SuperCHICO at GRETINA and TIGRESS

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SuperCHICO at GRETINA and TIGRESS

• C.Y. Wu and J.A. Becker
• Lawrence Livermore National Laboratory
  Livermore CA 94551
• D. Cline
• Dept. of Physics University of Rochester
  Rochester NY 14627

• CHICO at Gammasphere
• SuperCHICO at GRETINA and TIGRESS

This work was performed under the auspices of the
U.S. Department of Energy by the University of
California Lawrence Livermore National
Laboratory under contracts no. W-7405-ENG-48.
The work performed at University of Rochester was
supported by NSF and AFOSR.
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What is CHICO What is its function

• CHICO (Compact Heavy Ion COunter)
• Segmented 4 position-sensitive PPAC
• Co-located with Gammasphere as auxiliary
  instrument
• Developed at Rochester and funded by NSF
• Detection of binary reaction residue products in
  4 geometry
• Provides energetic heavy-ion mass and scattering
  angle
• Kinematic reconstruction event by event
• Distinguishes between the projectile-like and
  target-like nuclei
• Enables Doppler shift correction to maintain
  -ray resolution
• Campaigned as auxiliary instrument with
  Gammasphere
• A bit more than 10 of the Gammasphere beam time

• Doppler-shift correction enables precision -ray
  spectroscopy
• Enhances Gammasphere channel selectivity and
  sensitivity

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What does the kinematic-reconstruction do
Precision -ray spectroscopy
170Er 238U ELab 1358 MeV Raw
data Correction for U-like recoils Correction
for Er-like recoils
Wu et al. Phys. Rev. C 61 021305(R) (2002).
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Some examples

• Fragmentation of the two-phonon octupole
  vibrational states in 208Pb K. Vetter et al.
  PRC 58 R2631 (1998)
• Electromagnetic properties of the rotationally
  aligned band in 162Dy C.Y. Wu et al. PRC 64
  064317 (2001)
• Coulomb excitation paths of high-K isomer bands
  in 178Hf A.B. Hayes et al. PRL 89 242501
  (2002)
• The sudden onset of the band crossing for the
  aligned g9/2 orbitals a possible transition of
  a triaxial shapes from prolate to oblate H.
  Hua et al. PLB 562 201 (2003)
• 25 Journal articles including two Phys. Rev.
  Lett. and one Phys. Lett. B since 1998

• Enables cutting edge physics

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CHICO participating institutions
58 participants 17 institutions 5 Ph.D. theses
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Strong interest in physics enabled by CHICO
within the low-energy physics community

• 2005 experiments
• Nuclear Structure of neutron rich Ti and Cr
  isotopes
• A subshell closure at N 32
• Fielded successfully at ATLAS/Gammasphere in
  August 2005
• CHICO data rate 600k per second
• K mixing in 242mAm
• Fielded successfully at ATLAS/Gammasphere in
  August 2005
• Gammasphere data rate 800k per second
• Near-term plan
• Soft Dipole Resonances (pygmy) in neutron rich
  nuclei
• Nuclear structure evolution in the Cd isotopes
  with increasing neutron number (reconcile
  rotational and vibrational modes)
• Map the Island of Inversion near 32Mg

Nuclear-Structure Physics at the Forefront
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At ATLAS/Gammasphere in August 2005
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Beyond CHICO

• Shortcoming
• Specific design for Gammasphere
• Constant resolution independent of which
  implies the physical position resolution is about
  10 mm at 50o
• Inadequate for the Doppler-shift correction of
  rays detected by modern tracking Ge detector
  arrays with a position resolution better than 2
  mm
• Strategy
• Make design compatible with future tracking Ge
  arrays
• Improve position resolution
• Minimize activity accumulated in the chamber due
  to radioactive beams

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SuperCHICO a pixelated avalanche counter
-ray resolution improved from 1 to 0.3
0.5 for the next generation of highly segmented
Ge arrays and the sensitivity improved from 100
barn production cross section to 10 barn
Spherical chamber with a radius of 12.7 cm (fit
into the cavity of TIGRESS) Two hemispheres
and eight segments for each hemisphere Both
and coordinates defined by the pixelated
cathode board and the goal is 2 mm position
resolution Solid-angle coverage 2 sr.
with a minimum flight path 9 cm Downstream
electronics and gas handling system among
recycled from CHICO but replaced by FADCs and
computerized gas handling system eventually
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Layout of SuperCHICO
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Cathode board of SuperCHICO
coverage 30o75o 45 divisions x1.60 mm
coverage 5o40o 25 divisions ymin1.14 mm

ymax2.37 mm Total pixels 1125
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Cost details

• Most of work carried out at LLNL
• Mechanical
• Design 22 weeks 100k
• Fabrication 100k
• Electronics
• Amplifier
• Replace Watkins-Johnson hybrid circuit design
• Design 6-8 weeks 80k
• Fabrication 80k
• Downstream
• Recycled from CHICO
• Replaced by FADC and computer-controlled
  gas-handling system in the future
• Total cost 360k excluding the scientific
  manpower

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