Transcript Slide 1
Radioactive beams from e-beam driven photofission
TRIUMF
User’s Workshop Jim Beene ORNL August 1-3 2007 Managed by UT-Battelle for the Department of Energy
Outline
Some comments on HRIBF & our n-rich research program
The photofission reaction: some advantages, some disadvantages
An investigation of properties and capabilities of a e-beam driven facility
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25MV Tandem Electrostatic Accelerator Stable Ion Injector (ISIS)
HRIBF 2006
Injector for Radioactive Ion Species 1 (IRIS1) Oak Ridge Isochronous Cyclotron (ORIC) Daresbury Recoil Separator (DRS) Enge Spectrograph High Power Target Laboratory (HPTL) On-Line Test Facility (OLTF) 3 Managed by UT-Battelle for the Department of Energy Presentation_name Recoil Mass Spectrometer (RMS)
HRIBF Post-accelerated Beams 175 RIB species available (+26 more unaccelerated) 32 proton-rich species 143 neutron-rich species Post-accelerated Intensity
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Beam list increased by ~50% since 2003
Presentation_name
The first transfer measurements on N=82 nuclei on / near r-process path
130 Sn(d,p) 131 Sn - R. Kozub et al. 132 Sn(d,p) 133 Sn - K.L. Jones et al. 134 Te(d,p) 135 Te - S.D. Pain et al.
132 Sn(d,p) 133 Sn
• yields, angular distributions of low-lying states measured • first observation of p 1/2 state in 133 Sn • three other states in 133 Sn measured, calibrated with 130 Te(d,p) • evidence for numerous states in 131 Sn never seen before • evidence that the f 5/2 level in significantly higher energy 135 Te is at a 5 Managed by UT-Battelle for the Department of Energy Presentation_name K. Jones
Decay spectroscopy of exotic nuclei
b
-decay studies around 78 Ni with postaccelerated (3 MeV/u) pure neutron-rich RIBs Winger et al.
Discovery of superallowed
a
-decay
d
2 ( 105 Te)/
d
2 ( 213 Po) ~ 3
• Enhanced due to the same proton and neutron shell structure • rp-process termination • En route to 104 Te → 100 Sn
S. Liddick et al., PRL 97,2006,082501
Range out unwanted high-Z contamination with high pressure & tape transport • Absolute beta-delayed neutron branching ratios for 76-79 Cu and 83-84 Ga • Identification of new excited states in 77 Zn, 78 Zn, 82 Ge, 83 Ge, and 84 Ge • Systematics of single particle levels (e.g. neutron s 1/2 ) near doubly magic 78 Ni
• • • • •
Pioneering studies with neutron-rich radioactive beams of heavy nuclei Fusion & Fission Coulex
Probing the influence of neutron excess on fusion at and below the Coulomb barrier Large sub-barrier fusion enhancement has been observed Inelastic excitation and neutron transfer play an important role in the observed fusion enhancement Important for superheavy element synthesis ERs made with 132,134 Sn cannot be made with stable Sn
Shapira et al., Eur. Phys. J. A 25, s01, 241 (2005) Liang et al., PRL 91, 15271 (2003); PRC 75, 054607 (2007) Padilla-Rodal et al. Phys. Rev. Lett. 94, 122501 (2005) Yu et al., Eur. Phys. J. A 25, s01, 395 (2005) Radford et al., Nucl. Phys. A752, 264c (2005) Varner et al., Eur. Phys. J. A 25, s01, 391 (2005)
• Probing the evolution of collective motion in neutron-rich nuclei • Increasingly larger contributions of neutrons to B(E2) values above 132 Sn • Recoil-in-Vacuum technique used to measure the g-factor for the first 2 + state in 132 Te:
Stone et al., PRL 94, 192501 (2005)
RISAC Science Drivers
& the electron driver
Nuclear Structure
–
Probing the disappearance of shells
Spectroscopy & reactions in 132 Sn, 78 Ni regions
–
Evolution of collective motion
We can probe 112 Zr and 96 Kr regions (not 156 Ba)
–
Neutron Skins
Structure/reaction studies of the most n-rich
–
SHE
Reactions with 132 Sn (~10 9 ) and vicinity
For Z=112, N=184, reaction mech. Studies with 92,94 Sr (10 6, 10 7 ) Nuclear Astrophysics
–
Decay spectroscopy (
b
n,
t
) Stockpile Stewardship
–
Surrogate reactions (n transfer, etc.)
