Presentation on theme: "Initial Science Case For GRETINA at ATLAS M.P. Carpenter Physics Division, Argonne National Laboratory ANL Gretina Workshop March 1, 2013."— Presentation transcript:
Initial Science Case For GRETINA at ATLAS M.P. Carpenter Physics Division, Argonne National Laboratory ANL Gretina Workshop March 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) 100 Sn Region (Stable, FMA) Heavy Nuclei (Stable, FMA) 2 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.
3 Coulomb Excitation with CARIBU Beams Science Opportunity – study the development of collectivity as one moves away from doubly magic 132 Sn. 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 > 10 4
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 – 100 Zr (Priority 1) and 90 Kr (Priority 2). 4
5 Coulomb Excitation in Xe-Ba-Ce Region: Enhanced Octupole Collectivity S.J. Zhu et al., PLB 357 (1995) 273. Upper mass yield centered around 144 Ba. 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 144 Ba using Gammasphere and CHICO2.
6 Measurment 1: Beam Energy (from ATLAS): 601 MeV i.e. “safe” Coulomb excitation Beam intensity: 3400 141 Cs/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 141 Cs/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 141 Cs 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 141 Cs
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. 7
Deep Inelastic Reactions 8 Multi-nucleon swapping between projectile and target. 48 Ca + 208 Pb Identify neutron rich isotopes Thick target and stand alone Gammasphere. 232 Th Unsafe Coulomb excitation of beam 232 Th+ 208 Pb Thick targets – live off stopped components of gamma-rays.
Deep Inelastic with Chico + Gammasphere 9 University of Rochester M.W. Simon et al., NIMA 452 (2000) 205. Gammasphere + CHICO 48 Ca + 208 Pb 50 Ti
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. 10
GRETINA + FMA: 100 Sn Region 11 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: 100 Sn Region Using fusion evaporation, many open channels and dominated by charged particle evaporation. FMA can provide necessary selectivity e.g. 101 Sn. 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. 12
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. 13 254 No
GRETINA + FMA: Heaviest Elements 254 No 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. 14
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). 15