1. Pre-equilibrium emission: a tool to study dynamic effects and clustering structure in exotic nuclei
Letter of Intent
submitted to the
SPES scientific committee
T. Marchi
INFN - Laboratori Nazionali di Legnaro
for the Nucl-ex collaboration
SPES WORKSHOP May 2014

2. -clusters in light nuclei:
In 1968 Ikeda suggested that a-conjugate nuclei are observed as excited states close to decay threshold into clusters. The original idea was introduced by Hafstad and Teller in 1938.
The starting point is a quite reasonable observation:
Cluster structure appears close to the decay thresholds
The interest in nuclear clustering has been pushed strongly due to the study of neutron-rich and exotic weakly-bound nuclei
W. Von Oertzen et al., Phys. Rep. 432 (2006) 43
M. Freer et al., Rep. Progr. Phys. 70 (2007) 2149
Ebran et al., Nature 487 (2012) 341
Ikeda diagram
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

3. Extended Ikeda diagram
Extension of the clustering concepts
In light nuclei at the neutron drip-line, clustering might be the preferred structural mode
Nuclear states built on clusters bound by valence neutrons in their molecular
configurations might appear
Extended Ikeda diagram
Presently these structures are mainly described by theory, but must be experimentally verified at the new radioactive beam facilities
WHAT ABOUT HEAVY NUCLEI?
Pre-equilibrium processes
Coalescence vs Preformation
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

4. Light charged particles
From our experience on pre-equilibrium emission
E_beam h
Comp E*
16O + 116Sn
130 MeV
250 MeV
8 AMeV
15.8 AMeV
0.76
132Ce
100
206
16O+116Sn
192 MeV
12 AMeV
155
16O+65Cu
256 MeV
16 AMeV
0.60
81Rb
209
19F + 62Ni
304 MeV
16AMeV
0.53
240
19F + 63Cu
0.52
82Sr
243
Corsi et al., PLB 679 (2009) 197
Light charged particles
in coincidence with
Evaporation Residues
GARFIELD FW +
HECTOR + PPAC
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

5. “Our“ model: statistical + pre-equilibrium emission
Evaporative (statistical) emission:
Statistical decay of a Compound Nucleus is analyzed using modified PACE2 Monte Carlo code,
with level density parametrization [A.V. Ignatyuk et al. Sov. J.Nucl. Phys. 29 (1979) 450], decay
competition probability (n, p, a, g or fission), kinetic energy of emitted particles, binding energy,
transmission coefficients, angular momentum.
Insertion of non-equilibrium stage in the fusion reaction
All the process probabilities are calculated within the Hauser-Feshbach model
Pre-equilibrium emission:
The relaxation process in the nuclear system after fusion reaction is described by the Hybrid
exciton model based on Griffin model [J.J.Griffin Phys. Rev. Lett.17 (1966) 478].
The state of nuclear system produced in the collision is determined by the exciton number
n=p+ h, where p is the number of valence particles over the Fermi energy and h the number of
holes located under the Fermi energy, and by excitation energy E*.
The exciton number can be determined from the empirical trend [N.Cindro et al. Phys. Rev. Lett. 66 (1991) 868; E. Běták Fizika B12 (2003) 11]
Model Parameters:
n0 = p0 + h0
Number of excitons k
100 – 800 MeV3
g = 6a/π2
Level density parameter
O.V. Fotina et al. Int. Journ. Mod. Phys. E19 (2010) 1134
D.O. Eremenkoet al. Phys Atom. Nucl. 65 (2002) 18
O.V. Fotina et al. Phys. Atom. Nucl. 73 (2010) 1317c
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

