Two-neutron transfer reaction
mechanisms in 12C(6He,4He)!
D.Smalley et al., PRC 89 (2014) 024602
Fred SARAZIN
Colorado School of Mines
Duane Smalley
Credit: C.A.A.Diget, Univ. York (UK)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
RIBSS Center of excellence
•  Work at Mines – simulation support for VANDLE (and
HAGRID):
–  Sergey Ilyushkin (PhD at the other MSU) – postdoctoral fellow, expert in
G4 simulations
LeRIBBS
(ORNL)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
Optimized
VANDLE for β-n
NICOLE
(ISOLDE)
“Jolie Fest”, Berkeley CA, May 2014
RIBSS Center of excellence
•  Some student support for Duane Smalley, Keri Kuhn, Ryan Braid
Keri Kuhn
Ryan Braid
Duane Smalley
“Silicon photobomb”
Carl Unsworth
(TRIUMF)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
A strong Mines – Rutgers (JAC) connection
•  Mines to Rutgers:
–  Robert Hatarik (PhD 2005, Uwe Greife) ! Postdoc Rutgers / RIBSS ! …
! Staff LLNL
–  Kelly Chipps (PhD 2008, Uwe Greife) ! Postdoc Rutgers / RIBSS ! …
! joint appointment UT / ORNL
–  Brett Manning (UG 2009, FS) ! PhD student at Rutgers (JAC)
–  David Walter (MS 2012, FS) ! PhD student at Rutgers (JAC)
•  Rutgers to Mines
–  Patrick O’Malley (PhD 2012, JAC) ! Postdoc Mines (2012-2014) ! …
Robert Hatarik
Brett Manning
& David Walter
Kelly Chipps
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
Patrick O’Malley
“Jolie Fest”, Berkeley CA, May 2014
(6He,4He): an alternate surrogate reaction for 2n-transfer
•  (t,p):
– 
– 
– 
– 
Used very successfully in the past
Tritium beams now hard to come by
State-of-the-art detectors at RIB facilities
Tritium (implanted) target challenging
•  (6He,4He):
–  A few RIB facilities now have intense 6He beam (>107 pps) in the few A.MeV
range
•  Most intense 6He beams likely at SPIRAL and ISAC
–  Potentially more favorable than (t,p)
•  Large Q-value: higher excited states, more direct?
–  6He S2n=1.867 MeV
–  Triton S2n=6.257 MeV
•  Influence of the 6He halo?
–  Disadvantage: stable (or long-lived) target
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Influence of the 6He halo?
•  Focus on mechanism of transfer for
two-neutrons
–  Di-neutron – spatially correlated may
enhance 2n simultaneous transfer
–  Cigar Shape – spatially separated may
enhance 1n sequential transfer
•  Studies suggested 2n transfer
dominant
–  Traditionally assumed (over)simplified
model of 6He, two-body di-neutron
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
6He=4He+n+n
di-neutron (60%)
cigar (40%)
From: I. Brida and F.M. Nunes, Nucl. Phys. A 847(2010) 1-23
“Jolie Fest”, Berkeley CA, May 2014
Influence of the 6He halo?
65Cu(6He,4He)
@ SPIRAL
From A.Chatterjee et al., Phys. Rev. Lett. 101 (2008) 032701
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Influence of the 6He halo?
“
“
“
“
From A.Chatterjee et al., Phys. Rev. Lett. 101 (2008) 032701
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Benchmark experiment: 12C(6He,4He)14C*
From F. Ajzenberg-Selove et al., Phys. Rev. C17 (1978) 1283
•  Use a reaction for which (t,p) was well measured.
