Laser spectroscopy experiments on fission products
This presentation is the property of its rightful owner.
Sponsored Links
1 / 16

Laser spectroscopy experiments on fission products PowerPoint PPT Presentation


  • 36 Views
  • Uploaded on
  • Presentation posted in: General

Laser spectroscopy experiments on fission products. Introduction : hyperfine interaction. Principle : use the electronic cloud to probe the nuclear electromagnetic properties.

Download Presentation

Laser spectroscopy experiments on fission products

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Laser spectroscopy experiments on fission products

Laser spectroscopy experiments on fission products

Introduction : hyperfine interaction

Principle : use the electronic cloud to probe the nuclear electromagnetic properties

Measured quantities : spin I, magnetic moment mI, spectroscopic quadrupole moment Qs, evolution of the mean square charge radius d<r2>c

Physics case (part of)

Physics of medium mass nuclei produced by fission

Laser spectroscopy systems

Resonant Ionisation spectroscopy (RIS) : COMPLIS

Collinear Spectroscopy after beam cooling : future laser system at ALTO


Laser spectroscopy experiments on fission products

Hyperfine interaction

l=300 nm

1

2

n106 GHz

4GHz

hn04eV

191Ir

3

4

5

n

B

A

Nuclear structure

information

Measurement

Two hyperfine interaction energy terms

mI

YN

A

B

QS

Axial symmetry

3K2-

Nuclear quantities

QS

Q0

b2


Laser spectroscopy experiments on fission products

Isotope shift

  • Change of nuclear mass between isotopes:

MASSSHIFT

  • Change of the nuclear charge

  • density between isotopes :

VOLUME SHIFT

Measurement

Nuclear quantity

DniAA’

Nuclear droplet model


Laser spectroscopy experiments on fission products

Nuclear regions explored at ALTO

238U

30 keV

Expected intensities = SPIRAL2 /100

N=82

1+

50 MeV

N=50

target

source

Sn Z=50

Fission

Ni Z=28

e-

g

neutron rich nuclei produced by fission at ALTO (Orsay) and then at SPIRAL2 (GANIL)

Doubly magic regions 78Ni and 132Sn


Laser spectroscopy experiments on fission products

Ba

Cs

Xe

Production /s/µA

5 108 – 5 109

Z=50

Sn

108 – 5 108

In

5 107 – 108

Cd

107 – 5 107

5 106 – 107

N=82

106 – 5 106

5 105 – 106

105 – 5 105

N=50

104 – 105

Stable

Sr

Rb

Kr

Z=28

Expected yields at ALTO

Extrapolations from measured yields at PARRNe

Represented yields104pps

minimum yield for the laser set-up we envisage


Laser spectroscopy experiments on fission products

A “sample” of the physics motivations

Z=56 Ba

Rb (Z=37) C. Thibault Nucl. Phys. A367, 1 (1981)

mid-shell effect

Z=54

Xe

Sr (Z=38) F. Buchinger Phys. Rev. C 41, 2883 (1990)

b=0.4

b=0.3

b=0.2

d<r2>c

b=0.1

b=0

Shape transition

Sherical shell gap

N=82

N=60

N=50

The evolution of the charge distribution is very sensitive to the structural changes

  • The <r2>cvariations reflect both the change in volume and departures from spherical symmetry, the origins of which can be :

    • rigid deformation (rotor behaviour)

    • Zero point quadrupolar vibrations (or more generally dynamical effects)

    • Core polarization

<r2>c very rapidly when N 

<r2>c when N 


Laser spectroscopy experiments on fission products

Illustration of the core polarization effect

Origin : monopole part of the neutron-proton interaction  importance of the radial part of the orbital wave functions

2d5/2

50

n=2 n=3 n=4

1g9/2

n

40

2p1/2

38

N<50

2p3/2

1f5/2

p

2d5/2

50

1g9/2

n

40

2p1/2

38

N>50

2p3/2

1f5/2

p


Laser spectroscopy experiments on fission products

Illustration of the “dynamical” effects

Recent results from

the COMPLIS measurements

on tin

F. Le Blanc et al. to be published in Phys Lett B

Theoretical Data

NL3 : G.A Lalazissis et al., At. Data and Nucl. Data Tables 71 (1999)1.

