MP-41 Teil 2: Physik exotischer Kerne
13.4.
20.4.
27.4.
4.5.
11.5.
18.5.
25.5.
1.6.
8.6.
15.6.
22.6.
29.6.
6.7.
13.7.
Einführung, Beschleuniger
Schwerionenreaktionen, Synthese superschwerer Kerne (SHE)
Kernspaltung und Produktion neutronenreicher Kerne
Fragmentation zur Erzeugung exotischer Kerne
Halo-Kerne, gebundener Betazerfall, 2-Protonenzerfall
Wechselwirkung mit Materie, Detektoren
Schalenmodell
Restwechselwirkung, Seniority
Tutorium-1
Tutorium-2
Vibrator, Rotator, Symmetrien
Schalenstruktur fernab der Stabilität
Tutorium-3
Klausur
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Rare-Isotope Beam Experiments
Discovery of projectile-fragmentation reaction
at Bevalac @ LBL (Lawrence Berkeley Laboratory)
D.E. Greiner et al., Phys.Rev. Lett. 35 (1975) 152
12C, 16O
(2.1 AGeV) + Target (Be, C, Al, Cu, Ag, Pb)
- Several fragments are produced in reactions
- Velocity of fragments is almost the same as that of the beam
- Momentum distribution is narrow, and has no significant correlation
with target mass and beam energies
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Rare-Isotope Beam Experiments
Momentum distribution of fragments (example 34S fragments from 40Ar + C @ 213 AMeV )
34S
fragments: 400 MeV/c narrow
beam:
26600 MeV/c
40Ar
Momentum distribution of fragments
are represented by a simple formula
based on the Goldhaber model
  0 
F  A  F 
 A  1
A: Beam mass number
F: Fragment mass number
σ0 = 90 MeV/c
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Production of Radioactive Ion Beams
Spallation
Fragmentation
ISOL = Isotope Separator On Line
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
In-flight separation of Rare Isotope Beams
Primary (production) target
Secondary
(reaction) target
Peripheral nuclear reactions
Forward focused products
Experimental
area
Electromagnetic
separator
Stable HI projectile source
Selected radioactive beam
E ~ 1000 AMeV
E >> 20 AMeV
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Fragmentation at Relativistic Energies
projectile
projectile fragment
target nucleus
abrasion ablation
FRS
FRS
FRagment Separator
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
RIBs produced by fragmentation or fission
9Be
target
exotic nuclei (also neutron
deficient)
fragments nearly retain the
projectile direction and velocity
Interaction zone
208Pb
target, heavy beam (238U)
neutron rich nuclei
fragments can be faster than the
projectile
Coulomb field
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Radioactive Ion Beams at GSI
1GeV/u U + H
About 1000 nuclear
residues identified
A/Z-resolution ~10-3
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
The FRagment Separator FRS
131Sn
132Sn
in-flight A and Z selection
energy resolution: ~ 1 GeV
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Rare Isotope Selection at FRS: Bρ – ΔE – Bρ selection
primary beam
86Kr ~700 AMeV
fully striped
20m
Transmission
:
fragments
• 20-70 % for fragmentation
• < 2 %
for fission
secondary beam
78Ni ~ 100 AMeV
production target
9Be
magnetic dipoles
Br A/Z
degrader
DE Z2f
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
magnetic dipoles
Br A/Z
FRagment Separator
Primary
Beam
Beam & All
Fragmentation
Products
Secondary
Beam
Spacial
Dispersion
Isotope
Selection
Momentum
Selection
Wedge-shaped
Degrader
19Ne
at 600AMeV:
Phase-space imaging of differently
shaped degraders within the achromatic
ion-optical system. The results for a
homogeneous, an achromatic, and a
monoenergetic degrader are given. All
degraders have the same thickness on
the optical axis (d/r=0.5)
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Fragment Separation
40Ar
50MeV/u + Ta (100μm), wedge shaped Al (200μm) degrader
0.39 mrad
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
1.66mrad
Chromatic Aberration
When different colors of light propagate at different speeds in a medium, the
refractive index is wavelength dependent. This phenomenon is known as dispersion.
Longitudinal (axial) chromatic aberration:
The focal planes of the various colors do
not coincide.
Transverse (lateral) chromatic aberration:
The size of the image varies from one
color to the next.
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Production, Separation, Identification
SIS
FRS
projectile
projectile fragment
target nucleus
abrasion
ablation
FRagment
Separator
Standard FRS detectors
TPC-x,y
position
@ S2,S4
Plastic
scintillator
(TOF)
@ S4
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
MUSIC
(ΔE)
@ S4
Standard FRS and RISING detectors
production target
Z
multiwire chamber;
beam position
Y
Y
DE
ToF
reaction target
scintillator
MUSIC
ionization
chamber;
Z
X
A/Q X
scintillator

E
CATE
Si-CsI arrays;
(X,Y), Z,A
Ge-Cluster
detectors
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Scattering experiments at relativistic energies
xy position
from LYCCA
MP-41 Teil 2: Physik exotischer Kerne, SS-2012
Calculate the event-rate for the fragmentation reaction
124
54



Xe 1010 s 1  49Be 4 g / cm 2


100
50
Sn50
to produce the doubly magic nucleus 100Sn. The expected production cross section is
7.4·10-12 [barn].
9g of 9Be ≡ 6.02·1023 particles/cm2
4g of 9Be ≡ 2.68·1023 particles/cm2
luminosity = projectile [s-1] · target nuclei [cm-2]
= 1010 [s-1] · 2.7·1023 [cm-2]
event rate = luminosity [s-1 cm-2] · cross section [cm2]
= 2.7·1033 [s-1 cm-2] · 7.4·10-36 [cm2]
= 0.02 [s-1]
= 72 [h-1] = 1718 [d-1]
MP-41 Teil 2: Physik exotischer Kerne, SS-2012