The neutron magic numbers N=16, 20 & 28 for neutron rich exotic nuclei, as probed by nucleon transfer with radioactive beams

Wilton CatfordUniversity of Surrey, UK

Thank you to all my collaborators who made it possible to perform the experiments reported in this talkSURREY, PAISLEY, LIVERPOOL, YORK, BIRMINGHAM, DARESBURY with LPC CAEN, ORSAY, SACLAY, GANIL, SANTIAGO, TRIUMF

Learning about nuclear structure usingsingle neutron transfer reactions with reaccelerated radioactive beams

Wilton CatfordUniversity of Surrey, UK

Thank you to all my collaborators who made it possible to perform the experiments reported in this talkSURREY, PAISLEY, LIVERPOOL, YORK, BIRMINGHAM, DARESBURY with LPC CAEN, ORSAY, SACLAY, GANIL, SANTIAGO, TRIUMF

• those new magic numbers that appear all the time in PRL• How nucleon transfer helps us to understand structure evolution• Some details that affect how we need to design experiments• Examples of current experimental apparatus: TIARA, SHARC• Some examples of recent results in the neutron rich neon region

1967 208Pb(d,p)209Pb

Deuteron beam + targetTandem + spectrometer>1010 pps (stable) beamHelpful graduate students

1950’s1960’s

1967 208Pb(d,p)209Pb 1998 d(56Ni,p)57Ni 1999 p(11Be,d)10BeRehm ARGONNE Fortier/Catford GANIL

STAB

LE N

UCL

EI

RADI

OAC

TIVE

1950’s1960’s

1990’s2000’s……..

1p3/21p3/2

StableExotic

1p3/21p3/2

StableExotic

Utsuno et al., PRC,60,054315(1999)Monte-Carlo Shell Model (SDPF-M)

N=20

N=20

Exotic Stable

Removing d5/2 protons (Si O)

gives relative rise in n(d3/2)

Note:This changescollectivity,also…

Example of population of single particle state: 21O

0d 5/21s 1/2

0d 3/2

The mean field has orbitals, many of which are filled.We probe the energies of the orbitals by transferring a nucleonThis nucleon enters a vacant orbitalIn principle, we know the orbital wavefunction and the reaction theory

But not all nuclear excited states are single particle states…

0d 5/21s 1/2

energy of level measures this gap

Jp = 3/2+

Jp = 3/2+

2+

x 1/2+

We measure how the two 3/2+ statesshare the SP strength when they mix

A. SINGLE PARTICLE STATES – EXAMPLE

SINGLE PARTICLE STATES – SPLITTING

Plot: John Schiffer

If we want to measure the SPE,splitting due to level mixingmeans that all componentsmust be found, to measure the true single particle energy

A PLAN for how to STUDY STRUCTURE• Use transfer reactions to identify strong single-particle states, measuring their spins and strengths

• Use the energies of these states to compare with theory

• Refine the theory

• Improve the extrapolation to very exotic nuclei

• Hence learn the structure of very exotic nuclei

N.B. The shell model is arguably the best theoretical approach for us to confront with our results, but it’s not the only one. The experiments are needed, no matter which theory we use.

N.B. Transfer (as opposed to knockout) allows us to study orbitals that are empty, so we don’t need quite such exotic beams.

USING RADIOACTIVE BEAMS in INVERSE KINEMATICS

Single nucleon transfer will preferentially populate the states in the real exotic nucleus that have a dominant single particle character.

Angular distributions allow angular momenta and (with gammas) spins to be measured. Also, spectroscopic factors to compare with theory.

Around 10A MeV/A is a useful energy as the shapes are very distinctive for angular momentumand the theory is tractable.

Calculated differential cross sections show that 10 MeV/A is good (best?)

INCIDENT BEAM

The energies are onlyweakly dependent onmass of the beamso a general purposearray can be utilised

USING RADIOACTIVE BEAMS in INVERSE KINEMATICS

(d,d)justforward of 90°

(d,p)from 180° to

forward of 80°(d,t)forward of 45°

Forward Annular Si5.6 < lab < 36

Backward Annular Si144 < lab < 168.5

Barrel Si36 < lab < 144

Target Changing Mechanism

BeamVAMOS

Leaping ahead to preview resultshorizontal axis = gamma-ray energywith doppler correction appliedvertical axis = energy populated in (d,p)as calculated from proton angle and energy

25Na (d,p) 26Na

combining transfer and gamma-ray decays gives a rich insight into the structure

CX FUSION-EVAP

26Na had been studied a little, beforehand (N=15, quite neutron rich)

ALL of the states seen in (d,p) are NEW(except the lowest quadruplet)We can FIND the states with simple structure,Measure their excitation energies,and feed this back into the shell model

negative parity

positiveparity

TIARA

24Ne + d 25Ne + p 100,000 ppst 1/2 = 3.38 min

20O 10,000 ppst 1/2 = 13.51 s

26Ne < 3000 ppst 1/2 = 197 ms

2014/2015

26Ne (SPIRAL) ~10 A MeV3000 pps

1 mg/cm2

TIARA+MUST2+VAMOS+EXOGAM @ SPIRAL/GANIL

Focal Plane:

25Ne re-accelerated beamat pps, 10.A MeVisotopically pure beam,CIME at SPIRAL/GANIL

PURE

Results from a (d,p) experiment to study 25Ne

GAMMA RAY ENERGY SPECTRA

EXCITATION E_x FROM PROTONS

FIX E_x

W.N. Catford et al., PRL 104, 192501 (2010)

