C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” The n_TOF Collaboration, CERN EN/STI Student’s Coffee (17 th April 2012) An n_TOF experiment: the complete process from the data taken to the published results Carlos Guerrero CERN Physics Dpt. Fellow

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” The complete process from the data taken to the published results PHYSICS MOTIVATION BEHIND THE N_TOF EXPERIMENT AT CERN ONE PARTICULAR EXPERIMENT: Motivation How we make such an experiment: -Neutron source -Detectors Data taking Analysis What we do after!

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Physics Motivation behind the n_TOF Experiment at CERN NUCLEAR ASTROPHYSICS: stellar nucleosynthesis Neutron capture and (n,  ) cross section of stable (& radioactive) medium mass isotopes playing a role in the s- and r-processes responsible of the creation of elements heavier than Fe in the starts. NUCLEAR TECHNOLOGIES: ADS, Gen-IV and Th fuel cycle, Nuclear Medicine Neutron capture and fission cross sections of Actinides and Fission Fragments in the thermal, epithermal and fast energy range. Also reactions of interest for Nuclear Medicine (for instance 33 S n,  ) BASIC NUCLEAR PHYSICS: levels densities,  -ray strength funct. and angular distributions Time-of-flight measurements with dedicated detectors provide very valuable information on basic nuclear physics quantities. DETECTOR DEVELOPMENT AND TESTING, IRRADIATION WITH NEUTRONS: CVD diamonds, Fiber Bragg Gratings, Optical Fiber dosimeters, GEMs, MediPix, … The n_TOF Collaboration 38 Research Institutions from Europe, Asia and USA. Based at CERN: 5 FTE short term visitors E. Chiaveri (Spokesperson), E. Berthoumieux (Techn. Coord.), C. Guerrero (Run Coord.), C. Weiss (PhD), A. Tsinganis (PhD) (Also V. Vlachoudis and M. Calviani)

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” MOTIVATION

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Figura Nucleosintesi (frecce che si muovono) Foto FIC 239 Pu: 125 Kg/yr 237 Np: 16 Kg/yr 241 Am:11.6 Kg/yr 243 Am: 4.8 Kg/yr 241 Am:11.6 Kg/yr 243 Am: 4.8 Kg/yr 244, 245 Cm 1.5 Kg/yr 244, 245 Cm 1.5 Kg/yr FP LLFP 76.2 Kg/yr LLFP 76.2 Kg/yr Quantities refer to yearly production in 1 GW e LW reactor Neutrons and production of nuclear energy (& radioactive waste) +Energy

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” How do the competing (n,g) (n,f) cross sections look like? 235 U (even-odd): FISSILE 238 U (even-even): NON-FISSILE Similar behavior for all isotopes with ODD number of neutrons: 239,241 Pu, …, 245 Cm Similar behavior for all isotopes with EVEN number of neutrons: 237 Np, …, 240,242 Pu, 241,243 Am Thermal neutrons Fast neutrons

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Existing reactors have low burn-up efficiency and produce large amount of radioactive waste. In all cases, a large reduction of actinide inventory is achieved by means of neutron- induced reactions with FAST NEUTRONS (subsequent captures and fission). Generation IV reactors based on recycling of the spent fuel (in particular actinides). Neutrons and production of nuclear energy (& radioactive waste) Using fast neutrons it is possible to fission all actinides, thus reducing the high level waste!! Another possibility is to use dedicated burners (Accelerator Driven Systems [ADS])

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” (FCA) Fast Critical Assembly (JAEA) Soft Hard The criticality of current and fast future reactors must be known within % for operation/safety. Differences up to 2% in the measured and calculated criticality values for FCA (JAERI, Japan) assemblies with different hardness are due to 235 U  (n,  ) below 2.5 keV. Open Problems: Uncertainties in the capture 235 U cross section Sensitive mainly to the 235 U(n,  ) below 2.25 keV (RRR) GOAL: Measure 235 U  (n,  ) below 2.5 keV (First Goal: demonstrate feasibility)

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” GOAL: Measure 235 U  (n,  ) below 2.5 keV I (neutrons/cm 2 /s) n (atoms/cm 2 ) Reaction products Measuring the neutron cross sections requires: - A facility providing a neutron beam (The n_TOF facility). - A highly pure sample. - A detection system for counting the reactions (The TAC+MGAS set-up). -The analysis tools to determine the measured cross section with the required accuracy. The concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus.

