New insights on fission of 235U induced by high energy neutrons from a new measurement at nTOF
Consiglio Nazionale delle Ricerche, Bari
Details on PPFC+RPT measurements
Details on PPAC+RPT measurements
CERN nTOF facility. Protons (7 to 8.5E+12 protons/pulse, pulse width of 7 nsec) were accelerated to 20 GeV/c with repetition rate of 0.8 Hz at maximum.
1E+6 neutrons/pulse were produced in a Pb spallation target coupled to water moderators.
The diameter of the neutron beam at sample position is 2 cm.
| Heading | Explanation |
|---|---|
EN-RSL-HW
|
Half of bin width
|
Two 235U (92.699(5)%) and eight 235U (99.933(14)%) enriched samples mounted in PPFC and PPAC.
Two polyethylene sheets for n-p scattering measurement.
Flight path of 185 m
for separation of (n,p) events form (n,d), (n,t) and (n,a) events
Corrected for 12C(n,p) events by an additional measurement using graphite samples
n-p scattering cross section in the centre-of-mass system for proton at 20 and 25 deg in the laboratory system in LA150 library (VL40 wave analysis energy dependent phase-shift solution of Arndt above 26 MeV) interpolated by MCNP
+----------------------------------------------------+
Tlab (MeV) sigma,cm (mb/sr)
theta,lab=20.0 deg theta,lab=25.0 deg
------------------------------------------------------
20.0 151.1773 143.0919
25.0 119.6774 112.3854
30.0 98.2831 91.4940
35.0 82.9424 76.5152
40.0 71.5839 65.3763
45.0 62.8253 56.8485
50.0 55.9827 50.1418
55.0 50.5020 44.8111
60.0 46.0731 40.4603
65.0 42.4019 36.9134
70.0 39.3703 33.9688
75.0 36.8074 31.5020
80.0 34.6420 29.4214
85.0 32.7947 27.6482
90.0 31.2097 26.1335
95.0 29.8372 24.8245
100.0 28.6440 23.6949
110.0 26.6841 21.8386
120.0 25.1544 20.3961
130.0 23.9333 19.2479
140.0 22.9368 18.3085
150.0 22.1063 17.5243
160.0 21.3968 16.8537
170.0 20.7786 16.2632
180.0 20.2285 15.7369
190.0 19.7309 15.2568
200.0 19.2700 14.8089
210.0 18.8391 14.3918
220.0 18.4333 13.9956
230.0 18.0407 13.6170
240.0 17.6676 13.2522
250.0 17.3040 12.8977
260.0 16.9518 12.5551
270.0 16.6048 12.2189
280.0 16.2674 11.8915
290.0 15.9355 11.5723
300.0 15.6067 11.2609
310.0 15.2859 10.9539
320.0 14.9683 10.6510
330.0 14.6563 10.3578
340.0 14.3475 10.0676
350.0 14.0429 9.7806
+----------------------------------------------------+
Proofread by Elisa Pirovano and Alice Manna (2025-12-23)
| Date | Work | Remark |
|---|---|---|
| 2025-12-18 | Data received at the data center |
Data received from Elisa Pirovano
|
| 2025-12-18 | Compiled at the data center |
On+ED
|
PPFC+3S-RPT dataset
.PPFC+3S-RPT dataset
Parallel Plate Fission Chamber (PPFC) containing eight 235U samples (42 mm diam., 264 to 338 ug/cm2 determined by alpha counting), for measurement up to 145 MeV.
Recoil proton telescope Triple-stage RPT (3S-RPT) at 25 deg
* By Alice Manna and Elisa Pirovano (2025-12-04):
.PPFC+3S-RPT dataset
The cross section obtained with PPFC and 3S-RPT. In this detection system, the recoil proton telescope was at a proton emission angle theta,p of 25 deg.
In this case, the measured fission cross section is proportional to the differential proton emission cross section dsigma/dOmega,p at theta,p) in the laboratory frame.
