Exotic Beam Summer School 2019 Nuclear Structure Experiment THE SEQUEL! Christopher J. Chiara CCDC-ARL/ORAU ORGANIZATION OF THESE LECTURES We will explore the six Ws of experimental nuclear structure: Who? What? When?

Where? Why? hoW? (but not necessarily in that order) Selection of topics Shell structure recap Ground-state properties (briefly) Excited-state properties

Pulling it all together: Case study 1 Something different: Case study 2 NUCLEAR STRUCTURE (the HOW?) In Weds lecture, we left off with HOW to study nuclear structure using g-spectroscopy techniques. Ways to identify the origin of a g ray if nothing known Auxiliary devices coupled to g-ray detectors providing nuclide/reaction information (Z, A/q, reaction products, decay products, Coulomb excitation of projectile) Correlation with g rays from known reaction partner Placing g rays in a level scheme CJC perspective: Its like putting together a jigsaw puzzle when you dont know what the picture looks like and you

dont have all of the pieces. Logic, guidance from systematics and/or theory (use with caution!), gn coincidences BUILDING A LEVEL SCHEME Level and g properties Measured Egs level energies Efficiency-corrected g peak areas intensities, branching ratios, level populations g ADs/ACs, g polarizations, internal conversion multipolarity level spin, parity z Intensity of EM field (emitted photon) given by Poynting vector, which depends on spherical harmonics Ylm(q,f,ff), where q,f is relative to quantization axis q,f

BUILDING A LEVEL SCHEME Angular distributions Quantization axis = spin direction May be known event by event Reaction plane defines spin vector z= y x b q,f y x BUILDING A LEVEL SCHEME

Angular distributions Quantization axis = spin direction May be known event by event Reaction plane defines spin vector z= y x b Detect outgoing particle trajectory to determine reaction plane, measure angle f relative to that (f is the difference between lab angles fg and fp) f y x

BUILDING A LEVEL SCHEME Angular distributions Quantization axis = spin direction May be known event by event Reaction plane defines spin vector z= Stone et al., PRL94, 192501 (2005) y x b Detect outgoing particle trajectory to determine reaction plane, measure angle f relative to that

y x f Measure intensity as a function of angle (f is the difference between lab angles fg and fp) BUILDING A LEVEL SCHEME Angular distributions Quantization axis = spin direction May be known event by event or it may not! What to do then? ( )= 2 2 ( cos )

=0 Reaction plane still defines spin vector, even if not determined experimentally z= y x q,f Ensemble of spins perpendicular to beam direction, symmetrically distributed use beam axis for quantization y x Measure intensity as a function of angle BUILDING A LEVEL SCHEME

Angular distributions Quantization axis = spin direction May be known event by event or it may not! What to do then? ( )= 2 2 ( cos ) =0 Pure dipole only has P2 term, quad adds P4, oct has P6, etc. With M1/E2 mixing, A4 0; mixing ratio d* can be deduced, providing insight into underlying structure Strictly speaking, AD in singles; gated AD: gg coincidence with no angle condition on gating g (clean-up only) if 4p coverage, same AD as in singles * d2 = (E2 intensity)/(M1 intensity)

BUILDING A LEVEL SCHEME Angular distributions Quantization axis = spin direction May be known event by event or it may not! What to do then? Spins not aligned indefinitely AD attenuated through hyperfine interactions If there is no spin orientation, all substates contribute equally and W(q,f) = constant What to do if alignment is lost (or was never there), e.g. for gs below isomers? BUILDING A LEVEL SCHEME

Angular correlations W(y) Coincidence technique Detect first g defines quantization axis Detect second g determine relative angle ( )= 2 2 ( cos ) =0 Same form as for AD, different coefficients. L limit determined by lowest multipole. 1.10 E2-E2

1.05 1.00 E2-E1 E1-E1 0.95 0.90 0.85 W(y) 0 15 30

2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 y45 60 75 90 y

0+2+0+ 0 15 30 45 y 60 75 90

BUILDING A LEVEL SCHEME E2 E2 65 E2 M1/E2(d=-0.11) M1/E2(d=-0.11) M1/E2(d=-0.15) Cu ADs 48Ca+26Mg E3 M1/E2(d=1.0) Chiara et al., PRC85, 024309 (2012) 67 Cu ACs 64Ni+238U

