1. Radioactive beams from e-beam driven photofission
TRIUMF
User’s Workshop
Jim Beene
ORNL
August

2. 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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3. High Power Target Laboratory (HPTL)
HRIBF 2006
25MV Tandem Electrostatic Accelerator
Injector for Radioactive Ion Species 1 (IRIS1)
Stable Ion Injector (ISIS)
Oak Ridge Isochronous Cyclotron (ORIC)
Enge Spectrograph
Daresbury Recoil Separator (DRS)
High Power Target Laboratory (HPTL)
Recoil Mass Spectrometer (RMS)
On-Line Test Facility (OLTF)
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4. HRIBF Post-accelerated Beams
175 RIB species available
(+26 more unaccelerated)
32 proton-rich species
143 neutron-rich species
Post-accelerated Intensity
Beam list increased by ~50% since 2003
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5. The first transfer measurements on N=82 nuclei on / near r-process path
130Sn(d,p)131Sn - R. Kozub et al.
132Sn(d,p)133Sn - K.L. Jones et al.
134Te(d,p)135Te - S.D. Pain et al.
132Sn(d,p)133Sn
K. Jones
yields, angular distributions of low-lying states measured
first observation of p1/2 state in 133Sn
three other states in 133Sn measured, calibrated with 130Te(d,p)
evidence for numerous states in 131Sn never seen before
evidence that the f5/2 level in 135Te is at a significantly higher energy
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6. Decay spectroscopy of exotic nuclei
b-decay studies around 78Ni with postaccelerated (3 MeV/u) pure neutron-rich RIBs
Discovery of superallowed a-decay
d2(105Te)/d2(213Po) ~ 3
Winger et al.
Enhanced due to the same proton and neutron shell structure
rp-process termination
En route to 104Te → 100Sn
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 76-79Cu and 83-84Ga
Identification of new excited states in 77Zn, 78Zn, 82Ge, 83Ge, and 84Ge
Systematics of single particle levels (e.g. neutron s1/2) near doubly magic 78Ni

7. 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 132,134Sn cannot be made with stable Sn
Padilla-Rodal et al. Phys. Rev. Lett. 94, (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 132Sn
Recoil-in-Vacuum technique used to measure the g-factor for the first 2+ state in 132Te:
Shapira et al., Eur. Phys. J. A 25, s01, 241 (2005)
Liang et al., PRL 91, (2003); PRC 75, (2007)
Stone et al., PRL 94, (2005)

8. RISAC Science Drivers & the electron driver
Nuclear Structure
Probing the disappearance of shells
Spectroscopy & reactions in 132Sn, 78Ni regions
Evolution of collective motion
We can probe 112Zr and 96Kr regions (not 156Ba)
Neutron Skins
Structure/reaction studies of the most n-rich
SHE
Reactions with 132Sn (~109) and vicinity
For Z=112, N=184, reaction mech. Studies with 92,94Sr (106, 107)
Nuclear Astrophysics
Decay spectroscopy (bn, t)
Stockpile Stewardship
Surrogate reactions (n transfer, etc.)
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9. 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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10. 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 1013 /s scale.
A comparable upgrade to our p-rich capability would be far more expensive
Target development to support operation at >1013f/s (~50kW )is well in hand. Thus we are confident we can reach fission rates about 20 times larger than current HRIBF capability.
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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11. 238U photo-fission is dominated by the GDR
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12. 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 236,237U production is inevitable
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13. Photofission yields 1013 f/s “easily” achieved About 20x current HRIBF
But real gain >> 20x
238U(g,f)
(p,f) systematics from Tsukada
(g,F) from ORNL systematics + Jyvaskyla model
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14. A sample comparison with data: Sn isotopes
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15. Total neutron multiplicities are important figures of merit for our purposes
Proton induced fission at HRIBF energies
Ep=50 MeV nn=8.5
Ep=500 MeV nn~13
Electron induced photofission:
Ee=25 MeV  nn=3.3
Ee=50 MeV  nn=3.4
Neutron-induced fission is very similar in many ways to photofission. ~15 MeV has final state properties very similar to E0= MeV photofission.
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16. RIB production by photofission
1013 ph-f/s
10 mA 40 MeV p
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17. Conservative target design for performance determination
r=3 g/cm3
d=3 cm (0.3 RM)
t=30g/cm2 5X0 (10cm)
M=212 g
r=6 g/cm3
d=3 cm (0.6 RM)
t=30g/cm2 5X0 (5cm)
3 cm
Xo=6 g/cm2 (U)
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18. Photofission target issues/ limitations Direct bombardment
e-beam directly incident on targets
If 1013 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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19. Photofission target issues Converter + target
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20. An example of a somewhat more aggressive design
Similar power required to reach 1013 f/s 25 MeV)
r=6 g/cm3
t=30g/cm2 (5X0)
M=495 g
2.3 x UCx front surface area
compared to
3 cm dia. Cylinder
5 cm
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21. U(g,f) vs U(p,f) 1 GeV
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22. U(g,f) vs U(p,f) 1 GeV (p,f)  100 mA on 30 g/cm2  5x1013 f/s
(g,f)  f/s (~50 kW 25 MeV)
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23. U(g,f) vs U(p,f) 1 GeV (p,f)  100 mA on 30 g/cm2  5x1013 f/s
(g,f)  f/s (~50 kW 25 MeV)
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24. Conclusions I: RIB production
1013 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 & 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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25. Conclusions II: Shielding
Thick target bremsstrahlung:
q1/2~100/E0 degrees
Forward angle g dose rate
D~300 E0 (Gy h-1)(kW m-2)-1
D~1.5 x 107 Gy h-1 at 1 m for 50 MeV, 1MW e beam
6m concrete or ~1m Fe
900 g dose rate
D~70 (Gy h-1)(kW m-2)-1
D~7 x 104 Gy h-1 at 1m for 1MW e beam (E0> 20 MeV)
NCRP Report No 144 (2003)
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26. Electron Beam Facility Elevation
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27. e-Driver Upgrade Upper Level
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28. e-Driver Upgrade Lower Level
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29. Photo-fission yield
In target