2030

1680

= 2

= 0

5/2+

3/2+

1/2+

= 2

0.80

0.15

0.44

1/2+

3/2+

5/2+

3/2+

5/2+

9/2+7/2+

5/2+

0.49

0.10

0.11

0.004

n+24Negs

USD

0.63

In 25Ne we used gamma-gamma coincidencesto distinguish spinsand go beyond orbital AMFIRST QUADRUPLE COINCIDENCE (p-HI-g-g )RIB TRANSFER DATA

Inversion of 3/2+ and 5/2+due to monopole migration

Summary of 25Ne Measurements Negative parity states(cross shell) also identified

4030

3330 p = –

= 1

( = 3)7/2 –

3/2 –

0.73

0.75

W.N. Catford et al., PRL 104, 192501 (2010)

1 mg/cm2

TIARA+MUST2+VAMOS+EXOGAM @ SPIRAL/GANIL

Focal Plane:

80% 15N3+

21O

VAMOS

TIARA

(d,p)BOUND STATES

New Experimental Results: d(20O,p)21O and (d,t) and (d,d)

19O

A. Ramus et al. Ph.D. Paris XI

20O

Unbound

20O(d,d*)20O20O(p,p*)20O

20O(d,p)21O

TIARA

MUST2

TIARA

BOUND STATES: d(20O,t)19O (pick-up)

A. Ramus PhD. Thesis Universite Paris XI

C2S=4.76(94)

C2S=0.50(11)

0d5/2 =6.80(100)

1s1/2 =2.04(39)

Jπ= 1/2+

Jπ= 5/2+

Sum Rules:M. Baranger et al., NPA 149, 225 (1970)

v1s1/2 partially occupied in 20O : correlations

Full strength for 0d5/2 and 1s1/2 measured !

26Ne (SPIRAL) ~10 A MeV3000 pps

1 mg/cm2

TIARA+MUST2+VAMOS+EXOGAM @ SPIRAL/GANIL

Focal Plane:

PURE

27Ne IS THE NEXT ISOTONE

N=17 ISOTONES

Shell model predictionsvary wildly for fp intruders

Systematics show regionof dramatic change

27Ne Predictions

7/2 never seen3/2 known

27Ne BOUND STATES

The target was 1 mg/cm2 CD2

(thick, to compensate for 2500 pps)

Known bound states were selectedby gating on the decay gamma-ray(and the ground state by subtraction)

3/2 3/2+In these case, the spinswere already known.

The magnitude was thequantity to be measured.

27Ne results• level with main f7/2 strength is unbound• excitation energy measured• spectroscopic factor measured• the f7/2 and p3/2 states are inverted• this inversion also in 25Ne experiment• the natural width is just 3.5 1.0 keV

27Ne UNBOUND STATES

EXCLUDE

MISSINGMOMENTUM

25Ne 27Ne

27Ne17

d3/2 level is 2.030 25Ne

4.03

1.80

0.76

3.33

1.80 7/2

0.76 3/2

N=17 ISOTONES

ISOTOPECHAINS

Mg Ne

27Ne results

• we have been able to reproduce the observed energies with a modified WBP interaction, full 1hw SM calculation

• the SFs agree well also

• most importantly, the new interaction works well for 29Mg, 25Ne also

• so we need to understand why an ad hoc lowering of the fp-shell by 0.7 MeV is required by the data!

protons neutrons

d 5/2

s 1/2

d 3/2

f 7/2

p 3/2

25Na (d,p) 26Na

odd-odd final nucleus

High density of statesGamma-gating needed

The Next Step…

TIGRESSISAC2

~ 3 x 107 pps

SHARC at ISAC2 at TRIUMFChristian Diget

SHARC chamber(compact Si box)

TIGRESS

TIGRESS

TRIFOIL @ zero degrees

Bank of 500 preamplifierscabled to TIG10 digitizers

BEAM

WILTON CATFORD, SURREY

Doppler corrected (b=0.10) gamma ray energy measured in TIGRESS

Exci

tatio

n en

ergy

ded

uced

from

pro

ton

ener

gy a

nd a

ngle

ground state decays

cascade decays

Data from d(25Na,p)26Na at 5 MeV/A using SHARC at ISAC2 at TRIUMFGemma Wilson, Surrey

If we gate on a gamma-ray,then we bias our protonmeasurement, if the gammadetection probability dependson the proton angle.

And it does depend on the proton angle, because thegamma-ray correlation isdetermined by magneticsubstate populations.

However, our gamma-ray angularcoverage is sufficient that theintegrated efficiency for gammadetection remains very similar andthe SHAPE of the proton angulardistribution is unchanged by gating.

PRELIMINARY

PRELIMINARY

Designed to use cryogenic target CHyMENE and gamma-arrays PARIS, AGATA…A development of the GRAPA concept originally proposed for EURISOL.

FUTURE: • We have experiments planned with 16C, 64Ge at GANIL & 28Mg and others at TRIUMF• Many other groups are also busy! T-REX at ISOLDE, ORRUBA at ORNL etc• New and extended devices are planned for SPIRAL2, HIE-ISOLDE and beyond

TSR@ISOLDE

12C6+

electron capture limit

multiple scattering limit

Circumference 55.4m

• Existing storage ring• Re-deploy at ISOLDE• Thin gas jet targets• Light beams will survive• Increased luminosity• Supported by CERN• In-ring initiative led by UK• Also linked to post-ring helical spectrometer

The neutron magic numbers N=16, 20 & 28 for neutron rich exotic nuclei, as probed by nucleon transfer with radioactive beams

Wilton CatfordUniversity of Surrey, UK

Thank you to all my collaborators who made it possible to perform the experiments reported in this talkSURREY, PAISLEY, LIVERPOOL, YORK, BIRMINGHAM, DARESBURY with LPC CAEN, ORSAY, SACLAY, GANIL, SANTIAGO, TRIUMF