•  12,13,14C well known
Also a di-neutron fit (renormalized)
From M.Milin et al., Nucl. Phys. A730 (2004) 285
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
TRIUMF
Radioactive beam
Target - Source
500 MeV proton
Up to 100µA
DRIVER
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
ISAC-I and –II @ TRIUMF
Target/Source + Mass Separator (Underground)
TRIUMF Cyclotron – p+ 500 MeV ; I<100µA
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
SHARC + TIGRESS
SHARC: Silicon Highly-segmented Array for Reaction and Coulex
C.A.A.Diget et al., J. Inst. 6 (2011) P02005
TIGRESS: TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer
G.Hackman and C.E.Svensson, Hyperf. Int. 225 (2013) 241
6He
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Experimental setup
Target:
•  200 µg/cm2 12C (~1µm)
DoCD 1mm
• 
• 
4 x 1mm BB11 box
1 x 1mm QQQ2 CD
DiBx 140µm
SHARC configuration:
•  Upstream, only E
DoBx 1mm
DiCD 45 / 80 µm
•  Downstream
4 x 140µm BB1 box (DE)
4 x 1mm pad (E)
3 x 80µm QQQ2 CD (DE)
1 x 45µm QQQ1 CD (DE)
4 x 1mm QQQ1 pad
• 
Foil
UmBx
1mm
• 
• 
• 
• 
• 
12C
DoCD3 not working
SHARC angular resolution:
•  DCD / UCD ~ 1.5°
•  DBx / UBx ~ 0.5°
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
UmCD
1mm
6He
Beam
“Jolie Fest”, Berkeley CA, May 2014
TIGRESS
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
SHARC & TIGRESS angular coverage
SHARC:
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
TIGRESS:
“Jolie Fest”, Berkeley CA, May 2014
Particle Identification
•  Identification of
particles reduces
background
contribution to spectra
•  Not available for full
array
•  Data reduction required
–  Start with elastic
scattering
•  Apply developed
analysis to reaction of
interest
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Elastic (and inelastic) scattering
•  States expected to be populated
• 
0+(gs), 2+ (4.4MeV), 3- (9.64MeV)
•  Fixes microscopic optical potential
for 6He+12C (& 5He+13C )
• 
• 
Normalization on elastic
scattering data
(Inelastic gets model parameters
for nuclear excitation)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Validate data
analysis routines
with understood
reaction (elastic
scattering)
Particle ID
Coincident detection
12C(6He,6He)12C*
•  Data reduction
required
–  Start with DCD
particle ID
–  DBx where no
particle ID is
available
•  End result should
overlay expected
kinematics
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  No Cuts
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• No Cuts
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
• Angular cut
(phi)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
• Angular cut
(phi)
• Energy cut
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
• Angular cut
(phi)
• Energy cut
• Angular cut
(theta)
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
• Angular cut
(phi)
• Energy cut
• Angular cut
(theta)
• Kinematic cut
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Data reduction simulation
•  Applying DCD Particle ID
•  DBx data reduction
• No Particle ID
available
• Two DBx
detectors hit
• Angular cut
(phi)
• Energy cut
• Angular cut
(theta)
• Kinematic cut
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
DCD excitation Spectrum & elastic angular distribution
Elastic only:
Excitation spectrum (DCD):
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
TIGRESS γ-ray spectrum
•  2+ to 0+ 4.438MeV γ-ray transition
observed
• 
• 
Black: raw spectrum
Red: Doppler corrected
•  ~1% efficiency at 4MeV
•  Not enough statistics for α γ tagging
for angular distribution
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
12C(6He,4He)
•  6.09MeV to 7.34MeV excited states
•  α γ tagging required
•  High γ-efficiency
• 
12C(6He,4He)
angular distribution
only measured for 8.32MeV
(unbound) state
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
12C(6He,4He)14C*
SHARC
excitation and γ spectra
SHARC + TIGRESS
Proof of principle
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Transfer modes
Close collaboration with Filomena Nunes and Alex Brown (NSCL / MSU)
A benefit of being part of the Center!
• Simultaneous transfer
–  Two neutrons (not necessarily di-neutron)
transferred in one step
–  Three-body structure of 6He accounted for
• Sequential transfer
–  Two-neutrons transferred in two-steps
»  Transfer one neutron 12C
–  Form 5He+13C* system
»  Transfer second neutron to 13C
–  Form final 4He+14C* system
–  Microscopic structure of 13C,14C accounted
for
a) experimental energy levels
b) assumed energy levels for the
calculations
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Angular distributions: the good news…
D. Smalley et al. Physical Review C 89, 024602 (2014)
•  Simultaneous (sim)
transfer, dotted red line,
dominant aspect of
transfer
No renormalization
•  Sum of simultaneous
(sim) and sequential
(seq), solid black line,
provides best results
•  Two-body di-neutron
overestimates low angle
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
…and the bad news: re-analysis of data at 18 MeV
•  Our realistic model falls
short by about a factor 2.
D. Smalley et al. Physical Review C 89, 024602 (2014)
With data from: M.Milin et al., Nucl. Phys. A730 (2004) 285
No renormalization
•  Di-neutron model works
better (!), especially at
the forward θcm
•  Sensitivity study: the
most important factor is
the choice of the
parameters for the
entrance channel (6He
+12C).
•  Higher-order effects
needed as well?
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Summary
•  Two-neutron transfer in 12C(6He,4He) at 30MeV studied and angular
distribution extracted for the 8.32MeV state in 14C
•  Model shows preference for simultaneous transfer, however:
–  Interplay between simultaneous and sequential transfer needed for best fit
–  A pure di-neutron transfer does not provide best fit
–  Fit is very sensitive to entrance channel parameters
•  Re-analysis of data at 18MeV shows some discrepancies
–  More work needed!
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014
Acknowledgments
Fred Sarazin ([email protected])
Physics Department, Colorado School of Mines
“Jolie Fest”, Berkeley CA, May 2014