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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
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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
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1967 208Pb(d,p)209Pb
Deuteron beam + targetTandem + spectrometer>1010 pps (stable) beamHelpful graduate students
1950’s1960’s
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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……..
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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…
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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
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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
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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.
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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?)
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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°
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Forward Annular Si5.6 < lab < 36
Backward Annular Si144 < lab < 168.5
Barrel Si36 < lab < 144
Target Changing Mechanism
BeamVAMOS
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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
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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
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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
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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
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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)
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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)
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1 mg/cm2
TIARA+MUST2+VAMOS+EXOGAM @ SPIRAL/GANIL
Focal Plane:
80% 15N3+
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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
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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 !
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26Ne (SPIRAL) ~10 A MeV3000 pps
1 mg/cm2
TIARA+MUST2+VAMOS+EXOGAM @ SPIRAL/GANIL
Focal Plane:
PURE
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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
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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.
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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
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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
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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!
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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…
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TIGRESSISAC2
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~ 3 x 107 pps
SHARC at ISAC2 at TRIUMFChristian Diget
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SHARC chamber(compact Si box)
TIGRESS
TIGRESS
TRIFOIL @ zero degrees
Bank of 500 preamplifierscabled to TIG10 digitizers
BEAM
WILTON CATFORD, SURREY
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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
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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.
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PRELIMINARY
PRELIMINARY
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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
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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
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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