Masses and Moments via Precision Atomic Physics Techniques · 2017. 3. 3. · High intensities –good quality –element dependent ... nuclear multipole moments (dipole moment m

Masses and Moments via Precision Atomic Physics Techniques

Georg Bollen

• Rare isotopes – making them

• Atomic approaches to study rare isotopes

• Laser spectroscopy

• Direct mass spectrometry

• Summary

New territory to be

explored with FRIB

Rare Isotope Discoveries to Be Made

about 3000 known

isotopes

, Slide 2G. Bollen, PPPL 2015

Understanding their ground-state properties is important

Masses, radii, spins, moments

N

Z

The Atomic Physics Approach

G. Bollen, Survey of Nuclear Physics 2017 – Masses and Moments, Slide 3

Sources of information and

techniques

Complementary

approaches

Moments

Spins

Radii

Laser spectroscopy

Probing of atomic transitions

Nuclear polarization

Nuclear spectroscopy

Elastic and inelastic

reactions

Exotic atoms

Masses Direct mass spectrometry

ion motion in well defined

electromagnetic (or electric) fields

Energy balance of

decays and reactions

Determining ground-state properties with atomic physics techniques

The Atomic Physics Approach


Direct mass measurements and laser spectroscopy allow to determine fundamental properties of nuclei in ground or long-lived isomeric states: masses, spins, moments and radii

What do we learn?

Masses Nuclear binding energy

Basic test of nuclear models

Nuclear structure: shell closure, pairing, onset of

deformation, drip lines, halos

Test of fundamental interactions

Spins and

Moments

Microscopic nuclear structure: wave functions, coupling of

nucleons, configuration mixing, shell structure

Macroscopic nuclear structure: nuclear deformation

Charge Radii Nuclear structure: nuclear charge distribution,

deformation

Rare Isotope Production

Isotope Separation On-LineISOLDE

ISAC

HRIBFProtons - 1 GeV

High intensities – good quality – element dependent

Fusion evaporation/ fission - IGISOL in-flight separation/stopping

Heavy/light ions

few MeV/u

JYFL

Leuven

GSI/SHIP

ANL/ATLAS

Good intensities in local areas - SHE

Fast beam fragmentation and in-flight separation

Heavy ions

< 2GeV/u

NSCL, GSI

GANIL, RIKEN

FRIB

Universal and fast – far reach -- pure beam quality

GSI/SHIPTRAP

ANL/CPT

LEBIT &

BECOLA/NSCL

Preparing Fast Rare Isotopes for Precision Experiments with Atomic Physics Techniques

Linear gas stopper (heavier ion beams)

Cyclotron gas stopper (lighter ion beams)

Also important for reaccelerating rare isotope beamsG. Bollen, Survey of Nuclear Physics 2017 – Masses and Moments, Slide 6

Laser spectroscopy of rare isotopes


Resonant step-wise excitation of one (or more electrons in the electron shell of an atom with laser light of suitable wave length

Transition frequencies are unique fingerprints for elements and isotopes

Varying the laser wave length allows to probe different isotopes and elements – observed transitions and their frequency can provide information on the atomic nucleus.

Probing Nuclear Properties in Atomic Transitions


Hyperfine Structure


Splitting of atomic fine structure levels due to coupling of electron spin I and nuclear multipole moments (dipole moment mI, quadrupole moment Q)

Hyperfine constant A

Hyperfine constant B

Access to nuclear parameters I (number

of lines) and mI (size of splitting)

Access to spectroscopic quadrupole

moment nuclear deformation

parameters

Isotopic Shift in Atomic Transitions


Isotopic Shift = Mass Shift + Field Shift

mass shift = normal mass shift + specific mass shift MA A A A

A AN S, ' '

'

Expl: A=10: 10-5 A=200: 10-7 ; A=1

Field Shift:

due to change of nuclear charge distribution

F

A A A A

F Z r, ' , '

( ) 2

Expl: A=10: 10-7 A=200: 10-5

.... including deformation

r rdef sph

2 2 215

42

r Rsph

2 2 2 1 33 50 0

; R = 1.2 A fm

W. Nörtershäuser and Ch. Geppert, Lecture

Notes in Physics 879 (2014).

