1. Measurements of the 238U radiative capture cross section using C6D6
F. Mingrone
on behalf of the n_TOF Collaboration
ANDES Final Meeting
Bruxelles – October 21, 2013

2. Motivations NEA High Priority Request List
Advanced nuclear systems
Improvement in the design of
Nuclear fuel cycles
EXFOR DATABASE: 25 datasets in the resolved resonance region and a few less in the unresolved BUT still inconsistencies for the capture cross section up to 25 keV
EC-JRC-IRMM Gelina with C6D6 detection system
NEA High Priority Request List
UNCERTAINTY IN THE CROSS SECTION BELOW 2%
Nea high priority list
n_TOF with TAC detection system
n_TOF with C6D6 detection system

3. EXPERIMENTAL TECHNIQUE
Detector
Flight path L 
Sample under analysis
Proton beam
Neutron beam 
Spallation target

4. EXPERIMENTAL TECHNIQUE
Detector
Flight path L 
Sample under analysis
Proton beam
Neutron beam 
Spallation target
En [eV]
FWHM [cm]
DEn [eV] 1 3
3.2 × 10-4 10
3.2 × 10-3
102 4
4.3 × 10-2
103 5
5.4 × 10-1
104 11
105 27
2.9 × 102
106 49
5.3 × 103

5. EXPERIMENTAL TECHNIQUE
Using a Time of Flight (TOF) technique, capture cross section is determined through the measurement of the reaction yield YR(En):
N: normalization factor to obtain an absolute capture yield
Cw: weighted counts background subtracted
F: incident neutron fluence
ε = k x Ec: detection efficiency
The experimental yield can be expressed in terms of total (stot) and capture (sg) cross section:

6. EXPERIMENTAL TECHNIQUE
For capture measurements, detection efficiency have to be independent from g-spectrum multiplicity and from g-ray energy distribution
Total Absorption Detection
eg ~ 100 %
4p geometry detectors
Total Energy Detection
Low detection efficiency eg
Low solid angle
Basically we want to detect only one gamma ray per cascade

7. n_TOF facility at CERN
CERN Experiment PS213

8. n_TOF facility: characteristics
Proton beam momentum
20 GeV/c
Intensity (dedicated mode)
7 × protons/pulse
Repetition frequency
1 pulse/2.4 s
Pulse width
7 ns (rms)
Neutrons/proton
300
Lead target dimensions
=60 cm, h=40 cm
Cooling material
H2O
Moderation material
Borated Water (H2O % H3BO3)
Moderator thickness in the exit face
1 cm cooling material +
4 cm moderator

9. Radiative capture on 238U campaign
SAMPLE
DATE (YEAR 2012)
PROTONS
238U
10 d: March 29 – April 03, April 25 – 27, April 30 – May 02;
Filters – 7 d: April 5 – 6, April 11 – 16
7.85 ×
1.2 × 1018
Sample Out
6 d: March 28 – 2; Filters – 3 d: April 9 – 11
6.271 ×
1.64 × 1017
238U packing
2 d: April 21 – 22
9.65 × 1016
Beam off
0.25 d: March 28, April 5, April 11
Calibrations Pb
2d: April 03 – 04; Filters – 2 d: April 8 – 9
1.50 ×
1.53 × 1017
C (5 mm)
3 d: April 4 – 5, April 17; Filters – 2 d: April 7 – 8
1.46 × 1017
× 1017
C (10 mm)
2 d: April 19 – 20; Filters – 3 d: April 28 – 30
9.71 ×
1.11 × 1017
Au (50 µm)
2 d: April 5, April 16
4.86 × 1016
Au (300 µm)
2 d: April 17 – 18; Filters – 2 d: April 27 – 28
8.33 ×
9.93 × 1016 Ag
1 d: May 02
1.60 × 1016
238U(n,g) – TOT: 17 days

