identification of a possible new island of inversion
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Identification of a possible new island of inversion. Production of new neutron-rich isotopes @ NSCL Two stage separation 76 Ge beam 82 Se beam Momentum distributions Production cross sections - PowerPoint PPT PresentationTRANSCRIPT
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11-th Conference on Nucleus-Nucleus Collisions
Identification of a possible
new island of inversion
Oleg B. Tarasov
NCSL / MSU, U
SA
05 / 28 / 2012
1. Production of new neutron-rich
isotopes @ NSCL
Two stage separation
76Ge beam
82Se beam
2. Momentum distributions
3. Production cross sections
4. Exploration of a possibleisland of inversion Qg – systematics
“Temperature” plots
Summary
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Production of new isotopesO.T. et al., Phys.Rev. C 75, 064613 (2007)
Figure. 40Mg expected yield calculated for the A1900 fragment separator using extrapolation production cross section from the 44Si experiment
44Si T.Baumann et al.,Nature (London) 449, 1022 (2007)
Two-stage separation
• No detectors in beam line down to wedge selection slits (A1900 FP).
• Position (Brho) measurement in the dispersive focal plane in the second stage (S800BL)
• The first stage (A1900) of the system serves as a selector whereas the second stage (transfer hall line + S800BL) contains detectors and functions as analyzer
• All new fragment separators BigRIPS, SuperFRS, A2400 are multi-stage separators.
40Mg, 42Al, 43Al
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2009 : 76Ge (130 MeV/u)
Phys.Rev.Lett. 102, 142501 (2009) : New isotopes, indication of a new island of inversion
Phys.Rev.C. 80, 034609 (2009) : Set-up, cross sections, momentum distributions
NIM A 620, 578-584 (2010) : A new approach to measure momentum distributions
50Cl, 53Ar, 55,56K, 57,58Ca, 59,60,61Sc, 62,63Ti, 65,66V, 68Cr, 70Mn
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2009 : 76Ge (130MeV/u) - PID, resolution, new isotopes
For all particles stopped in the Si-telescope in the production
runs
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2011 : Newly-developed 82Se (139 MeV/u)
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64Ti, 67V, 69Cr, 72Mn70Cr 1event & 75Fe 1event
will be submitted soon
Beam E (MeV/u) I (pna) N/Z
82Se 139 35 1.41276Ge 130 20 1.375
DN / DZ=2
g
g
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82Se (139 MeV/u) + Be: New isotopes, PID
6
Production runs All runs
64Cr
62Ti
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2. Momentum Distributions
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Why? To obtain cross sections based on LISE++ transmission calculations with parameters of momentum distribution model obtained from the current experiment
“Classic: way:Brho scanningthin target
New method: Brho = constTarget thickness variation
A new approach to measure momentum distributions and production cross sections of neutron rich nuclei using fragment separators
O.T. et al.,NIM A 620, 578-584 (2010)
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Momentum Distributions : Target scanning method
8
76Ge analysis (2009) : point for fit in the middle of target
or weights = const
2012 update : using weights F(vp,s) from the momentum
distribution model with vp,s,
..which actually are fitted…… (!!!!)
target
mid
dle
More probableBased on vp & s
76Ge : 5 targets (max 3 isotopes for one element)82Se : 7 targets (max 8 isotopes for one element)
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82Se (139 MeV/u) + Be : Momentum Distributions – u/u0
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convolution
DJM
Borrel
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82Se (139 MeV/u) + Be : Momentum Distributions – Widths
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Momentum distributions analysis results
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76Ge (130 MeV/u) + Be, W : cross sections
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O.T. et al. Phys.Rev.C. 80, 034609 (2009)
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82Se (139 MeV/u) + Be, W : cross sections
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82Se (139 MeV/u) : W vs. Be targets
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New isotopes 76Ge+W New isotopes 76Ge+Be, 82Se+Be
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Qg- systematics
Figure. The variation of the cross sections for the production of neutron rich nuclei as a function of the two-body Q values [Qgg, left panels (a), (b)] and as a function of the one-body Q value [Qg, right panels (c), (d)]. Upper panels (a), (c) show data for W (Ta), lower panels (b), (d) for Be targets.
