1 / 40

Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2

Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2. Michael P. Carpenter. RIA Summer School Seminar July 2006. Outline of Lectures. Day 1 Nuclear Structure – a brief perspective Changing Shell Structure in the Neutron Rich world.

gaston
Download Presentation

Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Probing Shell Structure in Neutron-Rich Nuclei above 48Ca:Using the Tools at HandDay 2 Michael P. Carpenter RIA Summer School Seminar July 2006

  2. Outline of Lectures Day 1 • Nuclear Structure – a brief perspective • Changing Shell Structure in the Neutron Rich world. • b-decay studies and deep inelastic reactions to study excited states in 54Ti and 56Ti – looking for evidence of shell gaps at N=32 and N=34. Day 2 • Coulomb Excitation of 52,54,56Ti • 2-proton knockout and b-decay into 52Ca • 56,58,60Cr using Gammasphere and the FMA • Future plans.

  3. N = 32 Gap: YES N = 34 Gap: NO 32 34 28 1129 R.V.F. Janssens et al., PLB 546, 22 (2002) B. Fornal et al., PRC 70, 064304 (2004)

  4. Beyond 2+ Energies E(2+) values are a strong indicator of shell structure, but.. Additional evidence for the presence or absence of shell effects is most welcome and very desirable!  Measure B(E2; 0+ 2+) values At present, this can only be done with Ti nuclei from fragmentation  Intermediate Energy Coulomb Excitation!

  5. Coulex of 132,134Sn at HRIBF • g rays measured with BaF array for 132,134Sn • Surprise B(E2) increases for 132Sn. R. Varner et al., Eur. Phys. J. A25, s01 (2005) 391.

  6. Beyond 2+ Energies: B(E2; 0+ 2+) values ETi ≈ 80 MeV/nucl.  ≈ 0.4, g ≈ 1.1 bmin ≈ 20 fm “touching spheres”1.2(ATi1/3+AAu1/3) ≈ 11 fm Ti Primary Beam: 130 MeV/u 76Ge Yields: 24000 s-1 52Ti; 2400 s-1 54Ti; 75 s-1 56Ti SeGA array

  7. SEGA Array @ NSCL SEGA with 16 Ge beam The 75% Ge Crystal has its outer electrode divided into 8 segments along the crystal axis and 4 segments perpendicular to the axis, resulting in 32 fold segmentation W. Mueller et al., NIMA 466, 492 (2001)

  8. GRETINA (Segmented Ge-Shell) • Tapered hexagon shape. • Highly segmented 6x6=36 • 7 modules with 4 crystals each – cover ≈ 1π solid angle (cover 4π will take 30 modules).

  9. 340 150 140 30Na from 32Al Beam 175 370 190 250 410 175 30Na from 30Mg Beam 340 250 370 410 430 (3+--2+) 770 Gamma-ray energy (2keV/channel) SEGA and GRETINA Simulation SeGA Simulation GRETINA 30Mg (pn) →30Na (100 MeV/u) v/c=0.43 charge exchange reaction Gamma-gamma coincidence NSCL data SeGA (E. Rodriguez-Vieitez et al.)

  10. Particle Identification at the S800

  11. 76Ge and 197Au: the Test Cases Lab Frame Primary beam: 76Ge @ 140 MeV/nucl. Secondary beam: 76Ge @ 81 MeV/nucl.  = 0.392 197Au target thickness: 257.67 mg/cm2 Qmax = 3.06° (CM) Number of 76Ge particles detected: 26.1E6 • 197Au • Eg= 547.03(24) keV • (q<Qmax) = 94(20) mb • B(E2, ) = 4223(898) e2fm4 • Adopted values: • Eg= 547.5(3) keV • B(E2, ) = 4494(409) e2fm4 Projectile Frame • 76Ge • Eg= 562.6(6)keV • (q<Qmax) = 394(47) mb • B(E2, ) = 2923(346) e2fm4 • Adopted values: • Eg= 562.93(3)keV • B(E2, ) = 2780(30) e2fm4

  12. 197Au check: Do we know what we are doing? D.-C. Dinca et al., PRC 71, 041302(R) (2005)

  13. B(E2) values fromdifferent methods for 26Mg Adopted and measured B(E2) values for stable nuclei An accurate technique that allows for absolute B(E2) measurements J. Cook et al., (NSCL/MSU)