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Disclosure / Disclaimer
The discussion of a photo-fission driver that follows was originally developed based on HRIBF considerations.
We have boundary conditions that are largely irrelevant to ISAC:
–
A turn-key simple-to-maintain accelerator
–
A concept that “guarantees” a minimum level of performance without need of major targetry breakthroughs.
–
A capability dedicated to extending our reach toward very n-rich nuclei in a timely manner
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HRIBF as a two driver facility
We are developing a proposal for a turn-key electron accelerator (e machine), capable of providing CW ~ 100kW beams with energies at or above 25 MeV.
This accelerator would be dedicated to producing neutron-rich species by photofission of actinide targets. Such an accelerator is by far the most cost effective means to achieve in-target fission rates in the mid 10 13 /s scale.
A comparable upgrade to our p-rich capability would be far more expensive Target development to support operation at >10 larger than current HRIBF capability.
13 f/s (~50kW )is well in hand. Thus we are confident we can reach fission rates about 20 times The increase in fission rate is not, however a good comparative metric.
– –
Photofission is a “colder” process than proton induced fission.
It results in lower actinide excitation, and less neutron evaporation from both the excited actinide system and the fragments.
–
Consequently production of very neutron-rich species can be enhanced by a substantial factor compared to 50 MeV proton induced fission, at the same fission rate.
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238 U photo-fission is dominated by the GDR
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But photo-fission is not the dominant GDR decay channel Data from Livermore and Saclay groups
(
g
,n) and (
g
,2n) account for ~2/3 of GDR cross section Substantial 236,237 U production is inevitable
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Photofission yields
• • •
10 13 f/s “easily” achieved About 20x current HRIBF But real gain >> 20x
238
U(
g
,f)
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(p,f) systematics from Tsukada (
g
,F) from ORNL systematics + Jyvaskyla model
Presentation_name
A sample comparison with data: Sn isotopes
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Total neutron multiplicities are important figures of merit for our purposes
Proton induced fission at HRIBF energies
– – E
p =50 MeV
n
n =8.5
E
p =500 MeV
n
n ~13 Electron induced photofission:
– –
E e =25 MeV
E
e =
50
MeV
n
n =3.3
n
n =3.4
Neutron-induced fission is very similar in many ways to photofission. 238 U(n,F) @ ~15 MeV has final state properties very similar to E 0 =25-50 MeV photofission.
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RIB production by photofission
16 Managed by UT-Battelle for the Department of Energy 10 13
ph-f/s 10
m
A 40 MeV p
Presentation_name
Conservative target design for performance determination
r =3 g/cm 3 d=3 cm (0.3 R M ) t=30g/cm 2 5X 0 (10cm) M=212 g r =6 g/cm 3 d=3 cm (0.6 R M ) t=30g/cm 2 5X 0 (5cm) M=212 g X o =6 g/cm 2 (U) 17 Managed by UT-Battelle for the Department of Energy Presentation_name 3 cm
Photofission target issues/ limitations Direct bombardment
e-beam directly incident on targets
If 10 13 goal is to be met, beam energies less than ~80 MeV may give problems using current target technology without further testing and or development.
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Photofission target issues
Converter + target
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An example of a somewhat more aggressive design
Similar power required to reach 10 13 f/s (52kW @ r =6 g/cm 3 t=30g/cm 2 M=495 g (5X 0 ) 25 MeV) 2.3 x UC x front surface area compared to 3 cm dia. Cylinder 5 cm 20 Managed by UT-Battelle for the Department of Energy Presentation_name
U(
g
,f) vs U(p,f) 1 GeV
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U(
g
,f) vs U(p,f) 1 GeV
(p,f) ( g ,f) 100 m A on 30 g/cm 2 10 13 5x10 f/s (~50 kW 25 MeV) 13 f/s 22 Managed by UT-Battelle for the Department of Energy Presentation_name
U(
g
,f) vs U(p,f) 1 GeV
(p,f) ( g ,f) 100 m A on 30 g/cm 2 10 13 5x10 f/s (~50 kW 25 MeV) 13 f/s 23 Managed by UT-Battelle for the Department of Energy Presentation_name
Conclusions I: RIB production
10 13 f/s can be achieved with an ~50 kW facility
–
Requires only modest sized targets to achieve initial goals
3 cm x 5 c m (212 g)
– –
<10 kW deposited in target 25 MeV e beam can be used with converter
Additional technologies can be considered
Substantially larger yields can be achieved with larger targets and higher beam powers
– –
500g to 1kg & 100-150 kW What is release time?
