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Radiative capture width of the first 240 Pu resonance. Carlos GUERRERO CERN, Physics Department. Nuclear reactors with MOX fuel. The role of 240 Pu in MOX fuel reactors. Void coefficient and Doppler of 238 U and 240 Pu. 238 U@6.7 eV. 240 Pu@1.06 eV.

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## Radiative capture width of the first 240 Pu resonance

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**Radiative capture width of the first 240Pu resonance**Carlos GUERRERO CERN, PhysicsDepartment**Void coefficient and Doppler of 238U and 240Pu**238U@6.7 eV 240Pu@1.06 eV**The radiative width of the 1st240Pu resonance**Average from measurements(srel=4.5%) (n,g) (n,tot) (n,g) n_TOF 2008 (n,g) ENDF/B-VII = 30.6 meV (n,tot) JENDL-4.0 = 30.0 meV (n,tot) JEFF-3.1.2=29.14 meV**The Ggof the 1st240Pu resonance: MoX fuels**G. Noguere et al.,Improved MOX fuel calculations using new 239Pu, 241Am and 240Pu evaluations, EPJ Web of Conferences 42 05005 (2013) The combination of the 241Am and 239Pu evaluations demonstrates the necessity to improve the radiation width of the first resonance of 240Pu.**Why the n-TOF-Phase1 measurement can’t be used**• 240Pu sample used in n_TOF-Phase1 with the TAC: • 51,2 mg of PuO2 (Powder grain size 1-10 mm!!) • Number of “grain layers” ~7 self-shielding correction wrong when it is large • TAC data analyzed only above 110 eV (and below 2 keV because of Ti capsule) See: S. Kopecky, P. Siegler, and A. Moens. Low energy transmission measurements of 240,242Pu at GELINA and their impact on the capture width, Proc. Int. Conf. Nucl. Data for Sci. and Tech. 2007 (Nice-France), page 7391, 2007 )**The 240Pu(n,g) n_TOF measurement in 2012**4 samples of 240Pu received from IRMM (Geel) within ERINDA • 3 cm diameter PuO2 deposit • 0.25 mm aluminum backing (5 cm diameter) 240Pu = 1.096x10-6 atoms/barn Al backing = 0.903x10-2 atoms/barn ONE weekend (9-11thNovember 2012)**Energy calibration of C6D6 detectors**Linear calibration with “only” 137Cs (662 keV) and 88Y (898 and 1836 keV) [no Am/Be (4.5 MeV)] Ethreshold=250 keV ?**Calibrated ToF and Eg distributions**All Dummy All - dummy 1.056 eV All Dummy time-Tg (ms)**Data reduction (using TTOFSort by F. Gunsing)**Measurement over 48 hours: resonances observed up to 50 eV Below 1.056 eV resonance: 18.000 counts -> 0.7% statistical uncertainty Background (smooth, dominated by dummy) at 2% level Counting rate <0.01 counts/ms DT losses < 0.02% for t=30 ns DT losses < 0.6% for t=1000 ns a->AddDetector(kC6D6, 2); a->SetPriorCut(kC6D6, "PSpulse==1"); // ONLY DEDICATED PULSES a->UseCalibration(kC6D6, a2e_c6d61, a2e_c6d62); // apply amplitude-energy calibration a->SetNewCutsEg(kC6D6, 0.250, 5.5, 0.250, 5.5); // analyze 250 keV to 6 MeV a->SetNewBinParsT(kC6D6, 0.0, 1.0, 1.0, 600.0, 1e8); // 600 bins/decade a->SetNewFixedDeadtime(kC6D6, 30.); // Set fixed dead-time to 30 ns a->SetNewCoincidencetime(kC6D6, 30.); // Set coincidence time to 30 ns a->SetNewCutsTime(kC6D6, 12.5e6,13.5e6,12.5e6,13.5e6); // Cut in ToF for the 1st Pu resonance in C6D6**Open questions (problems?)**• Detector C6D6 #1 counts 25% less than C6D6 #2 • This is seen with beam, and also with calibration sources (although sources could be misplaced) • Simulations (M. Barbagallo) indicate that a change in sample-detector distance of 1 cm changes e by ~9%) • The resonance shows a structure in the “high En shoulder” Tests performed so far: Detector ID, Threshold Pulse type Run number, Dead-time Could be due to ping-pong in the different Al layers: detailed MC needed!**VERY preliminary results vs. previous data**Average from measurements(srel=4.5%) (n,g) (n,tot) (n,g) n_TOF 2008 (n,g) ENDF/B-VII = 30.6 meV (n,tot) (n,tot) JEFF-3.1.2=29.14 meV anRF numRF**Towards an efficient and useful evaluation**The NEA has “agreed to approve” a project involving n_TOF (Responsible Carlos Guerrero) and CEA-Cadarache (responsible Gilles Noguere) for the join analysis and evaluation of the radiative capture width of 240Pu’s first resonance. • Towards an efficient and useful evaluation in four steps: • Determine experimental capture yield from n_TOF [n_TOF] • Resonance Shape Analysis of capture and transmission [n_TOF/CEA] • Test/Comparison/Validation with integral experimental data [CEA/n_TOF] • New JEFF-3.1 evaluation on 240Pu [CEA] • Deadline: to be finished for the JEFF meeting of Fall 2013

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