N/Z Dependence of Isotopic Yield Ratios as a Function of Fragment Kinetic Energy

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N/Z Dependence of Isotopic Yield Ratios as a
Function of Fragment Kinetic Energy

• Carl Schreck
• Mentor Sherry Yennello
• 8/5/2005

J. P. Bondorf et al. Nucl. Phys. A443 (1985) 321
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Outline of Presentation

• Multifragmentation Reactions
• Motivation
• Experiment
• Results
• Acknowledgements

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What is Multifragmentation?

• A process by which an excited nucleus expands,
  cools, and breaks up into multiple pieces
• For example, when a projectile collides head on
  with a target, the projectile and the target fuse
  to form a composite nucleus (CN), which then
  expands and fragments

i ii iii iv
A significant portion of the nuclei overlap
Compression, heating, and exchange phase
Expansion and cooling phase
Fragmentation phase
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Motivation for Project

• It has been experimentally observed that neutron
  poor isotopes tend to have energy spectra that
  have greater mean energies, peak at higher
  energies, and have higher tails

• Spectra taken from a 3He natAg reaction
• ltE4Hegt lt ltE3Hegt
• Also seen with Li, Be, B, C, and N isotopes

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PRC, Vol. 44, Pg 44 (1991)
Viola et al., Phys. Rev. C 59, 2260 (1999)
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Difficulty of Bulk FragmentationModels to
Explain the Data

• Current bulk multifragmentation models cannot
  explain these results
• The mean energy for isotopes from an equilibrated
  fragmenting source in bulk models is predicted to
  increase with increasing mass
• ltEgt 3/2 kT 2 AmNltv2gt ltEcoulgt
• The thermal and (3/2 kT) coulomb terms are the
  same for all isotope of an element
• The bulk motion term predicts that increasing
  mass will correspond to increasing mean energies

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A Possible Explanation

• One explanation Pre-equilibrium emission
• Researcher at Michigan State University have
  recently employed the Expanding Emitting Source
  (EES) model, in which fragments are statistically
  emitted prior to equilibrium, to explain this
  trend for 11C, 12C fragments from the 112Sn112Sn
  reaction
• In this model, 11C is emitted preferentially
  prior to 12C
  (figure 1) and both isotopes tend to have a
  greater mean energy
  
  when emitted earlier
  
  (figure 2), leading to
  
  11C having a greater
  
  mean energy than 12C

Lynch, private communication (NSRC preprint, Liu
et al)
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figure 2
figure 1
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A Possible Explanation

• Model agrees well with mean energies for energy
  spectra of 11C, 12C and the mean energies of He,
  Li, Be, B, C, N and O
• Questions with explanation
• Does this trend occur in systems
  too light to for
  pre-equilibrium C emission?
• Is this trend is a relic of the beam's N/Z?

Energy spectra for 11C, 12C from data and EES
Mean energies for data and EES
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What reactions are we studying?

• Peripheral reactions resulting from isobaric
  projectiles
• Isobaric beams (same A), 20F, 20Ne, 20Na, on
  197Au
• Using isobaric projectiles allows us to gauge the
  impact of the beam's N/Z on the energy spectra of
  the fragments
• PLFs from peripheral reactions with little nuclei
  exchange
• Only events with ZZbeam,
  18 A 22, mult
  2
• Fragments are ejected
  mainly in the
  forward lab
  angle, while with central
  
  collisions fragments are
  ejected in
  the forward and
  backward angles

Angular spectrum for Carbon, 20Ne beam
Yield / Steradian (arbitrary units)
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Lab angles
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Experimental MARS(Momentum Achromat Recoil
Spectrometer)

• Radioactive (secondary) beams 20F and 20Na
  produced in the reactions 19F d ? 20F p and
  20Ne p ? 20Na n
• D1,D2,D3 allow tuning to a range in
  charge/momentum
• Velocity filter allow tuning to a range of
  velocities
• Q1,Q2,Q3,Q4,Q5,D3 focus beam

D1
Q1
Q2
Velocity filter
Q3
Q4, Q5
D2
Primary beam 19F or 20Ne
Secondary beam 20F, 20Ne, or 20Na
Primary target
MARS and FAUST pictures from Dr Doug Rowland
Secondary target (197Au) and FAUST
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Experimental FAUST(Forward Array Using Silicon
Technology)

• Forward Array Covers lab angles from 1.6 to 44.8
  degrees
• Isotopic identification up to Z 7

Real live FAUST
Looking down FAUST
Cross section of FAUST
Five rings of detectors and 13 different angles
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Pictures of MARS from Dr Doug Rowland
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FAUST Detection

• Detectors Silicon (?E) and CsI (E)
• Allows resolution of nuclei up to detector limit
  of Z 7

Light guide
CsI
?E
Si
C
Be
B
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E
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Procedure x 2
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Low Statistics and Sad Times for Sodium
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with 20F
beam
11C 12C 13C 14C
11C 12C 13C 14C
11C 12C 13C 14C
11C 12C 13C 14C
11C 12C 13C 14C
11C 12C 13C 14C