BUILDING A LEVEL SCHEME ADs/ACs multipole order L, but do not directly distinguish E vs M Pure DI=1 E1, e.g., looks the same as pure DI=1 M1 Nonzero mixing ratio may change that, as M1/E2 far more likely than E1/M2 For more direct determination of E or M: measure polarization (e.g. Clover detectors) or internal-conversion electrons Continuum Initial state L shell K shell Atomic System

Nuclear System Nuclear level decay via internal conversion (IC) first observed over 100 y ago [van Baeyer and Hahn, Physik. Z. 11, 488 (1910)] * ubiquitous process usable as analysis tool (cf. BrIcc, http://bricc.anu.edu.au/) Instead of g emission, energy transferred to atomic electron, which is ejected * nucleus discovered in 1911! BUILDING A LEVEL SCHEME Internal conversion

= + = + = + = (1+ ) = (1+ ) 1 1 / 2= 1/ 2, ( 1+ ) for ML transitions for EL transitions ICCs larger for: higher-Z elements innermost shells lower-E transitions M than for E

BUILDING A LEVEL SCHEME Conversion-electron spectroscopy Electron ejected with energy E = DEx |EB| measurable spectrum Multiple electron peaks for each g, from K, L, Mini-orange conversion-electron spectrometer (in-beam) Guerro et al., NIMA739, 32 (2014) Battaglia et al., EPJA52, 126 (2016) BUILDING A LEVEL SCHEME Conversion-electron spectroscopy Electron ejected with energy E = DEx |EB|

measurable spectrum Multiple electron peaks for each g, from K, L, Mini-orange conversion-electron spectrometer (in-beam) or delayed spectroscopy Dracoulis et al., PRC79, 031302 (2009) (K energies aligned to g peaks) Measure g and e- intensities, compare with calculated ICCs (e.g. BrIcc) multipolarity [http://bricc.anu.edu.au/] BUILDING A LEVEL SCHEME E0 decays Most transitions have g vs e- competition, but one case that never has a g: 0+ 0+

Transition would be E0 (monopole moment = charge), which cannot radiate to points external to nucleus Andreyev et al., Nature 405, 430 (2000) reduced a width: BUILDING A LEVEL SCHEME E0 decays Most transitions have g vs e- competition, but one case that never has a g: 0+ 0+ Transition would be E0 (monopole moment = charge), which cannot radiate to points external to nucleus Why never and not never? If E > 2mec2 = 1.022 MeV, internal pair (e+e-) production is possible. e+ subsequently annihilates with another e-, yielding 511-keV gs.

BUILDING A LEVEL SCHEME Level and g properties Measured Egs level energies Efficiency-corrected g peak areas intensities, branching ratios, level populations g ADs/ACs, g polarizations, internal conversion multipolarity level spin, parity Relative g times level half-lives, B(XL)s Reduced transition rates (2 +1) ( ) 1

1/ 2, can be a sensitive probe of matrix elements connecting initial and final states: 2 1 ( ; ) = 2 +1 MEASURING HALF-LIVES Excited-state half-lives range from ~10-23 s (>10-MeV resonances) to >4.5x1016 y (180mTa). Thats over 47 orders of magnitude! Most excited states have sub-ns half-lives; why are some exceptionally long?

Low transition energy Large spin difference Large difference in underlying configurations K-forbiddenness (change in spin projection on symmetry axis DK > L) No single approach to measuring half-lives will apply to all cases. MEASURING HALF-LIVES Observe exponential decay for half-lives of ~tens of ps or longer Measure g-ray time relative to a fast START signal START with preceding b decay in e.g. fast plastic or START with RF (clock tick marking reaction) or START with preceding g in e.g. Ge (T1/2 > ns) or LaBr3 (sub-ns)

Get half-life from slope of exponential T1/2 = 728(21) ps Kondev et al., PRC85, 027304 (2012) Zhu et al., NIMA652, 231 (2011) MEASURING HALF-LIVES Observe exponential decay for half-lives of ~tens of ps or longer Measure g-ray time relative to a fast START signal START with preceding b decay in e.g. fast plastic or START with RF (clock tick marking reaction)

or START with preceding g in e.g. Ge (T1/2 > ns) or LaBr3 (sub-ns) Get half-life from slope of exponentialor from centroid shift T1/2 = 40(3) ps Kondev et al., PRC85, 027304 (2012) Zhu et al., NIMA652, 231 (2011) MEASURING HALF-LIVES For ~ps half-lives, instrumentation not fast enough Exploit physics of in-beam measurement: Doppler shifts Brief Doppler diversion DOPPLER EFFECT FRIEND OR FOE?? Doppler broadening:

