1. The n_TOF facility at CERN: a scientific succes!
Daniel Cano Ott on behalf of the n_TOF collaboration

2. Physics motivation

3. Nuclear data for nuclear technologies
Neutron capture and fission cross sections for the transmutation of nuclear waste in Accelerator Driven Systems (NTOF-ND-ADS EU FP-5 project) and the design of new and future nuclear reactors.
Nuclear data for astrophysics
Neutron capture cross sections relevant to nuclear astrophysics, cosmochronometry, stellar nucleosynthesis…
Basic neutron reaction and nuclear structure data with neutron beams.
Fundamental cross sections.
Photon strength functions and nuclear level densities.

4. A brief history of the n_TOF facility
Concept by C.Rubbia validated by TARC exp. [CERN/EET/Int. Note 97-19]
May ’98 - Further development of the initial idea towards a working facility [CERN/LHC/98-02+Add]
Aug ’98 – CERN-GELINA joint Letter of Intent [CERN/SPSC/98-15, I220]
1999 – Construction started
Oct 2000 – First proton on the spallation target
2001 to 2004 – Experimental program of n_TOF-Ph1 (NTOF-ND-ADS 5th European Union Framework Programme).
2005 to 2007 – Shutdown due to the LHC startup + modifications of the spallation target
June 2007/January 2008 – n_TOF Review Pannels. Green light for a new target!
December 2007 / January 2008 – Inspection, removal and analysis of the old target.
March MoU signed by CERN.
November 2008 – Start of the n_TOF-Ph2 commissioning.

5. n_TOF has done key contributions to the neutron data community

6. The n_TOF facility itself!

7. Available facilities worldwide and uniqueness of n_TOF
Some of the existing neutron time of flight facilities (GELINA – EU, ORELA, RPI – USA) for cross section measurements are based on electron LINACS (photoproduction). They are and will be excellent tools for investigating stable or slightly radioactive materials:
Good energy resolution.
Low intensity per accelerator pulse / high repetition rate -> low duty cycle.
Need of “massive” samples (several 100 mg)
However, cross section data for radioactive isotopes available in small amounts ( mg) need high intensity sources: pulsed spallation sources like LANSCE-LANL (USA) and CERN (Europe):
Intrinsically worse energy resolution (partially at its185 m flight path!)
High intensity at even low repetition rates -> high duty cycle.
Measurements with samples of a few mg and high intrinsic activities (1 GBq).

8. The n_TOF Collaboration
40 Research Institutions
120 researchers
Spokesperson: E. González (CIEMAT)

9. The n_TOF facility

10. (A Google-view of) The n_TOF facility at CERN
n_TOF 185 m flight path
Proton Beam
20GeV/c
7x1012 ppp
Pb Spallation Target
Neutron Beam
10o prod. angle
Booster
1.4 GeV
Linac
50 MeV
PS 20GeV

11. n_TOF beam characteristics
The n_TOF facility was built and commissioned in a period of 2 years and provides unique features for measuring capture and fission cross sections of unstable (and also stable) isotpes.
White neutron beam: 0.1 eV up to 1 GeV
DE/E ~ 1·10-4 in the RRR
Capture and fission beams:
F=4 cm beam
F=8 cm beam
Performance Report, CERN-INTC , January 2003,CERN-SL ECT

12. A fully digital DAQ!

13. 2. The n_TOF data acquisition system
n_TOF has been the first neutron beam line world-wide proposing, building and operating a fully digital DAQ. Nowadays, it is becoming a standard at every laboratory.
The n_TOF DAQ consists of ~50 flash ADC channels with 8 bit amplitude resolution and sampling of 500 MSample/s.
The full history of EVERY detector is digitised during a period of 16 ms (0.7 eV < En < 20 GeV) and recorded permanently on tape.
The system has nearly zero dead time.
Simple electronics but everything needs to be done by software.

14. Pulse shape fitting, particle discrimination and pileup reconstruction for C6D6 detectors. C. Guerrero et al, submitted to NIM-A.
Pulse shape analysis and pileup reconstruction for the BaF2 detectors. E. Berthomiueux et al. To be submitted to NIM-A.

15. Advanced neutron detectors and monitors

16. A low mass neutron beam monitor
Small foil with 6Li deposit in the beam.
Si detectors outside the beam for α,t detection.
Carbon fiber scattering chamber (low neutron sensitivity).
6LiF
α,t n

17. n_TOF fission detectors
Position sensitive Parallel Plate Avalanche Chambers. Allow to reconstruct the trajectories of the fission fragments.
Tassan-Got et al. To be submitted to NIM-A
Fast induction chamber (FIC). Large number of samples inside a compact detector.
P. Cennini et al. Submitted to NIM-A

18. The low neutron sensitivity C6D6 detectors
Neutron beam
Sample changer
The low neutron sensitivity C6D6 detectors
Low neutron sensitivity C6D6 detectors with carbon fibre housing.
R. Plag et al. Published in NIM-A

