Nuclear fission studies in inverse kinematics with the R3B setup at the GSI-FAIR facility

Zakopane2022 conference

1. Nuclear fission studies in inverse kinematics
with the R
3
B setup at the GSI-FAIR facility
José Luis Rodríguez-Sánchez
University of Santiago de Compostela
2
nd
September 2022
Zakopane conference on nuclear physics
238
U

2. 2
Nuclear fission
Complex decay process
Understanding of nuclear fission still represents an important challenge in nuclear physics
J.L. Rodríguez-Sánchez
A diffusion process along the nuclear potential landscape based
on transport approaches like
Langevin equation
Fokker-Planck equation
dν
dt
=−βν−
1
m
∂
∂x
U(x)+
F'(t)
m
∂W
∂t
=[
−∂
∂x
ν+
∂
∂ν(
βν−
1
m
∂
∂x
U(x))
+
βκT
m
∂
2
∂ν
2]
W
The main inputs are the potential U(x) and the dissipation parameter β
Main observables: Fission probabilities & particle emission

3. 3
Nuclear fission
Complex decay process
Understanding of nuclear fission still represents an important challenge in nuclear physics
J.L. Rodríguez-Sánchez
A diffusion process along the nuclear potential landscape based
on transport approaches like
Langevin equation
Fokker-Planck equation
The main inputs are the potential U(x) and the dissipation parameter β
At low excitation energies the dynamics is governed by the
macroscopic and microscopic components of the nuclear
potential leading to shell effects in the mass asymmetry parameter
Main observables
Charge and mass distributions of the fission fragments
Symmetric
Asymmetric
dν
dt
=−βν−
1
m
∂
∂x
U(x)+
F'(t)
m
∂W
∂t
=[
−∂
∂x
ν+
∂
∂ν(
βν−
1
m
∂
∂x
U(x))
+
βκT
m
∂
2
∂ν
2]
W
Main observables: Fission probabilities & particle emission

4. 4
Reaction mechanisms to induce nuclear fission
J.L. Rodríguez-Sánchez
Complete kinematics measurements of fission products (fission fragments, light particles
and γ-rays) in inverse kinematics by using state-of-the-art detectors
Spallation-induced fission reactions
• Liquid hydrogen targets
• High excitation energies > 60 MeV
• Fission dynamics
Coulex-induced fission reactions
• Solid targets made of U and Pb
• Low excitation energies ~ 11 MeV
• Isospin dependence of fission fragment charge and
mass distributions
Quasi-free (p,2p) scattering reactions
• Liquid hydrogen targets
• Isospin and temperature dependencies of the fission
fragment charge and mass distributions
• Fission barriers

Therefore we need to measure a lot of observables and their correlations with high precision

5. 5
State-of-the art fission experiments within the R
3
B collaboration
Full identification in A, Z of both fission fragments and light-charged particles
J.L. Rodríguez-Sánchez et al.,
Phys. Rev. C 91, 064616 (2015)
E. Pellereau et al.,
Phys. Rev. C 95, 054603 (2017)
● Charge resolution 0.44 units
● Magnetic field 1.8 T
● Position resolution 200 µm
● ToF resolution 40 ps
J.L. Rodríguez-Sánchez
Twin-MUSIC

6. 6
State-of-the art fission experiments within the R
3
B collaboration
208
Pb+p at 500A MeV
σ = 0.19
J.L. Rodríguez-Sánchez et al., Phys. Rev. C 91, 064616 (2015)
J.L. Rodríguez-Sánchez

7. 7
R3B Fission dynamics
Dynamics at high excitation energies
Constraint of the presaddle dissipation coefficient
J.L. Rodríguez-Sánchez et al., Phys. Rev. C 90, 064606 (2014) Phys. Rev. C 92, 044612 (2015)
Phys. Rev. C 91, 064616 (2015) Phys. Rev. C 94, 034605 (2016)
208
Pb+p at 500A MeV
J.L. Rodríguez-Sánchez

8. 8
R3B Fission dynamics
Dynamics at high excitation energies
Constraint of the dissipation coefficient at large deformations (saddle-to-scission dynamics)
J.L. Rodriguez-Sánchez et al., Phys. Rev. C 94, 061601(R) (2016)
J.L. Rodríguez-Sánchez
~
~
~
n
n
n
The saddle-to-scission dissipation delays the fission
process and the fissioning system has more time to
evaporate neutrons

9. 9
R3B Fission dynamics
Dynamics at high excitation energies
Constraint of the dissipation coefficient at large deformations (saddle-to-scission dynamics)
J.L. Rodriguez-Sánchez et al., Phys. Rev. C 94, 061601(R) (2016) M. Feijoo, PhD thesis, University of Santiago de Compostela (2021)
236
U(650A MeV)+Al
J.L. Rodríguez-Sánchez

10. 10
R3B
Feijoo et al (2021)
Fission dynamics
J.L. Rodríguez-Sánchez

11. 11
Nuclear structure effects in the fission fragment distributions
Fission of Th isotopes
J.L. Rodríguez-Sánchez
A. Chatillon et al., Phys. Rev. C 99, 054628 (2019)
J.-F. Martin et al., Phys. Rev. C 104, 044602 (2021)
A. Chatillon et al., Phys. Rev. C 106, 024618 (2022)
A. Chatillon et al., Phys. Rev. Lett. 102, 202502 (2020)
• Clear observation of the transition from symmetric to
asymmetric fission
• Evidence of a new symmetric fission mode

