SuperCHICO at GRETINA and TIGRESS

1
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.
St. Louis Workshop
2
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

St. Louis Workshop
3
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).
St. Louis Workshop
4
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

St. Louis Workshop
5
CHICO participating institutions
58 participants, 17 institutions, 5 Ph.D. theses
St. Louis Workshop
6
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
St. Louis Workshop
7
At ATLAS/Gammasphere in August 2005
St. Louis Workshop
8
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

St. Louis Workshop
9
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
St. Louis Workshop
10
Layout of SuperCHICO
St. Louis Workshop
11
Cathode board of SuperCHICO
? coverage 30o?75o 45 divisions ?x?1.60 mm ?
coverage 5o?40o 25 divisions ?ymin?1.14 mm

?ymax?2.37 mm Total pixels 1125
St. Louis Workshop
12
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

St. Louis Workshop