Experiments with rare-isotope beams Ground-state properties. Wednesday. Nuclear masses Ground-state halflives. Friday

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1 Experiments with rare-isotope beams Ground-state properties Wednesday Nuclear masses Ground-state halflives Limits of existence Friday

2 Motivation Nuclear structure at extreme N/Z ratios or high A? Changes in the nuclear shell structure (not so magic numbers) New modes of collectivity Monday Shell structure of the heaviest elements Tuesday Nuclear ground states - Existence Bound excited states - Properties Single-particle properties Collective degrees of freedom and exotic modes Lifetimes and isomers Wednesday The limits of nuclear existence? Delineation of the nucleon drip lines Halo systems and nucleon skins Exotic decay modes (2p radioactivity) Figure from M. Huyse

Time-of-flight spectrometer (SPEG, TOFI, S800) Multi-turn (cyclotrons,

3 Masses Indirect Decay measurements and kinematics in two-body reactions Direct Conventional mass spectrometry Cern PS, Chalk River Time-of-flight spectrometer (SPEG, TOFI, S800) Multi-turn (cyclotrons, storage rings) Frequency measurements Penning traps Storage rings Adapted from D. Lunney

4 TOF mass measurements Spectrographs at NSCL N A. Estrade, in preparation (NSCL) 76 Zn 71 Ni 66 Fe 61 Cr 79 Ga 74 Cu 69 Co 64 Mn 82 Ge 77 Zn 72 Ni 80 Ga red δm>500kev blue δm<10kev 75 Cu TOF mass measurements on neutron-rich isotopes goal: δm = 0.2 MeV for A~70 δm/m=2 x10-6 A1900+S800 at NSCL TOF stop 58m flight path Ti 70 Co 65 Mn 78 Zn 73 Ni Ga Sc Cu Fe TOF [ns] Bρ=p/q=γm/q (dx/dt) Measure Bρ and TOF TOF start Measure many masses simultaneously Mass accuracy: m/m ~ 10-6 Beam rate: particles/min (e.g particles total for δm ~ 200 kev for A~100)

5 TOF mass measurement Cyclotrons at GANIL A~100 nuclei: 50 Cr+ 58 Ni at 250 MeV Heavy-ion primary beam delivered by CSS1 with a few MeV/nucleon The fusion-evaporation products formed in the reaction with the production target are injected into the CSS2 and accelerated detected in a silicon-detector telescope δm/m=δt/t h=#rf periods/turn

6 Mass measurements in the ESR storage ring at GSI F. Bosch, Lect. Notes Phys. 651, 137 (2004) γ t : relative change in path length by turn relative to change in Bρ

7 Mass measurements in the storage ring at GSI I. Schottky mass spectrometry Schottky spectrometry in storage ring (GSI), e.g. 184 Pt Mass excess for 184 Pt as determined in several runs using different reference isotopes and in different ionic charge states q. (dm/m= ) T. Radon et al., PRL 78, 4701 (1997)

8 Mass measurements in the storage ring at GSI II. Isochronous mass spectrometry Mass measurement of short-lived 44 V, 48 Mn, 41 Ti and 45 Cr (X-ray burst models) Accuracy of δm= kev was achieved (lifetimes ~ 100 ms) J. Stadlmann et al., PLB 586, 27 (2004)

B Mass measurements with Penning traps end cap q/m Mass measurement via determination of cyclotron frequency f c 1 = 2π q B m from characteristic motion of stored ions ring

9 B Mass measurements with Penning traps end cap q/m Mass measurement via determination of cyclotron frequency f c 1 = 2π q B m from characteristic motion of stored ions ring electrode z 0 r0 PENNING trap Strong homogeneous magnetic field of known strength B provides radial confinement Weak electric 3D quadrupole field provides axial confinement Ion source

Mass measurements with Penning traps Motion of an ion is the superposition of three characteristic harmonic motions: axial motion (frequency f z ) magnetron motion (frequency f ) modified cyclotron