12. 12
Fission induced by quasi-free (p,2p) scattering reactions
The kinematic properties of the proton pair provide information
of the excitation energy of the compound nucleus by using
energy and momentum conservation
Invariant massRest mass
238
U at 560A MeV
J.L. Rodríguez-Sánchez
The advantages of (p,2p) reactions
and the inverse kinematics technique
are combined to induce fission and
measure the E* of the compound nuclei
T. Noro et al., Prog. Theor. Exp. Phys. 093D02 (2020)
6 4 2 0
Excitation energy (MeV)

13. 13
First (p,2p)-fission experiment at GSI/FAIR (March 2021)
● CALIFA and Si-tracker: Proton momenta and γ-rays
Energy res. protons(gamma) 1%(5% at 1 MeV), Position res. 70µm
● MUSIC, ToF wall and MWPC detectors: Fission fragments
∆Z~0.37 , ToF~40ps, Position res. 200µm (FWHM)
● NeuLand: Neutron multiplicities (max. 10 neutrons)
● Magnetic field: 4 T
J.L. Rodríguez-Sánchez
Beam of
238
U at 560A MeV
experimental setup for complete kinematics measurements
GLADToF
See Han-Bum Rhee‘s poster
LH
2
CALorimeter for In-Flight detection of γ-rays
and high energy charged pArticles

14. 14
R3B First (p,2p)-fission experiment at GSI/FAIR (March 2021)
● Charge distribution of fission fragments and their correlations
J.L. Rodríguez-Sánchez
● A. Graña, PhD student working on the data analysis
Z
1
+Z
2
= 91
238
U+p at 560A MeV
Z
1
+Z
2
= 91
σ

= 0.16

15. 15
First (p,2p)-fission experiment at GSI/FAIR (March 2021)
● Reconstruction of quasi-free (p,2p) reactions with the CALIFA calorimeter and silicon tracker
J.L. Rodríguez-Sánchez
● G. García, PhD student working on the data analysis
Fission
fragments
Protons
Liquid hydrogen target
CALIFA
(p,2p) events:
238
U ->
237
Pa
Multi-nucleon removal
238
U ->
xxx
Pa

16. 16
First (p,2p)-fission experiment at GSI/FAIR (March 2021)
● Preliminary results for the evolution of the fission yields with the excitation energy
J.L. Rodríguez-Sánchez
● Experimental data
- Show sensitivity to the selection of (p,2p) events
- (p,2p) events result in fission decays at lower
excitation energies, highlighting asymmetric fission
- Validate the idea of use quasi-free (p,2p) reactions
for the study of fission

17. 17
First (p,2p)-fission experiment at GSI/FAIR (March 2021)
● Preliminary results for the evolution of the fission yields with the excitation energy
J.L. Rodríguez-Sánchez
● Experimental data
- Show sensitivity to the selection of (p,2p) events
- (p,2p) events result in fission decays at lower
excitation energies, highlighting asymmetric fission
- Validate the idea of use quasi-free (p,2p) reactions
for the study of fission
● Comparison to dynamical calculations
- Based on the intranuclear cascade model INCL
to describe the proton-Nucleus collision and the
de-excitation model ABLA to describe the fission
process
- The comparison leads to an average excitation
energy of 20-25 MeV for the (p,2p) events
INCL+ABLA: J. L. Rodríguez-Sánchez et al., Phys. Rev. C 105, 014623 (2022)

18. 18
R3B Conclusions & perspectives
● The first R
3
B experiments performed at GSI in 2012 allowed us to constrain the dynamics of
the fission process, in particular the value of the dissipation parameter, and to measure for
the first time new fission modes in the Th isotopic chain
● The first fission experiment based on quasi-free (p,2p) reactions looks promising
- All the detectors were stable during the experiment
- Charge distributions for the fission fragments are obtained with resolutions of σ=0.16 charge units
- Correlations between the two outgoing protons provided by the calorimeter CALIFA will allow us to
determine the excitation energy of our compound fissioning nuclei
- Preliminary results evidence the use of quasi-free (p,2p) reactions as a tool for investigating fission
● Development of a new pixel silicon tracker would be used to investigate fission reactions
of neutron-rich nuclei in the U-Th region, which will provide new data for
- Fission barrier heights and fission yields around N=152
- Evolution of shell and pairing effects with the excitation energy
- Neutron multiplicities and fission fragment correlations
- ...
J.L. Rodríguez-Sánchez

19. 19
collaboration
Sponsors:
Thank you for your attention!

20. 20
Future fission experiments at FAIR
Fragmentation reactions
J.L. Rodríguez-Sánchez
Super-FRS
SIS-100
Pre-separator (RIBs)
Main separator
Targets
R3B
Beam intensity 1×10 5
⁹
×10¹¹
Transmission for U 55 % 98 %
Parameter GSI FAIR

21. 21
Future (p,2p)-fission experiments at GSI/FAIR
High resolution pixel silicon tracking device
● Based on Monolithic Active Pixel Sensors
● Two barrels surrounding the LH
2
target
- Sensor thickness of 50 μm
- Barrels of 30 cm long
- 4-5 cm radius
- Threshold of few eV per channel
- Azimuth and polar angle range: 0-360 and 8-80
- Missing energy resolutions of 1-2 MeV
● Goals for the next experiments
- Measurement of fission barriers of neutron-rich
nuclei in the U-Th region
- Fission yield dependencies on isospin and excitation
energy
Beam
J.L. Rodríguez-Sánchez