19. 10B doped carbon fibre capsules
The n_TOF Total Absorption Calorimeter (TAC) for (n,g) measurements
40 BaF2 crystals covering 95% of 4p.
98% detection efficiency for capture g-ray cascades.
C12H20O4(6Li)2
Neutron absorber
10B doped carbon fibre capsules
n beam
237Np sample

20. Cross section analysis techniques

21. High accuracy Pulse Height weighting technique
The efficiency of the C6D6 detectors for detecting capture cascades depends on the de-excitation pattern of the capturing nucleus. It can be made proportional to the capture cascade by using the Pulse Height Weighting technique:
n_TOF has demonstrated that it is necessary to obtain the Weighting Functions for each specific setup and that it is possible to do it with Monte Carlo simulations.
Taín et al. Published in NIM-A

22. The experimental programme

23. n_TOF experiments 2002-4 Capture Fission
151Sm
204,206,207,208Pb, 209Bi
232Th
24,25,26Mg
90,91,92,94,96Zr, 93Zr
139La
186,187,188Os
233,234U
237Np,240Pu,243Am
Fission
233,234,235,236,238U
209Bi
237Np
241,243Am, 245Cm
n_TOF experiments
Measurements of neutron cross sections relevant for Nuclear Waste Transmutation and related Nuclear Technologies
Th/U fuel cycle (capture & fission)
Transmutation of MA (capture & fission)
Transmutation of FP (capture)
Cross sections relevant for Nuclear Astrophysics
s-process: branchings
s-process: presolar grains
Neutrons as probes for fundamental Nuclear Physics
Nuclear level density & n-nucleus interaction
High energy part is based on Simulated flux… since the g-flash was generating an oscillation for a few 2-3 us

24. (n,f) cross sections Measurements with PPACs.
L. Tassan-Got et al. In preparation.
C. Paradela et al. In preparation

25. (n,f) cross sections with FIC
Targets interesting for the Th/U cycle and transmutation purposes:
235U, 233U, 245Cm, 241Am, 243Am
M. Calviani et al. In preparation.
233U
235U: some discrepancies in the resonance valleys with evaluated libraries and exp’ts
Discrepancies in the epithermal region

26. Ratio with FIC2 fission can be extracted up to 300 MeV
Fission measurements with the Fission Ionization Chamber (FIC) – 2/2
245Cm: poor previous experimental results
Statistical error bars
Sistematic errors ~8%
238U/235U: both isotopes are fission standards up to 200 MeV.
PRELIMINARY
Ratio with FIC2 fission can be extracted up to 300 MeV
PRELIMINARY
241Am
241Am has 239Pu contaminant which significantly contributes to the total σ.

27. (n,g) cross section measurements with C6D6 detectors
Resolved Resonance Region
Unresolved Resonance Region
232Th
level spacing
reduced neutron width distribution
mass (232Th) = g
diameter = 1.5 cm
purity = 99.5%
F.Gunsing, Nuc. Data. Conf.-2007
G. Aerts et al. (n_TOF Collaboration), Phys. Rev. C 73, (2006)

28. 24,25,26Mg(n,γ) measurements first known Impurities Mg resonance
Motivation:
Neutron poison for s-process
Strength of 22Ne(α,n)25Mg neutron source
Magnesium anomalies in presolar grains
first known
Mg resonance
at 20 keV
Impurities
In, Sb
M.Heil (FZK), Nuclei in the Cosmos IX, Geneva 2005

29. 90,91,92,93,94,96Zr(n,γ) measurements 90Zr is neutron magic
Zr abundances are sensitive to the neutron flux in AGB models.
s-process branching at 95Zr

30. Cosmochronometer: tu = 15 ± 2 Gy
186,187,188Os (n,γ) measurement
Cosmochronometer: tu = 15 ± 2 Gy
M. Mosconi et al., Int. Conf. Nuc. Phys. in Astrophysics 2007, Dresden
K. Fujii et al., Nuc. Data. 2007, Nice

31. 204,206,207Pb, 209Bi (n,γ) measurement 204Pb 206Pb
C.Domingo-Pardo et al. (n_TOF Collaboration), Phys. Rev. C 74/75, 2006/7

32. 151Sm(n,γ) measurement
U. Abbondanno et al. (n_TOF Collaboration), Phys. Rev. Lett. 93 (2004),
S. Marrone et al. (n_TOF Collaboration), Phys. Rev. C 73 (2006) 03604

33. 151Sm(n,γ) measurement
U Abbondanno et al. Phys. Rev. Lett. 93 (2004),
S. Marrone et al. Phys. Rev. C 73 (2006) 03604
n_TOF
MACS-30 = ± 160 mb
<D0> = 1.48 ± 0.04 eV, S0 = (3.87 ± 0.20)×10-4

34. 233,234U (n,γ),233,234,235U(n,f) measurement
Neutron induced capture
Neutron induced fission
ENDF/B-VI
n_TOF (PPACS)
W.Dridi, PhD-Thesis, C.Paradela, PhD-Thesis, 2005

35. 237Np (n,γ) measurement with the TAC
43.3 mg, 1.29 MBq
- En=2keV upper limit due to the Ti-canning resonances contaminations
- Total systematic uncertainty of 6%
- Large number of overlaping resonances (about half eV level spacing)
- Simultaneous fit transmission+capture-> total CS unchanged, relative ratio capture/scatt changes
C. Guerrero et al. (n_TOF Collaboration), Proc. Int. Conf. Nuc. Data for Sci. and Tech. 2007, Nice.

