1. Energy-broadened proton beam for production of quasi-stellar neutrons
4/4/11
Energy-broadened proton beam for production of quasi-stellar neutrons
G. Feinberg1,2, M. Paul2, A.Shor1, D. Berkovits1, Y. Eisen1, M. Friedman2, G. Giorginis3, T. Hirsh1, A. Krasa3, A. Plompen3
1Nuclear Physics and Engineering Division, Soreq NRC, Yavne, Israel, 81800
2Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel, 91904
3EC-JRC-IRMM, Retieseweg 111, 2440 Geel, Belgium

2. Outline
Motivation
Previous astrophysical studies of a semi-Maxwellian neutron source
SARAF RF linear accelerator at Soreq NRC
High intensity liquid lithium target
Experiments and results with narrow and broad proton beam
Future study

3. He-burning stage: 13C(α,n)16O 22Ne(α,n)25Mg s-only T≈350 MK ~ 30 keV86 87 88
T≈350 MK
~ 30 keV 80 82
s-only 76 70 64

5. neutron density and time scales
low mass AGB stars (main component, Zr – Bi)
He burning at 100 – 300 MK (kT = 10 – 25 keV)
107 < nn < 1011 cm-3
massive stars (weak component, Fe – Zr)
He burning at 300 MK ( kT = 25 keV)
nn ≈ 106 cm-3
C burning at 1 GK (kT = 90 keV)
nn ≈ 1012 cm-3

6. The 7Li(p,n)7Be reaction for production of stellar neutrons
Ep = 1912 keV
ΔE=1 keV
Q = keV
Eth= 1880 keV
W. Ratynski and F. Kaeppeler,
PR C 37, 595 (1988)
FZ Karlsruhe, Germany

7. SARAF Accelerator Complex
Parameter
Value
Comment
Ion Species
Protons/Deuterons
M/q ≤ 2
Energy Range
5 – 40 MeV
Current Range
0.04 – 2 mA
Upgradeable to 4 mA
Operation
6000 hours/year
Reliability
90%
Maintenance
Hands-On
Very low beam loss
Phase I
Phase II 7 7

8. SARAF today targets Phase I - 2010 Beam line - 2010 MEBT PSM LEBT RFQ
D-plate
Beam dumps
EIS
Situation in beginning of 2011:
Phase I is not commissioned yet to full specs (CW deuterons), but accelerator is operational
The concept of Phase II is being developed in collaboration with accelerator laboratories
Input Power [kW]
Duration [hrs]
190 (CW) 12
210 (CW) 2
240 (CW)
0.5
260 (DC = 440 Hz)
Protons:
1) ~1 mA, ~3 MeV on beam dump for 9 hr
Low losses inside the cryomodule
2) ~300 µA, 3.5 MeV on target (HAVER foil cooled by NaK eutectic metal) 8 8 8

9. Beam lines downstream the linac
PSM
Beam lines downstream the linac
Beam dump
target

10. LiLiT The activation experiment scheme Secondary activation target
Ep = 1912 keV
ΔE > 7 keV
SARAF phase I
En ≈ 30 keV
Eth=1880 keV
The unique opportunity at SARAF:
High intensity proton beam Liquid lithium target
High intensity neutron beam

11. Prototype SC Module (PSM)
General Design:
Houses 6 HWR and 3 superconducting solenoids
Accelerates protons and deuterons from 1.5 MeV/u β=9%)
Very compact design in longitudinal direction
Cavity vacuum and insulation vacuum separated
2500 mm
M. Peiniger, LINAC 2004
M. Pekeler, SRF 2003
M. Pekeler, LINAC 2006 11 11 11 11

12. Energy gain
cavity 6
cavity 1

13. LiLiT

14. Lithium target
SARAF phase I
Ep=1912 keV
dE=15 keV (1σ)

15. LiLiT Liquid lithium jet target Proton energy: ~2 MeV.
Proton current: <3.5 mA.
Up to 81010 n/sec
T ≈ 2300C.
Tmax ≈ 3500C.
Feinberg et al,
Nucl Phys A827
(2009) 590C

16. Wall assisted lithium jet.
Jet: 18 mm x 1.5 mm.
Lithium velocity: 20 m/s.
Wall assisted lithium jet. Au Sr Au

17. Measurements at the JRC-IRMM VdG facility at Geel
The IRMM-Soreq-HU collaboration has performed measurements at the VdG facility at the IRMM laboratory to obtain information on the systematics of the 7Li(p,n)7Be reaction to be anticipated at SARAF.
Neutron spectra at various laboratory angles were measured with a narrow proton beam typical of a VdG accelerator, and compared to spectra obtained with a broadened proton beam (using a gold foil degrader), at a level of broadening as is expected at SARAF.
These measurements will help to better understand the characteristics and limitations to be expected at the SARAF RF- linac accelerator.

18. JRC-IRMM VdG Accelerator
7 MV VdG accelerator producing either continuous or pulsed ion beams
fast pulsing generating proton beam pulse width of 1.5 ns and pulse repetition rates of 2.5, 1.25 or MHz
Large low-scatter experimental hall and facilities

19. Experimental Setup the JRC-IRMM VdG facility at Geel, Belgium.
detector:
(1.8 MeV equivalent  energy)

20. Broad beam via gold foil degrader
Proton beam before Au degrader: Ep≈2.09 MeV p ≈ 1 keV
Proton beam after Au degrader:
Ep ≈ 1.91 MeV p ≈ 15 keV
Straggling calculated with TRIM code and verified by performing threshold reaction energy curve.
Suppressor

22. Neutron Time of Flight with 2” 6Li-glass detector at 00
Typical TOF spectrum showing gamma peak (off-scale) to the right, and neutron contribution at longer flight times to the left. Inset shows the gamma TOF distribution with FWHM < 5 ns.
Scatter plot, TOF on the x-axis and pulse height on the y-axis

23. 6Li-Glass neutron detection efficiencies
Efficiencies of the 6Li-glass detector for neutron capture determined with GEANT4 and the MCNP simulation codes. Both codes contain up to date libraries (ENDF/B6) for the neutron scatter and capture cross sections.