Example: Isotopic Shift in the Osmium to Lead Region


Shape coexistence

Hg (Z=80): • even A: near spherical shape

• odd A <= 185: strong prolate deformation

Au (Z=79)• onset of strong prolate deformation at

A=187

Pt (Z=78): • towards strong prolate deformation via

triaxial shape

prolateoblate triaxial

Laser Spectroscopy


Laser spectroscopy has been staple at ISOL facilities for many years

• CERN/ISOLDE

• JAEA

• Jyväskylä/IGISOL

• TRIUMF/ISAC

Extension to fast beam facilities

• BECOLA @ NSCL/MSU

Laser Beam

Ion Beam

Deflection

Retardation

ChargeExchange

Excitation and OpticalDetection

Optical Pumping

Deceleration

Charge Exchange Atom Counting

Ion Counting

Differential Pumping

Gas inletV|

Atom Beam

Magnet

Asymmetry Detection

PolarizationN

SCollinear laser spectroscopyCOLLAPS at ISOLDE

V|| V||

Deflection

Collinear Laser SpectroscopyPrinciple


Frequency tuning by

change of ion velocity

Making atoms

out of ions

Collinear Laser Spectroscopy


velocity bunching due to constant energy spread

E = [1/2 mv2] = m [vv] = const

v decreases as ion or atom speed v increases

• Thermal motion (energy spread E) leads to Doppler shift

and line broadening (typically a few GHz for atoms from an

oven)

• Accelerating ions (or atoms) to higher velocity and collinear

interaction with laser beam reduces line broadening E = KT

laser system

cooler/buncher

laser injection

collinear laser spectroscopy

radioactive beams

laser/ionbeams

K. Minamisono et al, NIMA 709, 85 (2013), D. M. Rossi et al., RSC 85, 093503 (2014).

offlineion source

BECOLA (shown in this slide)

- existing, available for Day One exp.

- only laser spec. facility for in-flight separation and gas

stopping

- laser spectroscopy on ~ 30 keV beam

- polarized beam available

CRIS (collinear resonant laser ionization spec.)

- future development for 1 ion/s type exp.

- isomerically pure beam may be available

BECOLA facility at NSCL/MSUBEam COoling and LAser spectroscopy


K. Minamisono et al, Phys. Rev. Lett. 117, 252501 (2016).

Atomic hyperfine structures for 52, 53Fe isotopes

relative to stable 56Fe.

Ca

Fe

The extracted charge radii of 52, 53Fe show characteristic

discontinuity (kink) at N = 28, similar to that for Ca chain.

Steep rise of 52Fe radius is due mainly to deformation effect

Kink at N = 28

Steep rise of52Fe radius

Collinear laser spectroscopy was applied for the first time to beams prepared via an in-flight

separation followed by gas stopping at NSCL/MSU.

BECOLA: Charge radii of neutron-deficient Fe isotopes

G. Bollen, Survey of Nuclear Physics 2017 – Masses and Moments, Slide 16P. Mantica, K. Minamisono NSCL

Masses provide key information

Magic Numbers

Evolution of Shell Structure

Halos and Skins

Isospin Symmetry

Pairing

Exotic decays

Fundamental

Interactions

Stability of SHE

+ constraints for nuclear models and mass formulas


Binding Energies and Nuclear Structure

Loosely bound systems - halos

Evolution of shell structure

H. Savajols et al., Eur. Phys. J. A direct (2005)

Observables

Shell effects

Deformation effects

Pairing

Test of theoretical predictions

r

er

r

)(

nSm

2

1-neutron halo

Sn neutron separation energy

11Li, 14Be, 19C, 22N, …


Nuclear Synthesis

100 120 140 160 180 200 22010

-4

10-3

10-2

10-1

100

101

Example r-process

ETFSIQ (shell quenching)

ETFSI1 (no shell quenching)

solar

Difference due to shell quenching for neutron-rich

nuclei, or a problem with astrophysical model?

Pfeiffer & Kratz,

Mainz

A

rela

tive a

bundance

Supernova (HST)

Rapid proton capture (rp) process and and the rapid neutron capture (r) process are

the important processes involving rare isotopes.

Masses and half-lives are key data required for their understanding.

R-process abundances


Standard model tests in super-allowed 0+ 0+ -decays

Conserved-vector-current (CVC) hypothesis:

Vector part of weak interaction not influenced by strong interaction

Theoretical Corrections:

δC – isospin symmetry breaking correction

(Coulomb, strong interaction)

δR – radiative correction (Bremsstrahlung etc.)