Therefore, it is possible to re-normalized it in case of change of the neutron-proton elastic scattering cross section at the corresponding neutron scattering angle.
| Heading | Lower limit (%) | Upper limit (%) | Correlation | Remark |
|---|---|---|---|---|
ERR-T
|
Total uncertainty
|
|||
ERR-S
|
Statistical uncertainty
|
|||
ERR-SYS
|
Total systematic uncertainty
|
|||
ERR-2
|
Systematic uncertainty correlated between PPFC
and PPAC datasets:
|
|||
ERR-1
|
PPFC/3S-RPT systematic uncertainty uncorrelated
with PPAC/MSR-RPTs systematic uncertainty:
|
------------------------------------------------------------------------------------------------ EN EN-RSL-HW DATA 1ERR-T 1ERR-S 1ERR-SYS 1ERR-1 1ERR-2 MEV MEV MB MB MB MB PER-CENT PER-CENT ------------------------------------------------------------------------------------------------ 10.63 0.63 11.95 0.70 13.44 0.79 15.12 0.89 17.01 1.00 19.14 1.13 21.86 1.60 25.30 1.85 29.22 0.71 2175. 125. 76. 99. 4.5 30.68 0.75 2131. 121. 73. 97. 4.5 32.21 0.79 2158. 123. 74. 98. 4.5 33.82 0.83 2174. 113. 51. 101. 4.6 35.51 0.87 2087. 108. 49. 97. 4.6 37.29 0.91 2105. 110. 51. 97. 4.6 39.16 0.95 1987. 105. 50. 92. 4.1 2.1 41.12 1.01 1968. 105. 51. 91. 4.1 2.1 43.17 1.05 1962. 106. 54. 91. 4.1 2.1 45.33 1.11 2025. 104. 43. 94. 4.1 2.1 47.59 1.16 2034. 105. 47. 94. 4.1 2.1 49.97 1.22 1880. 98. 45. 87. 4.1 2.1 52.73 1.54 1946. 100. 43. 90. 4.2 1.9 55.89 1.63 1894. 99. 45. 88. 4.2 1.9 59.25 1.73 1870. 99. 48. 87. 4.2 1.9 62.80 1.83 1829. 99. 51. 85. 4.2 1.9 66.57 1.94 1805. 100. 53. 84. 4.2 1.9 70.57 2.06 1769. 99. 55. 83. 4.3 1.9 74.80 2.18 1717. 99. 58. 80. 4.3 1.9 79.28 2.31 1761. 103. 63. 82. 4.3 1.9 84.04 2.45 1697. 101. 62. 79. 4.3 1.9 89.09 2.60 1685. 105. 70. 79. 4.3 1.9 94.43 2.75 1586. 100. 66. 74. 4.3 1.9 100.10 2.92 1569. 107. 79. 72. 4.2 1.9 106.62 3.61 1591. 127. 105. 72. 4.2 1.7 114.08 3.86 1516. 125. 104. 69. 4.2 1.7 122.06 4.13 1498. 135. 116. 68. 4.2 1.7 130.61 4.42 1454. 122. 102. 66. 4.2 1.7 139.75 4.72 1498. 131. 111. 69. 4.2 1.7 149.53 5.06 161.55 6.96 176.08 7.58 191.93 8.27 209.20 9.01 228.03 9.82 248.56 10.71 270.93 11.67 295.31 12.72 321.88 13.86 350.85 15.11 384.26 18.30 422.69 20.13 ------------------------------------------------------------------------------------------------
PPAC+MSRPT dataset
.PPAC+MSRPT dataset
Parallel Plate Avalanche Counter containing two 235U samples (80 mm diam., 263 ug/cm2 and 282 ug/cm2)
Recoil proton telescope
* By Alice Manna and Elisa Pirovano (2025-12-04):
.PPAC+MSRPT dataset
The cross section obtained with PPAC and MS-RPTL and MS-RPTH. In this detection system two recoil proton telescopes were used, positioned at 25 deg and 20 deg, respectively.