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” The n_TOF facility

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” PS 20 GeV Linac 50 MeV Booster 1.4 GeV Proton Beam 20 GeV/c 7x10 12 ppp Pb Spallation Target Neutron Beam 10 o prod. angle n_TOF 185 m flight path The n_TOF Facility at CERN: a view neutron start neutron stop neutron time-of-flight experiment time 185 meters

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” The n_TOF Facility at CERN Access Area & Escape line & DAQ Experimental Area

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Detection system for (n,  ) reactions [fissile isotopes] Total Absorption Calorimeter (TAC) for (n,  ) 40 BaF 2 crystals 4  geometry (95% coverage) 16% energy resolution at 662 keV Used for  (n,  ) of actinides since 2004 C. Guerrero et al., NIM-A 608 (2009) n  -rays Results: distributions E sum, m cr & E n BUT… (n,el) reaction: neutrons (n,  ) reaction:  -rays (n,f) reaction: Fission fragments  -rays [similar to (n,g)!!!] neutrons

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Total Absorption Calorimeter (TAC) for (n,  ) 40 BaF 2 crystals 4  geometry (95% coverage) 16% energy resolution at 662 keV Used for  (n,  ) of actinides since 2004 MicroMegas (MGAS) for (n,f) Based on Bulk technology Double stage GAS detector: conversion +amplification ~90% efficiency for Fission Fragments (FF) Used for neutron monitoring since 2009 C. Guerrero et al., NIM-A 608 (2009) S. Andriamonje et al., NIM-A 481 (2002) 120–129 n n  -rays FF1 FF2 Results: distributions E sum, m cr & E n Results: distributions Amp. & E n We need to detect capture and fission reactions simultaneously! Detection system for (n,  ) reactions [fissile isotopes] Use of TAC and MGAS in “anticoincidence”!!

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Detection system for (n,  ) reactions [fissile isotopes]

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Data taking at n_TOF n_TOF DAQ n_TOF Run Control n_TOF Event Display Sounds familiar to n_TOF shifters?

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Analysis and Results

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” 1.Time and energy calibration of the TAC. 2.Coincidence algorithm among the TAC crystals. 3.Time calibration of the MGAS detectors with respect to the TAC 4.Loop runs over all MGAS events (ordered in time for each neutron pulse) 5.Loop over the TAC selecting coincident candidates (with TOF TAC Є[TOF MGAS -300 ns, TOF MGAS +50]) 6.Select TAC fission event. If more than one candidate, select the highest energy and multiplicity Analysis in coincidence of TAC and MGAS detectors FWHM~20 ns

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” Information from (n,  ) [and fission  -rays] with the TAC Neutron energy Multiplicity Deposited energy Protons (20 GeV) Neutrons (meV-GeV) Sweeping magnet Collimators   

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” RESULTS: deposited energy and multiplicity distributions Deposited energy (m cr >2) and multiplicity (E sum >3)distributions corresponding to resonances: - 32% of fission events fall above m cr >9 - 98% of capture events fall below m cr <9 - 33% of fission events fall above E sum >7.5 MeV - 100% of capture events fall below E sum <7.5 MeV 98% 68% 98% 67% S n ( 236 U)~6.5 MeV All – fission Background Fission All – fission – backg. Fission

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” RESULTS: neutron energy distributions Under the selected conditions, the counts/pulse information can be directly related to the corresponding cross sections

