Preparation of an isomerically pure beam and future experiments Outline TAS Workshop, Caen, March 30-31, 2004 Klaus Blaum for the ISOLTRAP Collaboration CERN PH-IS Geneva and GSI Darmstadt Motivation Summary Preparation of an isomerically pure beam Experimental setup and procedure Future experiments

Motivation: The identification puzzle in 70 Cu (1+) (2) (3-) 101.1(3) 33(2) (6-) 242.4(3) 6.6(2) J  E / keV T 1/2 / s IT  5% IT  50%  –  95%  –  50%  – =100% Mass excess Lit: (15) keV Ground and isomeric states of 70 Cu Problems / unknown parameters: - number of isomeric states - spin assignement - order of states - mass excess value of ground state Requirements: - clear state to mass assignement - high selectivity - high efficiency - ultra-high resolving power Solution: Combination of laser resonance ionization,  -decay spectroscopy and Penning trap mass spectrometry

1. Surface Ionization Ion Source: No isobaric selectivity, limited applicability 2. Plasma Ion Source (ECR-Source): No isobaric selectivity 3. Resonance Ionization Laser Ion Source (RILIS): High isobaric selectivity by resonant laser ionization Limitation by surface ionized isobars Resonance Ionization Laser Ion Source (RILIS)

Example: Cupper excitation scheme

Principle of Penning Traps Cyclotron frequency: B q/mq/m PENNING trap Strong homogeneous magnetic field Weak electric 3D quadrupole field ring electrode end cap Frans Michel Penning Hans G. Dehmelt

Ion Motion in a Penning Trap 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 + ) The frequencies of the radial motions obey the relation Typical frequencies q = e, m = 100 u, B = 6 T  f - ≈ 1 kHz f + ≈ 1 MHz

Excitation of Radial Ion Motions Dipolar azimuthal excitation Either of the ion's radial motions can be excited by use of an electric dipole field in resonance with the motion (RF excitation)  amplitude of motion increases without bounds Quadrupolar azimuthal excitation If the two radial motions are excited at their sum frequency, they are coupled  they are continuously converted into each other Conversion of radial motions Magnetron excitation:   Cyclotron excitation:  +

TOF Resonance Mass Spectrometry Scan of excitation frequency Quadrupolar radial excitation near f c  coupling of radial motions, conv. Time-of-flight (TOF) measurement Ejection along the magnetic field lines  radial energy converted to axial energy Dipolar radial excitation at f -  increase of r m Time-of-flight resonance technique Resolving power:

Mean time of flight /  s Excitation frequency f rf / Hz T 1/2 =  TOF Cyclotron Resonance Curve (Stable Nuclide) Determine atomic mass from frequency ratio with a well-known reference mass TOF as a function of the excitation frequency Centroid:

TOF Cyclotron Resonance Curve (Radionuclide) Determine atomic mass from frequency ratio with a well-known reference mass TOF as a function of the excitation frequency Centroid: f rf

Triple-Trap Mass Spectrometer ISOLTRAP G. Bollen, et al., NIM A 368, 675 (1996) F. Herfurth, et al., NIM A 469, 264 (2001) cluster ion source preparation Penning trap precision Penning trap stable alkali ion reference source ion beam cooler and buncher removal of contaminant ions (R = 10 5 ) determination of cyclotron frequency (R = 10 7 ) B = 4.7 T B = 5.9 T Nd:YAG 532 nm 1.2 m 10 cm K. Blaum et al., EPJ A 15, 245 (2002) 10 cm

ISOLTRAP Setup 1 m

Isomer Separation Isomerism in 68 Cu: as produced by ISOLDE isolation of the 1 + ground state isolation of the 6 - isomeric state Resolving power of excitation: R ≈ 10 7  Population inversion of nuclear states  Preparation of an isomerically pure beam K. Blaum et al., Europhys. Lett., submitted (2004).

