# Presentation: 154727

## Experiments with rare isotopesThe limits of experiments at the limits of stabilityThomas GlasmacherMichigan State University

**The 2nd LACM-EFES-JUSTIPEN Workshop **
- Joint Institute for Heavy Ion Research, Oak Ridge, Tennessee, USA Oak Ridge National Laboratory January 23-25, 2008

## Our shared goal: To develop a predictive theory of atomic nuclei and their reactions

- Optimize progress by investing resources wisely:
- Measure observables that can (in principle) be calculated
- Calculate observables that (in principle) can be checked inexperiments

**Notes:**
Need
Beams of rare isotopes
Detectors
Luminosity

Modification of magic numbers, canonical ones disappear, new ones emerge
Reduction in spin-orbit force

Measure q.m. observables to check theories

Most exotic nuclei accessible for light nuclei

## Rare isotopes are a wise investment and Tasks for experimenters

- Stable nuclei are well-described with closed-shell nuclei as key benchmarks
- Rare isotopes show evidence for
- disappearance of canonical shell gaps,
- appearance of new shell gaps,
- reduction of spin-orbit force,
- influence of continuum states

- Experimental task: Quantify changes encountered in rare isotopes and measure with defined certainty observables that are calculable and can be used to discriminate between theories

**Notes:**
Need
Beams of rare isotopes
Detectors
Luminosity

Modification of magic numbers, canonical ones disappear, new ones emerge
Reduction in spin-orbit force

Measure q.m. observables to check theories

Most exotic nuclei accessible for light nuclei

## Facts of life for experimentalists

- Nobs/  NRNT × NB × 

- beam

- target

- reactedbeam

- Nobs observed reactions	 detection efficiency
- NR reaction rate 		NT atomic density of target
- NB beam rate			 cross section

## Facts of life for experimentalists

- Nobs/  NRNT × NB × 

- beam

- target

- reactedbeam

- Nobs observed reactions	 detection efficiency
- NR reaction rate 		NT atomic density of target
- NB beam rate			 cross section

**Build more efficient detectors**

**Use targets with more scattering centers**

**Make more beam**

**Given by nature**

## Experimental observables in experiments with in-flight produced rare isotope beams

- Stopped beam experiments
- Possible experiments and quality of observables depend on number of beam particles
- Discovery (few particles total)
- Half live(few ten particles)
- Mass** **(few hundred particles)
- Fast beam experiments
- Possible experiments and quality of observables depend on luminosity
- Interaction radii(few particles per hour)
- g-factors(hundreds of particles per second)

- Fast beam experiments (cont’d)
- Excited state energies, transition matrix elements
- Elastic and inelastic scattering(ten particles per second)
- Electromagnetic
- Hadronic
- Lifetimes from -ray line shapes(hundreds of particles per second)
- Occupation numbers
- Nucleon removal
- Single nucleon(particles per second)
- Two-nucleon(hundreds of particles per second)
- Multi-nucleon(hundreds of particles per second)
- Nucleon addition(hundreds of particles per second)

## Stopped beam experiment: Discovery of new isotopes near the n-dripline: 40Mg, 42Al, 43Al, 44Si

- 4x1017 48Ca beam particles
- Two-stage separator (one-stage did not provide sufficient clean-up)
- First observation of 40Mg (3 events), 42Al, 43Al

**2007**

**1990:**	**GANIL** Guillemaud-Mueller *et al*., Z. 	Phys. A 332, 189
**1997:**	**GANIL** Tarasov *et al*., Phys. Lett. B 	409, 64
**1999:**	**RIKEN** Sakurai *et al*., Phys. Lett. B 	448, 180
**2002:**	**RIKEN** Notani *et al*., Phys. Lett. B 	542, 49
- 	**GANIL** Lukyanov *et al*., J. Phys. G 	28, L41
**2007:**  	**NSCL **Tarasov *et al*, Phys. Rev. C 75 	(2007) 064613; Baumann *et al*, 	Nature 449 (2007) 1022

## Stopped beam experiment: Mass measurement Stop fast exotic beams in gas cell, extract, and use in experiments

- 38Ca: T1/2 = 440 ms, 0+  0+ +-emitter
- new candidate for the test of the conservedvector current (CVC) hypothesis
- MELEBIT = -22058.53(28) keV
- m = 280 eV, m/m=8·10-9
- AME 03: m  = 5 keV