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” With two different detectors and two different types of reactions to detect, it is important to define clearly the different efficiencies that play a role in the measurement and their interrelations. When a neutron capture occurs, it can only be detected in the TAC →  TAC (n,  ) When a fission reaction occurs, it can be detected: a)in both detectors, →  MGAS (n,f) ∙  TAC (n,f) b)in none of them, → (1-  MGAS (n,f)) ∙ (1-  TAC (n,f)) c)only in the MGAS →  MGAS (n,f) ∙ (1-  TAC (n,f)) d)only in the TAC. → (1-  MGAS (n,f)) ∙  TAC (n,f) RESULTS: Detection efficiencies:  MGAS (n,f),  TAC (n,f) and  TAC (n,  ) The efficiency for detecting fission reactions in each detector is independent from the other, but the calculation from experimental data requires that these four probabilities are properly taken into account.  MGAS (n,f),  TAC (n,f) and  TAC (n,  )

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” E sum >7 MeV m cr >3  exp (n,f)~0.90 MC simulations Samples are 318  g/cm 2, nearly identical to those of the 235 U samples (316 mg/cm 2 ) used in FIC, for which simulations with FLIKA give  MC (n,f)~0.94 (6% losses due to absorption in the sample). Experimentally: Fission events produce high-energy, high-multiplicity TAC events. Assumption →  TAC ~100% for such events. Then, the detection efficiency of the FTMGs can be calculated as the ratio of tagged to all events for multiplicities higher than ~10 (no capture events).  MC (n,f)~0.94 &  exp (n,f)~0.90   FTMG (n,f)~0.92 RESULTS: Detection efficiencies:  FTMG (n,f),  TAC (n,f) and  TAC (n,  ) Calculation of  FTMG (n,f)

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” m cr >0m cr >1m cr >2m cr >30<m cr <91<m cr <92<m cr <93<m cr <9 0.1<E sum <E sum <E sum <E sum <E sum < <E sum < <E sum < <E sum < A coincident event in the TAC is found for 97% of the FTMG events (MGASamp>20 channels). This value represents the TAC efficiency for fission events,  TAC (n,f), and is very similar to the efficiency of  TAC (n,  )=0.974(4) for capture events in 197 Au (from GEANT4 Monte Carlo simulations). The efficiency  TAC (n,f) depends on the analysis conditions for the deposited energy and multiplicity values. Efficiency of the TAC for detecting fission events under different conditions in deposited energy and crystal multiplicity. RESULTS: Detection efficiencies:  FTMG (n,f),  TAC (n,f) and  TAC (n,  ) Calculation of  TAC (n,f)

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results”  TAC (n,  )=0.70(3) [E sum >3 MeV and m cr >2] The detection efficiency  TAC (n,  ) can be calculated accurately by means of Monte Carlo simulations when both the experimental set-up and the details of the capture cascades are properly considered. RESULTS: Detection efficiencies:  FTMG (n,f),  TAC (n,f) and  TAC (n,  ) Calculation of  TAC (n,  ) Geant4 simulation of the TAC C. Guerrero et al., NIM-A 671 (2012)

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” RESULTS: Capture and Fission Cross Sections of 235 U

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” RESULTS: Capture and Fission Cross Sections of 235 U C. Guerrero et al. (The n_TOF Collaboration), Simultaneous measurement of neutron- induced capture and fission reactions at CERN, European Physical Journal A 48 (2012) 29

C. CERN EN/STI Student's Coffee (April 17 th 2012) “An n_TOF experiment: the complete process from the data taken to the published results” ① December 2010 / April 2011: Results presented to the n_TOF Collaboration ② June 2011: Results presented to the scientific community in the ANIMMA Int. Conf. ③ October 2011: New proposal submitted (and accepted) to the CERN INTC committee: “Measurements of neutron-induced capture and fission reactions on U-235: cross sections and alpha ratios, photon strength functions and prompt gamma-ray from fission” ⑥ June 2012: New measurement (see ③ ) scheduled at n_TOF ④ December 2011: Paper submitted to the European Physical Journal A ⑤ February 2012: Paper accepted for publication in the Eur. Phys. J. A 48 (2012) 29 The work is not over after finalizing the analysis! ⓪ Summer 2010: Data taken at n_TOF You are welcome to visit nTOF any time!!!