6. Comparison with the model (130 MeV)
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

7. Comparison with the model (250 MeV)
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

8. “Our“ model: statistical + pre-equilibrium emission + CLUSTERING
Evaporative (statistical) emission:
Statistical decay of a Compound Nucleus is analyzed using modified PACE2 Monte Carlo code ,
with level density parametrization [A.V. Ignatyuk et al. Sov. J.Nucl. Phys. 29 (1979) 450], decay
competition probability (n, p, a, g or fission), kinetic energy of emitted particles, binding energy,
transmission coefficients, angular momentum.
Insertion of non-equilibrium stage in the fusion reaction
All the process probabilities are calculated within the Hauser-Feshbach model
Pre-equilibrium emission:
The relaxation process in the nuclear system after fusion reaction is described by the Hybrid
exciton model based on Griffin model [J.J.Griffin Phys. Rev. Lett.17 (1966) 478].
The state of nuclear system produced in the collision is determined by the exciton number
n=p+ h, where p is the number of valence particles over the Fermi energy and h the number of
holes located under the Fermi energy, and by excitation energy E*.
The exciton number can be determined from the empirical trend [N.Cindro et al. Phys. Rev. Lett. 66 (1991) 868; E. Běták Fizika B12 (2003) 11]
Clustering:
Pre-formation probability of cluster and exciton energies for cluster/light ion induced reactions [M. Blann et al. Phys Rev. C 62 (2000) ]
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

9. 2 possible starting configurations are considered in 16O nucleus
Adding a-clusters preformation probability to the decay model:
2 possible starting configurations are considered in 16O nucleus
116Sn
16O
100 - N(%)
nO=16p+0(1)h
16O
nC=12p+0(1)h
N(%) = ??
na=4p+0(1)h
e12C
e – clusters energy
x – random number ea
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

10. 250 MeV 16O + 116Sn a-particles spectra
Experimental results ( ) – with clustering:
--- No a-clustering in 16O
__ 10% a-clustering in 16O
__ 50% a-clustering in 16O
Exp
250 MeV 16O + 116Sn
a-particles spectra
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

11. Proposed reactions 114-116Sn + 30-28Si
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

12. Proposed reactions 132Sn + 27Al @ 11 AMeV
Sn + 11 AMeV
132Sn
2,0 107
116Sn
124Sn
130Sn
1,6 108
114Sn
Sn Si
SPES beam intensities are referred to
Ep=40 MeV -- Ip=200 mA on Ucx tgt
87Rb
1,6 108
96Rb
2,0 107
94Rb
2,7 108
85Rb
SPES
Day 1 Beams!
(I /40)
94-96Rb Si
85-87Rb Si
STABLE targets
28 Si
30 Si
27Al
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

13. Preliminary calculation 132Sn+27Al
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

14. GARFIELD (full) + RCo RIPEN Proper ER trigger ?
Experimental setup:
GARFIELD (full) + RCo
Slow (ch)
Fast (ch)
p, d,t
3He, a
256 MeV 16O + 65Cu
qgr =8.2°
RIPEN
Dq = 8.6° ÷ 17° at P = 25 mbar CF4
Ring Counter IC-Si
Proper ER trigger ?
T. Marchi – Letter of intent on pre-equilibrium emission – Legnaro, May 2014

15. Collaboration

16. Only one volume of gas for all sectors
Experimental setup: GARFILED + …
Microstrip Drift Chamber + CsI(Tl)
Only one volume of gas for all sectors
Here you can see a cross section of the two chambers together with the detail of each sector. The drift chambers in this dE-E configuration can identify ions from Z=1 to up to Z=28. The DE-E correlation are obtained through the utilization of CSI(Tl) residual energy signal toward the DE signal coming from gas microstrip detectors, that I will describe later. The CSI crystal s are 4 per sector and covers around 15 degrees in Theta and phi. In the forward chameber they are 96 while in the backward they are 84.
The DE signal is coming from gas microstrip detectors the details of which I will give you in my next slide. The particles produced in the studied reactions are emitted radially from the target, pass through the window of the drift chamber (made of few micro n of mylar) and then ionize the gas (normally we use CF4 at mbar) joining at the end (if theit energy iis large enough ) the Csi cristals. These last are geometrically positioned so that their front face are radially perpendicular with respect to the trajectory of the particles outcoming the target.
Charge resolution: from Z=1 to Z=28
Energy resolution CsI(Tl) crystal : 3.0% for 5.5 MeV . Identification threshold : MeV/u
Detection Threshold : few tens of keV
Angular resolution q=1°, f=7.5°
Double stage ΔE-E: Micro Strip Gas Counter (MSGC)+ CsI(Tl) telescopes
(in total for the 2 chambers)
Forward Chamber Backward Chamber
29°<q<83° °<q<151°
0°< f<70° °<f<360°
110°< f<360°
F. Gramegna et al., IEEE Nucl. Sci. Symp. Conf. Proc. 2, 1132 (2004)
A.Moroni et al. NIM A556 (2006) 516
M. Bruno et al., EPJ A 49 (2013) 128