Even with thick converters, cannot isolate production target from beam power and still produce fission at high rates
Pulsed e-beam can aggravate thermal and mechanical stress issues in target .
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Conclusions II: Shielding
1E+7
Thick target bremsstrahlung:
– – q
1/2 ~100/E 0 degrees Forward angle
g
dose rate D~300 E 0 (Gy h -1 )(kW m -2 ) -1
D~1.5 x 10 7 Gy h -1 at 1 m for 50 MeV, 1MW e beam
–
6m concrete or ~1m Fe
–
90 0
g
dose rate D~70 (Gy h -1 )(kW m -2 ) -1 D~7 x 10 4 Gy h -1 at 1m for 1MW e beam (E 0 > 20 MeV) 1E+6 Forward Direction (zero degrees) 1E+5 1E+4 1E+3 Sideward Direction (90 degrees) 20 40 60 Electron Energy (MeV) 80 100 NCRP Report No 144 (2003
) 25 Managed by UT-Battelle for the Department of Energy Presentation_name
Electron Beam Facility Elevation
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e-Driver Upgrade Upper Level
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e-Driver Upgrade Lower Level
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Photo-fission yield
In target
Photo-fission yield
From ion source
Photo-fission yield
Post-accelerated
Science highlights with e-driver upgrade
Will test the evolution of nuclear structure to the extremes of isospin Will improve our understanding of the origins of the heavy elements Evolution of single-particle structure Transfer reactions at 132 Sn & beyond Collective properties in extended neutron radii Coulomb excitation near 96 Kr 32 Managed by UT-Battelle for the Department of Energy Reaction mechanisms for the formation of superheavy nuclei Decay properties of nuclei at the limits Crucial for understanding the formation of elements from iron to uranium Presentation_name
Broad program to study reactions with and structures of neutron-rich nuclei
• • •
Structure studies:
Isospin-dependent changes in single-particle properties collectivity symmetries pairing
Reaction studies:
interplay between structure and reaction (SHE synthesis) one- and multi-nucleon transfer
Domain:
Uncharted- or barely-explored regions - at or near doubly magic 78 Ni & 132 Sn around magic numbers Z=28, 50 and N=50, 82 new transitional nuclei (N=50-60, 82-90) unexplored deformed nuclei (N~90) •
Tools :
Newly developed techniques and detectors 33 Managed by UT-Battelle for the Department of Energy Presentation_name
• • •
Measurements to probe shell structure far from stability Gross properties:
•
Masses (binding energies)
•
Half lives
• • •
Radii Level densities
s
(n,
g
) -- related to r-process abundances, [use (d,p)] Single-particle properties:
•
Energy, spin, parity, spectroscopic factors, g-factors
•
Parallel momenta in knock out reactions (fast beams) Collective properties:
•
Low-lying energy spectra (
e.g.,
2 + states, 4 + )
• •
B(E2) & electromagnetic moments Higher spin states (band structures)
We will have an unparalleled opportunity to use transfer, decay and in-beam spectroscopic tools to employ these probes in uncharted regions of n-rich nuclei.
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Conclusion (for HRIBF-scale facility)
An electron-beam based facility can produce intense beams in a cost-effective way
Such a facility would be competitive world-wide for neutron-rich beams until FRIB is available
Cost containment is important
There is a relatively short window during which such a facility is relevant.
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Some Comments (for ISAC-scale facility)
An electron-beam based facility can produce intense n-rich beams in a uniquely cost-effective way
It is not possible to isolate the production target from beam power, as fully as is done with (d,n)
(n,F) two-step facilities.
Pulsing of high-power beams at low rates can be a serious problem for target performance
Substantial yields of a few alpha –emitters can be expected
If power can be handled, a MW scale photo fission facility could produce ~ mid 10 14 f/s.