Solving the Identification Puzzle in 70 Cu (6-) (2) (3-) 101.1(3) 33(2) (1+) 242.4(3) 6.6(2) I  E / keV T 1/2 / s IT  5% IT  50%  –  95%  –  50%  – =100% Mass excess Lit: (15) keV Isomerism in 70 Cu: Hyperfine structure of 70 Cu isomers (using laser ionization):    16% 4%4% 80% (spectrum provided by U. Köster) Intensity ratio: normalized to the area J. Van Roosbroeck et al., Phys. Rev. Lett. 92, (2004).

Identification of Triple Isomerism in 70 Cu    16% 4%4% 80% Intensity ratio: normalized to the area    with cleaning of 6 – state Unambiguous state assignment!  (6 – ) state = gs  (3 – ) state = 1.is  1 + state = 2.is R  1·10 7 Preparation of an isomerically pure beam! ME of ground state is 240 keV higher than literature value! Excellent agreement with decay studies. 101(3) keV 242(3) keV

New Detector Setup Drift tube Window (open access) Channeltron detector Spare MCP detector Feed- through Ions from the precision trap

Open Detector Geometry DeTech Channeltron Principle of a CDEM -2.5 kV -5 kV  Typical gain at 2.5 kV: ~5  10 7  Dark noise: ~20 mHz (measured)  Pulse width / Dead time: ~25 ns (measured)  Rinse time: ~5 ns (measured)  Detection efficiency (low energy ions): >90%  Typical gain at 2.5 kV: ~5  10 7  Dark noise: ~20 mHz (measured)  Pulse width / Dead time: ~25 ns (measured)  Rinse time: ~5 ns (measured)  Detection efficiency (low energy ions): >90%

Beta-Counter and Tape Station (Courtesy W. Geithner) Isomerically pure ion beam Tape station available at GSI! Beta-counter

Applications Help, advice and good ideas are welcome!  Identification of unknown contaminations  Collection of isomerically pure samples  Background-free decay studies  Background-free half-life measurements  Preliminary studies of further applications, e.g. post-acceleration with REX-ISOLDE  Identification of unknown contaminations  Collection of isomerically pure samples  Background-free decay studies  Background-free half-life measurements  Preliminary studies of further applications, e.g. post-acceleration with REX-ISOLDE BUT: Number of ions at present limited to about 10 ions/proton pulse.

Conclusion and Outlook ISOLTRAP can perform high-precision mass measurements (< ) on very short-lived nuclides (< 100 ms) that are produced with very low yields (< 100 ions/s) ISOLTRAP can prepare isomerically pure beams and demonstrated population inversion of nuclear states Isomerically pure beams open a new area in low-energy nuclear physics research Setup of a tape station, decay spectroscopy and half-life measurements on an isomerically pure beam are planned within the next few years

Thanks to my co-workers: G. Audi, G. Bollen, D. Beck, P. Delahaye, C. Guénaut, F. Herfurth, A. Kellerbauer, H.-J. Kluge, D. Lunney, D. Rodríguez, C. Scheiden- berger, S. Schwarz, L. Schweikhard, G. Sikler, C. Weber, C. Yazidjian..., and the ISOLTRAP and ISOLDE collaboration Thanks for the funding and support: GSI, BMBF, CERN, ISOLDE, EU networks EUROTRAPS, EXOTRAPS, and NIPNET Thanks a lot for your attention. Not to Forget …

New Detector Setup Drift tube Feedthrough Spare MCP detector Channeltron detector Window (open access) Ions from precision trap

Isotope ratio 40 Ca count rate / Hz Dead time measurement  : dead time R: isotope ratio n A : count rate  = = (R-R 0 )/n A 1-R slope axis section  Typical gain at 2.5 kV: ~5  10 7  Dark noise: ~20 mHz (measured)  Pulse width / Dead time: ~25 ns (measured)  Rinse time: ~5 ns (measured)  Detection efficiency (low energy ions): >90%  Typical gain at 2.5 kV: ~5  10 7  Dark noise: ~20 mHz (measured)  Pulse width / Dead time: ~25 ns (measured)  Rinse time: ~5 ns (measured)  Detection efficiency (low energy ions): >90% Specification of the CDEM