10 Mass measurements with Penning traps Motion of an ion is the superposition of three characteristic harmonic motions: axial motion (frequency f z ) magnetron motion (frequency f ) modified cyclotron motion (frequency f + ) Typical frequencies q = e, m = 100 u, B = 6 T The frequencies of the radial motions obey the relation 1 q f + + f- = f c = B 2π m Adapted from K. Blaum f - 1 khz f + 1 MHz Excite the cyclotron motion with multipolar RF (Goal: excite the cyclotron motion to resonance) Transform radial to axial energy (gradient db/dz) and eject ions Measure time of flight (TOF) - the shorter TOF, the closer is the excitation frequency to the resonance

11 Mass measurements with Penning traps Eject thermalized ions from buncher Capture ions in Penning trap Perform RF excitation Eject ions and measure TOF ME= (28) kev δm=280 ev G. Bollen et al., PRL 96, (2006)

12 Trap measurements Overview J. Aysto (Trento, spring 2008)

13 Masses what are they good for? Structure information Shell closures and deformation from separation energies (δm/m < 10-5 ) Astrophysics (Nucleosynthesis) r process (δm/m < 10-5, δm < 10 kev) rp process (δm/m δ ~ 10-7 ) Fundamental interactions and symmetries (δm/m<10-8 ) CVC hypothesis (postulates that the vector-current part of the weak interaction is not influenced by the strong interaction) Unitarity of CKM matrix

from separation energies (δm/m < 10-5 ) Astrophysics (Nucleosynthesis) r

14 Masses what are they good for? Nuclear structure Structure information Shell closures and deformation from separation energies (δm/m < 10-5 ) Astrophysics (Nucleosynthesis) r process (δm/m < 10-5, δm < 10 kev) rp process (δm/m ~ 10-7 ) Fundamental interactions and symmetries (δm/m<10-8 ) CVC CKM

15 Masses what are they good for? Constrain theory Model di ifference (MeV/c 2 ) Measured masses Groote et al., 1976 Masson & Janecke, 1988 Janecke & Masson, 1988 Tachibana et al., 1988 Comay et al., 1988 Moeller et al., 1995 Duflo & Zuker, 1996 Aboussir et al., N (Z = 37) Needed for r-process

16 Masses what are they good for? Nuclear astrophysics

17 Takeaway Nuclear masses and resulting nucleon separation energies are an indicator of nuclear structure and indicate changes in the shell structure in the exotic regime Exotic nuclei can be produced with different methods and reactions Masses of short-lived nuclei can be measured in different ways Time of flight mass measurements Storage rings Penning traps Masses are important input for nuclear astrophysics and the study of fundamental symmetries

18 Related review articles Masses Traps for rare isotopes, G. Bollen, Lect. Notes Phys. 651, 169 (2004) Measurements of mass and beta lifetime of stored exotic nuclei, F. Bosch, Lect. Notes Phys. 651, 137 (2004) Recent trends in the determination of nuclear masses, D. Lunney, J.M. Pearson, C. Thibault, Rev. Mod. Phys. 75, 1021 (2003) Mass measurements of short-lived nuclides with ion traps, G. Bollen, NPA 693, 3 (2001) Precision nuclear measurements with ion traps, G. Savard and G. Werth, Annu. Rev. Nucl. Sci. 50, 119 (2000) Mass measurement far from stability, W. Mittig and A. Lepine-Szily, Annu. Rev. Nucl. Sci. 47, 27 (1997)

19 Half-lives

20 Exotic nuclei - halflives Sunday Monday Nuclear ground states - Existence Nuclear ground states Half-life α, β, p, 2p decay Thursday Friday

21 4 basic decay modes Nuclei decay via 4 basic modes: Alpha decay (Z-2, N-2) Beta(-) decay (Z+1, N-1) Beta(+) decay (Z-1, N+1) Fission into two large fragments and a few neutrons There is also one-proton and two-proton radioactivity

22 β-decay bulk activity measurements λ=ln2/t 1/2 t i =t d =4 x t 1/2 Implant activity in active stopper material for time t i. Cease implantation and observe decay for time t d. Adapted from P. F. Mantica

23 Adapted from P. F. Mantica Event-by-event correlation technique

24 Adapted from P. F. Mantica Beta counting systems Example: BCS at NSCL

25 A. Stolz (2003) 101 Sn β-decay

26 Caught in the act: 140 Pr 140 Ce electron capture in the

, PRL 97, 082501 (2006) 109 Xe implant ms α ns α

27 109 Xe 105 Te 101 Sn α-decay chain Digital DAQ S.N. Liddick et al., PRL 97, (2006) 109 Xe implant ms α ns α identify 100 events among implanted ions and 1.7*10 7 decays Adapted from S. N. Liddick

