Cross Section Measurements using a 4π BaF 2 Array & High-Energy Neutron Activation Experiments at SPIRAL-2

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1 Cross Section Measurements using a 4π BaF 2 Array & High-Energy Neutron Activation Experiments at SPIRAL-2 Dave Vieira Los Alamos National Laboratory SPIRAL-2 Workshop, Caen, Dec , 2004 Outline: 1. n-tof + 4π BaF2 array (+ fission tagging) - DANCE at Los Alamos (n,γ) and (n,γ)/(n,fission) - possibilities at SPIRAL-2 2. Fast neutron activation measurements - (n,xn) and (n,x) measurement possibilities LA-UR

2 DANCE at the Los Alamos Neutron Scattering Center Detector for Advanced Neutron Capture Experiments 160 element BaF2 gamma array Highly segment, fast response, fast acquisition so can run with radioactive targets (~1 mg, <1 Ci) Total calorimetry (Eγ sum) to gate on Q-value for (n,γ) rxn. of interest 6 cm thick 6LiH neutron absorber to reduced scatter neutrons Capture on BaF2 is not too large, but 6 stable isotopes can confuse / contaminate Eγ sum

3 LANSCE Lujan Center - DANCE 800-MeV Proton LINAC Proton Storage Ring Facility is driven by the 800-MeV proton accelerator using a proton storage ring to accumulate beam, I p 100 µa, 20 Hz, _t = 200 ns Moderated W target gives white neutron spectrum, ~14 neutrons/proton DANCE is on a 20 m flight path / ~1 cm φ beam after collimation Φ 8.7 x 10 4 n/(cm 2 -sec) / E n (ev) Integral flux 2 x 10 5 n/(cm 2 -sec) per energy decade

4 First Commissioning Runs on DANCE ( ) 1 st year shakedown of flight path, detector, electronics, DAQ, neutron monitors, bkgd. reduction/characterization, radioactive target handling, data analysis Stable Targets: 139 La, 45 Sc, 55 Mn, 59 Co, Cu, V, Rb, Sr (gaps in s-process) 62 Ni, 102 Pd rp-process 151,153 Eu neutron-flux monitor Preliminary E.-I. Esch et al. Radioactive Targets: 237 Np AFCI 234,236,238 U AFCI, stockpile stewardship 151 Sm key s-process branch point 235 U fission-tagging test DANCE collaboration: Los Alamos, Col. School of Mines, Berkeley, N. Carolina St. Univ., Livermore, Bruyeres-le-Chatel, Karlsruhe J.L. Ullmann, R.S. Rundberg, R. Reifarth, T.A. Bredeweg, J.M. Wouters, L. Hunt, E.-I Esch, D.J. Vieira, D.D. Strottman, J.B. Wilhelmy, R.C. Haight, J.M. O Donnell, A. Kronenberg, A. Alpizar, R. Hararik, U. Greife, J.M. Schwantes, D.C. Hoffman, U. Agvaanluvsan J.A. Becker, T. Ethvignot, T. Grainer, F. Kaeppeler, M. Heil

5 Neutron-TOF Exps. Using a 4π γ-array at SPIRAL-2 production target (moderated) collimator pulsed beam neutron flight path 4π γ-array Pulsed beam: 40-MeV deuteron from super-accel. operating at ~88 MHz - desire pulses at ~88 khz (~1/1000 th of fund.) while maintaining 5 ma ave. current! high instantaneous intensity places demands on ion source, pre-buncher/ accumulator / frontend, beam loading of accelerator (also possible activation concerns?) Production target: deuteron breakup, moderate target to down shift E n to desire energy region of interest (~1-100 kev) see calc. of X. Ledoux (can t normalized to thermal σ) Neutron flight path: 88 khz -> ~11 µs between pulses (frame-to-frame overlap problem) kev neutrons, TOF/L = 11 µs/5m 1.1 µs/5m => 5 + m flight path needed neutron-beam must be collimated, detector room needs to be well shielded 4π γ-array: like existing BaF 2 arrays, but optimized for fast DAQ and low deadtime

6 Low energy neutron beam (neutron flux) DANCE - Neutron flux kev : _ n/cm 2 /s kev : _ n/cm 2 /s With L=5 m and macro =50 ns - Flux of the same order as n-tof & Geel in the kev range - Thermal neutron background : shielding of detector needed at NFS Workshop SPIRAL-2 GANIL, Caen, France: December 2004 Contact: xavier.ledoux@cea.fr

