Radioactive beams from e-beam driven photofission TRIUMF User’s Workshop Jim Beene ORNL August 1-3 2007

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 Presentation_name

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) Presentation_name

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 Presentation_name

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 Presentation_name

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

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, 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 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, 15271 (2003); PRC 75, 054607 (2007) Stone et al., PRL 94, 192501 (2005)

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.) Presentation_name

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 Presentation_name

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. Presentation_name

238U photo-fission is dominated by the GDR Presentation_name

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 Presentation_name

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 Presentation_name

A sample comparison with data: Sn isotopes Presentation_name

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. 238U(n,F) @ ~15 MeV has final state properties very similar to E0=25-50 MeV photofission. Presentation_name

RIB production by photofission 1013 ph-f/s 10 mA 40 MeV p Presentation_name

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) Presentation_name

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. Presentation_name

Photofission target issues Converter + target Presentation_name

An example of a somewhat more aggressive design Similar power required to reach 1013 f/s (52kW @ 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 Presentation_name

U(g,f) vs U(p,f) 1 GeV Presentation_name

U(g,f) vs U(p,f) 1 GeV (p,f)  100 mA on 30 g/cm2  5x1013 f/s (g,f)  1013 f/s (~50 kW 25 MeV) Presentation_name

U(g,f) vs U(p,f) 1 GeV (p,f)  100 mA on 30 g/cm2  5x1013 f/s (g,f)  1013 f/s (~50 kW 25 MeV) Presentation_name

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 & 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. Presentation_name

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) Presentation_name

Electron Beam Facility Elevation Presentation_name

e-Driver Upgrade Upper Level Presentation_name

e-Driver Upgrade Lower Level Presentation_name

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 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 Presentation_name

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 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. all best done at MAFF deal with these: RIB production: isol /frag/ advantages ria -- detectors: greta mass targets Presentation_name

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. Presentation_name

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. Presentation_name

Initial Concept of Two Plugs in a Common Vacuum Envelope Presentation_name

The Target Plug Presentation_name

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 Presentation_name

High-Power Converter Target Designs Based on ORELA Target Design There will be a converter target as part of each target ion source plug Presentation_name

First Beam Filter – Second Plug Presentation_name

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

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 0.65 bn-branching ratio Ibn 77Cu 0.46 Ibn, n- levels in N=47 77Zn 78Cu 0.35 Ibn, Ip of 78Cu49 revised 79Cu 0.19 bng decay observed first time 83Ga 0.30 bng,bg, ns1/2 in N=51 83Ge 84Ga 0.08 2+ in N=52 84Ge, ns1/2 in 83Ge 85Ga ~0.07 rate of 0.1pps… 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 84Ga g g b n b 84Ga 84Ge* 83Ge* (ns1/2) 83Ge(nd5/2) 84Ga 84Ge* (2+) 84Ge (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) Presentation_name

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 132Sn(d,p)133Sn @ 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 Presentation_name

13C(134Te,12C)135Te neutron transfer Particle-gamma angular correlations 2109 keV 929 1180 929 1279 657 657 1279 929

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 3000 134Sn/s Presentation_name

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.

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) Presentation_name

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. 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 1014 f/s. Presentation_name

Neutron transfer reactions Accessible at HRIBF Accessible with e-machine Presentation_name

Coulex (1-step) Accessible at HRIBF Accessible w e-machine Presentation_name

Multi-step Coulex Accessible at HRIBF Accessible w e-mach Presentation_name

g-factor measurements Accessible at HRIBF Accessible w e-mach Presentation_name

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 Presentation_name

Appendix Presentation_name

238U+p (1 GeV) Presentation_name

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. Presentation_name

Neutron transfer reactions Accessible at HRIBF Accessible with 1 MW ISOL Presentation_name

g-factor measurements Accessible at HRIBF Accessible with 1 MW ISOL Presentation_name

Fission rate and power in target Presentation_name

Distribution of E deposit and fission Presentation_name

Photo-fission yield From ion source Presentation_name

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 Presentation_name