36. 240Pu (n,γ) measurement 51.2 mg, 458 MBq
ENDF/B-VII
n_TOF
Bouland et al.
‹D0› (eV)
12.1
12.1±0.1
12.06
‹Gg›(meV)
30.6
32.4±0.8
31.9
S0(10-4)
1.13
1.04±0.08
1.07
- Huge activity of the sample, measurable at n_TOF with the TAC
C. Guerrero et al. (n_TOF Collaboration), Proc. Int. Conf. Nuc. Data for Sci. and Tech. 2007, Nice.

37. 243Am (n,γ) measurement with the TAC
-g-ray contaminations from the Am-243 sample have a very large E (comp. to Pu, Np), this makes high pileup effects, need more work.
First (n,γ) measurement EVER. 10 mg, 75 MBq
D. Cano-Ott et al. (n_TOF Collaboration), Proc. Int. Conf. Capture Gamma-Ray Spec.
2005, Santa Fe.

38. geometry used for the MC simulations with GEANT4
Nuclear structure: TAC as a γ-ray spectrometer
Analysis of the calorimeter data and comparison to realistic Monte Carlo simulations of its response to the EM cascades.
geometry used for the MC simulations with GEANT4
Cascade Generator model by J.L Tain (IFIC-Spain)
Sn+En
Statistical region
Known region
A+1Z

39. TAC response 197Au(n,g): Esum and mg
Adjusted PSF + Egidy’s NLD good reproduction of the 197Au(n,g) TAC data not only for deposited energy (with and without conditions in mg) but also for mg (Esum>1.5 MeV).
mg>0
mg>2

40. TAC response 197Au(n,g): Ecr vs. mg

41. TAC response 197Au(n,g): Esum vs. mg

42. 237Np TAC data Experimental MC simulation Experimental MC simulation
Fits on actinides are not as accurate as for 198Au, it can be attributed to :
Level scheme not as well know as for 198Au
Tunning of the GammaRayStrengrth function (only 2 weeks while 1 month for 198Au)
The sahpe is irrelevan to some extend, important is the effcieincy.

44. 240Pu TAC data

45. 240Pu TAC data
The precision in the estimation of edet is better than 2% even if the shape of the Esum spectrum is not perfectly reproduced.

46. The n_TOF publications
All details can be found in the n_TOF web server
Summary of the papers published since 2002
7 Phys. Rev. C
11 Nucl. Instr. Meth. A
3 Nucl. Phys. A
1 Phys. Lett.
2 Phys. Rev. Lett.
3 international publications
~50 international conference proceedings
+ 10 publications in preparation to be published in 2008

47. Future plans

48. n_TOF experiments 2008-… Capture Fission Stable Isotopes:
Mo,Bi, Ru: r-process residuals
Fe, Ni, Zn, Se: s-process and structural materials
Radioactive Isotopes:
234,236U, 231,233Pa: Th/U fuel cycle
239,240,242Pu,241,243Am, 245Cm: transmutation of minor actinides
Fission
231Pa,234,235,236,238U
241Pu,245Cm,241,243Am, 244,245Cm
234U: study of vibrational resonances below the bareer

49. Better experimental conditions
Photon time distribution (E>1MeV)

50. New experimental area at 20 m
The (future) second n_TOF experimental area
New experimental area at 20 m
n_TOF target
Experimental area at 185 m
Flight-path length : ~20 m
at 90° respect to p-beam direction
100 times more intense!

51. New target design (ready in 2008)
Pb target with enhanced water cooling and corrosion resistant:
Moderator is de-coupled from the cooling circuit (10B or other liquids)
Compatible to the vertical flight path
Chemical monitoring of the coolant
protons

52. Summary and conclusions
CERN is a first class neutron Time Of Flight facility coupled to a spallation neutron source: 185 m flight path, favorable duty cycle and excellent energy resolution.
It allows to measure 1 mg mass samples of highly radioactive materials .
Excellent facility for measuring neutron capture and fission cross sections of Minor Actinides: Np, Pu, Am, Cm…
High performance detectors for fission (PPAC and FIC) and capture (TAC) cross section measurements
Fully digital Data Acquisition System.
Accurate cross section measurements.
The n_TOF operation was interrupted in 2004 for the LHC startup and will restart in 2008 FINALLY!