)1(2)1)(1(

2 V

RV

CRG

KftFT

22

VV MG

Kft

Quantities to be measured:

branching ratios, half-lives t

Q-values = mass differences f

5Qf

Q

dQ

f

df5

Δ+1=++2

ub

2

us

2

ud VVV

Unitarity of the Cabbibo-Kobayashi-Maskawaquark eigenstates of the weak interaction - mass eigenstates

of the strong interaction

2

A

2

V2

ud =G

GV

m

0+0+ -decay

Pure leptonic m decay

Kaon decay

J. Hardy, I. Towner


Halos and skins

Pairing

Exotic decays

Element synthesis

via rp process

Element synthesis

via r process

Evolution of

nuclear shell

structure

m/m = 10-7

10-7< m/m < 10-6

m/m < 10-8

m/m = 10-7

Test of Fundamental

Interactions

Masses: What do we know? What do we need?

100 120 140 160 180 200 22010

-4

10-3

10-2

10-1

100

101

10-8

10-7

10-6

10-5

unknown

m/m

Mass Uncertainties

50

50

82

2820

8


Tools for Mass Measurements on Rare Isotopes


Time-of-flight spectrometrysingle turn: S800multi turn: storage ring ESR/GSI, RIBF ring/RIKEN,

HIRFL-CSR/IMP

Frequency measurementsstorage ring ESR/GSI,

Penning traps LEBIT/NSCL, ISOLTRAP/ISOLDE, JYFLTRAP/JYFL, CPT/ANL, SHIPTRAP/GSI, TITAN/TRIUMF, TRIGA-TRAP/Mainz

start stop

momentumanalysis p=mv L

B

wc = q/m B

+ Q-values from reactions and decays

Time-of-flight spectrometry 2.0Multireflection time-of-flight MS

ISOLTRAP/CERN, RIBF/RIKEN

Storage Ring Mass Measurements

Uses beams from projectile fragmentation/fission and in-flight separation

About 13% in mass-over-charge range

Nuclei with half-lives as short as 20 msm/q range: 2.4-2.7

0

100

200

300

400

500

600

700

506 506.2 506.4 506.6 506.8 507

106 41+Mo

106 41+Nb

unknown mass

119 46+Ag

119 46+Pd

88 34+Se

132 51+Sb

101 39+Y

114 44+Rh

114 44+Ru

127 49+In

known mass

127 49+Sn

83 32+Ge

96 37+Rb

Experimental Storage Ring at GSI DarmstadtIMS: Time-of-Flight Spectra

Penning Trap Mass Spectrometry Penning Trap Primer


Uniform Magnetic Field + Quadrupolar Electrostatic Field = Penning Trap

(radial confinement) (axial confinement) (3D confinement)

harmonic

oscillation in

the z-direction“cyclotron

frequency”

Motion of an ion is the superposition of three characteristic harmonic motions:

• reduced cyclotron motion (+)

• magnetron motion (-)

• axial motion (z)

Example ωc:

• Singly charged

• B = 9.4 T

• Mass 100 uωc ~ 9 MHz

Penning traps mass spectrometry

wc = (q/m)B

B = 9.4 T, A = 38, Q=2 c = 8 MHz

Tobs = 125 ms:

width c 1/ Tobs = 8 Hz

Resolving power R = c/ c = 106

1000 detected ions

stat. uncertainty c/ c = 1/ (R N1/2) =

3.10-8

magnetron (-) cyclotron (+)

axial (z)

wc = w+ + w-G. Bollen, Survey of Nuclear Physics 2017 – Masses and Moments, Slide 26

Cyclotron Frequency Measurement

wc = w+ + w- = (q/m)B

Apply quadrupolar RF field: wRF = wc = w+ + w-

Change of radial energy

magnetron (-) cyclotron (+)

axial (z)

G. Bollen et al., J. Appl.Phys. 68 (1990) 4355

M. König et al., Int. J. Mass Spectr. 142 (1995) 95


Time-of-Flight Cyclotron Resonance Detection

• Capture ion(s)

• Apply RF (Er increases if f = fc)

• Eject ion(s)

• Measure time of flight

cyclotron energy

axial energy

F = -m B/z = -(Er/B0) B/z

B0


100 MeV/u 1 eV

Gas stoppingIon

detector

Projectile Fragmentation

and In-Flight Separation

Fast

Universal

Chemistry independent

Penning Trap Mass

Spectrometry

High-precision

High Sensitivity

Penning trap mass

spectrometer

LEBIT (Low Energy Beam Ion TRAP)The only Penning trap mass spectrometer at a fast beam facility


