Mass measurements using low energy ion beams

-1- C. Thibault 31 mars 2004

• Motivations to measure masses

• Present status

• Experimental methods for direct mass measurements

• Current developments

• Nuclear Structure

• Astrophysics

• Weak interaction

Motivations

-2- C. Thibault 31 mars 2004

Nuclear structure

-3- C. Thibault 31 mars 2004

Neutron number

Shell closure deformations

Accuracy : 100 keV 10-6 at A=100

r-process

Mass models

-4- C. Thibault 31 mars 2004

35 40 45 50 55 60 65 70 75 80

-6

-4

-2

0

2

4

6

Janecke,

Masson &

1988Aboussir et al., 1992

Duflo & Zuker, 1996

Moeller et al., 1995

Comay et al.,

1988

Tachibana et al., 1988

Janecke &Masson, 1988

Groote et al., 1976

Measured masses

Mo

de

l dif

fere

nc

e (

Me

V/c

2)

N (Z = 37)

High accuracy• Nuclear Structure

shell quenchings10-6

Pairing, halos10-7

• Astrophysics

new shells far from stability 10-5

• Weak interaction

superallowed transitions CVC tests10-8

High sensitivity• rare nuclei production (much) less than

1000/s

• short-lived nuclei half-life (much) less than 100 ms

Requirements

-5- C. Thibault 31 mars 2004

Merit of experimental methods

-6- C. Thibault 31 mars 2004

Lunney et al. 2003

Mass measurements accuracy

-7- C. Thibault 31 mars 2004

Nucleus 2003

Recent mass measurements

-8- C. Thibault 31 mars 2004

Lunney et al. RMP 75 (2003) 1021

α, β-, β+ Decay- energies

-9- C. Thibault 31 mars 2004

Masses measured since 1994 and used in AME 2003:

Qα 4 – 30 keV ~ 300 ~ 100 isomers

Qβ- 10 – 100 keV ~ 80

Qβ+ 50 – 100 keV ~ 50

Qα : α or α-γ spectroscopy

Qβ : β-γ spectroscopy or Total Absorption Spectrometry

Low energy direct measurements

-10- C. Thibault 31 mars 2004

Mass Cyclotron frequency

πB

mqfc 2

B calibration 2-mass comparison

c1

c2

2

2

1

1ff

qm

qm

At constant B :

Mistral principle

-11- C. Thibault 31 mars 2004

RF modulator

RF modulation

RF demodulation

Beam ejection

Exit slit

Inlet slitBeam injection

Mass measurement at ISOLDE with a Transmission and RAdiofrequency spectrometer on-Line

cRF fnf )21(

Cyclotron frequency measurement

MIS RAL

2-mass comparison

Mistral layout

-12- C. Thibault 31 mars 2004

2211 EmEm

MIS RAL

Penning trap scheme

-13- C. Thibault 31 mars 2004

Trajectory in a Penning trap

-14- C. Thibault 31 mars 2004

A = 100, q = 1, B = 6T

a x ia l m o tio n : o sc illa tio n in E -f ie ld

20

md

qVz

• Axial pulsation

z 44 kHz242

22zcc

• Reduced cyclotron rotation

+ 1 MHz

242

22zcc

• Magnetron rotation (slow)

– 1 kHz

B

ω+ + ω– = ωc

Isoltrap layout

-15- C. Thibault 31 mars 2004

ISOLDE60 keV ion beam

MCP Time-of-flightDetector

RFQ-Cooler-BuncherBeam preparation

Preparation Penning Trap

Cooling of ion beamCleaning of isobars

Precision Penning Trap

mass measurement:Cyclotron frequency

determination

Penning traps at work

-16- C. Thibault 31 mars 2004

beam prepa measures main topics

Isoltrap Isolde 1+ ~200 N~Z, n-rich, isotopic series CERN

Smiletrap Crysis ++++ ~10 Qββ , ν massStockholm

Jyfltrap Igisol 1+ [~10] N~Z, (refractory elements)Jyväskylä 2

CPT gas cell 1+ ~10 n-rich (Cf fission), N~ZArgonne

Penning traps in development

-17- C. Thibault 31 mars 2004

beam prepa status main topics

Shiptrap gas cell 1+ injection OK TransactinidesDarmstadt Superheavies Lebit 9T trap gas cell 1+ injection tests N~Z, n-rich MSU trap construction (very short half-lives)

Mafftrap [Isol] construction n-rich (fission) München gas cell 1+ Transuranides, Superheavies

TITAN ISAC construction (very short half-lives)Vancouver Ebit +++ 2005?

-18- C. Thibault 31 mars 2004

Mass connections

-19- C. Thibault 31 mars 2004

A. H. Wapstra et al. Nucl. Phys. A729 (2003) 129

TITAN layout

-20- C. Thibault 31 mars 2004

ISACDC

ion beam

RFQCooler

+ buncher

EBITCharge breeder

m/qSelection

stage

PrecisionPenning

trap

EBIT

Mass predictions

-21- C. Thibault 31 mars 2004

Lunney et al. RMP 75 (2003) 1021

Mass connections

-22- C. Thibault 31 mars 2004

G. Audi et al.

Mistral examples

-23- C. Thibault 31 mars 2004

Cyclotron frequency

Phase selection after first modulation

cf

radiofrequency radiofrequency

480324.92

0.11 kHz 2.10-7

cf 70000

cf

21n 23n21n

MIS RAL

Mistral measurements

-24- C. Thibault 31 mars 2004

N = 37

8784 85 86 88 897574 76 77 7978 80 81 82 838683 84 8574 75 7877 79 81 82

SrRb 888776 80

T1/2 1 s stable MISTRAL T1/2 100 ms

11Li 25-26Ne 26-30Na 29-33Mg 74Rb

Ne23 24 25

21 24 26 27N = 20

Na

28 29Al

2831

34

29 3022

3330 31

23

323124 25 26 28 29Mg 30 3227 33

27

26 27 28 29 3025

3231He

6 73 6 8

N = 8

Li4

7 10Be 12 1498 9 11

11

ISOLTRAP components