7 Fast waveform digitization system at DANCE Data acquisition 160 detectors >2 ms multi-hit time digitization high counting rates (>2 khz) DANCE waveform digitization 8-bit, 500 Msamples/sec (ACQIRIS DC-265) two digitizers/detector hi & lo gain channels 320+ channels / 14 compact PCI crates Two data collection modes segmented: trigger by Mγ > 1 fast logic only hit segments digitized (2 µs) continuous: trigger by each beam pulse (T 0 ) 20 Hz limited memory limits time range / En range waveforms pre-processing (<50 ms): outputs are: detector ID leading edge TOF recorded in 2 time stamps fast component integral total (fast+slow) component integral 0 ) (V -0.5 T P U T U -1 O R IE L-1.5 IP T L U M -2 O T O -2.5 P H TIME (ns) At SPIRAL-2: BaF 2 waveform for γ-ray slow component: t 1/2 ~ 600 ns fast component: t 1/2 ~ 0.6 ns expect similar data rates ~2 khz w/ 88 khz beam pulse segmented mode is best option - major issue is deadtime problem in digitizers - we currently use a fixed 3 µs deadtime (DT corrections at >200 kev for DANCE), SPIRAL-2 -> ~50 kev? - solution is to reconfigure digitizers for 1 µs, but care must be taken to minimize deadtime issue

8 DANCE Solar Cell Fission-Tagging Test April 04 DANCE + 6 LiH neutron beam Lujan Center T.A. Bredeweg, Th. Ethvignot, Th. Grainer et al. Fission tagging

9 DANCE fission-tagging test Solar cell U deposit w/ fission tag (n,f) only E n = 8 12 ev between Ag resonances w/o fission tag (n,γ) + (n,f) Enables good σ γ and α = σ γ /σ f measurement

10 3cm irradiation zone ( 56 Fe at 50%) C converter (0.8 cm thick) 40MeV d-beam ( 4.00 or 2.83cm) 6cm IFMIF 4*Spira Activation experiments with small quantities of radioactive materials

11 High-Energy Activation Experiments at SPIRAL-2 Interest in measuring cross sections for (n,xn), (n,pxn) and (n,α) rxns. on small radioactive samples with E n =1-16 MeV Consider 241 Am(n,2n) 240 Am for nuclear attribution / forensics - extend measurements to lower energies Extract a cross section, if the neutron spectrum is well characterized - shift the incident deuteron energy down to lower En Consider using D(d,n) to produce a more mono-energetic n source - requires a deuterium gas target Typically 10 µg 100 mg rad. samples irradiated in high flux region for 1 hr-10 d - some radiochemistry & counting capabilities desired on site Many cases to study 49 V(n,2n) (n,α) 73 As(n,2n), 150 Eu(n,2n), 168 Tm(n,2n), 173,174 Lu(n,2n), 195 Au(n,2n)

12 Neutron Facility

13 Neutron / Radiochemistry Facility at RIA D breakup Line D(d,n) Line 7 Li(p,n) Line Proposed by LLNL-LANL Separately funded by DOE/NNSA Neutrons provide by 7 Li(p,n) E n = MeV D(d,n) E n = 4-12 MeV D breakup E n > 12 MeV DANCE Cave Radiochemistry hotcells & mass separator 40-MeV Linac Low energy, 10 khz Accel. n-tof & activation exp. using radioactive targets (t 1/2 = d) as collected at RIA for nuclear astrophysics nuclear attribution/forensics stockpile stewardship nuclear waste disposal & advanced reactor design

14 Summary n-tof measurements with a 4π γ-array is feasible for (n,γ) and (n,γ)/(n,f) cross sections at kev - need: pulsed, high-instantaneous deuteron beam - down shift neutron energy spectrum using moderated target & lower deuteron energy - 5+ m flight path / well-shielded cave / array w/ fast DAQ High-energy neutron activation experiments are attractive using small radioactive samples - need: access to high-neutron flux region - implies an automated activation channel system (insert/remove samples within hours) - radioactive sample preparation possible via (d,xn) or (p,xn) reactions (using H 2 1+ accelerated ions) - implies a high-intensity beam line / cave with suitable target handling capabilities hot cell, radiochemistry, and on-site counting also valuable to produce biomedical isotopes