R. Ringle, G. Bollen NSCL

LEBIT at NSCL

60keV rare

isotope

beam

7 T SIPT

magnet

9.4 T LEBIT

magnetRFQ cooler

buncher

MCP in Daly

Configuration

Off-line

Ion sources

Electronic racks

Only Penning trap mass

spectrometer in the world to study

rare isotope produced by

projectile fragmentation


Mass measurements near the dripline

Superallowed decayQ-value

Neutron shell closure at N=40 near Z=28

Recent LEBIT online Results

72Br : Valverde, et al., PRC 91 037301 (2015)14O : Valverde, et al., PRL 114 232502 (2015)11C : Gulyuz, et al., PRL 116, 012501 (2016)21Na : Eibach, et al., PRC 92, 045502 (2016)68,69Co : under analysis

72m,gBr+, T1/2=1.3 m, 10.6 s

14O+, T1/2=71 sm = 25 eV dm/m = 2·10-9

11C+, T1/2=20 m

243 ions

21Na+, T1/2=22.5 s

T=1/2 mirror decayQ values

-60 -40 -20 0 20 40 60

25

30

35

40

45

50

55

Me

an

Tim

e o

f F

ligh

t [u

s]

vrf - 4232480 [Hz]

68Co+2, T1/2=1.3 s


ground state

isomer

Pushing the Sensitivity LimitTowards mass measurements with one single rare isotope ion


• Synthesis of elements• Doubly magic nuclei and

their vicinity

• 78Ni & 100Sn and neighboring isotopes• important for nuclear structure

studies and nuclear model tests• Mass measurements are challenging

due to low production rates• Production at NSCL: 1-3 per day

Single Ion Trap Project at LEBIT/NSCL

Weak

Signal~fA

FFT

I

Narrowband Fourier Transform – Ion Cyclotron Resonance (FT-ICR) to enable

high-precision mass measurements of rare isotopes produced at low rates

Traditional Time-Of-Flight Ion Cyclotron Resonance (TOF-ICR) technique requires

~ 100 detected ions to obtain a resonance curve

Amplify and

supress noiseAnalyze Get ion frequency

4K

Detection of a Single Rare Isotope


The Single Ion Penning TrapComing Alive


7 T SIPT

magnet

9.4 T LEBIT

magnetRFQ cooler

buncher

Off-line

Ion sources

-300 -200 -100 0 100 200 300

15.0

15.2

15.4

15.6

15.8

16.0

16.2

16.4

16.6

16.8

Tim

e o

f F

ligh

t [µ

s]

Frequency - 2,759,224.7 [Hz]

data

fit

39K

+

Figure1-FirstFT-ICRsignalofionsfromSIPT.39K+IonsfromLEBITstableionsourceweresentthroughLEBITcoolerbuncherintoSIPTbeamlineandcapturedintheSIPTPenningtrap.AfterRFexcitationtheirimage-chargesignalwasrecorded.ThefigureshowstheFouriertransformationofthissignalw ithapeakatthecyclotronfrequencyof39K +ions.

0

0.0005

0.001

0.0015

0.002

0.0025

3000 3200 3400 3600 3800 4000

Amplitude[V]

Frequency- 2748647.833[Hz]

SIPTFT-ICR(5averages,256msacquisition)

WithIons

WithoutIons

Figure 4 – (Left) First TOF-ICR signal of ions from SIPT. (Right) First FT-ICR signal of ions from SIPT. In both cases, 39K+ Ions from a LEBIT stable ion source were sent through LEBIT cooler buncher into SIPT beam line and captured in the SIPT Penning trap. For TOF-ICR, after RF excitation the ions were ejected and their time of flight to a multichannel plate detector was recorded. A theoretical fit to the data is shown by the red line. For FT-ICR, after RF excitation the image-charge signal

from the ions was recorded. The figure on the right shows the Fourier transformation of this signal with a peak at the cyclotron frequency of 39K+ ions.

Summary


• Rare isotopes – discovery potential

• Atomic techniques provide means to

determine fundamental nuclear properties

• Laser spectroscopy

• Direct mass spectrometry

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Masses and Moments via Precision Atomic Physics Techniques · 2017. 3. 3. · High intensities –good quality –element dependent ... nuclear multipole moments (dipole moment m