Transcript DOE ONP Program Managers Briefing

23rd Winter Workshop on Nuclear Dynamics
La Jolla, California
March 11-19, 2006
The Radioactive Beam
Program at Argonne
Birger Back
Argonne National Laboratory
Argonne National Laboratory is managed by
The University of Chicago for the U.S. Department of
Energy
Outline
• Physics Motivation for Radioactive Beams
• Past and Present Radioctive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
• Future Plans
- CARIBU: Accelerated 254Cf fission fragments (G. Savard)
- Superconducting Solenoid Spectrometer (B.Back)
- RIA ?
2
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Important physics questions
• modification of nuclear structure in neutron-rich systems
•
•
- shell-structure quenching
- single particle structure near neutron-rich magic nuclei
- pairing interaction in weakly-bound systems
collective behavior in neutron-rich systems
r-process path
- ground-state information
• mass
• lifetime
- neutron capture rate
- fissionability of very heavy neutron-rich isotopes
3
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Past and Present Radioactive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
4
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ATLAS facility at Argonne
New addition
being built
Solenoid
Spectrometer
Secondary beam
production target
CARIBU
5
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In-flight radioactive beams at ANL: e.g. 6He beams
Reaction: 7Li+d => 3He+6He
Focusing
solenoid
D2 gas cell
7Li
from ATLAS
81 MeV
3 X 1011 particles/sec
Rebunching
resonator
7Li
Magnetic
separator
7Li
+ 6He
7Li
+ 6He
*B. Harss, K. E. Rehm et al.,
Rev. Sci. Instrum. 71, 380 (2000)
7Li
6He
10,000 pps
6
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Radioactive beams at ATLAS
Beams available
after CARIBU upgrade
Beams available
“now”
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RIA beams – delayed ‘til 2011 (Bodman)
8
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Past and Present Radioactive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
9
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12C(a,g)16O
.. single most important nuclear physics uncertainty..
DoE Milestones: Reduce Uncertainties of the most crucial stellar
evolution nuclear reactions (e.g. 12C(a,g)16O) by a factor of two.
ANL:
J. Greene, A. Hecht, D. Henderson, R. Janssens, C. L. Jiang,
E. F. Moore, M. Notani*, R. C. Pardo, K. E. Rehm, G. Savard,
J. P. Schiffer, B. Shumard, S. Sinha, X. D. Tang
Hebrew University:
M. Paul
Northwestern University:
L. Jisonna, R. E. Segel
Ohio University:
C. Brune
University of North Carolina:
A. Champagne
Western Michigan University: A. Wuosmaa
*supp. by JINA
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Interference
Need width of sub-threshold 1- state
to determins S-factor at Gamow window
Obtain width from interference structure
on low-energy side of above-threshold
1- state
High intensity 16N beam
Detector with no b-sensitivity
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Twin-Ionization Chamber
E(a)
Anode (Energy)
16N(T =7.1s)
½
Frisch grid
(angle)
Ea ~ 1.82 MeV
No radiation damage
cathode
•Available with large areas
•Improved homogeneity
•Practically no sensitivity to b’s
Frisch grid
•No dead layer
•Smaller pulse height defects
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E(12C)
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
anode
12
Experimental setup
4 Ionization
chambers
16N
beam
T ½=7.1 s
Stepping
motor,
encoder
Rotating wheel/cathode
Rotating wheel,
cathode
13
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16N
- 16O  12C+ a first test results
b
PRELIMINARY
No b background
a
14
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Past and Present Radioactive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
15
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Example: 7He (Wuosmaa et al., PRC 72, 061301 (2005)
•
7He:
- Unbound neutrons – halos – significant current interest
- Theories generally agree but uncertainty in experimental results
- Where is the 1st excited state? Is there one? What is it’s spin?
•
Can be studied with (d,p) reactions using unstable beams
16
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Experimental setup
Monitor EDE
telescope
Au Monitor target
proton
CD2 target
540 mg/cm2
Beam axis
6He
4,6He
Annular proton detectors
Wlab ~ 3.5 sr
qlab=109o-159o
Forward-angle EDE
detectors
qlab=1o-7o
Our secondary-beam intensities are ~1-5X104 particles/sec
Event rate for 10 mb/sr ~ 10-50 counts/hour
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17
Efficiency corrected data
Calibration Reaction 2H(7Li,p)8Li
showing empirical background
2H(6He,p)7He
Fit with ground state,
broad resonance, background
