaction Rates from
Statistical Model Calculations”,
ADNDT 75 (2000) 1-351
SHE’s production
 ER   capture  PCN  Psurv
Capture of two nuclei
in the attractive
potential pocket.
Probability of forming a
compact compound
nucleus (CN).

Survival probability
against fission.
Evaporative process:
Statistical Model
Isospin effects on the level density parameter a
Form A:
Form B:
20<A<110 ENSDF
Form C:
Form C provides the
best reproduction of
experimental level
densities
Strong reduction
of level density
for exotic nuclei
Isospin effects on the level density parameter a
Study with RIB’s from SPIRAL2
Standard
N-Z
Z-Zo
3
10
Observables
2
Counts
10
n
- (xn channels)
1
10
84Ge
+ 4He
- n en. spectra
0
10
0
1
2
3
4
5
6
- ER yields
En,cm(MeV)
Standard
N-Z
Z-Zo
3
10
2
Counts
10
n
1
10
134Sn
0
10
0
1
2
+ 4He
3
4
5
6
En,cm (MeV)
A strong sensitivity on isospin is also expected for the evaporation residue yields
Experimental setup: NEDA coupled to the gamma ray spectrometers EXOGAM
or AGATA and/or the spectrometer VAMOS. (NEDA: TOF Measurements 3%
resolution, energy threshold  1 MeV). Lcp could be also measured by Diamant.
Fission dynamics of neutron-rich intermediate
fissility systems (under study)
Open questions in fission dynamics: Fission delay, nature of dissipation (one or
two body) and its dependence on temperature and nuclear deformation
Systems of intermediate fissility (A  150): possibility to measure observables in
both fission and evaporation residue channels
Measurements on nuclei with the same Z and different isospin allow to
Study of the role of isospin in fission dynamics:
Preliminary results from a dynamical model based on three dimensional Langevin
equations
Fission Barrier
Bf (L=50 )
(MeV)
n- Prescission
multiplicity
Mn
Fission time
<Tfiss>
(10-21 s)
124Ce
16.3
0.046
61
144Ce
29.7
2.1
103
230 MeV 32S + 92Mo
Lcrit = 74 
750 MeV 118Pd + 26Mg Lcrit = 81 
Ex122 MeV
Experimental setup: NEDA coupled to fission fragment detectors
Nuclear Structure : N=Z nuclei
Probe of the T=0 correlations in N=Z nuclei:
The structure of 92Pd
Coulomb Energy Differences in isobaric multiplets:
T=0 versus T=1 states
Coulomb Energy Differences and Nuclear Shapes
Low-lying collective modes in proton rich nuclei
Probe of the T=0 correlations in N=Z nuclei:
The structure of 92Pd
(LNL, Stockholm, York collaboration)
Neutron multiplicity information + charged particle
+ gamma ray information
56Ni
(108pps) + 40Ca
92Pd
(1 mb), 94Ag (1 mb)
Coulomb Energy differences in isobaric
multiplets: T=0 versus T=1 states
(Sofia, Padova, York, Ganil, LNL collaboration)
Neutron multiplicity ( and energy) information +
Charged particle + gamma ray informations
Example: Electromagnetic Transition
Probabilities
If Isospin Symmetry is valid:
E1 (T=0) transitions in N=Z nuclei are forbidden
E1 transition in mirror pairs have identical strength
(higher sensitivity due to interference)
Crucial Probe of the isospin symmetry and of its validity with
increasing A and Z
Electromagnetic Transition Probabilities
Observation of a forbidden E1 transition in 64Ge
64
64Ge
32
forbidden E1?
32
EUROBALL IV + Plunger
experiment
Dobaczewski and Hamamoto
Phys. Lett. B345 181 (1995)
E. Farnea et al.
Phys. Lett. 551B, 56 (2003)
32S+40Ca
125 MeV
Isospin Mixing in Mirror Pairs
In the validity of
isospin symmetry
1) Charge invariance of the nuclear interaction
2) Long-wavelength approximation
B(E1) strengths are identical in T=1/2 mirror pairs
Isospin mixing via the IVGMR
provides an induced isoscalar
component
In mirror T=0 transitions
• Isovector terms have opposite sign
• Isoscalar terms have equal sign
B(E1) = BIS(E1) – BIV(E1)
B(E1) = BIS(E1) + BIV(E1)
J. Ekman et al. PRL 92, 132502 (2004)
Electronic timing measurements
67Se
67As
N=Z nuclei: Reactions with RIBS
•
34Ar
+ 40Ca (105-120 MeV)
– 69Br + ap 1 mb
– 71Kr + 2pn 5 mb
– 68Br + apn 0.2 mb
– 72Rb + pn 0.1 mb
– How do we study the proton unbound cases e.g. 68,69Br?
•
58Cu
–
•
81Nb
56Ni
–
+ 28Si (~200 MeV)
+ an
0.1 mb
+ 28Si (~200MeV)
79Zr
+ an
0.2 mb
Coulomb Energy Differences and Nuclear
Shapes
(York, LNL, Padova, Sofia collaboration)
Neutron multiplicity information, charged
particle and gamma information
N=Z nuclei: Reactions with RIBS
•
34Ar, 30S
+ 40Ca (105-120 MeV)
– 69Br, 65As + ap 1 mb
– 71Kr, 67Se + 2pn 5 mb
– 68Br, 64As + apn 0.2 mb A=64, 68 T=1 triplet
– 72Rb, 68Br + pn 0.1 mb
– How do we study the proton unbound cases e.g. 68,69Br?
•
58Cu
–
•
81Nb
56Ni
–
+ 28Si (~200 MeV)
+ an
0.1 mb
+ 28Si (~200MeV)
79Zr
+ an
0.2 mb
Nuclear Structure :
Low-lying collective modes in proton rich nuclei
Valencia, INFN LNL , Paris, INFN MI collaboration.
Neutron multiplicity (and energy), charged particle and
High energy gamma information
34Ar
34Ar
+ 16O
108 pps
44Cr
+ a2n
Dipole Excitations towards the Proton Drip-Line
CENTROID
ENERGY OF THE
LOW-LYING
STRENGTH
LOW-LYING
TRANSITION
STRENGTH
B(E1)
Paar, Vretenar, Ring, Phys. Rev. Lett. 94, 182501 (2005)
PROTON PYGMY
DIPOLE
RESONANCE
Dipole Excitations towards the Proton Drip-Line
CENTROID
ENERGY OF THE
LOW-LYING
STRENGTH
24Mg(p,p2n) 22Mg
22Mg
+ 16O
32Ar
LOW-LYING
TRANSITION
STRENGTH
B(E1)
Paar, Vretenar, Ring, Phys. Rev. Lett. 94, 182501 (2005)
PROTON PYGMY
DIPOLE
RESONANCE
22Mg
108 pps
+ a2n
Thanks for attention
• Present LOIs still under development
• Please join LOIs or present new ones
• Upgrading of the physics case is on the
way
• Definition of the “day one” experiments