- Penning trap mass measurements of rare isotopes produced in-flight:
- Since Summer 2005:
- 33Si, 29P, 34P
- 37Ca, 38Ca
- 40S, 41S, 42S, 43S, 44S
- 63Ga, 64Ga
- 64Ge, 65Ge, 66Ge
- 66As, 67As, 68As, 80As
- 68Se, 69Se, 70Se, 81Se, 81mSe
- 70mBr, 71Br

- 66As: T1/2 = 96 ms
- LEBIT: m   20 keV,  m/m  3x10-7
- 20-fold improved masses in region critical to rp process

- G. Bollen *et al*. Phys. Rev. Lett. **96** (2006) 152501

## Exploring the boundaries of Island of Inversion

- C. Thibault *et al*: PRC 12 (1975) 64631,32Na, local increase of S2n  *N=20* shell gap decreased
- X. Campi *et al*: NPA 251(1975) 193explained by deformation via filling of (f7/2)
- C. Detraz *et al*: PRC19 (1979) 16432Na  32Mg  decay, low 2+ in 32Mg
- E. Warburton *et al*: PRC 41 (1990) 1147*Z=10-12* and *N=20-22* have ground state wavefunctions dominated by (sd)-2(fp)+2  configurations
- T. Motobayashi *et al*: PLB 346 (1995) 9large B(E2;0+ 2+) in 32Mg
- See also
- 29Na V. Tripathi *et al*. Phys. Rev. Lett. **94** (2005) 162501 (2005)
- 31Mg G. Neyens *et al*. Phys. Rev. Lett. **94** (2005) 022501 (2005)
- 27Ne A. Obertelli *et al*., Phys. Lett **B 633** (2006) 33
- 28Ne H. Iwasaki *et al.*, Phys.Lett. **B 620** (2005) 118
- 34Al P. Himpe, G. Neyens *et al*. Phys.Lett. **B 658** (2008) 203

- Single-neutron removal to look for negative parity states, indicating the presence of f7/2 intruder configurations in the ground state of the parent: (30Mg,29Mg+) (26Ne,25Ne+) (28Ne,27Ne+)
- (38Si,36Mg+) two-proton removal

## Single-neutron removal from 26,28Ne and 30Mg

- 25Ne level structure known
- A.T. Reed *et al*., PRC **60** (1999) 024311
- S. Padgett et al., PRC **72 **(2005) 064330

- 25Ne is well-described in *sd* shell with no evidence for intruder states below 3 MeV
- No evidence for intruder configurations in the ground state wave function of 26Ne

- J.R. Terry *et al.*, Phys. Lett. **B 640** (2006) 86

## Single-neutron removal from 26,28Ne and 30Mg

## Single-neutron removal from 26,28Ne and 30Mg

- J.R. Terry *et al.*, Phys. Lett. **B 640** (2006) 86

- Ground states for 28Ne, 30Mg have significant 2h f7/2 intruder configurations
- See also31Mg G. Neyens *et al*. Phys. Rev. Lett. **94** (2005) 022501 (2005)27Ne A. Obertelli *et al*., Phys. Lett **B 633** (2006) 33

## +

- 38Si

- p

- n

- p

- n

- p

- n

- Monte-Carlo Shell Model (MCSM) calculations: SDPF-M interaction of       Y. Utsuno, T. Otsuka *et al*.

- 38Si: no significant intruder configurations in g.s. 36Mg: MCSM predicts strong intruder admixtures for the low-lying states
- 2p knockout from 38Si reaches only 0h components in 36Mg
- Comparison of measured cross sections and those calculated assuming the population of 0h components of the final states by the direct 2p knockout reaction: Only 32(8)% and 38(8)% of the w.f. of the g.s. and 2+ state, respectively, are 0hcomponents, the rest is proposed to be of intruder character
- Intruder domination places 36Mg inside the “Island of Inversion”

- A Gade *et al*., Phys. Rev. Lett. 99, 072502 (2007)

- Reaction theory: J.A. Tostevin and B.A. Brown, PRC  74,** **064604 (2006),

- N=20

## Proton scattering in inverse kinematics

- Many experiments at GANIL (MUST detector)
- Some experiments at MSU
- Thin target to avoid angular and energy straggeling of low-energy protons

- p(56Ni,p’) at GSI G. Kraus *et al.*, PRL  **73** (1994) 1773

- Normal kinematics

- Inverse kinematics

- F. Maréchal *et al.*, PRC  **60** (1999) 034615

## Inelastic scattering to measure transition rates: Thick-target -tagged inelastic proton scatteringPioneering experiment at RIKEN p(30Ne,30Ne)Y. Yanagisawa et al. PLB 566 (2003) 84 

