Physics LOI for NEDA

Istanbul 19 june 2009

R. Wadsworth University of York , G. de Angelis INFN LNL

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

rapid proton capture,

Reaction Paths in Nuclear Astrophysics

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(,n) 11B ReactionMichael Hass

for theWeizmann-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(,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(,n)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]Michael Hass - 8Li(,n)11B

11B

Under current R&D:

• Diffusion and effusion in the material• Ionization and extraction• Choice of ion source

Fig. 3 The proposed experimental setup.

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

Michael Hass - 8Li(,n)11B

Neutron (energy) + charge particle detections

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.

(Naples, Debrecen, LNL, Florence collaboration)

Isospin effects on the symmetry energy and stellar collaps

SYMMETRY ENERGY

m(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)[m(T)-1 – m(0)-1]

m(T)=m + [m(0) – m]exp(-T/To)

Framework: Dynamical ShellModel

Hartree-Fock Coupling single particle statesto suface vibrations

Nucleon effective mass

m

mmm k

Isospin effects on the symmetry energyStudy with RIB’s from SPIRAL2

The isospin effects are larger than those due to the change of level density parametera from A/8 to A/10. A strong sensitivity on isospin is also expected for the ER yields. (Same observables and experimental setup)

109Mo Ex=16 MeV1n channel

105Zr + 4He 109Mo

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

Capture of two nuclei in the attractive potential pocket.

ER capture PCN Psurv

Survival probability against fission.

Probability of forming a compact compound nucleus (CN).

Evaporative process: Statistical Model

Isospin effects on the level density parameter a

20<A<110 ENSDF

Form A:

Form B:

Form C:

Form C provides the best reproduction ofexperimental leveldensities

Strong reduction

of level density

for exotic nuclei

0 1 2 3 4 5 6

100

101

102

103

Co

un

ts

En,cm(MeV)

Standard N-Z Z-Zo

0 1 2 3 4 5 6

100

101

102

103

Co

un

ts

En,cm (MeV)

Standard N-Z Z-Zo

Isospin effects on the level density parameter aStudy with RIB’s from SPIRAL2

A strong sensitivity on isospin is also expected for the evaporation residue yields

Experimental setup: NEDA coupled to the gamma ray spectrometers EXOGAMor AGATA and/or the spectrometer VAMOS. (NEDA: TOF Measurements 3% resolution, energy threshold 1 MeV). Lcp could be also measured by Diamant.

84Ge + 4He

134Sn + 4He

n

n

Observables

- xn channels)

- n en. spectra

- ER yields

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

Fission BarrierBf (L=50 )

(MeV)

n- Prescissionmultiplicity

Mn

Fission time <Tfiss>

(10-21 s)

124Ce 16.3 0.046 61

144Ce 29.7 2.1 103

Measurements on nuclei with the same Z and different isospin allow to Study of the role of isospin in fission dynamics:

230 MeV 32S + 92Mo Lcrit = 74 750 MeV 118Pd + 26Mg Lcrit = 81 Ex122 MeV

Preliminary results from a dynamical model based on three dimensional Langevin equations

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

Observation of a forbidden E1 transition in 64Ge

64 32 32

64Ge

EUROBALL IV + Plunger experiment

E. Farnea et al. Phys. Lett. 551B, 56 (2003)

forbidden E1?

32S+40Ca 125 MeV

Electromagnetic Transition Probabilities

Dobaczewski and HamamotoPhys. Lett. B345 181 (1995)

Dobaczewski and HamamotoPhys. Lett. B345 181 (1995)

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)

J. Ekman et al. PRL 92, 132502 (2004)

B(E1) strengths are identical in T=1/2 mirror pairs

B(E1) = BIS(E1) + BIV(E1)

Isospin Mixing in Mirror Pairs

In the validity of isospin symmetry

1) Charge invariance of the nuclear interaction

2) Long-wavelength approximation

67Se 67As

Electronic timing measurements

N=Z nuclei: Reactions with RIBS

• 34Ar + 40Ca (105-120 MeV)– 69Br + p 1 mb – 71Kr + 2pn 5 mb– 68Br + pn 0.2 mb– 72Rb + pn 0.1 mb– How do we study the proton unbound cases e.g. 68,69Br?

• 58Cu + 28Si (~200 MeV)– 81Nb + n 0.1 mb

• 56Ni + 28Si (~200MeV) – 79Zr + n 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 + p 1 mb – 71Kr, 67Se + 2pn 5 mb– 68Br, 64As + pn 0.2 mb– 72Rb, 68Br + pn 0.1 mb– How do we study the proton unbound cases e.g. 68,69Br?

• 58Cu + 28Si (~200 MeV)– 81Nb + n 0.1 mb

• 56Ni + 28Si (~200MeV) – 79Zr + n 0.2 mb

A=64, 68 T=1 triplet

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 + 16O 44Cr + 2n

34Ar 108 pps

Dipole Excitations towards the Proton Drip-Line

CENTROID ENERGY OF THE LOW-LYING STRENGTH

CENTROID ENERGY OF THE LOW-LYING STRENGTH

LOW-LYING TRANSITION STRENGTH B(E1)

LOW-LYING TRANSITION STRENGTH B(E1)

PROTON PYGMY DIPOLE RESONANCE

PROTON PYGMY DIPOLE RESONANCE

Paar, Vretenar, Ring, Phys. Rev. Lett. 94, 182501 (2005)

Dipole Excitations towards the Proton Drip-Line

CENTROID ENERGY OF THE LOW-LYING STRENGTH

CENTROID ENERGY OF THE LOW-LYING STRENGTH

LOW-LYING TRANSITION STRENGTH B(E1)

LOW-LYING TRANSITION STRENGTH B(E1)

PROTON PYGMY DIPOLE RESONANCE

PROTON PYGMY DIPOLE RESONANCE

Paar, Vretenar, Ring, Phys. Rev. Lett. 94, 182501 (2005)

24Mg(p,p2n) 22Mg

22Mg + 16O 32Ar + 2n 22Mg 108 pps

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