10. Radiative capture on 238U campaign
SAMPLE
DATE (YEAR 2012)
PROTONS
238U
10 d: March 29 – April 03, April 25 – 27, April 30 – May 02;
Filters – 7 d: April 5 – 6, April 11 – 16
7.85 ×
1.2 × 1018
Sample Out
6 d: March 28 – 2; Filters – 3 d: April 9 – 11
6.271 ×
1.64 × 1017
238U packing
2 d: April 21 – 22
9.65 × 1016
Beam off
0.25 d: March 28, April 5, April 11
Calibrations Pb
2d: April 03 – 04; Filters – 2 d: April 8 – 9
1.50 ×
1.53 × 1017
C (5 mm)
3 d: April 4 – 5, April 17; Filters – 2 d: April 7 – 8
1.46 × 1017
× 1017
C (10 mm)
2 d: April 19 – 20; Filters – 3 d: April 28 – 30
9.71 ×
1.11 × 1017
Au (50 µm)
2 d: April 5, April 16
4.86 × 1016
Au (300 µm)
2 d: April 17 – 18; Filters – 2 d: April 27 – 28
8.33 ×
9.93 × 1016 Ag
1 d: May 02
1.60 × 1016
BACKGROUND – TOT: 14.5 days

11. Radiative capture on 238U campaign
SAMPLE
DATE (YEAR 2012)
PROTONS
238U
10 d: March 29 – April 03, April 25 – 27, April 30 – May 02;
Filters – 7 d: April 5 – 6, April 11 – 16
7.85 ×
1.2 × 1018
Sample Out
6 d: March 28 – 2; Filters – 3 d: April 9 – 11
6.271 ×
1.64 × 1017
238U packing
2 d: April 21 – 22
9.65 × 1016
Beam off
0.25 d: March 28, April 5, April 11
Calibrations Pb
2d: April 03 – 04; Filters – 2 d: April 8 – 9
1.50 ×
1.53 × 1017
C (5 mm)
3 d: April 4 – 5, April 17; Filters – 2 d: April 7 – 8
1.46 × 1017
× 1017
C (10 mm)
2 d: April 19 – 20; Filters – 3 d: April 28 – 30
9.71 ×
1.11 × 1017
Au (50 µm)
2 d: April 5, April 16
4.86 × 1016
Au (300 µm)
2 d: April 17 – 18; Filters – 2 d: April 27 – 28
8.33 ×
9.93 × 1016 Ag
1 d: May 02
1.60 × 1016
NORMALIZATION – TOT: 3.5 days

12. Radiative capture on 238U campaign
SAMPLE
DATE (YEAR 2012)
PROTONS
238U
10 d: March 29 – April 03, April 25 – 27, April 30 – May 02;
Filters – 7 d: April 5 – 6, April 11 – 16
7.85 ×
1.2 × 1018
Sample Out
6 d: March 28 – 2; Filters – 3 d: April 9 – 11
6.271 ×
1.64 × 1017
238U packing
2 d: April 21 – 22
9.65 × 1016
Beam off
0.25 d: March 28, April 5, April 11
Calibrations Pb
2d: April 03 – 04; Filters – 2 d: April 8 – 9
1.50 ×
1.53 × 1017
C (5 mm)
3 d: April 4 – 5, April 17; Filters – 2 d: April 7 – 8
1.46 × 1017
× 1017
C (10 mm)
2 d: April 19 – 20; Filters – 3 d: April 28 – 30
9.71 ×
1.11 × 1017
Au (50 µm)
2 d: April 5, April 16
4.86 × 1016
Au (300 µm)
2 d: April 17 – 18; Filters – 2 d: April 27 – 28
8.33 ×
9.93 × 1016 Ag
1 d: May 02
1.60 × 1016
ENTIRE CAMPAIGN: 35 days

13. EXPECTED RADIOACTIVITY
Samples
Enriched metallic uranium rectangular plate (53×30 mm2, 235 µm thick) enveloped inside a 20 mm aluminum and a 25 mm kapton thick foils.
Provided by the EC-JRC-IRMM
MASS
6.125 ± g
9.6×10-4 atoms/barn
% 238 U
99.99 %
% 235 U
< 11 ppm
% U
< 1 ppm each
EXPECTED RADIOACTIVITY
12.4 kBq/g
(76 kBq)
Isotopic analysis IRMM in 1984

14. ATOMIC DENSITY [atoms/barn]
Samples
The other samples analyzed have been chosen with geometry as similar as possible to that of the 238U.
197Au
SAMPLE
SIZE [mm]
MASS [g]
ATOMIC DENSITY [atoms/barn]
197Au
53.30 × 29.65
9.213 Pb
53.77 × 30.19
9.44 C
53.35 × 30.20
28.89 Fe
53.71 × 30.22
3.225 Ag
53.75 × 30.30
4.620 C
natPb

15. New 2012 measurement: EXPERIMENTAL SET–UP
Two different setups for capture measurements
Total Absorption Calorimeter
40 BaF2 crystals in a 4p geometry
Detects the entire g cascade (together with background n)
Two C6D6 scintillation detectors
Optimized for an extremely low neutron sensitivity
Only one g–ray detected per cascade
 Total Energy Detection System with PHWT
BaF2
C6D6
C6D6
NEUTRON FLUX

16. Calibrations 137Cs 88Y Am-Be
accurate study of the calibrations between the flash-ADC channels and the deposited energy was performed on a weekly basis using three standard sources: 137Cs (661.7 keV), 88Y (0.898 and MeV) and Am/Be (4.44 MeV).
Comparing the different calibration spectra for each isotope, we notice that they are not stable, and for this reason we extracted six calibration lines from the different measurements made.