O.T. et al., Phys.Rev. C 75, 064613 (2007)
48Ca(140MeV/u) + W,Be
A simple systematic framework was found to describe the production cross sections based on thermal evaporation from excited prefragments that allows extrapolation to other weak reaction products.
Compilation with data from M. Mocko et al.,
Phys. Rev. C 74, 054612 (2006)
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76Ge (130MeV/u) + W,Be : Qg- systematics
B.A. Brown, Prog. Part. Nucl. Phys. 47, 517
(2001).
The fact that the cross sections of the most neutron-rich nuclei with Z = 19 to 22 are enhanced relative to the lighter isotopes may indicate that these nuclei and their precursors are more bound than predicted and is reminiscent of the discovery of the island of inversion at N = 20.
O.T. et al. Phys.Rev.C. 80, 034609 (2009)
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Islands of inversion
Figure: Measured 12Be (N = 8) and 31Na (N = 20) and predicted (N=40) islands of inversion across the neutron-rich side of the nuclear chart. [1].
•Particle-hole excitations across a shell gap into the next higher oscillator shell can become energetically favored if stabilized by deformation and pairing correlations [1].
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[1] “Isotope Science Facility at Michigan State University”, MSUCL-1345, 11-2006
[2] D. Guillemaud-Mueller et al., Nucl. Phys. A426, 37 (1984).[3] T. Motobayashi et al., Phys. Lett. B 346, 9 (1995).
•Strong quadrupole deformations have been observed in the neutron-rich nuclei around N = 20 [2,3],
[4] A. Navin et al., Phys. Rev. Lett. 85, 266 (2000).[5] H. Iwasaki et al., Phys. Lett. B 481, 7 (2000).
•and around N = 8 [4,5].
[6] B.A. Brown, Prog. Part. Nucl. Phys. 47, 517 (2001)[7] S.M. Lenzi et al., Phys. Rev. C 82, 054301 (2010)
•Such an anomalous deformation is suggested to appear in the heavier region around N = 40 (62Ti [6], 64Cr [7]).
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Search for the new island of inversion
Evidence for increased collectivity at N = 40 in neutron-rich 64Cr
A.Gade et al., Phys. Rev. C 81, 051304 (2010)
The large experimental R4/2 ratio of 62Cr is an indication for the development of deformation:
N. Aoi et al., PRL 102, 012502 (2009)
The observation of low-energy 2+ states in 60,62Cr suggests that these isotopes are strongly deformed
O. Sorlin et al., Eur. Phys. J. A 16, 55 (2003)
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Possible new island of inversion? (76Ge)
O.T. et al., Phys.Rev.C. 80, 034609 (2009)
O.T. et al., Phys.Rev.Lett. 102, 142501 (2009)
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82Ge (139MeV/u) + Be : Qg- systematics
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82Ge (139MeV/u) + Be : Qg- systematics
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O.T.. et al., Phys.Rev.C. 80, 034609 (2009)
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Inverse slope parameter T
Will be submitted soon
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“Next” Calcium isotopes
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76Ge approved proposal from MSU @ RIKEN
Intensity factor 2Target thick. factor 10Secondary reactions factor 55 (for 60Ca)?
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82Se (140MeV/u) + Be : cross section new record?
*reduced, assuming 100% transmission, 100% time just for one production run
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Summary & Outlook for Possible Island of inversion
○ More than two dozens of neutron-rich isotopes (12 ≤ Z ≤ 26) have been observed in the first time
○ Evidence for a Change in the Nuclear Mass Surface in two experiments with different primary beams 76Ge & 82Se : new island of inversion (62Ti)?
○ Measurement of cross sections and momentum distributions in wide regionwith different beam-target combinations
○ A new approach to measure momentum distributions
Incoming experiments
○ Time-of-Flight Mass Measurements of Neutron Rich Nuclei (MSU) -- done
○ Gamma-ray spectroscopy of neutron-rich isotopes (MSU and …)
○ Exploration of the possible new island of inversion with the discovery of neutron rich nuclei (RIKEN)
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82Se experiment participants
This work was supported by NSF #PHY-06-06007 grant.
