The neutron magic numbers N=16, 20 & 28 for neutron rich exotic nuclei, as probed by nucleon transfer with radioactive beams Wilton Catford University of Surrey, UK Thank you to all my collaborators who made it possible to perform the experiments reported in this talk SURREY, PAISLEY, LIVERPOOL, YORK, BIRMINGHAM, DARESBURY with LPC CAEN, ORSAY, SACLAY, GANIL, SANTIAGO, TRIUMF

Learning about nuclear structure using single neutron transfer reactions with reaccelerated radioactive beams Wilton Catford University of Surrey, UK Thank you to all my collaborators who made it possible to perform the experiments reported in this talk SURREY, 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

Pb(d,p) 209 Pb Deuteron beam + target Tandem + spectrometer >10 10 pps (stable) beam Helpful graduate students 1950’s 1960’s

Pb(d,p) 209 Pb1998 d( 56 Ni,p) 57 Ni1999 p( 11 Be,d) 10 Be Rehm ARGONNEFortier/Catford GANIL STABLE NUCLEI RADIOACTIVE 1950’s 1960’s 1990’s 2000’s……..

1p3/2 Stable Exotic 1p3/2 Stable Exotic Utsuno et al., PRC,60,054315(1999) Monte-Carlo Shell Model (SDPF-M) N=20 Exotic Stable Removing d5/2 protons (Si  O) gives relative rise in (d3/2) Note: This changes collectivity, also…

Example of population of single particle state: 21 O 0d 5/2 1s 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 nucleon This nucleon enters a vacant orbital In principle, we know the orbital wavefunction and the reaction theory But not all nuclear excited states are single particle states… 0d 5/2 1s 1/2 energy of level measures this gap J  = 3/ x 1/2 + We measure how the two 3/2 + states share 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 mixing means that all components must 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 momentum and the theory is tractable. Calculated differential cross sections show that 10 MeV/A is good (best?)

INCIDENT BEAM The energies are only weakly dependent on mass of the beam so a general purpose array can be utilised USING RADIOACTIVE BEAMS in INVERSE KINEMATICS (d,d) just forward of 90° (d,p) from 180° to forward of 80° (d,t) forward of 45°

Forward Annular Si 5.6  <  lab < 36  Backward Annular Si 144  <  lab <  Barrel Si 36  <  lab < 144  Target Changing Mechanism Beam VAMOS

Leaping ahead to preview results horizontal axis = gamma-ray energy with doppler correction applied vertical axis = energy populated in (d,p) as calculated from proton angle and energy 25 Na (d,p) 26 Na combining transfer and gamma-ray decays gives a rich insight into the structure

CX FUSION-EVAP 26 Na 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 positive parity

TIARA 24 Ne + d  25 Ne + p 100,000 pps  1/2 = 3.38 min 20 O 10,000 pps  1/2 = s 26 Ne < 3000 pps  1/2 = 197 ms 2014/2015

26 Ne (SPIRAL) ~10 A MeV 3000 pps 1 mg/cm 2 SPIRAL/GANIL Focal Plane: PURE

Results from a (d,p) experiment to study 25 Ne GAMMA RAY ENERGY SPECTRA EXCITATION E_x FROM PROTONS FIX E_x W.N. Catford et al., PRL 104, (2010)

= 2 = 0 5/2+ 3/2+ 1/2+ = /2+ 3/2+ 5/2+ 3/2+ 5/2+ 9/2+ 7/2+ 5/ n+ 24 Ne gs USD 0.63 In 25 Ne we used gamma-gamma coincidences to distinguish spins and go beyond orbital AM FIRST QUADRUPLE COINCIDENCE (p-HI-  -  ) 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  = – = 1 ( = 3) 7/2 – 3/2 – W.N. Catford et al., PRL 104, (2010)

1 mg/cm 2 SPIRAL/GANIL Focal Plane: 80% 15 N 3+

21 O VAMOS TIARA (d,p) ‏ BOUND STATES New Experimental Results: d( 20 O,p) 21 O and (d,t) and (d,d)‏ 19 O A. Ramus et al. Ph.D. Paris XI 20 O Unbound 20 O(d,d*) 20 O 20 O(p,p*) 20 O 20 O(d,p) 21 O TIARA MUST2 TIARA

BOUND STATES: d( 20 O,t) 19 O (pick-up)‏ A. Ramus PhD. Thesis Universite Paris XI C 2 S=4.76(94) C 2 S=0.50(11) 0d 5/2 = 6.80(100) 1s 1/2 = 2.04(39) J π = 1/2+ J π = 5/2+ Sum Rules: M. Baranger et al., NPA 149, 225 (1970) v1s1/2 partially occupied in 20 O : correlations Full strength for 0d 5/2 and 1s 1/2 measured !

26 Ne (SPIRAL) ~10 A MeV 3000 pps 1 mg/cm 2 SPIRAL/GANIL Focal Plane: PURE

27 Ne IS THE NEXT ISOTONE N=17 ISOTONES Shell model predictions vary wildly for fp intruders Systematics show region of dramatic change 27 Ne Predictions 7/2  never seen 3/2  known

27 Ne BOUND STATES The target was 1 mg/cm 2 CD 2 (thick, to compensate for 2500 pps) Known bound states were selected by gating on the decay gamma-ray (and the ground state by subtraction) 3/2  3/2 + In these case, the spins were already known. The magnitude was the quantity to be measured.

27 Ne results level with main f 7/2 strength is unbound excitation energy measured spectroscopic factor measured the f 7/2 and p 3/2 states are inverted this inversion also in 25 Ne experiment the natural width is just 3.5  1.0 keV 27 Ne UNBOUND STATES EXCLUDE MISSING MOMENTUM

25 Ne 27 Ne 27 Ne 17 d3/2 level is Ne /2  /2  N=17 ISOTONES ISOTOPE CHAINS MgNe

27 Ne 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 29 Mg, 25 Ne 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 25 Na (d,p) 26 Na odd-odd final nucleus High density of states Gamma-gating needed The Next Step…

TIGRESS ISAC2

~ 3 x 10 7 pps SHARC at ISAC2 at TRIUMF Christian Diget

SHARC chamber (compact Si box) TIGRESS zero degrees Bank of 500 preamplifiers cabled to TIG10 digitizers BEAM WILTON CATFORD, SURREY

Doppler corrected (  =0.10) gamma ray energy measured in TIGRESS Excitation energy deduced from proton energy and angle ground state decays cascade decays Data from d( 25 Na,p) 26 Na at 5 MeV/A using SHARC at ISAC2 at TRIUMF Gemma Wilson, Surrey

If we gate on a gamma-ray, then we bias our proton measurement, if the gamma detection probability depends on the proton angle. And it does depend on the proton angle, because the gamma-ray correlation is determined by magnetic substate populations. However, our gamma-ray angular coverage is sufficient that the integrated efficiency for gamma detection remains very similar and the SHAPE of the proton angular distribution is unchanged by gating.

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 16 C, 64 Ge at GANIL & 28 Mg 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

12 C 6+ 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 Catford University of Surrey, UK Thank you to all my collaborators who made it possible to perform the experiments reported in this talk SURREY, PAISLEY, LIVERPOOL, YORK, BIRMINGHAM, DARESBURY with LPC CAEN, ORSAY, SACLAY, GANIL, SANTIAGO, TRIUMF