In this case the normalization is not straightforward, therefore we are proposing a method (outlined in ????) for the re-normalization.
| Heading | Explanation |
|---|---|
MISC
|
[w(20 deg)*phi(20 deg)]/[w(25 deg)*phi(25 deg)]
|
| Heading | Lower limit (%) | Upper limit (%) | Correlation | Remark |
|---|---|---|---|---|
ERR-T
|
Total uncertainty
|
|||
ERR-S
|
Statistical uncertainty
|
|||
ERR-SYS
|
Total systematic uncertainty
|
|||
ERR-2
|
Systematic uncertainty correlated between PPFC
and PPAC datasets:
|
|||
ERR-1
|
PPAC/MS-RPTs systematic uncertainty
uncorrelated with PPFC/3S-RPT systematic uncertainty:
|
------------------------------------------------------------------------------------------------------------ EN EN-RSL-HW DATA 2ERR-T 2ERR-S 2ERR-SYS 2ERR-1 2ERR-2 MISC 2 MEV MEV MB MB MB MB PER-CENT PER-CENT NO-DIM ------------------------------------------------------------------------------------------------------------ 10.63 0.63 1795. 147. 88. 117. 6.5 0.000 11.95 0.70 1768. 137. 73. 116. 6.5 0.000 13.44 0.79 1887. 142. 71. 123. 6.5 0.000 15.12 0.89 2040. 152. 73. 133. 6.5 0.000 17.01 1.00 2094. 153. 69. 137. 6.5 0.000 19.14 1.13 1982. 140. 52. 130. 6.5 0.000 21.86 1.60 2112. 147. 50. 138. 6.5 0.000 25.30 1.85 2134. 149. 53. 140. 6.5 0.000 29.22 0.71 30.68 0.75 32.21 0.79 33.82 0.83 35.51 0.87 37.29 0.91 39.16 0.95 2007. 102. 62. 81. 3.4 2.1 0.000 41.12 1.01 1991. 104. 67. 80. 3.4 2.1 0.000 43.17 1.05 1925. 102. 66. 77. 3.4 2.1 0.000 45.33 1.11 1972. 104. 67. 79. 3.4 2.1 0.000 47.59 1.16 1874. 101. 67. 75. 3.4 2.1 0.000 49.97 1.22 1916. 103. 68. 77. 3.4 2.1 0.000 52.73 1.54 1826. 94. 62. 71. 3.4 1.9 0.000 55.89 1.63 1847. 90. 53. 72. 3.4 1.9 0.000 59.25 1.73 1797. 88. 53. 70. 3.4 1.9 0.000 62.80 1.83 1800. 89. 54. 71. 3.4 1.9 0.000 66.57 1.94 1744. 87. 54. 68. 3.4 1.9 0.000 70.57 2.06 1697. 85. 54. 66. 3.4 1.9 0.000 74.80 2.18 1696. 86. 55. 66. 3.4 1.9 0.000 79.28 2.31 1642. 84. 54. 64. 3.4 1.9 0.000 84.04 2.45 1671. 81. 48. 65. 3.4 1.9 2.180 89.09 2.60 1632. 79. 46. 64. 3.4 1.9 5.072 94.43 2.75 1627. 79. 47. 64. 3.4 1.9 6.778 100.10 2.92 1707. 82. 48. 67. 3.4 1.9 5.915 106.62 3.61 1602. 77. 44. 63. 3.5 1.7 12.657 114.08 3.86 1540. 75. 44. 61. 3.6 1.7 13.809 122.06 4.13 1528. 75. 45. 61. 3.6 1.7 4.796 130.61 4.42 1523. 76. 46. 61. 3.6 1.7 4.143 139.75 4.72 1442. 72. 43. 58. 3.6 1.7 2.360 149.53 5.06 1519. 75. 44. 61. 4.0 4.163 161.55 6.96 1535. 74. 41. 62. 4.0 3.959 176.08 7.58 1396. 70. 40. 57. 4.1 3.600 191.93 8.27 1505. 75. 43. 62. 4.1 3.540 209.20 9.01 1523. 78. 46. 63. 4.2 3.545 228.03 9.82 1448. 75. 45. 60. 4.2 3.531 248.56 10.71 1453. 75. 46. 60. 4.1 1.940 270.93 11.67 1407. 74. 46. 58. 4.1 1.804 295.31 12.72 1579. 84. 53. 65. 4.1 2.162 321.88 13.86 1378. 75. 48. 57. 4.2 1.886 350.85 15.11 1501. 83. 54. 63. 4.2 2.069 384.26 18.30 1620. 90. 59. 68. 4.2 1.941 422.69 20.13 1481. 84. 55. 63. 4.2 2.074 ------------------------------------------------------------------------------------------------------------