17. Very small pre-equilibrium contribution in proton spectra
CM Spectra at different angles
Proton in CM
ECM
19F + 62Ni
16O + 65Cu
Alpha in CM
ECM
19F + 62Ni
16O + 65Cu
Larger pre-equilibrium contribution in 19F induced reaction a-spectra with respect to 16O reaction
Very small pre-equilibrium contribution in proton spectra

18. “Dynamic Dipole“: GARFIELD (digital) + Phoswich
16O + 116Sn Eb = 192 MeV (12 AMeV)
Let me give you some few details about GARFIELD: It is made by 2 drift chambers as you can see in the slide. We have a rail system which permits to move the two chambers accordingly to the specific necessity. The Target is positioned in between the two chambers (when the two are used or, in any case on the center of the back of one the two.
The two drift chambers are essentially made by two alluminum cylinders which are containers for the gas and for the gas detector system. The two drift chambers give the DE signal for the energy loss of impinging particles. Inside the chambers as I will show we have also a number of Cesium iodide crystals for the residual energy information.
The front chamber is made by 24 sectors covering from theta 29 to 83 and 4pi in phi. The backward chamber has instead only 21 sectors as one regione have been left free for the insertion of different The empty region corrwespond to 45 degrees in phi.
T.o.F. (a.u.)
S. Sambi, Master Thesis, LNL and Univ. Bologna
A. Giaz et al., submitted to PRC

19. Experimental results (192 MeV):

20. Experimental results (192 MeV):

21. The two systems have the same projectile velocity.
“ACLUST 2013”: GARFIELD + Rco
16O + 65Cu Eb = 256 MeV (16 MeV/u) 19F + 62Ni Eb = 304 MeV (16 MeV/u)
CN 81Rb* E*(16O) = 209 MeV
E*(19F) = 240 MeV
Comparing the light charged particles emitted in fusion reactions where an a-cluster projectile (16O) and projectile without a clusterization (19F) are used.
The two systems have the same projectile velocity.
From Cabrera systematics the pre-equilibrium emission is mainly dependent on the projectile velocity [J. Cabrera et al. Phys. Rev. C68 (2003) ]
Let me give you some few details about GARFIELD: It is made by 2 drift chambers as you can see in the slide. We have a rail system which permits to move the two chambers accordingly to the specific necessity. The Target is positioned in between the two chambers (when the two are used or, in any case on the center of the back of one the two.
The two drift chambers are essentially made by two alluminum cylinders which are containers for the gas and for the gas detector system. The two drift chambers give the DE signal for the energy loss of impinging particles. Inside the chambers as I will show we have also a number of Cesium iodide crystals for the residual energy information.
The front chamber is made by 24 sectors covering from theta 29 to 83 and 4pi in phi. The backward chamber has instead only 21 sectors as one regione have been left free for the insertion of different The empty region corrwespond to 45 degrees in phi.
50% a-clustering in 16O
Unified Code, O.V. Fotina, Moscow State University

22. Summary:
Preliminary results seem NOT to confirm the predicted difference between the two systems (16O+65Cu and 19F+62Ni) due to a-clustering effects in 16O induced reactions.
Using the same parameters the Hybrid Exciton Model describes resonably the a-particles but strongly overestimates the protons. Cluster preformation has to be considered to take into account the alpha – protons emission competition.
Elab (MeV)

23. Summary: Analysis is in progress….
Elab (MeV)
Analysis is in progress….
To extract energy spectra for all particles p, d, t, 3He, a also for the most forward angles of the Rco
where the pre-equilibrium emission and any possible difference are maximized.
To study angular and energy correlations of the emitted particles event-by-event.
To perform more selective coincidences with evaporation residues, as a function of their energies
and of the detected angles.
To complete the Hybrid Exciton Model calculations for all particles and for all the measured angles.

24. Empty slide
T. Marchi – Pre-equilibrium emission as a tool to study dynamic effects and clustering structure… (LoI) – SPES Workshop - LNL, May 2014