- Hydrogen has the most scattering centers per energy loss
- Inelastic *p* scattering using two cocktail beam settings to study chains of isotopes accessible in a consistent approach
- Determine excited state energies and collectivity towards *N*=28
- Univ. Tokyo, RIKEN, Rikkyo Univ., Michigan State Univ. collaboration

- 40Si

- N

- Z

- 36Si

- Sulfur

- Silicon

- RIKEN/Kyushu/Rikkyo LH2 target:H. Ryuto *et al*., NIM **A 555** (2005) 1
- 30 mm diameter
- 9 mm thick, nominal
- Negligible contaminant  reactions

## Evolution of 2+ energies towards N=28

- Above *Z*=20Ti, Cr and Fe

- Below *Z*=20Si, S and Ar

- 40Si

- 986(6) keV

- 1.5 million 40Si beam particles
-  p,p’ = 20(3) mb
- ~30 counts in the photopeak
- Low energy indicative of neutron collectivity in 42Si

- C.M. Campbell *et al.*, PRL  **97** (2006) 112501

- Discovery of low-lying 2+ state in 42Si at GANIL B. Bastin, S. Grévy *et al.* PRL **99**, 022503 (2007)

## Higher excited states in 40Si

- Higher excited states in 40Si

- Two additional -rays in fragmentation channel 42P-*p-n*
- States at 1.62(1) MeV and 1.82(1) MeV?
- Not enough statistics to test if the two transitions are in coincidence
- Independent of the sequence, the second excited state is low in energy
- In the shell model second excited state is *ph-*excitation across *N*=28
- Low energy supports narrowing of the *N*=28 gap in 40Si

- C.M. Campbell *et al.*, PRL  **97** (2006) 112501

## Evolution and character of collectivity

- Prior data from F. Maréchal *et al*, PRC **60**, 034615 (1999)
- P.D. Cottle *et al*., PRL **88**, 172502 (2002)

- N

- N

- Rotational limit

- Vibrational limit

- Sulfur

- Silicon

- Enhanced collectivity towards N=28 in silicon
- Sulfur transitions from vibrational mid-shell to rotational towards N=28
- Silicon vibrational mid-shell

- C.M. Campbell Ph.D. PLB **652** (2007) 169

## Nucleon addition complements knockout

- Traditionally performed in normal kinematics at lower beam energies, e.g. (*d*,*n*), (3He,*d*), (,*t*), ...
- At higher energies momentum less well matched
- Trick: Pickup of a strongly-bound nucleon S. Shimoura *et al*., JPG 31, S1759
- Pioneering inverse kinematics experiment at RIKEN, (,*t*) reaction at 60 MeV/nucleon                                       S. Michimasa *et al*., PLB 638, 146 (2006)
- Few mb cross sections observed at intermediate energies
- NSCL: Pickup of a well-bound proton from 9Be [*S*p(9Be) = 16.9 MeV]First test case: 9Be(20Ne,21Na)X

**Inverse-kinematics proton-adding direct reactions with fast beams**

- 9Be(20Ne,21Na+)X
- 63.4 MeV/nucleon

- A.M. Mukhamedzhanov *et al*.
- PRC 73 (2006) 035806

- Population pattern broadly consistent with
- low-energy transfer reactions (and shell model)

- Total=1.2 mb

- A. Gade *et al*., PRC **76** (2007) 061302(R)

## Summary and Outlook

- Measurements and interpretation go hand-in-hand to advance knowledge
- For experiments with rare isotopes, beam rates limit which observables can be measured, even after we
- Build more efficient detectors
- Use targets with more scattering centers
- Make more beam
- Beam rate is the “Limit of experiments at the limits of stability”
- New robust experimental techniques have been developed that allow sensitive experiments with much decreased beam rates required
- New theoretical approaches are enabled by compute power and ingenuity
- New facilities are operational, under construction, and envisioned
- A dawn for discovery in science of atomic nuclei

