1. N_TOF fission data of interest for ADS

2. Nuclear data needs
Simulation and design of Gen-IV and ADS systems require accurate nuclear data
Current data libraries present important discrepancies and lacks.

3. Fission Cross Sections
1eV
1MeV

4. Thorium fuel 232Th + n  233Th  233Pa  233U (fissile) 232U 233U 234U
Neutron
Capture
 decay
230Th
231Th
232Th
233Th
234Th

5. Experimental Campaign
A set of measurements of neutron-induced fission in actinides was launched within the FP5.
Fission measurements in the framework of the n_TOF Collaboration and construction of the n_TOF facility.

6. n_TOF facility

7. Fission Chambers @ n_TOF
PPAC chamber
FIC chamber

8. Fission Ionization Chamber Assembly
… n_TOF
Fission Ionization Chamber Assembly
Ionization chamber
Gas used: Ar (90 %) CF4 (10 %).
Gas pressure: 720 mbar
Electric field: 600 V/cm
Gap pitch: 5 mm
Deposit diameter: 5 cm
Deposit thickness: 125 µg/cm
Support thickness: 100 µm (Al)
Deposits on both sides.
Electrode diameter: 12 cm
Electrode thick.: 15 µm (Al)
Windows diameter: 12 cm (KAPTON 125 µm)

9. Inside FIC1 Photo 2

10. List of Targets ----FIC0---- 235U - 47mg (3 targets)
232Th - 80mg (2 targets)
236U - 20mg (2 targets)
237Np - 10mg (1 target)
234U - 34mg (6 targets)
----FIC1----
235U - 30mg (1 targets)
238U - 90mg (2 targets)
241Am - 2mg (4 targets)
243Am - 10mg (4 targets)
245Cm - 2mg (2 target)
233U - 20mg (2 targets)

11. Some FIC results

12. Fission Chambers @ n_TOF
PPAC chamber
FIC chamber

13. PPAC setup

14. PPACs @ n_TOF 10 detectors  9 targets U-234(2) and Th-232(5)
Two reference targets: U-235 y U-238
Less than 1 % of flux attenuation in the full setup.

15. Measured isotopes Minor actinide : 237Np
Thorium cycle : 233U, 234U, 232Th
Spallation target : 209Bi, natPb
Reference isotopes : 235U, 238U

16. Fission Detection Setup
Fissile target in a thin backing sandwiched by two detectors  Detection of both fission fragments in coincidence.
Fission event reconstruction: target position and emission angle. Efficiency limited by the cut at large angles.

17. Discrimination with coincidences
U-234: coincidences
U-234: singles

18. Cathode Positioning (I)
Positioning by using stripped cathodes and delay line readout.
The cathode signal is split in the delay line and transmitted to both ends
Stripped Cathode
Delay Line

19. Cathode positioning (II)
Diagonal condition:
(Tch1-Tanode)+(Tch2-Tanode)=DLT
DLT: Total delay line length (~320 ns)
The time difference
between both cathode
ends provides
the position of the signal.

20. Targets (I) Epoxy frame Uranium target 80 mm Ø 300 µg/cm2
2 µm Al backing

21. Targets (II)
Measurement of thickness and homogeneity by alpha counting and/or proton scattering.
High purity samples (> 99 % for U-234).
234U
Y (mm)
X (mm)
 activity

22. The n_TOF Data Acquisition System
The n_TOF DAQ consists of 54 flash ADC channels with 8 bit amplitude resolution and sampling of 500 MSample/s.
The full history of EVERY detector (BaF2 crystals and monitors) is digitised during a period of 16 ms (0.7 eV < En < 20 GeV) and recorded permanently on tape. Very useful feature since the raw data can be always re-investigated.
The system has nearly zero dead time.
7.5 TB disk space for temporary storage.
Typical data rate of 2-3 TB/day on tape after compression.
Pulse shape analysis is performed on the fly at the LXBATCH Linux Batch Farm at CERN (30 CPUs exclusively dedicated) and stored in highly compressed Data Summary Tapes.
Quasi on-line analysis of the data with full statistics.
One of the big successes of n_TOF. Many TOF facilities are following the n_TOF example and moving to digital electronics!

23. PPAC signal analysis Negative loop should be first
Xpos-Xneg < constant
const1 < Hneg/Hpos < const2

24. Light vs. Heavy Fission Fragments
LFF
HFF
Target Energy < 10 MeV (Assymetric fission)

25. Light vs. Heavy Fission Fragments
Cathode signals for En around 1 MeV

26. Cross Section Analysis
 (E): fission cross section
n (x,y,E): fission rate obtained from raw data
 (x,y): surface density of the target
 (E): detection setup efficiency
a (x,y,E)/ b (x,y,E) ≈ 1 ± 0.01 (1%)

27. Angular acceptance
Simulations
Measurements
50º
50º

28. Fission Fragment Angular Distribution
Cos ()
Log E =5.6
Log E =5.4
Log E =5.8
Log E =5.5
Log E =6.0
Log E =5.9
U-234 FFAD for neutron energies near the fission threshold

29. Dependence of anisotropy with energy
238U

30. n_TOF beam at fission campaign
Neutron spectrum in the whole energy range.
Beam profile
X (mm)
Y (mm)

31. Th-232 results

32. U234(n,f)
U234 resonances

33. 234U
Previous data
(IRMM report)
Better energy resolution achieved at nTOF

34. Np237(n,f)
Np237 resonances

35. Conclusions
The coincidence method has been used to obtain the fission results for the extensive n_TOF neutron energy range.
Th233, U234, Np237 results have been already produced and U233 is in progress.
Important discrepancies have been found in the Np237 resonance region.

36. Fission Chamber @ n_TOF
PPAC chamber
FIC chamber

37. n_TOF
CERN

38. FIC Design Gas – Ar 90%+CF4 10% Pressure – 600 mbar Distance – 5 mm
HV – 300 V
17 targets in the beam
“noise” electrode