24. Experimental Neutron Energy Spectra vs. 

25. Experimental Spectra - angle integrated
Measured total angle integrate neutron energy spectra for the 7Li(p,n)7Be reaction.
narrow energy beam, =1.5 keV, and for a broad energy beam, ≈15 keV.
Both spectra contain same normalization coefficient.
Fit to a semi-Maxwellian yields kT=27 keV

26. Gold foil target activation measurements

27. Activation measurements Measure 197Au(n,)198Au activation via 411
Activation measurements Measure 197Au(n,)198Au activation via keV line Measure 7Be activity via 478 keV line

28. 197Au MACS - results

30. Example: Neutron intensity: 6*1010 n/sec 90Sr sample diameter: 25 mm
90Sr sample activity: 50 µCi
σ = 9 mb
Irradiation period: 24 hr
~104 91Sr atoms
Detector efficiency: 4% (556 keV)
~3*10-3 cps

31. 209Bi(n,)210m,gBi cross section measurement

32. 209Bi(n,)210m,gBi ground state (5d)  210Po (138d)  206Pb
Determine the 30 keV isomer and ground state cross sections of the 209Bi(n,)210m,gBi reaction.
ground state (5d)  210Po (138d)  206Pb
metastable state (3·106 y)  206Tl  206Pb
209Bi irradiation at SARAF
 transfer irradiated sample to Belgium for γ measurements at the underground-laboratory HADES

33. END

34. RFQ power gain vs. forward power
RFQ voltage squared as a function of RFQ input power
For 3 MeV Deuterons: MHz 1.6 Kilpatrick
~ 255 kW CW w/o beam 65 kW/m
Forward power (kW)
deuterons
2008
Input Power [kW]
Duration [hrs]
190 (CW) 12
210 (CW) 2
240 (CW)
0.5
260 (DC = 440 Hz)
protons
A. Nagler et al., LINAC08
Parting from the linear relation indicates onset of dark current due to poor conditioning
All 4 RFQ pickups showed similar results 34 34 34 34

36. Comparison of neutron spectra with simulation program SimLiT
Program SimLiT for simulating 7Li(p,n)7Be reaction and calculating neutron yields and spectra.
Code contains experimental energy dependent reaction cross section and the proton stopping power dE/dX. Reactions occur in c.m., with appropriate transformation to laboratory system.
Prior to this experiment, wide use of SimLiT was useful for planning and optimizing the experiment.
It is important to be able to simulate accelerating parameters for a-priori information on new experimental configurations.

37. Narrow-energy beam - Integral Spectrum for the 7Li(p,n)7Be reaction.
Experimental results and comparison with simulations using SimLiT code.
Comparison with data of Ratynski and Käppeler 1988.

38. Double differential spectra at selected angles, narrow-energy and broad-energy proton beam.
Experimental data and calculated spectra using SimLiT code. Actual data was taken at 5 degrees intervals

39. Gold foil activation measurements: narrow-energy and broad-energy proton beams
Gold foil activation measurements used by Ratynski and Käppeler to characterize the integral energy distribution of neutrons emitted in the reaction 7Li(p,n)7Be
They used a hemispherical gold target to extract an experimental average cross section of 5868 mb for gold activation with neutrons produced by a 1912 keV narrow-energy proton beam on a thick Li target.
Gold foil activation has since served as the standard for determining the energy averaged neutron fluence in activation measurements.
Compare gold foil activation cross sections for narrow-energy and broad-energy proton beams, to validate the technique for broad-energy beams anticipated in planned facilities

40. Activation Measurements: Results

41. Determining Maxwellian average cross section  from activation data
Activation cross section  is given by the activity A according to following formula:
A = 198Au activity in Bq, R is the neutron rate (1/sec),  is the (Maxwellian averaged) activation cross section in barns, d is the thickness of the gold foil in g/cm2, =0.693/T1/2 , T1/2 is the half life, for 198Au is days, and t is the irradiation time in days.
Corrections factor is necessary to correct for a cone beam incident on a planar target sample that covers less than 4 in solid angle
Correction factor determined from running detailed simulation with SimLiT for neutron distribution and GEANT4 for geometry and efficiencies.

42. Au activation cross section - results
Compare to calculations using know cross section for neutron activation of gold and

43. Motivation – ADS subcritical reactors
The 209Bi(n,)210g,mBi reaction is important in design and safety analysis of reactors and for planning eutectic lead-bismuth targets for accelerator driven systems (ADS).
ADS consists of a subcritical reactor that produces fission without achieving criticality. Instead of a sustaining chain reaction, a subcritical reactor uses additional neutrons from an outside source, mostly via spallation reactions of energetic protons from particle accelerators on high z targets, i.e. Pb-Bi.

44. 6Li-Glass Scintillators for neutron detection
4He
Neutrons deposit 1.8 MeV equivalent  energy

45. Neutron peak 1.8 MeV  equivalent
prompt ’s:
p+Li  p’ + *Li
*Li   (478 keV)
p+F   + *O
*O   (6.13
6.9
7.2 MeV)
+ ’s in continuum

46. Underground γ-ray Spectrometry
HADES = High Activity Disposal Experimental Site
Located at SCK•CEN, Mol, Belgium, operated by EURIDICE