A.M.Amthor 2, L.Bandura 2, T.Baumann 1, D.Bazin1, J.S.Berryman1, G.Chubarian3, N.Fukuda4, A.Gade 1,5, T.N.Ginter 1, M.Hausmann 2, N.Inabe 4, T.Kubo 4,
D.J.Morrissey1,6, J.Pereira 1, M.Portillo 2, B.M.Sherrill1,2,5, A.Stolz 1, C.Sumithrarachchi 1, O.B.T. 1, M.Thoennessen 1,5, and D.Weisshaar 1
1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA2Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824-1321, USA3Cyclotron Institute, Texas A&M University, 3366 TAMU, College Station, TX, 77843-3366, USA
4RIKEN Nishina Center, RIKEN, Wako-shi, Saitama 351-0198, Japan5Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
6Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
The authors would like to acknowledge the operationsstaff of the NSCL for developing the intense 76Ge and
82Se beams necessary for this study
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NSCL Friday evening game: Connect points! v.4 (A=3Z+c)
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N=40
Circle – 62Ti
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1. Production of new isotopes. Exploring the limits of nuclear existence
The limits of nuclear stability provide a key benchmark of nuclear models:
Exploring nuclei with unusual properties Exploring changes in shell structure Exploring nuclear shapes
The context of astrophysics: What is the origin of the heavy elements? Understanding the r-process abundance patterns of elements
Production mechanism study: reaction choice, production cross sections, momentum distributions
Secondary beam intensities predictions. Planning new experiments, set-ups (FRIB)
The first step in the study of a new exotic nucleus is its observation, which for neutron-rich nuclei demonstrates its stability with respect to particle emission.
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82Se (139 MeV/u) : W vs. Be targets
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82Se (139 MeV/u) + Be -> N-2Z
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Exploration of unknown neutron-rich region
2009: RIBF @ RIKEN238U 345 MeV/u, 109 pps @ 2009
2011: 238U 345 MeV/u, 1010 pps @ 2011
2017?: GSI – new isotope production with preseparator, 1.5 GeV/u, 1012 pps
2020?: FRIB @ MSU200-250 MeV/ u , 400 kW
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Yields per 1 second
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A total of 47 primary beams were used for FRIB yield
analysis. These cover nearly 90% of the optimum
primary beams for the production of all isotopes.
RIBF @ RIKEN (2011)238U 345 MeV/u, 2pnA
GSI ,1.5 GeV/u, 1012 pps
F-RIB @ MSU200-250 MeV/ u , 400 kW
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FRIB Estimated rates
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http://groups.nscl.msu.edu/frib/rates/http://groups.nscl.msu.edu/frib/rates/FRIB_rates_readme.pdfReadme file :
Excel version Java version
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FRIB : new isotopes per 1 week
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v.2. # e09016 : W-target Qg-systematics (Z=14-19)
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# e09016 : W-target Qg-systematics (Z=20-25)
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# e09016 : W-target Qg-systematics (Z=26-28)
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Connect points! v.1 (Z-line)
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Connect points! V.2 (N-line)
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2530
49
50
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Connect points! V.3 (a-line)
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Supplemented slides
d Mass
-2
-1
0
1
2
3
4
5
6
7
8
53 54 55 56 57 58 59 60 61 62 63 64
A
dM, M
eV
ScTi
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Limiting temperature (A)
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Targets vs Energies
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LISE++ Abrasion-Dissipation-Ablation model (ADA)
• A-A : two step process, A-D-A : three step process**
• Dependence from projectile energy, N/Z target ratio, target nucleus size.Advantage of heavy targets to produce neutron-rich nuclei.
• Mass prediction for unknown isotopes becomes very crucial
** -- “Universal parameterization”: three step projectile fragmentation model has been already used in LISE++ to describe momentum distributions.O.T., Nucl.Physics A734 (2004) 536-540
Under construction
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Statistics issue