Weighted average of PPFC/3SRPT and PPAC/MSRPT datasets
| Heading | Explanation |
|---|---|
MISC1
|
w(PPFC/3S-RPT)
|
MISC2
|
w(PPAC/MS-RPTL)
|
| Heading | Lower limit (%) | Upper limit (%) | Correlation | Remark |
|---|---|---|---|---|
DATA-ERR
|
The uncertainty results from the procedure
to calculate the weighted average.
|
* By Alice Manna and Elisa Pirovano (2025-12-04):
The final cross section obtained as weighted average of the two independent results (in which we have a contribution from both the neutron-proton elastic scattering differential cross section).
This data set contains the weights used to calculate the weighted mean, which makes it possible to re-calculate the weighted mean of the re-normalized fission cross sections measured with the two experimental configurations PPFC/3S-RPT and PPAC/MS-RPTL(H).
As discussed in E.Pirovano et al. "Absolute cross section for neutron-induced fission of 235U in the energy range from 10 MeV to 400 MeV" (to be published in Phys.Rev.C and arXiv), these two data sets are partially correlated, as the same polyethylene samples and beam intensity monitors were employed.
However, a small re-normalization of the differential neutron-proton scattering cross section will not effect the stated relative uncertainty of the final fission cross section.
Datasets from PPFC/3SRPT and PPAC/MSRPT
------------------------------------------------------------------------ EN EN-RSL-HW DATA DATA-ERR MISC1 MISC2 MEV MEV MB MB NO-DIM NO-DIM ------------------------------------------------------------------------ 10.63 0.63 1795. 147. 0. 1. 11.95 0.70 1768. 137. 0. 1. 13.44 0.79 1887. 142. 0. 1. 15.12 0.89 2040. 152. 0. 1. 17.01 1.00 2094. 153. 0. 1. 19.14 1.13 1982. 140. 0. 1. 21.86 1.60 2112. 147. 0. 1. 25.30 1.85 2134. 149. 0. 1. 29.22 0.71 2175. 125. 1. 0. 30.68 0.75 2131. 121. 1. 0. 32.21 0.79 2158. 123. 1. 0. 33.82 0.83 2174. 113. 1. 0. 35.51 0.87 2087. 108. 1. 0. 37.29 0.91 2105. 110. 1. 0. 39.16 0.95 1997. 79. 0.4828 0.5172 41.12 1.01 1980. 80. 0.4966 0.5034 43.17 1.05 1943. 79. 0.4793 0.5207 45.33 1.11 1999. 79. 0.5068 0.4932 47.59 1.16 1951. 79. 0.4816 0.5184 49.97 1.22 1897. 77. 0.5256 0.4744 52.73 1.54 1882. 73. 0.4703 0.5297 55.89 1.63 1868. 71. 