Physics at the extremes with large gamma-ray arrays Lecture 3 Robert V. F. Janssens The 14 th CNS International Summer School CNSSS15 Tokyo, August 26 – September 1, 2015

Outline: 2 Lecture 1: - Introduction to Gamma-ray Arrays - At the limits of spin Lecture 2:- Spectroscopy at the proton drip line - Spectroscopy of the heaviest nuclei Lecture 3:- Spectroscopy of neutron-rich nuclei via deep- inelastic reactions Lecture 4:- Spectroscopy of neutron-rich nuclei continued Robert V. F. Janssens CNSSS15

N-Rich Nuclei: Surprises everywhere you look Robert V. F. Janssens CNSSS15 3

Physics at the neutron dripline: 4

Basic “facts” of nuclear physics that may be wrong in far-from-stability nuclei  The charge-independence of the strong interaction makes isospin a good quantum number.  The radius and diffuseness of the neutron and proton distributions are similar. R=1.2 A 1/3, a~ 0.55 fm  The magic numbers of the shell model are fixed.  The deformations of the neutrons and protons are similar.  Valence single-particle states are only occupied at the 60% level due to short- range correlations. Robert V. F. Janssens CNSSS15 5

Some of the Physics Questions How does the asymmetry in the proton and neutron Fermi surfaces impact the nucleus; i.e. What is the impact on the mean field as reflected in: the single particle energies the shapes and spatial extensions the modes of excitation the binding energy, etc. What is the impact on correlations in the medium as reflected in: the effective interactions the effective charges the transition rates, etc. Ultimate goal: A unified theory of the nucleus Robert V. F. Janssens CNSSS15 6

Possible Changes in Structure for Skin Nuclei 82 1g N=5 N=4 2d 3s 1h 2f 3p g 9/2 g 7/2 d 5/2 d 3/2 s 1/2 h 11/2 p 3/2 h 9/2 p 1/2 i 13/2 f 5/2 f 7/ g 9/2 g 7/2 d 5/2 d 3/2 s 1/2 h 11/2 h 9/2 f 5/2 f 7/2 p 3/2 p 1/2 harmonic oscillator harmonic oscillator very diffuse surface neutron drip line very diffuse surface neutron drip line no spin orbit exotic nuclei/ hypernuclei no spin orbit exotic nuclei/ hypernuclei around the valley of  -stability around the valley of  -stability J. Dobaczewski and W. Nazarewicz Robert V. F. Janssens CNSSS15 7

40 Ca fp Playground for today Robert V. F. Janssens CNSSS15 8

Impacts of tensor force on nuclear structure in fpg shell 1)T. Otsuka et al., Phys. Rev. Lett. 87, )T. Otsuka et al., Phys. Rev. Lett. 104, As protons are removed from the  f 7/2 shell, the monopole pairing interaction weakens:   f 7/2 – f 5/2 : attractive, f 5/2 goes up in energy   f 7/2 – g 9/2 : repulsive, g 9/2 comes down in energy N=32 N=34 N=40 relative momentum small large N=50 Robert V. F. Janssens CNSSS15 9

First Experimental Evidence for N=32 Gap — Exp. ○ FPD6 As protons are removed from the f 7/2 shell (Z=28 to Z=20), the  f 7/2 - f 5/2 monopole interaction strength weakens and the f 5/2 orbital pushes up in energy.  possible shell gaps at N=32 and N=34. Shell model calculations with new GXPF1 interaction predict shell gaps at : N=32, 34 for Z≤ 24 (Cr) and for Z≤22 (Ti). J.I. Prisciandaro et al., PLB 501, 17 (2001) 52 Ca tentative (?) Robert V. F. Janssens CNSSS15 10

GXPF1: A New Effective Interaction for pf Shell M. Honma, T. Otsuka, B.A. Brown, T. Mizusaki PRC 65, (R) N = 32 or N=34 ? N=34 Robert V. F. Janssens CNSSS15 11