Doppler shift: Ge Dq,f v 2 1 ( / ) =0 1( / )cos 0 ( / ) sin Ions lose energy while traversing a medium v/c decreases with time. By modelling the energy loss, time-dependent Doppler shift determined

Doppler-shift attenuation and (differential) plunger techniques MEASURING HALF-LIVES For ~ps half-lives, instrumentation not fast enough Exploit physics of in-beam measurement: Doppler shifts Recoil-distance method (plunger) Produce nucleus of interest with initial velocity v0 via Coulex or

KO reactions Observe Doppler-shifted gs emitted between target and degrader Ion slows in the degrader to velocity vd < v0 Observe Doppler-shifted gs emitted after degrader Increase distance between target and degrader; change in relative peak intensities depends on T1/2 T1/2 ~ 10-100s of ps can be measured v ~ 0.3c Figure: adapted from K. Starosta

MEASURING HALF-LIVES Double-degrader plunger T1/2 B(E2) indicator for collectivity Behavior of the 4+ and 2+ states in 72Kr suggest rapid shape evolution occurring Iwasaki et al., PRL112, 142502 (2014). MEASURING HALF-LIVES For ~ps half-lives, instrumentation not fast enough Exploit physics of in-beam measurement: Doppler shifts Recoil-distance method (plunger) Doppler-broadened line shapes T1/2 = 0.13 ps 0.19 ps

If ion slows substantially in foil, variation in Doppler shift line shape Sensitive to sub-ps T1/2s Chiara et al., PRC61, 034318 (2000) 0.17 ps With all of that in mind, lets now consider a case study. CASE STUDY: 68Ni Lets say youre interested in the neutron-rich Ni (Z = 28) region deformation Protons have filled up to Z = 28 gap. Starting on n-deficient side of stability, 56

Ni (N = 28) is doubly magic. 40 N = 28 Z = 28 Nilsson diagram of region deformation Protons have filled up to Z = 28 gap. Starting on n-deficient side of stability, 56 Ni (N = 28) is doubly magic. N = 40 40

Filling of upper n(fp) shell drives shape away from sphericity. At 68Ni, n(fp) is filled, ng9/2 subshell lies above N = 40 gap. Z = 28 Is 68Ni doubly magic? Nilsson diagram of region deformation Protons have filled up to Z = 28 gap. Starting on n-deficient side of stability, 56 Ni (N = 28) is doubly magic. N = 40 40

Filling of upper n(fp) shell drives shape away from sphericity. At 68Ni, n(fp) is filled, ng9/2 subshell lies above N = 40 gap. Z = 28 Is 68Ni doubly magic? Do excitations to shape-driving orbitals result in different coexisting shapes? Nilsson diagram of region CASE STUDY: 68Ni Robustness of shell gaps called into question: N=40 not magic in neighbors, e.g. 66Fe, 64Cr, 67Ni Proposed proton intruder states important in the low-lying structure of 64,66Mn, 65-68Co, 67,69,71Cu pp3/2 from

above Z=28 Fe: Hannawald et al., PRL82, 1391 (1999) 64 Cr: Gade et al., PRC81, 051304(R) (2010) 67 Ni: Zhu et al., PRC85, 034336 (2012) 64,66 Mn: Liddick et al., PRC84, 061305 (2011) 65 Co: Pauwels et al., PRC79, 044309 (2009) 66 pf7/2 from below Z=28 Co: Pauwels et al., PRC78, 041307(R) (2008) Co: Liddick et al., PRC85, 014328 (2012) 67

Cu: Chiara et al., PRC85, 024309 (2012) 69 Cu: Ishii et al., PRL84, 39 (2000) 71 Cu: Oros-Peusquens and Mantica, NPA669, 81 (2000) 67 66,68 CASE STUDY: 68Ni Q: How might one populate excited states in 68Ni? Implantation/decay Transfer reaction (SIB) Transfer reaction (RIB) Deep-inelastic scattering Fusion-evaporation Knockout reaction Coulomb excitation

CASE STUDY: 68Ni Q: How might one populate excited states in 68Ni? Implantation/decay Transfer reaction (SIB) Transfer reaction (RIB) Deep-inelastic scattering Fusion-evaporation* Knockout reaction Coulomb excitation A: Any of the above! All have been (*or soon will be) performed. Complementary production methods, and complementary measurements. CASE STUDY: 68Ni 211 ns Bernas et al., PLB113, 279 (1982) and JPhLett45, 851 (1984), from 70Zn(14C,16O)