Gogny : M. Girod and S. Péru, Private comm. (2001)

SLy4 and SLy7 : P. Bonche and J. Meyer, Private comm. (2002).


Laser spectroscopy experiments on fission products

Resonant ionization mass spectroscopy system :

COMPLIS

Ionization

Target

Excitation

Excitation

Desorption

Magnet

Emergent beam at 59 kV

Incident beam at 60 kV

Ion detector (MCP)

INJECTOR

Magnet

Ion source (stables)


Laser spectroscopy experiments on fission products

Characteristics of the COMPLIS set-up

resolution

total

efficiency

10-5-10-6

YAG

pumping

10 Hz

Ionization continuum

desorbed atoms

Ionization zone

1 atome/100

YAG

beam

646,58 nm (rouge)

Dye laser

lambda-physik

graphite

2

323,29 nm (UV)

2

351,7 nm (UV)

ZOOM

tunable

monomode

dye laser

« compulsé »

Ground state

First stage

beam

Ionization

beams

YAG

pumping

10 Hz

a

Ionization volume


Laser spectroscopy experiments on fission products

Principle of the fast beam collinear laser spectroscopy

dv

dnD=n0

c

n

n

Laser source fixed frequency

Velocity v

n

Velocity v+dv

Frequency in the rest frame of the atoms

The kinematic compression of the velocity distribution

results in a reduction of the residual doppler width

dE=mv dv

Energy spread

velocity spread

Residual doppler width

The hyperfine structure is scanned by a beam energy scan

with U=10-4,  ~50MHz


Laser spectroscopy experiments on fission products

COLLINEAR laser spectroscopy system

Ion source

Photomultiplier

electrons

Mass

separator

Ellipsoïdal

mirror

Charge-exchange

cell

Separated beam

Retardation

system

RFQ

cooler-buncher

High resolution laser


Laser spectroscopy experiments on fission products

Efficiency

  • . Transport : 70 %

  • . Neutralization : 80 %

  • . Feeding probability of the selected metastable state : 30%

  • . Spatial overlap between laser beam and ion beam : 5 10- 3

  • . Resonance efficiency : 100%

  • . De-excitation efficiency : 50%

  • . Collection efficiency : : 5 %

  • . Detection efficiency : 90 %

  • TOTAL : ~10-5

but : signal/noise ratio strongly increased by the use of the cooler buncher


Laser spectroscopy experiments on fission products

A few details on the cooler…

grounded

Buffer gas

Ucavity

UHV

UHV

Pulsed cavity

transfert

Ions

Ions

Ekin=e.( UHV-Ucavity )

Ions

Ucavity

UHV

trapping

Longitudinal potential shape

ejection

F. Herfurth NIM A 469 (2001) 254

(ISOLTRAP)

Ion deceleration   10eV


Laser spectroscopy experiments on fission products

First measurements at ALTO

206 nm

547.7 nm

303.9 nm

422.7 nm

  • Ag (Z=47) : from A=111 to A=123 (or further from the stability line depending on the effective productions) complete the measurements on this isotopic chain on the right side of the valley of stability

  • Transition : Z.Phys. A274 (1975)79.

  • Ge (Z=32) : from A=77 to A=83  N=50 crossing

  • then, les Br, As and Ga towards Ni, Sb, I, ...

N=50


Laser spectroscopy experiments on fission products

Miroir

ellipsoïdal

Lentilles

d’accélération

ralentissement

Cellule à

échange

de charge

Laser haute

résolution

Coût et main d’œuvre

F. Le Blanc IPN

  • Ligne de faisceau, éléments d’optique ionique et pompage : 50 k€

  • Cellule à échange de charge : LAC ou Mainz

  • Détection : 10 k€

  • Lasers et optique : 200 k€

  • Acquisition et commande : 40 k€

  • Total : 300 k€

Durée du montage et de la mise au point : 2 ans à 2 chercheurs plein temps plus aide service technique (construire l’acquisition et réaliser la ligne de faisceau)


  • Login