0.4463 0.5537 59.25 1.73 1828. 70. 0.4314 0.5686 62.80 1.83 1813. 71. 0.4375 0.5625 66.57 1.94 1770. 70. 0.4248 0.5752 70.57 2.06 1727. 69. 0.4169 0.5831 74.80 2.18 1705. 69. 0.4206 0.5794 79.28 2.31 1688. 69. 0.3887 0.6113 84.04 2.45 1681. 67. 0.3769 0.6231 89.09 2.60 1650. 67. 0.3408 0.6592 94.43 2.75 1612. 65. 0.3686 0.6314 100.10 2.92 1658. 69. 0.3513 0.6487 106.62 3.61 1599. 68. 0.2514 0.7486 114.08 3.86 1534. 66. 0.2504 0.7496 122.06 4.13 1521. 67. 0.221 0.779 130.61 4.42 1505. 66. 0.2628 0.7372 139.75 4.72 1454. 65. 0.2177 0.7823 149.53 5.06 1519. 75. 0. 1. 161.55 6.96 1535. 74. 0. 1. 176.08 7.58 1396. 70. 0. 1. 191.93 8.27 1505. 75. 0. 1. 209.20 9.01 1523. 78. 0. 1. 228.03 9.82 1448. 75. 0. 1. 248.56 10.71 1453. 75. 0. 1. 270.93 11.67 1407. 74. 0. 1. 295.31 12.72 1579. 84. 0. 1. 321.88 13.86 1378. 75. 0. 1. 350.85 15.11 1501. 83. 0. 1. 384.26 18.30 1620. 90. 0. 1. 422.69 20.13 1481. 84. 0. 1. ------------------------------------------------------------------------
Averaged data processed by smoothing filter.
The smoothed data starts from 149 MeV, below this energy the averaged cross section is reported.
| Heading | Lower limit (%) | Upper limit (%) | Correlation | Remark |
|---|---|---|---|---|
DATA-ERR
|
The uncertainty on the smoothed data
results from the fitting procedure.
|
U5vsnp-smo
Averaged cross section
------------------------------------------------ EN EN-RSL-HW DATA DATA-ERR MEV MEV MB MB ------------------------------------------------ 10.63 0.63 1795. 147. 11.95 0.70 1768. 137. 13.44 0.79 1887. 142. 15.12 0.89 2040. 152. 17.01 1.00 2094. 153. 19.14 1.13 1982. 140. 21.86 1.60 2112. 147. 25.30 1.85 2134. 149. 29.22 0.71 2175. 125. 30.68 0.75 2131. 121. 32.21 0.79 2158. 123. 33.82 0.83 2174. 113. 35.51 0.87 2087. 108. 37.29 0.91 2105. 110. 39.16 0.95 1997. 79. 41.12 1.01 1980. 80. 43.17 1.05 1943. 79. 45.33 1.11 1999. 79. 47.59 1.16 1951. 79. 49.97 1.22 1897. 77. 52.73 1.54 1882. 73. 55.89 1.63 1868. 71. 59.25 1.73 1828. 70. 62.80 1.83 1813. 71. 66.57 1.94 1770. 70. 70.57 2.06 1727. 69. 74.80 2.18 1705. 69. 79.28 2.31 1688. 69. 84.04 2.45 1681. 67. 89.09 2.60 1650. 67. 94.43 2.75 1612. 65. 100.10 2.92 1658. 69. 106.62 3.61 1599. 68. 114.08 3.86 1534. 66. 122.06 4.13 1521. 67. 130.61 4.42 1505. 66. 139.75 4.72 1454. 65. 149.53 5.06 1498. 21. 161.55 6.96 1486. 22. 176.08 7.58 1475. 22. 191.93 8.27 1468. 22. 209.20 9.01 1464. 22. 228.03 9.82 1464. 23. 248.56 10.71 1466. 24. 270.93 11.67 1470. 26. 295.31 12.72 1475. 29. 321.88 13.86 1480. 31. 350.85 15.11 1485. 32. 384.26 18.30 1489. 37. 422.69 20.13 1490. 55. ------------------------------------------------