2p transfer reaction with long-lived (5700 y) beam Magnetic spectrograph energy and Ip = 0+ Conversion-electron detector T1/2 Broda et al., PRL74, 868 (1995), from 64 Ni+130Te DI reactions 0.86 ms 211 ns Bernas et al., PLB113, 279 (1982) and JPhLett45, 851 (1984), from 70Zn(14C,16O)

Sorlin et al., PRL88, 092501 (2002), from 68Ni Coulex Mueller et al., PRC61, 054308 (2000), from b decay (2-)?! (1 x+) x Flavigny et al., PRC91, 034310 (2015), from Mn b decay chain Liddick et al., PRC85, 014328 (2012), from Fe b decay chain Broda et al., PRL74, 868 (1995), from 64

Ni+130Te DI reactions 0.86 ms 211 ns Bernas et al., PLB113, 279 (1982) and JPhLett45, 851 (1984), from 70Zn(14C,16O) Mueller et al., PRC61, 054308 (2000), from b decay (2-)?! (1 x+) x Flavigny et al., PRC91, 034310 (2015), from Mn b decay chain

Ishii et al., PRL84, 39 (2000), isomer-scope following 70Zn+198Pt DI reactions Liddick et al., PRC85, 014328 (2012), from Fe b decay chain Broda et al., PRL74, 868 (1995), from 64 Ni+130Te DI reactions t1/2=23ns 0.86 ms 211 ns

Bernas et al., PLB113, 279 (1982) and JPhLett45, 851 (1984), from 70Zn(14C,16O) 4208 8+ 3999 6+ 3148 4+ CASE STUDY: 68Ni Angular correlations in 68Ni, relative to the 2033-keV 2+ 0+ gating transition delayed gg prompt gg, with additional gate on delayed Po g Chiara et al., PRC86, 041304(R) (2012); 70Zn + 208Pb DI reaction

After ~30y unchallenged, concurrent analyses of three experiments revealed Ex(0+2) = 1604 keV, not 1770 keV! Recchia et al., PRC88, 041302(R) (2013) 4x8 CsI(Na) array behind Al plate delayed gs S800 spectrograph A1900 fragment separator Production target 423 mg/cm2 9Be

GRETINA <10 states below 3.5 MeV 3 of the lowest 4 are 0+ states! hallmark of shape coexistence Suchyta et al., PRC89, 021301(R) (2014) deformation 40 superdeformed? What lies on top SD band?? Subject of upcoming

fusion-evap experiment Nilsson diagram of region NUCLEAR PHYSICS WITH NOT-SO-EXOTIC BEAMS It may seem strange to say this at an Exotic Beam Summer School, but: Dont be misled into believing that the only remaining pursuits worth taking lie out at the very extremes, requiring RIBs to access. Sometimes run-of-the-mill stable beam + target combos reveal surprises. (Such experiments can still be challenging!) Case study: Nuclear Excitation by Electron Capture in 93Mo CASE STUDY: NEEC Despite ~separable scales of atom and nucleus, they do affect each other #protons determines # and Es of electrons

shape and charge distribution change with #neutrons interaction between nuclear moments and atomic EM fields A. Plffy, Contemp. Phys. 51:6, 471 (2010) nuclear transition affects atomor vice versa CASE STUDY: NEEC Coupled atomic-nuclear processes Nuclear level decay via internal conversion (IC) first observed over 100 y ago

ubiquitous process usable as analysis tool Continuum Initial state L shell K shell Atomic System Nuclear Excitation by Electron Capture (NEEC) inverse of IC requires DE matching predicted [Goldanskii and Namiot, PLB62, 393 (1976)] but never

observed experimentally Nuclear System Continuum Intermediate state L shell Initial state K shell Atomic System EB + Ee = DEn Nuclear System

CASE STUDY: NEEC Coupled atomic-nuclear processes Nucleus may start in isomeric state rather than g.s. [Zadernovsky & Carroll, Hyp. Int. 143, 153 (2002)] could induce isomer depletion through alternate path to g.s. g- and x-ray energies distinct Nuclear Excitation by Electron Capture (NEEC) inverse of IC requires DE matching predicted [Goldanskii and Namiot, PLB62, 393 (1976)] but never observed experimentally

Continuum L shell Intermediate state Isomer K shell Ground state Atomic System EB + Ee = DEn Nuclear System CASE STUDY: NEEC

What makes NEEC observation such a challenge? Nucleus must be in NEEC-able state (long-lived, with nearby intermediate state) Ion stripped to high charge state Source of electrons of appropriate kinetic energy Need clear signature of effect Experimental approach*