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Initial Concept of Two Plugs in a Common Vacuum Envelope
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The Target Plug
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The Target Plug – Some Features
Ion source mounted on high-voltage deck inside a grounded outer vessel
Outer vessel vacuum tight except at e-beam entrances and RIB Beam exit
–
Use fast apertures over both locations
Converter target directly in front of fission target – also at high voltage
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High-Power Converter Target Designs Based on ORELA Target Design There will be a converter target as part of each target ion source plug
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First Beam Filter – Second Plug
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Decay studies pushing the frontier of n-rich nuclei Examples with eMachine Ion 200 keV (ions/s) 0.3
Tandem (ions/s) 0.001
t 1/2 (s) 0.11
78 Ni 80 Cu 81 Cu 82 Zn 1000 7 5000 4 0.3
0 ?
?
?
94 Br 96 Br 137 Sn 138 Sn 137 Sb 140 Sb 1x10 4 56 1800 89 9x10 5 980 100 4 45 2 2x10 4 17 0.07
?
0.19
?
?
?
149 Cs 2x10 4 4 ?
0.1 ions/s
t 1/2 &
b
n rates for many r process nuclei are accessible Energy levels test evolving nuclear structure
The evolution of single-particle levels and shapes in very neutron-rich nuclei beyond the N=50 shell closure
b
-decay experiments with postaccelerated (3 MeV/u)
pure
neutron rich RIBs, Oct-Nov 2006 beam T 1/2 (s) main results 76 Cu 0.65
77 Cu 0.46
78 Cu 0.35
79 Cu 0.19
83 Ga 0.30
84 Ga 0.08
85 Ga ~0.07
b
n
-
branching ratio I
b n
I
b n
,
n
- levels in N=47 77 Zn I
b n
,
I p b
n
g
of
78
Cu 49 revised decay observed first time
b
n
g
,
bg
,
n
s 1/2 2 + in N=51 83 in N=52 84 Ge,
n
s 1/2 Ge in 83 Ge rate of 0.1pps…
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Jeff Winger et al., RIB-108 and 122
Presentation_name
The evolution of single-particle levels and shapes in very neutron-rich nuclei beyond the N=50 shell closure Nov’06 : experiment with 2 pps of 3 MeV/u 84 Ga
b
n
g
84 Ga 84 Ge* 83 Ge* (
n
s 1/2 ) 83 Ge(
n
d 5/2 )
b g
84 Ga 84 Ge* ( 2+ ) 84 Ge ( 0+ ) N=51 83 Ge N=52 84 Ge 248 keV 625 keV
b
-gated
g
-spectrum (0.5 keV/ch)
b
-gated
g
-spectrum (0.5 keV/ch)
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Transfer reactions: shell structure of n-rich nuclei
Single-particle states around closed shells provide a fundamental shell model test
Example: (d,n)-like reactions neutron s.p. levels RIB Recoils detected in coincidence
132 Sn(d,p) 133 Sn @ HRIBF
Jones et al.
6x10 4 ions/s Single-particle transfer near 78 Ni and 132 Sn
Reactions of interest
(d,p) ( 9 Be, 8 Be) ( 3 He,d) ( 3 He, a ) ( 7 Li, 8 Be) E P (channels) 45 Managed by UT-Battelle for the Department of Energy E x Presentation_name Ion 84 Ge 88 Se 96 Sr 98 Sr 134 Sn 138 Te 140 Te Intensity (ions/s) 3x10 5 3x10 4 7x10 4 1x10 4 3x10 6 5x10 6 2x10 4 t 1/2 (s) 0.9
1.5
1.1
0.65
1.0
1.4
?
13 C( 134 Te, 12 C) 135 Te neutron transfer 2109 keV
929 1180
Particle-gamma angular correlations 929 1279 657 657 929 1279
Coulomb excitation in n-rich systems
Probes the evolution of collective motion in loosely-bound, neutron-rich nuclei
BaF Array n-rich beams C, Ti, Zr target Beam Charged-particle Gamma array CLARION
Radford et al.
Beene et al.