 54 Ti will not be produced with a fusion-evaporation reaction until a next generation exotic beam facility with reaccelerated beams come along!  That is no reason to wait!! Approach:  decay spectroscopy of fragments with (A,Z) selections  prompt spectroscopy following deep inelastic reactions & Coulomb excitation of fragments Combining  -decay & deep-inelastic data: Quest for 54 Ti Robert V. F. Janssens CNSSS15 12

Deep-inelastic reactions as a tool for nuclear spectroscopy 4 R. Broda et al., Phys.Lett. B 251,245 (1990) Robert V. F. Janssens CNSSS15 13

48 Ca U (thick target) 48 Ca 66 Ni Robert V. F. Janssens CNSSS15 14

Detailed product yield distribution measured with the thick-target technique for the system: 64 Ni Pb at 350 MeV 208 Pb 64 Ni N/Z( 208 Pb)=1.54 N/Z( 64 Ni)= W. Krolas et al., Nucl. Phys. A724, (2003) Robert V. F. Janssens CNSSS1515

W. Krolas et al., Nucl. Phys. A724, (2003) Robert V. F. Janssens CNSSS15 16

48 Ca 208 Pb 238 U N/Z=1.54 N/Z=1.59 N/Z=1.4 Robert V. F. Janssens CNSSS15 17 Deep-inelastic reactions: production of 54 Ti

N=28 N=50 48 Ca Pb N= Ca Ti Cr Ar Fe Ni S ATLAS & Gammasphere at Argonne NL 48 Ca (305 MeV) Pb (thick) Robert V. F. Janssens CNSSS1518

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Beta-decay of the 54 Sc parent measured at NSCL following fragmentation of a Kr beam Deep-inelastic reaction data 48 Ca Pb, Gammasphere, ATLAS R.V.F. Janssens et al., PLB 546, 22 Robert V. F. Janssens CNSSS15 21

54 Ti 53 Ti 54 Ti Robert V. F. Janssens CNSSS1522

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2+2+ (8 + ) (9 + ) (10 + ) Robert V. F. Janssens CNSSS1524 Power of Gammasphere: - coincidences - angular correlations

Robert V. F. Janssens CNSSS Ti: Identification 53 Ti 54 Ti

Even –Even Ti Isotopes: where does 54 Ti fit? Robert V. F. Janssens CNSSS15 26

Shell Model Interpretation and N = 32 Gap 32 R.V.F. Janssens et al., PLB 546, 22  (f 7/2 ) 2,J p ] x [  f 7/2 ) 8 (p 3/2 ) 4,J n =0] [ (f 7/2 ) 8 (p 3/2 ) 3 (f 5/2 ) 1, J n =3,4] [  (f 7/2 ) 2,J p =6] x [ (f 7/2 ) 8 (p 3/2 ) 3 (p 1/2 ) 1, J n =2] 8+8+ Robert V. F. Janssens CNSSS15 27

Search for 56 Ti and the N=34 gap Expectations: GXPF1 calculation predicts: a high E(2 + )  1516 keV a large gap between the 6 + and 8+ levels  2308 keV 56 Ti Robert V. F. Janssens CNSSS15 28

Same Techniques:  decay and Deep Inelastic reactions CCF : 86 Kr fragmentation A1900 fragment separator Sc implants < 1% of all implants ATLAS & Gammasphere 48 Ca (330 MeV) U (thick) Use 238 U as a reservoir of neutrons (N/Z = 1.59 for 238 U vs 1.54 for 208 Pb) BUT Target-like products of 238 U fission  Identification based on cross- coincidence between gamma rays from reaction partners almost impossible.  Need to know at least one gamma ray! relative 6 + state feeding yields, normalized to 50 Ti Search for 56 Ti and the N=34 gap Robert V. F. Janssens CNSSS15 29

48 Ca U: does one see anything? Robert V. F. Janssens CNSSS15 30

56 Sc Observables 1129 SURPRISE!! E(2 +  0 + ): 1129 keV NOT 1516 keV (GXPF1) T 1/2 = 36 (6) ms S. N. Liddick et al, PRL 92, Robert V. F. Janssens CNSSS15 31 Search for 56 Ti: Start from  decay

