identification of a possible new island of inversion

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

111th Conference on Nucleus-Nucleus Collisions

11th Conference on Nucleus-Nucleus Collisions 2

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


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


2009 : 76Ge (130MeV/u) - PID, resolution, new isotopes

For all particles stopped in the Si-telescope in the production

runs

2011 : Newly-developed 82Se (139 MeV/u)


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


82Se (139 MeV/u) + Be: New isotopes, PID

6

Production runs All runs

64Cr

62Ti

2. Momentum Distributions


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)


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)

82Se (139 MeV/u) + Be : Momentum Distributions – u/u0


convolution

DJM

Borrel


82Se (139 MeV/u) + Be : Momentum Distributions – Widths

Momentum distributions analysis results


76Ge (130 MeV/u) + Be, W : cross sections


O.T. et al. Phys.Rev.C. 80, 034609 (2009)

82Se (139 MeV/u) + Be, W : cross sections


82Se (139 MeV/u) : W vs. Be targets


New isotopes 76Ge+W New isotopes 76Ge+Be, 82Se+Be


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)


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)

17

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].


[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]).

18

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)



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)


82Ge (139MeV/u) + Be : Qg- systematics

O.T.. et al., Phys.Rev.C. 80, 034609 (2009)


Inverse slope parameter T

Will be submitted soon

“Next” Calcium isotopes


76Ge approved proposal from MSU @ RIKEN

Intensity factor 2Target thick. factor 10Secondary reactions factor 55 (for 60Ca)?


82Se (140MeV/u) + Be : cross section new record?

*reduced, assuming 100% transmission, 100% time just for one production run


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)


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

NSCL Friday evening game: Connect points! v.4 (A=3Z+c)


N=40

Circle – 62Ti


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.

82Se (139 MeV/u) : W vs. Be targets


82Se (139 MeV/u) + Be -> N-2Z



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

Yields per 1 second


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

FRIB Estimated rates


http://groups.nscl.msu.edu/frib/rates/http://groups.nscl.msu.edu/frib/rates/FRIB_rates_readme.pdfReadme file :

Excel version Java version

FRIB : new isotopes per 1 week



v.2. # e09016 : W-target Qg-systematics (Z=14-19)

35


# e09016 : W-target Qg-systematics (Z=20-25)

36


# e09016 : W-target Qg-systematics (Z=26-28)

37

Connect points! v.1 (Z-line)


Connect points! V.2 (N-line)


2530

49

50

Connect points! V.3 (a-line)



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


Limiting temperature (A)


Targets vs Energies


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


Statistics issue

identification of a possible new island of inversion

Documents

2gg11th conference

new approach

mevu11th conference

production of new isotopeso

momentum distributionsnim

stage a1900

stage separators

stage separation