Doubly magic nucleus accelerates synthesis of heavy elements Particle identification in rare-isotope beam from NSCL at Michigan State University Model calculation for synthesis of heavy elements

28 Doubly magic nucleus accelerates synthesis of heavy elements Particle identification in rare-isotope beam from NSCL at Michigan State University Model calculation for synthesis of heavy elements during the r-process in supernova explosions 1.E+02 Observed Solar Abundances 78 Ni Abundance (A.U.) 1.E+01 1.E+00 1.E-01 Model Calculation: Half-Lives from Moeller, et al. 97 Same but with present 78Ni Result 1.E Mass (A) Measured half-life of 78 Ni with 11 events This is the most neutron rich of the 10 possible classical doubly-magic nuclei in nature. Result: ms P. Hosmer et al. PRL 94, (2005) Models produce excess of heavy elements with new shorter 78 Ni half-life the synthesis of heavy elements in nature proceeds faster than previously assumed a step in the quest to find the origin of the heavy elements in the cosmos Adapted from H. Schatz

29 Limits of nuclear existence

30 Location of the driplines Experimental task: How to find a needle in a haystack

31 How many neutrons can a proton bind? The limit of nuclear existence is characterized by the nucleon driplines B. Jonson: "The driplines are the limits of the nuclear landscape where additional protons or neutrons can no longer be kept in the nucleus - they literally drip out. P. G. Hansen & J. A. Tostevin: "(the dripline is) where the nucleon separation energy goes to zero."

32 Where is the neutron dripline? Predictive power, anybody??

Dripline history and a plan 48 Ca (Z=20,

Phys. A 332, 189 1997: Tarasov et al., Phys.

Lett. B 448, 180 2002: Notani et al., Phys.

33 Dripline history and a plan 48 Ca (Z=20, N=28) Target Production of 40 Mg from 48 Ca: Net loss of 8 protons with no neutrons removed! 1990: Guillemaud-Mueller et al., Z. Phys. A 332, : Tarasov et al., Phys. Lett. B 409, : Sakurai et al., Phys. Lett. B 448, : Notani et al., Phys. Lett. B 542, 49 Lukyanov et al., J. Phys. G 28, L41

34 Proof of existence? Detect and identify it! Energy loss: de ~Z 2 The ion s time of flight is proportional to A/Z x flight path/magnetic rigidity 48 Ca beam + nat W target separator optimized on 29 F

A long way Two test experiments at the end of the fragment separator During the tests: Production cross sections of neutronrich isotopes and discovered 44 Si along the

35 A long way Two test experiments at the end of the fragment separator During the tests: Production cross sections of neutronrich isotopes and discovered 44 Si along the way Implemented the concept of a two-stage separator to discriminate against low-z events and finally ran the search for 40 Mg in April 2007 nat W( 48 Ca, 29 F) 140 MeV/u

36 40 Mg and more! T. Baumann et al., Nature 449, 1022 (2007) Data taking: 7.6 days at 5 x10 11 particles/second 3 events of 40 Mg 23 events of 42 Al 1 event 43 Al

37 The existence of 42,43 Al T. Baumann et al., Nature 449, 1022 (2007) The existence of 42,43 Al indicates that the neutron dripline might be much further out than predicted by most of the present theoretical models, certainly out of reach at present generation facilities.

