Initial Science Case For GRETINA at ATLAS

M.P. CarpenterPhysics Division, Argonne National Laboratory

ANL Gretina WorkshopMarch 1, 2013

Science Opportunities with Gretina at ATLAS

Coulomb Excitation (Stable, CARIBU, Super CHICO)

Deep Inelastic Studies to study Neutron Rich Nuclei (Stable, CARIBU, Super CHICO)

100Sn Region (Stable, FMA)

Heavy Nuclei (Stable, FMA)

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Summary of report submitted to DOE to make the case of siting Gretina at ATLAS. The sciences cases here were discussed in the report and are not meant to represent all possibilities.

This report attempted to identify opportunities where GRETINA gave enhanced capabilities over Digital Gammasphere.

This report was put together by Kim Lister following discussions with PHY staff and postdocs.

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Coulomb Excitation with CARIBU Beams

Science Opportunity – study the development of collectivity as one moves away from doubly magic 132Sn.•Sr-Zr-Mo region – nuclei with most deformed ground states•Xe-Ba-Ce region – one of only a few regions exhibiting enhanced octupole collectivity.

~225 isotopes are expected to have accelerated yields > 104

Coulomb Excitation in Sr-Zr-Mo Region: Enhanced Deformation.

Sr-Zr-Mo region – Nuclei with most deformed ground states

Static quadrupole moments measured from Coulomb excitation will provide information which will distinguish different theoretical interpretation. Two experiments have been approved by PAC – 100Zr (Priority 1) and 90Kr (Priority 2).

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Coulomb Excitation in Xe-Ba-Ce Region: Enhanced Octupole Collectivity

S.J. Zhu et al., PLB 357 (1995) 273.

• Upper mass yield centered around 144Ba.

• Many examples of enhanced octupole collectivity inferred from level structures e.g. parity doublets.

• No direct measurement of matrix elements, B(E1) or B(E3), connecting negative and positive parity states.

• Open question on the degree of ocutpole collectivity in this region.

• PAC approved measurement on 144Ba using Gammasphere and CHICO2.

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•Measurment 1:•Beam Energy (from ATLAS): 601 MeV • i.e. “safe” Coulomb excitation •Beam intensity: 3400 141Cs/second•Measuring time: 62 hours • (with Gammasphere)•Purpose: Measure transition probability• B(E2;369 keV ray) = 20(5) W.u

•Measurment 2:•Beam Energy (from ATLAS): 850 MeV • i.e. “unsafe” Coulomb excitation •Beam intensity: 4300 141Cs/second•Measuring time: 14.5 hours • (with Gammasphere)•Purpose: demonstrate feasibility & study backgrounds from stable beam contamination and decay

•Result: From B(E2) value deduced deformation of 141Cs Important to understand onset of octupole deformation in this region of the nuclear chart & compare with theory

• 601 MeV

• 850 MeV

First Experiment with Reaccelerated CARIBU Beam:Coulomb Excitation of 141Cs

Coulomb Excitation with GRETINA and SuperCHICO Coulomb excitation experiments using Gammasphere and Chico

result in typical energy resolutions of 1.5-2% or 15 to 20 keV for 1 MeV rays.

SuperChico improves angular resolution in both θ and φ to ~1 degree.

GRETINA coupled to SuperCHICO should improve energy resolution to ~5 keV for 1-MeV rays.

Conclusion: The sharper photo peak reconstruction would enhance sensitivity by ~5-10, as long as the eventual “Peak-to-Total” ratio in GRETINA can be improved close to Gammasphere. Without this improvement, the GRETINA advantage will be deteriorated to ~2-5.

For CARIBU beams, increased resolution should decrease the minimum ion/sec to perform a successful experiment. Allow for observation of more transitions/nucleus.

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Deep Inelastic Reactions

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• Multi-nucleon swapping between projectile and target.

• 48Ca + 208Pb

• Identify neutron rich isotopes

• Thick target and stand alone Gammasphere.

232Th• Unsafe Coulomb

excitation of beam

• 232Th+208Pb

• Thick targets – live off stopped components of gamma-rays.

Deep Inelastic with Chico + Gammasphere

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University of Rochester

M.W. Simon et al., NIMA 452 (2000) 205.

Gammasphere + CHICO48Ca + 208Pb

50Ti

Deep Inelastic with Gretina and CHICO

Physics cases dependent on region, but ultimate goal is to reach higher in spin than possible with thick target.

Energy resolution of gamma-ray spectrum using SuperCHICO should improve between Gammasphere and Gretina. Due to large spread in energies of final products, a Gretina should deliver roughly a factor of 2 increase in energy resolution relative to Gammasphere i.e. 1% vs 2%.

Gretina would need to operate at maximum throughput i.e. ~20,000 triggered -rays/sec. Need high-fold gamma-multiplicity gate.

Unsafe Coulomb excitation of CARIBU beams maybe possible in order to extend known level structures to higher spin.

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GRETINA + FMA: 100Sn Region

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Physics case - Quantify the size of the shell gaps, and the sequence of states near the Fermi surface (which are still far from clear) and quantifying the residual interactions between nucleons, both in particle and hole states.

GRETINA + FMA: 100Sn Region

Using fusion evaporation, many open channels and dominated by charged particle evaporation.

FMA can provide necessary selectivity e.g. 101Sn. When using Gammasphere + FMA, target is ~90 cm from first Quad.

Optimal target position is 30 cm. For Gretina, target can be placed at 30 cm affording largest possible

efficiency for FMA. Core breaking transitions will be of high-energy and thus increased energy resolution and efficiency will also help.

New digital electronics is compatible with Gretina electronics. To optimize these measurements, high beam currents are

necessary and crystal counting rates of ~50,000 are desired.

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Gretina + FMA: Heaviest Elements

Physics Case: The spectroscopy of heavy nuclei (Z > 100) revolves around locating states near the Fermi level, especially those responsible for the very heaviest elements with Z~120. Deformation and rotation can move some of the key states towards to the Fermi level in the center of this deformed region and permit spectroscopy. Establishing the position of Nilsson-like quasi-particle states, then extrapolating to the near-spherical very heavy region is a key goal for understanding super heavy nuclei and the limits of the nuclear chart.

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254No

GRETINA + FMA: Heaviest Elements

254No campaign with GRETINA at BGS - “Hardest Case for Tracking Array” – Augusto Macchiavelli, earlier today.

Gretina gains over Gammasphere at FMA due to closer distance to first quadrupole: 90cm vs 30cm.

Increase in energy resolution due to Doppler reconstruction is not a significant feature of the device for these measurements.

Due to increased acceptance of FMA, GRETINA + FMA is more efficient than digital Gammasphere + FMA in singles mode. However, for gamma-ray coincidence, digital Gammasphere + FMA appears to be a more optimal device.

For these measurements, maximum count rate/crystal is necessary. New FMA digital electronics will offer improvements for these

types of measurements.

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Summary

Summary of report submitted to DOE to make the case of siting Gretina at ATLAS. The sciences cases here were discussed in the report and are not meant to represent all possibilities.

This report attempted to identify opportunities where GRETINA gave enhanced capabilities over Digital Gammasphere.

This report was put together by Kim Lister following discussions with PHY staff and postdocs.

What are the requirements for GRETINA to maximize the science opportunities: these case

– Optimized position resolution for enhanced energy resolution – required on day 1.

– Maximum -ray throughput (Deep Inelastic, Some FMA experiments)

– Maximum count rate capabilities per crystal (FMA experiments).

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