30. Photo-fission yield
From ion source

31. Photo-fission yield
Post-accelerated

32. 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 132Sn & beyond
Collective properties in extended neutron radii
Coulomb excitation near 96Kr
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
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33. reactions with and structures of neutron-rich nuclei
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 78Ni & 132Sn
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
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34. 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.
all best done at MAFF
deal with these:
RIB production: isol /frag/
advantages
ria --
detectors:
greta
mass
targets
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35. 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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36. 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 1014 f/s.
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37. Initial Concept of Two Plugs in a Common Vacuum Envelope
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38. The Target Plug
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39. 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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40. 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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41. First Beam Filter – Second Plug
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42. Decay studies pushing the frontier of n-rich nuclei
Examples with eMachine
Ion
200 keV
(ions/s)
Tandem
t1/2 (s)
78Ni
0.3
0.001
0.11
80Cu
81Cu
1000 7 4 ?
82Zn
5000
94Br
96Br
1x104 56
100
0.07
137Sn
138Sn
1800 89 45 2
0.19
137Sb
140Sb
9x105
980
2x104 17
149Cs
0.1 ions/s
t1/2 & n rates for many r process nuclei are accessible
Energy levels test evolving nuclear structure

43. 76Cu 0.65 bn-branching ratio Ibn
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 T1/2 (s) main results
76Cu bn-branching ratio Ibn
77Cu Ibn, n- levels in N=47 77Zn
78Cu Ibn, Ip of 78Cu49 revised
79Cu bng decay observed first time
83Ga bng,bg, ns1/2 in N=51 83Ge
84Ga in N=52 84Ge, ns1/2 in 83Ge
85Ga ~0.07 rate of 0.1pps…
Jeff Winger et al., RIB-108 and 122
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44. 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 84Ga g g b n b
84Ga Ge* Ge* (ns1/2) Ge(nd5/2)
84Ga Ge* (2+) Ge (0+)
N=51 83Ge
N=52 84Ge
248 keV
625 keV
b-gated g-spectrum (0.5 keV/ch)
b-gated g-spectrum (0.5 keV/ch)
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45. 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
protons detected in Si-array
HRIBF
with the e-driver
3p3/2
Jones et al.
Ion
Intensity
(ions/s)
t1/2 (s)
84Ge
3x105
0.9
88Se
3x104
1.5
96Sr
98Sr
7x104 1x104
1.1
0.65
134Sn
3x106
1.0
138Te
140Te
5x106
2x104
1.4 ?
6x104 ions/s
Single-particle transfer near
78Ni and 132Sn
2f7/2
3p1/2?
2f5/2
Reactions of interest
(d,p)
(9Be,8Be)
(3He,d)
(3He,)
(7Li,8Be)
EP (channels) Ex
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46. 13C(134Te,12C)135Te neutron transfer
Particle-gamma angular correlations
2109 keV
929
1180
929
1279
657
657
1279
929

47. 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
With eMachine: neutron-rich nuclei from N=50 to N=82 (and beyond) are accessible
Ion
Intensity
(ions/s)
t1/2 (s)
84Ge
3x105
0.9
88Se
3x104
1.5
98Sr
1x104
0.65
136Sn
700
0.25
138Te
140Te
5x106
2x104
1.4 ?
Radford et al.
Beene et al.
HRIBF
Sn/s
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48. Heavy ion fusion reactions
HRIBF Results
Probes the influence of neutron excess on fusion at and below the Coulomb barrier
 important for superheavy element synthesis
with eMachine
More n-rich projectiles
Further below barrier 134Sn below 10 mb
Transfer reaction studies on the same system will help to understand reaction mechanism
Ion
Intensity
(ions/s)
t1/2 (s)
92Br
2x105
0.34
134Sn
136Sn
3x106
600
1.0
0.25
Liang et al.

49. Unattenuated angular correlations: Theory & experiment
130Te SIB
Hyball Ring 2
qg = 90°
qg = 132°
qg = 155°
130Te beam
scattered 130Te
stopped in Cu
12C recoil Df
180° q 0°
W(q,Df)
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50. Magnetic moment: RIV attenuated angular correlations

51. 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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52. 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 1014 f/s.
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53. Neutron transfer reactions
Accessible at HRIBF
Accessible with e-machine
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54. Coulex (1-step) Accessible at HRIBF Accessible w e-machine
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55. Multi-step Coulex Accessible at HRIBF Accessible w e-mach
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56. g-factor measurements
Accessible at HRIBF
Accessible w e-mach
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57. 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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58. Appendix
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59. 238U+p (1 GeV)
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60. Measurements of g-factors by Recoil in Vacuum
F = I + J
J = electron spin -- randomly oriented
Target Foil
I = nuclear spin -- aligned by reaction
Beam
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.
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61. Neutron transfer reactions
Accessible at HRIBF
Accessible with 1 MW ISOL
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62. g-factor measurements
Accessible at HRIBF
Accessible with 1 MW ISOL
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63. Fission rate and power in target
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64. Distribution of E deposit and fission
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65. Photo-fission yield
From ion source
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66. 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 132Sn & beyond
Collective properties in extended neutron radii
Coulomb excitation near 96Kr
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
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