7He
data with fit including state with
EX=600 keV, G=750 keV,
Strength with expected
spectroscopic factor
18
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Past and Present Radioactive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
- L.-B. Wang,UIUC
- APS/DNP Thesis prize (2006)
19
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Charge Radii Measurements
Methods of measuring nuclear radii (interaction radii, matter radii, charge
radii)
 Nuclear scattering – model dependent
 Electron scattering – stable isotope only
 Muonic atom spectroscopy – stable isotope only
 Atomic isotope shift
RMS point proton radii (fm) from theory and experiment
6He
QMC Theory
He-3
He-4
He-6
He-8
1.74(1)
1.45(1)
1.89(1)
1.86(1)
?
?
1.95(10) GG
1.81(09) GO
1.68(7) GG
1.42(7) GO
m-He Lamb Shift
Atomic Isotope Shift
p-He Scattering
1.474(7)
1.766(6)
G.D. Alkhazov et al., Phys. Rev. Lett. 78, 2313 (1997);
D. Shiner et al., Phys. Rev. Lett. 74, 3553 (1995).
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Experimental Setup - Schematic
ATLAS
12C(7Li,6He)13N
7Li3+:
2S-2P, 1083 nm
100 pnA, 60 MeV
2S-3P, 389 nm
6He
Produced
389 nm
6He
Mixing
chamber
Kr,
4He
Transversal
Cooling
extracted: ~ 106 s-1
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MOT
RF discharge
Kr or 4He
Carrier gas
6He
Zeeman Slower
He*
1083 nm
389 nm
Photon
Counter
6He
trapped: ~ 10-2 s-1
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
21
Single Atom
Spectroscopy
1200
xc: 0.034 +/- 0.030 MHz
w: 5.737 +/- 0.095 MHz
photon counts
1000
800
4He
600
400
200
0
-8
-6
-4
-2
0
2
4
6
8
frequency (MHz)
300
xc: -0.008 +/- 0.106 MHz
w: 5.135 +/- 0.298 MHz
~
150
6He
atoms in one hour
April 6, 2004
photon counts
250
200
6He
150
100
50
-8
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-6
-4
-2
0
2
4
Winter Workshop on Nuclear Dynamics, LaJolla
March 11-19,
2006
frequency
(MHz)
B.B.Back, Argonne National Laboratory
6
8
22
A Proving Ground for Nuclear Structure Theories
Experiments
L.-B. Wang et al., Phys. Rev. Lett. 93, 142501 (2004) (Nucl-ex/0408008)
Reaction collision
Tanihata et al 92
Elastic collision
Alkhazov et al 97
Atomic isotope shift
This work 04
First modelindependent
determination
Csoto 93
Funada et al 94
Varga et al 94
Cluster models
Wurzer et al 97
Theories
Esbensen et al 97
No-core shell model
Navratil et al 01
Pieper&Wiringa 01
(AV18 + IL2)
Quantum MC
(AV18 + UIX)
(AV18)
Pieper&Wiringa 05 (AV18+IL2)
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1.7
1.8
1.9
2.0
2.1
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back,
Argonne NationalRadius
Laboratory
Point-Proton
of 6He (fm)
23
Outline
• Physics Motivation for Radioactive Beams
• Past and Present Radioctive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
• Future Plans
- CARIBU: Accelerated 254Cf fission fragments (G. Savard)
- Superconducting Solenoid Spectrometer
- RIA ?
24
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Neutron-rich ions for free – 252Cf spontaneous
fission
1 Ci 252Cf source
about 20% of total activity
extracted as ions
works for all species
large improvement over existing
ISOL based facilities
r-process path
25
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CARIBU – new building under construction
Courtesy: R. Pardo
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26
CARIBU:
RFQ cooler
ECR Charge breeder
Gas cell
252Cf
source
27
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Courtesy:
R. Pardo
Winter Workshop
on Nuclear
Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
Yields for Representative Species
Calculated maximum beam intensities for a 1 Ci 252Cf fission
source using expected efficiencies.
Isotope Half-life Low-Energy Beam
Accelerated Beam
(s)
Yield (s-1)
Yield (s-1)
104Zr
1.2
6.0x105
2.1x104
143Ba
14.3
1.2x107
4.3x105
145Ba
4.0
5.5x106
2.0x105
130Sn
132Sn
138Xe
110Mo
111Mo
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222.
40.
846.
9.8x105
3.7x105
9.8x106
3.6x104
1.4x104
7.2x105
2.8
0.5
6.2x104
3.3x103
2.3x103
1.2x102
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
28
Outline
• Physics Motivation for Radioactive Beams
• Past and Present Radioctive Beam Studies
- Nuclear Astrophysics Studies (K.E.Rehm)
- Light Nuclei & ab initio structure calculations (A.H.Wuosmaa)
- Nuclear Charge radius of 6He and 8He (Z.-T. Lu et al.)
• Future Plans
- CARIBU: Accelerated 254Cf fission fragments (G. Savard)
- Superconducting Solenoid Spectrometer
- RIA ?
29
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Solenoidal spectrometer
A new concept for studying light-ion reactions
Strong MRI magnet
Measured quantities
Flight time:
Tflight=Tcyc
Position:
z
Energy:
Elab
Derived quantities
Part. ID:
m/q
Energy:
Ecm
Angle:
qcm
p,d,t,3He,a
m eΒ