## Collaborators

- P. Adricha), N. Aoic), D. Bazina), M. D. Bowena,b), B. A. Browna,b), C. Campbella,b),J. M. Cooka,b), D.-C. Dincaa,b), A. Gadea,b), M. Horoid), S. Kannoe), K. Kemperk), T. Motobayashic), A. Obertellia), T. Otsukaa,c,h), L. A. Rileyf), H. Sagawag), H. Sakuraic), K. Starostaa,b), H. Suzukih), S. Takeuchic), J. R. Terrya,b), J. Tostevini), Y. Utsunoij),  D. Weisshaara), K. Yonedac), H. Zwahlena,b)
- a) National Superconducting Cyclotron Laboratory, Michigan State University
- b) Department of Physics and Astronomy, Michigan State University
- c) RIKEN Nishina Center for Accelerator-Based Science
- d) Physics Department, Central Michigan University
- e) Department of Physics, Rikkyo University
- f) Department of Physics and Astronomy, Ursinus College
- g) Center for Mathematical Sciences, University of Aizu
- h) Department of Physics, University of Tokyo
- i) Department of Physics, University of Surrey
- j) Japan Atomic Energy Research Institute
- k) Physics Department, Florida State University

## Intermediate-energy Coulomb excitation of 32MgLarge transition matrix element indicates breakdown of the N=20 shell gap

- Intermediate-energy Coulomb excitation of 32MgLarge transition matrix element indicates breakdown of the *N*=20 shell gap

**Experiment:**
- Max.  determines min. impact param.

- Impact parameter

- Scattering angle

- Coul = 87 mb
- B(E2↑) = 454(78) e2fm4 = <0+||**O**(2)||2+>
- 2| = 0.49(4)

- Shell model

- Valence nucleonmodel

- T. Motobayashi, R. Casten *et al.*, Phys. Lett. **B** **346** (1995) 9
- T.G. Ann. Rev. Nucl. Part. Sci. **48** (1998) 1

**Notes:**
Masses and S2nC. Thibault et al., Phys. Rev. C 12, 644 (1975)C. Detraz et al., Nucl. Phys. A 394, 378 (1983)n (pf)-shell intruder statesX. Campi et al. Nucl. Phys. A251, 193 (1975)

## E2 transition strengths in 32,34Mg

- 34Mg Rate 10 atoms/s, run time 96 hrs, APEX detector
- 32Mg B(E2) in agreement with RIKEN, MSU results
- 26Mg B(E2) in agreement with adopted value
- 34Mg E(2+) and B(E2)=541(102) e2fm4 in agreement with RIKEN result

- J. Church *et al.*, Phys. Rev. C **72** (2005) 054320

## Intermediate-energy Coulomb excitationAn accurate technique that allows for absolute B(E2) measurementsJ. Cook et al., Phys. Rev. C 73 (2006) 024315Scheit, Gade, Glasmacher, Motobayashi, Phys. Lett. B 659 (2008) 515

- Active programs at GANIL, GSI, MSU and RIKEN
- One-step process
- Sensitive to *E*1, *E*2, *E*3 excitations

## Structure of 23F: Multiple reactions in one experiment~35 MeV/nucl,100 mg/cm2 liquid helium target at RIKEN

- A. Michimasa *et al*. Phys. Lett. **B 638** (2006) 146

## Single-proton addition

- Traditionally performed in normal kinematics at lower beam energies, e.g. (*d*,*n*), (3He,*d*), (,*t*), ...
- Few mb cross sections observed at intermediate energies

- Proton well-bound in 9Be*S*p(9Be) = 16.9 MeV
- 8Li has only one bound excited state

- Beam identification

- Reaction product identification

## Measure coincident -rays and particle momenta

## Approaching the “Island”:  9Be(30Mg,29Mg)X

- Level scheme of 29Mg is known
-  decay and -n decay:
- P. Baumann et al., PRC 36, 765 (1987)
-                               PRC 39, 626 (1989)
- 30Si(13C,14O)29Mg and 28Si(13C,14O)27Mg:
- C.L. Woods et al., NPA 476, 392 (1988)
- Levels at 1.431 and 1.095 MeV are assigned as 7/2- and 3/2-.
**Our experiment: **Momentum distributions are consistent with these previous  assignments and the states are directly populated in the knockout.
- Spectroscopic factors extracted from our data quantify intruder content in the gs of 30Mg

- C2S extracted from experiment

- J. Russ Terry et al., PRC, in press

**p****||**** (GeV/c)**

## The structure of 36Mg via 38Si →36Mg+

- The structure of 36Mg via 38Si →36Mg+

- Beam rate too low for 36Mg inelastic scattering and -decay impossible (36Na *n*-unbound)
- 48Ca primary beam, 1500 38Si per second secondary projectile beam (purity exceeded 95%)
- cross section: =0.10(1)mb              (~1 out of 400,000 38Si)
- 42(6)% of the cross section to 2+, 58(6)% to the ground state

- A. Gade *et al*., Phys. Rev. Lett. 99, 072502 (2007)