56 Ti from 48 Ca U GXPF1 did so well for Ti, i.e. for N = 28 – 32, but fails for N=34 B. Fornal et al., PRC 70, Robert V. F. Janssens CNSSS15 32

Ti isotopes: Situation in 2012 R.V.F. Janssens et al., PLB 546, 22, B. Fornal et al., PRC 70, Robert V. F. Janssens CNSSS

Beyond 2 + Energies E(2 + ) values are a strong indicator of shell structure, but.. Additional evidence for the presence or absence of shell effects is most welcome and very desirable!  Measure B(E2; 0 +  2 + ) values At present, this can only be done with Ti nuclei from fragmentation  Intermediate Energy Coulomb Excitation! Robert V. F. Janssens CNSSS15 34

Beyond 2 + Energies: B(E2; 0 +  2 + ) values Ti E Ti ≈ 80 MeV/nucl.  ≈ 0.4,  ≈ 1.1 b min ≈ 20 fm “touching spheres” 1.2(A Ti 1/3 +A Au 1/3 ) ≈ 11 fm SeGA array Primary Beam: 130 MeV/u 76 Ge Yields: s Ti; 2400 s Ti; 75 s Ti Robert V. F. Janssens CNSSS15 35

56 Ti E  = 1129(7) keV  (  <  max ) = 155(51) mb B(E2,  ) = 599(197) e 2 fm 4 54 Ti E   = 1497(4) keV  (  <  max ) = 83(15) mb B(E2,  ) = 357(63) e 2 fm 4 52 Ti E   = 1050(2) keV  (  <  max ) = 119(16) mb B(E2,  ) = 593(81) e 2 fm 4 B(E2; 0 +  2 + ) values D.-C. Dinca et al., PRC 71, (R) Robert V. F. Janssens CNSSS15 36

Shell Effects in Ti isotopes: Energies and B(E2)’s 48Ti50Ti52Ti54Ti56Ti B ( E2,  ) ( e 2 fm 4 ) N From an experimentalist’s point of view: N = 28 and N=32 gaps are quite visible in BOTH the E(2 + ) energies and in the B(E2;0 +  2 + ) values and there is no experimental evidence for a N=34 gap D.-C. Dinca et al., PRC 71, (R) Intermediate Energy Coulex at NSCL b decay & deep inelastic reactions Robert V. F. Janssens CNSSS15 37

From GXPF1 to GXPF1A 48Ti50Ti52Ti54Ti56Ti E(2 + ) GXPF1 26 E(2 + ) Energy (keV) N GXPF1A e p = 1.5, e n = 0.5 GXPF1A vs GXPF1: T=1 matrix elements involving p 1/2 and f 5/2 modified  p 1/2 - f 5/2 ) gap reduced by ~0.5 MeV D.-C. Dinca et al., PRC 71, (R) Robert V. F. Janssens CNSSS15 38

Value of effective charges? B(E2) = (A p e p + A n e n ) 2 A Ap An Robert V. F. Janssens CNSSS15 39

From GXPF1 to GXPF1A 48Ti50Ti52Ti54Ti56Ti E(2 + ) GXPF1 26 E(2 + ) Energy (keV) N GXPF1A GXPF1A vs GXPF1: T=1 matrix elements involving p 1/2 and f 5/2 modified  p 1/2 - f 5/2 ) gap reduced by ~0.5 MeV e p = 1.15 e n = 0.8 du Rietz et al., PRL 93, (2004) Robert V. F. Janssens CNSSS15 40 D.-C. Dinca et al., PRC 71, (R)

Testing GXPF1A Further 55 Ti & 55 V How good a semi-magic nucleus is 54 Ti? Let’s look at particle excitations Robert V. F. Janssens CNSSS15 41

New data: 55 V and another technique 55 V from 48 Ca( 9 Be,pn) 55 V at 172 MeV 55 Ti  p  b   3n/4n  mb 55 V  p,n  b Robert V. F. Janssens CNSSS15 42