• The difference between the mid and
  forward/backward angles for all three beam can be
  seen
• However, for 20Na beam, the spectra will be for
  all angles since statistics are low

Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
Normalized Energy Spectra for C Isotopes with
20Na beam
Normalized Energy Spectra for C Isotopes with 20F
beam
Normalized Energy Spectra for C Isotopes with
20Ne beam
11C 12C 13C 14C
11C 12C 13C 14C
11C 12C 13C 14C
Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
mid angles
mid angles
mid angles
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
Normalized Energy Spectra for N Isotopes with
20Na beam
Normalized Energy Spectra for N Isotopes with 20F
beam
Normalized Energy Spectra for N Isotopes with
20Ne beam
13N 14N 15N 16N
13N 14N 15N 16N
13N 14N 15N 16N
Yield (arbitrary units)
Yield (arbitrary units)
Yield (arbitrary units)
forward/backward angles
forward/backward angles
forward/backward angles
Energy (MeV/A)
Energy (MeV/A)
Energy (MeV/A)
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Results
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Normalized Energy Spectra for C Isotopes with 20F
beam
11C 12C 13C 14C
Yield (arbitrary units)

• Spectra for middle cm angles for F, Ne and all cm
  angles for Na
• 14C data not shown where statistics are low
• For all three beams, heavier isotopes correspond
  to smaller mean kinetic energies

11C ltEgt 4.38 12C ltEgt 3.47 13C ltEgt
2.54 14C ltEgt 2.02
Energy (MeV/A)
Normalized Energy Spectra for C Isotopes with
20Na beam
Normalized Energy Spectra for C Isotopes with
20Ne beam
11C 12C 13C
11C 12C 13C 14C
Yield (arbitrary units)
Yield (arbitrary units)
11C ltEgt 3.92 12C ltEgt 3.29 13C ltEgt
2.86 14C ltEgt 2.31
11C ltEgt 4.28 12C ltEgt 3.47 13C ltEgt
3.19 14C ltEgt 2.90
Energy (MeV/A)
Energy (MeV/A)
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Results
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Normalized Energy Spectra for N Isotopes with 20F
beam
13N 14N 15N 16N
Yield (arbitrary units)

• Spectra for middle cm angles for F, Ne and all cm
  angles for Na
• 16N data not shown where statistics are low
• Since it is very unlikely that a system this
  light (20 nucleons) would emit C or N
  pre-equilibrium, this trend most likely is a
  product of a different process

13N ltEgt 3.06 14N ltEgt 1.54 15N ltEgt
1.28 16N ltEgt 1.45
Energy (MeV/A)
Normalized Energy Spectra for N Isotopes with
20Na beam
Normalized Energy Spectra for N Isotopes with
20Ne beam
13N 14N 15N
13N 14N 15N
Yield (arbitrary units)
Yield (arbitrary units)
13N ltEgt 3.14 14N ltEgt 2.08 15N ltEgt
1.63 16N ltEgt 1.40
13N ltEgt 3.21 14N ltEgt 2.68 15N ltEgt
1.93 16N ltEgt 1.90
Energy (MeV/A)
Energy (MeV/A)
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More Results
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• Relative Yields for middle angles (even for 20Na)
• Plots show the yield of carbon isotopes divided
  by the yield of all carbon isotopes as a function
  of energy
• The relative yield of 12C and 14C is
  significantly different for the Fluorine than for
  the other beams

Relative Yield for 11C Isotopes
Relative Yield for 13C Isotopes
Y(11C)/Y(totC)
Y(13C)/Y(totC)
Energy (MeV/A)
Energy (MeV/A)
Relative Yield for 14C Isotopes
Relative Yield for 12C Isotopes
20F beam 20Ne beam 20Na beam
Y(14C)/Y(totC)
Y(12C)/Y(totC)
Energy (MeV/A)
Energy (MeV/A)
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More Results
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• Relative Yields for middle angles (even for 20Na)
• The behaviour of the relative yield for 15N is
  significantly different for the Fluorine beam
  than the other beams
• Is this behaviour reproducable with theoretical
  multi-fragmentation codes such as DIT/SMM?

Relative Yield for 15N Isotopes
Relative Yield for 13N Isotopes
20F beam 20Ne beam 20Na beam
Y(15N)/Y(totN)
Y(13N)/Y(totN)
Energy (MeV/A)
Energy (MeV/A)
Relative Yield for 16N Isotopes
Relative Yield for 14N Isotopes
Y(16N)/Y(totN)
Y(14N)/Y(totN)
Energy (MeV/A)
Energy (MeV/A)
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Conclusion

• As expected, the spectra for Be, C, and N
  fragments exhibit a greater mean energy for the
  lightest isotopes
• The relative yield plots show a difference
  between the 20F beam and the other beams,
  signifying a dependence of isotope yield ratios
  on the N/Z of the beam
• Future work
• Compare data to DIT/SMM, DIT/GEMINI, EES
  theoretical codes
• Look at fragment yield dependence on excitation
  energy

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Thanks to

• Cyclotron Institute at
  Texas AM University
• Sherry Yennello and the SJY Group
• 
  Department of Energy
• National
  Science Foundation

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