HRIBF
3000 134 Sn/s
With eMachine: neutron-rich nuclei from N=50 to N=82 (and beyond) are accessible
Ion 84 Ge 88 Se 98 Sr 136 Sn 138 Te 140 Te Intensity (ions/s) 3x10 5 3x10 4 1x10 4 700 5x10 6 2x10 4 t 1/2 (s) 0.9
1.5
0.65
0.25
1.4
?
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Heavy ion fusion reactions
Probes the influence of neutron excess on fusion at and below the Coulomb barrier
important for superheavy element synthesis
HRIBF Results
Ion
with eMachine
92 Br 134 Sn 136 Sn Intensity (ions/s) 2x10 5 3x10 6 600 t 1/2 (s) 0.34
1.0
0.25
More n-rich projectiles Further below barrier 134 Sn below 10 mb Transfer reaction studies on the same system will help to understand reaction mechanism Liang et al.
Unattenuated angular correlations: Theory & experiment
2.0
130Te 90 degree gamma ring
130
Te SIB 1.5
Hyball Ring 2 q g
= 90 °
1.0
130 Te beam 0.5
0.0
0 60 120 q g
= 155 °
180 240 300 0 q g
= 132
132 degree gamma ring
°
60 120 180 [degrees] 240 300 0 60 120 180 240 300 360 12 C recoil W ( q, ) scattered 130 Te stopped in Cu 49 Managed by UT-Battelle for the Department of Energy Presentation_name 180° q 0°
Magnetic moment: RIV attenuated angular correlations
Conclusion (for HRIBF-scale facility)
An electron-beam based facility can produce intense beams in a cost-effective way
Such a facility would be competitive world-wide for neutron-rich beams until FRIB is available
Cost containment is important
There is a relatively short window during which such a facility is relevant.
51 Managed by UT-Battelle for the Department of Energy Presentation_name
Some Comments (for ISAC-scale facility)
An electron-beam based facility can produce intense beams in a cost-effective way
It is not possible to isolate the production target from beam power, as is done with (d,n)
(n,F) two-step facilities.
Pulsing of high-power beams is a serious problem
Substantial yields of a few alpha –emitters should be expected
If power can be handled, a MW scale photo fission facility could produce ~ mid 10 14 f/s.
52 Managed by UT-Battelle for the Department of Energy Presentation_name
Neutron transfer reactions
Accessible at HRIBF Accessible with e-machine
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Coulex (1-step)
Accessible at HRIBF Accessible w e-machine
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Multi-step Coulex
Accessible at HRIBF Accessible w e-mach
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g-factor measurements
Accessible at HRIBF Accessible w e-mach
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A Photo-fission Facility
-Driver
Requirements
– –
~25 MeV or higher, CW, turnkey 100 kW or more at 25 MeV
–
80 kW or more at 50 MeV
Turnkey options
–
25 MeV rhodotron
–
50 MeV SC linac
Costs are similar
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Appendix
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238
U+p (1 GeV)
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Measurements of g-factors by Recoil in Vacuum F
=
I
+
J J
= electron spin -- randomly oriented Target Foil Beam
I
= nuclear spin -- aligned by reaction Coulex recoil Target recoil • After recoil into vacuum, the ionic B field direction is randomly oriented. • The nuclear spin of the recoil is initially aligned in the plane of the target, but precesses about total angular momentum F by hyperfine interaction. • The angular distribution of decay gamma emission is thereby attenuated. 60 Managed by UT-Battelle for the Department of Energy Presentation_name
Neutron transfer reactions
Accessible at HRIBF Accessible with 1 MW ISOL 61 Managed by UT-Battelle for the Department of Energy Presentation_name
g-factor measurements
Accessible at HRIBF Accessible with 1 MW ISOL 62 Managed by UT-Battelle for the Department of Energy Presentation_name
Fission rate and power in target
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Distribution of E deposit and fission
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Photo-fission yield
From ion source
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Science highlights with e-driver upgrade
Will test the evolution of nuclear structure to the extremes of isospin Will improve our understanding of the origins of the heavy elements Evolution of single-particle structure Transfer reactions at 132 Sn & beyond Collective properties in extended neutron radii Coulomb excitation near 96 Kr 66 Managed by UT-Battelle for the Department of Energy Reaction mechanisms for the formation of superheavy nuclei Decay properties of nuclei at the limits Crucial for understanding the formation of elements from iron to uranium Presentation_name