  14. B(E2; 0+  2+) values 52Ti, 2+ 0+ (g.s.) 54Ti, 2+ 0+ (g.s.) 56Ti, 2+ 0+ (g.s.) 52Ti Eg= 1050(2) keV (q<Qmax) = 119(16) mb B(E2, ) = 593(81) e2fm4 54Ti Eg= 1497(4) keV (q<Qmax) = 83(15) mb B(E2, ) = 357(63) e2fm4 56Ti Eg = 1129(7) keV (q<Qmax) = 155(51) mb B(E2, ) = 599(197) e2fm4 D.-C. Dinca et al., PRC 71, 041302(R) (2005)

  15. N 28 30 34 26 32 34 26 28 30 32 2000 1800 800 1600 ) 4 fm 1400 600 2 e ( E(2+) Energy (keV) 1200 ) ­ E2, 1000 ( 400 B 800 600 200 48Ti 50Ti 52Ti 54Ti 56Ti 48Ti 50Ti 52Ti 54Ti 56Ti Shell Effects in Ti isotopes: What do we know? From an experimentalist’s point of view: N = 28 and N=32 gaps are quite visible in BOTH the E(2+) energies and in the B(E2;0+ 2+) values and there is no experimental evidence for a N=34 gap D.-C. Dinca et al., PRC 71, 041302(R) (2005)

  16. N N 34 26 28 30 32 28 30 26 32 34 2000 800 1500 ) 4 ) Energy (keV) fm 1000 600 2 e ( ) + ­ GXPF1 E(2 E2, 500 + E(2 ) ( 400 B GXPF1 0 48Ti 50Ti 52Ti 54Ti 56Ti 200 48Ti 50Ti 52Ti 54Ti 56Ti Comparison with GXPF1 ep = 1.5, en = 0.5 • The Shell Model with the GXPF1 interaction has problems with • N=34 and with • the B(E2) values for ALL Ti D.-C. Dinca et al., PRC 71, 041302(R) (2005)

  17. Possible Interpretation

  18. FPD6 FPD6 and GXPF1 The data may be telling us that the gap between p3/2 and p1/2 is at least as large as GXPF1 says, but that p1/2 and f5/2 are at least as close together as FPD6 indicates

  19. Recent Theory Development: GXPF1A GXPF1A vs GXPF1: T=1 matrix elements involving np1/2 and nf5/2 modified  (np1/2 - nf5/2) gap reduced by ~0.5 MeV 34 32 (6+) (4+) M. Honma et al., Proc. ENAM (2004)

  20. 31 33 exp Recent Theory Development: GXPF1A B. Fornal et al., PRC in press

  21. N 34 26 28 30 32 800 ) 4 fm 600 2 e ( ) ­ GXPF1 E2, ( 400 B 200 48Ti 50Ti 52Ti 54Ti 56Ti Comparison with GXPF1A N 28 30 26 32 34 2000 1500 ) Energy (keV) 1000 GXPF1A + GXPF1A E(2 500 + E(2 ) GXPF1 0 48Ti 50Ti 52Ti 54Ti 56Ti M. Honma et al., Proc. ENAM (2004)

  22. Value of effective charges? B(E2) = (Apep + Anen)2 A Ap An 48 8.8 15.4 50 10.7 9.5 52 9.0 14.4 54 10.7 10.6 56 10.3 11.4

  23. Value of effective charges? B(E2) = (Apep + Anen)2 A Ap An 48 8.8 15.4 50 10.7 9.5 52 9.0 14.4 54 10.7 10.6 56 10.3 11.4 Withep= 1.15en= 0.8 according to R. du Rietz et al., PRL 93, 222501 (2004)

  24. — Exp. ○FPD6 (?) Experimental Evidence for N=32 Gap: 52Ca E(2+) in 52Ca comes from a 1983 ISOLDE b-decay study (A.Huck et al., PRC 31, 2226 (1985)) where the separation between b decay and n-delayed b decay was a problem At NSCL 52Ca intensity is too small for a Coulex experiment  2p knockout!! 28 34 GXPF1 32 J.I. Prisciandaro et al., PLB 501, 17 (2001)

  25. 2p knockout into 52Ca Direct process Knock-out of 2 f7/2protons from 54Ti Cross section is small (~ 0.32 mb)  52Ca is magic No direct feeding of 2+ state:  Consistent with a Neutron excitation A. Gade et al., PRC in press.

  26. 2p knockout into 52Ca 3- is p((d3/2 or s1/2)-1 (f7/2)) excitation 2p knockout provides a way to study proton cross-shell excitations in n-rich nuclei A. Gade et al., PRC in press.