38 Proof of non-existence: 26 O and 28 O Guillemaud-Mueller et al., PRC 41, 937 (1990) Tarasov et al., PLB 409, 64 (1997) N=2Z-1 48 Ca on Ta at 44 MeV/u (GANIL) 36 S on Ta at 78 MeV/u (GANIL) Counts N=2Z N=2Z+2 Report absence of 26 O in N=2Z+2 systematics Report absence of 28 O in the systematics of produced N=20 isotones

39 Decay modes at the proton drip line One-proton radioactivity Direct proton emission from ground states or isomeric excited states (heaviest proton emitter 185 Bi (isomeric state), the heaviest gs emitter: 177 Tl Two-proton radioactivity Two-proton emission from even- Z nuclei, for which, due to the pairing force, one proton emission is energetically forbidden, while two-proton emission is allowed (so far, 45 Fe, 54 Zn, indications in 48 Ni) β-delayed charged particle emission (βp, β2p, for heavier nuclei βα, βαp) Half-lives are dominated by β-decay, proton emission proceeds at half-lives of femto seconds or shorter not considered as proton radioactivity

40 Where is the proton dripline? Proton dripline is established up to Z=28 for odd-z nuclei and partially between Z=29 and Z=82 M. Thoennessen, Rep. Prog. Phys (2004)

41 Proton radioactivity/emission Centrifugal (l=5) Coulomb Radius (fm) Nuclear Light proton emitters: (Very) short lifetimes due to small Coulomb and no or very small angular momentum barrier (l=0,1,2) Produced in transfer reactions or fragmentation Identify by complete kinematic reconstruction in flight

Heavy proton emitters Long lifetimes due to Coulomb and angular momentum barrier Typically produced in fusion evaporation reactions or fragmentation

42 Heavy proton emitters Long lifetimes due to Coulomb and angular momentum barrier Typically produced in fusion evaporation reactions or fragmentation Separate and subsequently stop in a detector for identification Use segmented silicon strip detectors for a delayed decay (e.g., DSSD) Setup at ANL [C. N. Davids]

43 Proton emitters between Z=53 and 83 B. Blank and M.J.G. Borge, PPNP 60, 403 (2008)

45 Fe: 2-proton decay in OTPC at NSCL 2007 45 Fe 2p-decay caught in the act Recorded by CCD

45 Fe enters from the left, short tracks are protons (~ 600 kev) emitted 535 µs after

44 45 Fe: 2-proton decay in OTPC at NSCL Fe 2p-decay caught in the act Recorded by CCD camera (25 ms exposure). 45 Fe enters from the left, short tracks are protons (~ 600 kev) emitted 535 µs after implantation Time profile of the total light intensity measured by photomultiplier tube 2p radioactivity but no simple 2 He (di-proton) picture K. Miernik et al., PRL 99, (2007)

45 45 Fe: Correlation of the protons? Pfutzner, Grigorenko et al. K. Miernik et al., PRL 99, (2007)

46 Take away Experiments to establish the neutron dripline are hard. And the dripline might be further out than expected... More exciting physics to be discovered! Spectroscopy beyond the proton dripline gives information on nuclear structure and proton-proton correlation Different ways to measure half-lives of short-lived nuclei Bulk-activity measurements Event-by-event correlation technique Storage rings again

47 Related review articles The driplines Reaching the limits of nuclear stability, M. Thoennessen, Rep. Prog. Phys. 67, 1187 (2004) Proton radioactivity Two-proton radioactivity, B. Blank and M. Ploszajczak, Rep. Prog. Phys. 71, (2008) Nuclear structure at the proton drip line: Advances with nuclear decay studies, B. Blank and M.J.G. Borge, Prog. Part. Nucl. Phys. 60, 403 (2008) Nuclei beyond the proton drip-line, P. J. Woods and C. N. Davids, Annu. Rev. Nucl. Part. Sci. 47, 541 (1997) Beta decay halflives. β and isomer spectroscopy of neutron-rich nuclei with fragmentation beams at the NSCL, P. F. Mantica, J. Phys. G: Nucl. Part. Phys. 31 (2005) S1617 S1622

48 Two-proton radioactivity Predicted by Goldanskii in 1960 Discovered recently in 45 Fe, 54 Zn and possibly 48 Ni Implantation/Decay (Long lifetimes) Beta-Delayed Emitters Ground-State Emitters Light two-proton emitters: In-Flight decay (Short lifetimes) Adapted from R. Grzywacz

Experiments with exotic nuclei I. Thursday. Preliminaries Nuclear existence Decay modes beyond the driplines Ground-state half-lives.

Experiments with exotic nuclei I Thursday Preliminaries Nuclear existence Decay modes beyond the driplines Ground-state half-lives Friday Motivation Nuclear structure at extreme N/Z ratios or high A? Changes