GRETINA at ATLAS. (and GRETA Too!!) C.J. (Kim) Lister Gretina / Greta Pre-Town Meeting F.S.U. August th 2006

Transcription

1 GRETINA at ATLAS (and GRETA Too!!) C.J. (Kim) Lister Gretina / Greta Pre-Town Meeting F.S.U. August th 2006

2 Overview Philosophy Where is our field of nuclear structure going? What role does gamma-ray spectroscopy play? Where can we expect real breakthroughs? Physics Politics What key experiments do we envision? Where does GRETINA come in..and GRETA? How do we ensure the momentum continues? The GRETA ---RIA linkage 2

3 Overview Philosophy Where is our field of nuclear structure going? What role does gamma-ray spectroscopy play? Where can we expect real breakthroughs? Physics Politics What key experiments do we envision? Where does GRETINA come in..and GRETA? How do we ensure the momentum continues? The GRETA ---RIA linkage 3

4 Our Field Understanding the nature of all nuclear matter from the lightest elements to neutron stars Understanding the synthesis of elements, and key reactions in stars and in cataclysmic astronomical events Searching for physics beyond the Standard Model through precision measurements of β-decay 4

5 Specific Short Term Goals Establish reaction rates for understanding how the light elements are created in supernovae. Make measurements in new regions of nuclear structure. Construct GRETINA, revolutionizing gamma-ray detector technology. 5

6 Our Nuclear Domain Superheavy Elemens Transuranium Elemens Stable Elemens Spherical Shell 208 Pb Spherical Shell Sea of Instability GRETA/GRETINA Pre-Town-meeting Workshop. From: F.S.U. Yu Ogenessian, th Aug 2006 DUBNA6

7 Overview Philosophy Where is our field of nuclear structure going? What role does gamma-ray spectroscopy play? Where can we expect real breakthroughs? Physics Politics What key experiments do we envision? Where does GRETINA come in..and GRETA? How do we ensure the momentum continues? The GRETA ---RIA linkage 7

8 The Role Of Gamma Ray Spectroscopy ALL the workshops for equipment for RIA identified Gamma rays as absolutely key tools. In Reaction physics In Astrophysics In Fundamental Interactions In Structure So it is ours to lose...and we can lose unless we are INCLUSIVE in defining what is interesting. 8

9 Overview Philosophy Where is our field of nuclear structure going? What role does gamma-ray spectroscopy play? Where can we expect real breakthroughs? Physics What key experiments do we envision? Where does GRETINA come in..and GRETA? Politics How do we ensure the momentum continues? The GRETA ---RIA linkage 9

10 Gammasphere 10

11 Home Run Experiments THIS IS OUR CHALLENGE NOW! We need a short list of experiments that will have impact OUTSIDE our community. Astrophysics Reaction Mechanisms Fundamental Interactions Structure 11

12 Home Run Experiments What experiment would I do if GRETINA (GRETA) came to ATLAS tomorrow? i.e. What is MY best guess at a Home Run which would have impact outside our field? HEAVY ELEMENT SPECTROSCOPY 12

13 Heavy Elements Arguably, we have a paradigm shift on how to learn about the heaviest elements. FROM Synthesis of a a few atoms and inferring structural information from alpha decay energies. TO Detailed level spectroscopy to measurement of the quantum numbers of states. AND study dynamics. KEY ISSUE: How heavy can you do spectroscopy? 13

14 254 No Key Observations: Fission barrier is more robust that one may think...rotation above J=20 does NOT lead to fission, as one may expect from a liquid drop. Deformation β~0.27 Moment of inertia suggests pairing in very heavy nuclei may be reduced. 14

15 Odd-A Spectroscopy in 253 No, 255 Lr 15

16 Heaviest nuclei: Evidence for K-Isomers in 254 No K π = qp K π = 7 - E γ (kev) K π = 8 - K π = qp σ tot ~ 3 μb 16

17 Heaviest nuclei: Evidence for K-Isomers in 254,252,250 No K π =? 43(15) μs Isomer decays by fission and/or γ decay (.9) μs 250 No 148 SF D. Peterson et al., PRC submitted S.K. Tandel et al., PRL submitted 17

18 Numerical Reality Check Above Z=100 the cross-sections are very low, falling from ~3μb at 254 No Z=102 to ~ nb at Z=106. To combat this fall we have little wriggle room: For decay and isomer studies you can raise the beam intensity... to 100 s pna...but not target thickness. But for in-beam experiments total gamma count rate is the limiting factor...and a more efficient array means the beam must be cut DOWN unless count rate capability improves 18

19 Numerical Reality Check ( In-Beam ) Gretina Will really help 1) Geometry: With all the detectors upstream, the FMA can be moved closer to the target, increasing recoil detection by a factor ~2-3 2) Geometry: Plenty of space for a big target wheel. 3) Geometry: Near zero degrees you get radiation (n,γ) from the beamdump. This can be shielded (gain ~2) 4) Raw Countrate: Digital electronics, optimized for countrate will allow data collection >50KHz/crystal (gain ~5) UPSHOT: Can gain maybe Current RDT limit is ~50nb so ~few nb spectroscopy DOES appear possible...i.e. Z ~

20 Numerical Reality Check (Isomer Expts.) It is not clear where we can take this focal plane physics: Experience suggests >500pna may be possible. In which case we can certainly study K-isomers to Z > 106 where the axial deformation begins to decline. Even with such an intense beam, this would be only yield a few decay events/day...but data is FAR richer than straight α spectroscopy. BUT YOU NEED MECHANICAL FLEXIBILITY 20

21 Where Does this go? So there IS physics opportunity here... A close-packed configuration of GRETINA would be very good... better than any CLOVER array. BUT Needs mechanical flexibility 21

22 GRETA 4π gets you really interesting calorimetry and information on how fusion of heavy elements works. (but not for very high Z) It is also IDEAL for low intensity beams, like from CARIBU. Specifically for heavy elements: unless you can build-in target wheel and shielding appropriately, it is hard to crank up the beam... and Multiplicity is LOW SO For heavy element spectroscopy, half of GRETA is best. 22

23 Other Interesting GRETINA Experiments at ATLAS: Compared to Gammasphere...this is NOT totally obvious. The SINGLE big advantage is in potential count rate capability. Followed by better Doppler Correction to sharpen the lines. For Coulex and Deep inelastic transfers this could gain ~ 5 times in rate, ~2 in lineshape. 23

24 Power of proper Doppler Correction Fission products Deep-inelastic products Fission products Deep-inelastic products 24

25 Overview Philosophy Where is our field of nuclear structure going? Physics Politics Where can we expect real breakthroughs? What role does gamma-ray spectroscopy play? What key experiments do we envision? Where does GRETINA come in..and GRETA? How do we ensure the momentum continues? The GRETA ---RIA linkage 25

26 Politics The biggest danger I see is GRETINA will be seen an end not a beginning. Our Physics case MUST be for GRETA, as a critical element for the next-generation RIB facility. We must build the device as quickly as possible, so it will be fully ready for the new facility. We must have a realistic but modest cost for finishing the job. (< $30M) Any stable beam physics that comes is gravy. 26