 Tflight
q 2
Field: 5 Tesla
Particle
Tcyc (ns)
p
13.1
d,a
26.2
t
39.3
3He
19.7
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Heavy-Ion
2
E cm  E lab  12 mVcm
-
qcm
Inverse kinematics
VcmqeB
z
2
 1

qeBz - 2mVcm


 arccos
 2 2mE  m 2 V 2 - mV qeBz /  
lab
cm
cm


Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
30
p(44Ti,p’)44Ti kinematics
Simulation
10
Simulation
Ep (MeV)
8
DElab=50 keV
Dq=1 deg
6
q=60o
4
2
0
30
40
50
60
70
qp (degrees)
80
90
10
DElab=50 keV
Dz=1 mm
DTflight=1 ns
Ep (MeV)
8
6
z=25 cm
4
2
0
0
10
20
30
40
50
zp (cm)
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Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
B.B.Back, Argonne National Laboratory
Acceptance
F-acceptance: ~100%
(q,Elab) acceptance depends
on solenoid geometry and
magnetic field strength
With the target located at the
center of a 150 cm long
solenoid of 50 cm bore the
acceptance is shown here.
The lower energy cut-off
arises from the outer diam.
of the Si detector and its
proximity to the target (5cm)
Acceptance can be optimized
to specific reaction by moving
target and Si detectors along
beam axis
32
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Advantages of Solenoid Spectrometer
• Automatic particle I.D.
• Excellent center-of-mass energy resolution
• Large acceptance and solid angle
• Simple detector and electronics - few channels
• Excellent center-of-mass angle resolution
• Suppression of backgrounds
33
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Physics opportunities
• Single particle structure
- Mapping out the single-particle strength near closed shells
• Astrophysics
- Studies of the s, r, and rp-processes using (d,p) and (3He,d) reactions on
radioactive nuclei
• Pair transfer
- Probing the nature of pair correlations in a new domain away from stability
using (p,t), (t,p), and (3He,p) reactions
• Inelastic scattering
- Study collective aspects of nuclear structure in radioactive species using p,
a, and other light particles
• Knockout reactions
- Study of deep-lying particle orbits via (p,2p) reactions
• Surrogate reactions
- Simulation of n-capture cross section on short-lived isotopes by comparison
to (d,p) reactions. Needed for stockpile stewardship program
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34
Summary - Conclusions
• Present: Argonne has a substantial radioactive beam program
-
Nuclear Astrophysics
Structure of light nuclei – GFMC ab-initio theory
Laser spectroscopy – nuclear charge radii
Other
• Future:
-
CARIBU – weak but very neutron-rich beams
New Solenoid Spectrometer
RIA???
National Academy of Science – Rare Isotope Science
Assessment Committee – see
http://www7.nationalacademies.org/bpa/RISAC_Presentations.html
35
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Atomic Isotope Shift
Gordon Drake, High precision theory of atomic helium, Phys. Scripta T83: 83 (1999)
Isotope Shift
Mass shift:
due to nucleus recoil
ee-
dnMS
Measured
dn  dnMS  dnFS
Field shift:
due to nucleus size
A - A'

AA '
Calculated
e-
dnFS
 Z  D[(0)]2  d<r2>
Measured Derived
IS(23S1 - 33P2) = 43,196.202(16) + 1.008(<r2>He4 - <r2>He6) MHz
---- G. W. F. Drake, Nucl. Phys. A737c, 25 (2004)
36
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Layout
Solenoid:
50 cm bore x 150 cm long superconducting
5.0 Tesla axial field
Cryo-coolers
Target:
1 mm thick cooled gas target w. Ti windows
Si-detectors:
12 pos. sensitive Si detectors 1x10 cm
Recoil detectors: DE-E Si array for A<20 recoils
Ionization chamber for heavier recoils
Target wheel/cell
Vacuum chamber
Solenoid
Si-detector array
37
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(d,p) Angular Distributions
2H(8Li,p)9Li
DWBA calculations,
QMC predictions, no normalization
2H(6He,p)7He
g.s.
DWBA calculations
QMC calculations
Optical-model parameters from Schiffer et al, PRC 164
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38
Nuclear Astrophysics with Radioactive Beams:
PRL 82, 3964(1999)
PRC 65, 035803(2002)
21Na(p,a)18Ne
15O(a,g)19Ne
neutron-star
56Ni(p,g)57Cu
PRL 80, 676(1998)
PRC 67, 065808(2003)
PRC 67, 065809(2003)
17F(p,a)14O
novae
11C(p,a)8B
Supermassive stars
NPA 734, 615(2004)
8B(b,n)
2a
12C(a,g)16O
sun
massive stars
supernovae
44Ti(a,p)47V
39
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PRL 91, 252501(2003)
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
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PRL 84, 1651(2000)
Energy Level Fits
a+2n
8He+2n
6He+2n
40
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S. Pieper and R. Wiringa
Winter Workshop on Nuclear Dynamics, LaJolla March 11-19, 2006
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