Populate 93mMo through fusion-evaporation reaction in inverse kinematics (heavy beam + light target) high recoil velocity of ions Fast ions initially stripped to high qmean in target Surrounding detectors to ID signature 268gs Fast ions run into stationary electrons of target; in moving frame, equivalent to incident electron beam *Adapted from Karamian & Carroll, Phys. At. Nucl. 75, 1362 (2012)

CASE STUDY: NEEC Mo nestled among stable neighbors. 93 Variety of fusion-evaporation reactions using stable beam + target combos can get you there. We opted for 90 Zr + 7Li 93mMo + p3n. CASE STUDY: NEEC Doppler shift: v/c > 10%

2 1 ( / ) =0 1( / )cos v/c rapidly diminishes v/c = 0 CASE STUDY: NEEC Signature 2475 268 685 1478 coincidence NEEC ORGANIZATION OF THESE LECTURES

We will explore the six Ws of experimental nuclear structure: Who? What? When? Where? Why? hoW? REFERENCES

Electroweak Interactions Group Department of Physics Colorado School of Mines http://electroweak.mines.edu + full treatment of ADs/ACs/polarizations in In-Beam Gamma-Ray Spectroscopy by Morinaga & Yamazaki Backups BUILDING A LEVEL SCHEME ADs/ACs multipole order L, but do not directly distinguish E vs M Pure DI=1 E1 looks the same as pure DI=1 M1, e.g. Nonzero mixing ratio may change that, as M1/E2 far more likely than E1/M2 For more direct determination of E or M: measure polarization Measure Compton scattering within and perpendicular to reaction plane

+ (a corrects for different intrinsic count rates) MEASURING g-FACTORS Angular correlations Half-lives g-factors Stuchbery et al., PRC88, 051304 (2013) Recoil-in-vacuum (RIV) technique Nucleus produced in reaction in oriented state Recoil exits target into vacuum spin is deoriented by hyperfine interactions Deorientation dependent on g-factor

( , , ) =1+ ( ) 0 ( , , 0) rotation matrix giving angle dependence of correlation P(cosq,fg) angles of p(articles) and gs statistical tensor defining initial spin alignment attenuation factor for finite g detector size usual F coefficients for ACs/ADs

MEASURING g-FACTORS RIV in 134Te Coulex of 134Te RIB (and also 130Te SIB) Simultaneously measure B(E2) and g-factor for 2+ Observe attenuated ACs relate to Gk g-factor Stuchbery et al., PRC88, 051304 (2013) Evidence in favor of N = 40 gap: large 2+ energy in 68Ni low-collectivity B(E2) in 68Ni Evidence against N = 40 gap: different behavior in neighboring isotope chains masses do not reveal magic behavior Gunaut et al., PRC75, 044303 (2007)

Neidherr et al., PRC80, 044323 (2009) The Progression of Gamma-Ray Detection K.G. Leach EBSS 2018: Nuclear Structure Experiment - II Wednesday, June 27, 2018 Electroweak Interactions Group Department of Physics Colorado School of Mines http://electroweak.mines.edu KGL Nuclear Excited State Decay EURICA Decay Spectroscopy at RIBF (RIKEN)

Heavy Element Studies at RITU Nucleon knockout at the S800 Decay at NSCL Heavy-ion reactions with the FMA HLC Introducing.Large-Scale Clover and Cluster HPGe Arrays K.G. Leach EBSS 2018: Nuclear Structure Experiment - II Wednesday, June 27, 2018

Electroweak Interactions Group Department of Physics Colorado School of Mines http://electroweak.mines.edu KGL Gamma-Ray Tracking Arrays AGATA and GRETA KGL SELECTION RULES Jip Ei E (L) Jf p

Ef The transition probability for at state decaying by transition of multipole order L i Weisskopf estimates HLC/KGL GAMMA-RAY ANGULAR DISTRIBUTIONS If we produce unequal populations p(mi) angular distributions W(q,f) will be non-constant Nuclear Orientation HLC

CASE STUDY: 68Ni Suchyta et al., PRC89, 021301(R) (2014); implantation/decay Recchia et al., PRC88, 041302(R) (2013); fragmentation reaction After ~30y unchallenged, analyses of three experiments within the same year revealed Ex(0+2) = 1604 keV, not 1770 keV! CASE STUDY: 68Ni Levels observed at similar energies, but no transition between them ??? Highly collective transition, possibly

superdeformed B(E2) transition strengths (measure of collectivity) SM calc exp't