  27. 2p-knockout “by-products” First Transitions in 55Ti from 2p-knockout with 57Cr

  28. Pushing towards n-rich Cr: 59,60Cr • 59Cr from 48Ca(13C,2p)59Cr at 130 MeV • 60Cr from 48Ca(14C,2p)60Cr at 130 MeV • s(2p) < 1 mb  s(3n/4n) ~ 100 mb S.J. Freeman et al., PR C 69, 064301 (2004)

  29. 60/17 60/17 57/16 57/16 56/16 56/16 Pushing towards n-rich Cr: 60Cr 14C(48Ca,2p)60Cr @ 130 MeV DE ET2 Ni Ni Fe Fe Mn Mn Cr Cr Ti Ti Ca scattered beam Ca scattered beam E M/Q

  30. Fe 824 1291 438 339 129 250 Mn 569 10071070 Cr 643 60Cr 643 815 810 1033 986 607 g-ray energy (keV) Pushing towards n-rich Cr: 60Cr M=60 data M=60 Z=24 data with subtractions S. Zhu et al., to be published

  31. 815 Gate on 644 keV 985 Gate on 810-815 keV 985 643 Counts per channel 1033 keV Gate on 985 keV 815 643 985 keV 815 keV 2+ g-ray energy (keV) 643 keV 0+ 60 Cr Pushing towards n-rich Cr: 60Cr (N=36) M=60Z=24 g-g data S. Zhu et al., to be published

  32. A=57 A=57 Z=24 g-g Pushing towards n-rich Cr: 57Cr (N=33) 14C(48Ca,an)57Cr @ 130 MeV A. N. Deacon et al., PLB 622, 151 (2005).

  33. 57Cr: signs of collectivity Good agreement with GXPF1 g9/2 prolate structure also seen in 55Cr A. N. Deacon et al., PLB 622, 151 (2005).

  34. 2+ 880 0+ 58 Cr Interpretation: 59Cr (N=35) and the Shell Model 9/2+ @ only 503 keVOblate deformation?Weak coupling? 13C(48Ca,2p)59Cr @ 130 MeV Honma, Otsuka, Brown and Mizusaki: full fp basis, GXPF1 interaction Fed in 59V β decay, most likely in νf5/2 → πf7/2, expect at least 5/2− to have νf5/2 parentage S.J. Freeman et al., PR C 69, 064301 (2004)

  35. + 9/2 [404] - 3/2 [301] - 1/2 N=34 - 5/2 [303] - 1/2 Deformation Forms Shell Gaps Too!

  36. Prolate band, terminating Oblate structure 503 keV & isomer 1.6 MeV 57,59Cr: Shape Driving by the g9/2 orbital S. Freeman et al. PRC 69, 064301 (2004) A. Deacon et al. PLB 622, 151 (2005)

  37. 56Cr32 58Cr34 60Cr36 More from the Deep Inelastic • E(2+0+) decreases with A • Level sequence not regular just yet! • ? Small oblate deformation ? 48Ca + 238U and 48Ca + 208Pb Zhu et al., to be published

  38. Conclusions & Outlook • Neutron-rich nuclei continue to surprise us! - there is a N=32 shell gap just above 48Ca  in Ti (and Cr) confirmed by level structure and B(E2; ) - first indications for the onset of oblate(?) deformation (and the shape driving influence of the g9/2 orbital) seen in 59,60Cr - 54Ca is an important measurement (N=34 gap) • Theory needs work - the GXPF1 interaction is not the complete answer - the location of the p1/2 and f5/2 orbitals in n-rich nuclei above 48Ca needs further study - the g9/2 intruder needs to be included

  39. Where did we go and what did we do Approach: b-decay spectroscopy of fragments with (A,Z) selections  NSCL, ISAC  prompt g-ray spectroscopy following deep inelastic reactions (thick & thin targets) ATLAS  Coulomb excitation NSCL, (HRIBF)  fusion-evap. reactions @ radioactive targets  ATLAS  knockout reactions from fast fragments NSCL Data obtained with each of these techniques and facilities complement each other!

  40. Don’t Forget your Collaborators! • ANL: R.V.F. Janssens, S Zhu, M.P. Carpenter F.G. Kondev et al., • NSCL: P. Mantica, S. Liddick, et al., A. Gade, D.-C. Dinca, D. Bazin, et al., • Cracow: B. Fornal, R. Broda et al. • Manchester: S. Freeman, A. Deacon, et al. • Lowell: P. Chowdury • FSU: S. Tabor et al. • TRIUMF: G. Hackman, C. Morton et al. • Theory: M. Honma, T. Otsuka, B.A. Brown, T. Mizusaki

More Related