17. Calibrations
137Cs
88Y
Am-Be

18. Simulated Detectors Response: Uniform emission
Detector response convoluted with the experimental resolution of the det

19. Simulated Detectors Response: Exponential attenuation

20. Weighting Functions
238U
197Au

21. Flux stability

22. C6D6 counts stability
238U first resonance

23. C6D6 counts stability
238U first resonance

24. C6D6 counts stability

25. 238U(n,g)239U: TOF spectra
Linee energia

26. Background subtraction

27. Background subtraction
Natural radioactivity
Empty Frame and Dummy
Scattered neutrons
In-beam gamma rays

28. Background subtraction
Natural radioactivity
Empty Frame and Dummy
Scattered neutrons
In-beam gamma rays EF U Pb Au C

29. Background subtraction
Natural radioactivity

30. Background subtraction
Natural radioactivity
Empty Frame and Dummy
Scattered neutrons
In-beam gamma rays

31. Background subtraction
Empty Frame and Dummy
Natural radioactivity
Scattered neutrons
In-beam gamma rays

32. Background subtraction
Natural radioactivity
Empty Frame and Dummy
Scattered neutrons
In-beam gamma rays

33. Background subtraction
Scattered neutrons
50 bin per decade

34. Background subtraction
Scattered neutrons

35. Background subtraction
Scattered neutrons

36. Background subtraction
Scattered neutrons
50 bin per decade

37. Background subtraction
Scattered neutrons
– 238U
– Scattered neutrons

38. Background subtraction
Natural radioactivity
Empty Frame and Dummy
Scattered neutrons
In-beam gamma rays

39. Background subtraction
Scattered neutrons
– 238U
– natPb

40. Background subtraction
– 238U background subtracted

41. Normalization: saturated resonance technique

42. 197Au YIELD: analysis validation

43. 197Au YIELD: analysis validation

44. 197Au YIELD: analysis validation

45. 197Au YIELD: analysis validation

46. 197Au YIELD: analysis validation

47. 197Au YIELD: analysis validation

48. 197Au YIELD: analysis validation

49. 197Au YIELD: analysis validation

50. 197Au YIELD: analysis validation

51. 197Au YIELD: analysis validation

52. 197Au YIELD: analysis validation

53. 197Au YIELD: analysis validation

54. 238U CAPTURE YIELD

55. 238U CAPTURE YIELD

56. 238U CAPTURE YIELD

57. 238U CAPTURE YIELD

58. 238U CAPTURE YIELD

59. 238U CAPTURE YIELD

60. 238U CAPTURE YIELD

61. 238U CAPTURE YIELD

62. 238U CAPTURE YIELD

63. 238U CAPTURE YIELD

64. 238U CAPTURE YIELD

65. 238U CAPTURE YIELD

66. 238U CAPTURE YIELD

67. 238U CAPTURE YIELD

68. 238U CAPTURE YIELD

69. 238U CAPTURE YIELD

70. CONCLUSIONS
Accurate data rejection and calibrations (6 calibration lines extracted)
Accurate background subtraction (analysis of the background level with filters ongoing)
SOURCE OF UNCERTAINTY
1 eV < En < 1-3 keV
THERMAL + URR
Sample mass
0.03%
Neutron flux (shape in En)
~0.5%
Neutron flux (abs. value) [i.e. normalization]
<1%
Background (at resonance peek)
0-1%
4-5%
Overall %
5-6%

71. Thank you! Federica Mingrone mingrone@bo.infn.it
Università di Bologna, Dipartimento di Fisica e Astronomia
Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

72. BACKUP

73. 238U(n, g)239U: TOF spectra
Linee energia

74. Background subtraction

75. Unresolved Resonance Region: GOLD

76. Yield Au: thermal

77. Yield Au: eV

78. Yield 238U: eV

79. Counting statistic uncertainties
100 bin per decade