New data: 55 V and another technique  f 3 7/2 ) x  f 8 7/2 p 4 3/2 )  f 3 7/2 ) x  f 8 7/2 p 3 3/2 f 5/2 ) Problems above 19/2 N=32 gap present by E   MeV just like in 54 Ti S. Zhu et al., Phys. Lett. B, in press Branching ratios reproduced as well S. Zhu et al., Phys. Lett. B 650, 137 Robert V. F. Janssens CNSSS15 43

54 Ti x p 1/2 54 Ti x f 5/2 54 Ti(4 + ) x p 1/2 54 Ti(6 + ) x p 1/2 54 Ti(4 + ) x f 5/2 54 Ti Core broken (~ 1.8 MeV as in 54 Ti) 300 keV difference  f 5/2 - p 1/2 too large? S. Zhu et al., Phys. Lett. B 650, 137 exp GXPF1A Robert V. F. Janssens CNSSS15 44 New data: 55 Ti

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— Exp. ○ FPD6 J.I. Prisciandaro et al., PLB 501, Ca tentative (?) E(2 + ) in 52 Ca comes from a 1983 ISOLDE  -decay study (A.Huck et al., PRC 31, 2226 (1985)) where the separation between  decay and n-delayed b decay was a problem Attempts to identify 52 Ca via deep- inelastic reactions was unsuccessful At NSCL 52 Ca intensity was too small for A Coulex experiment  2p knockout!! Robert V. F. Janssens CNSSS15 46 Experimental Evidence for N=32 Gap: 52 Ca

2p knockout into 52 Ca Direct process Knock-out of 2 f 7/2 protons from 54 Ti Cross section is small (~ 0.32 mb)  52 Ca is magic No direct feeding of 2 + state:  Consistent with a neutron excitation A. Gade et al., PRC 74, (R) Scheme confirmed since in new  decay expt., F. Perrot et al., PRC 74, Robert V. F. Janssens CNSSS15 47

2p knockout into 52 Ca 2p knockout provides a way to study p cross-shell excitations in n-rich nuclei 3 - is  ((d 3/2 or s 1/2 )-1 (f 7/2 )) excitation A. Gade et al., PRC 74, (R) Robert V. F. Janssens CNSSS15 48

52 Sc 51 Ca 55V55V 55 Ti GXPF1A tested further: the N=31 nuclei Robert V. F. Janssens CNSSS15 49

CLARA PRISMA 48 Ca B. Fornal et al., PRC 77, Robert V. F. Janssens CNSSS Ca (330 MeV) U at LNL Legnaro with PRISMA+CLARA

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F. Perrot et al., Phys.Rev. C 74, B. Fornal et al., PRC 77, Robert V. F. Janssens CNSSS15 52

Identification of p 1/2 and f 5/2 in 51 Ca and 52 Sc 2 (8 + ) 2 51 Ca (9/2 - ) (5/2 - )  f 7/2 p 3/2 f 5/2 p 3/2 f 5/2 2 2 p 3/2 p 1/2 2 (6+)(6+)  f 7/2 p 3/2 p 1/2 2 Robert V. F. Janssens CNSSS15 53

53 Ti 52 Sc 51 Ca  f 7/2 p 3/2 f 5/ p 3/2 f 5/2 2 B. Fornal et al., PRC 77, Robert V. F. Janssens CNSSS15 54

Take Away Message: 55 Robert V. F. Janssens CNSSS15 - the large arrays, combined with deep-inelastic reactions, are a powerful tool to study neutron-rich nuclei; - experiments are challenging as many channels are produced at the same time  this is where the resolving power of the arrays is essential; - depending on the projectile-target combination, identification through cross- channel excitations might be possible; this is impossible if one of the reaction partners fissions; (and 238 U is the best neutron reservoir); - identification can also come from  decay, or from data from fragmentation facilities, or from identification through detection of the reaction product in separators; - the use of thick targets limits the technique to the observation of states with lifetimes longer than the stopping time in the target; there are also limitations due to multiplicity requirements; - we used the n-rich nuclei just above 48 Ca as examples  more physics in the next lecture