Recent Developments in Neutron Measurements at the European Commission Joint Research Centre IRMM

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1 Recent Developments in Neutron Measurements at the European Commission Joint Research Centre IRMM CCRI(III) meeting of 04 to 06 March 2015 Stephan Oberstedt European Commission, Joint Research Centre Institute for Reference Materials and Measurements Retieseweg 111, Geel Belgium The European Joint Research Centre operates two complementary neutron sources. One source, GELINA, is dedicated for neutron time-of-flight measurements. A typical operating parameter setting is 100 MeV average electron energy, 10 ns pulse length, 800 Hz repetition rate, 12 A peak and 100 µa average current. With a post-acceleration pulse compression system, the electron pulse width can be reduced to approximately 1 ns (FWHM) while preserving the current, resulting in a peak current of 120 A. The accelerated electrons produce Bremsstrahlung in a uranium target, which in turn, by photonuclear reactions, produces neutrons. Within a 1 ns pulse a peak neutron production of neutrons is achieved (average flux of neutrons/s). The extremely narrow neutron pulse provides the highest neutron energy resolution in the world. The second, 7MV Van-de-Graaff driven neutron source provides quasi mono-energetic neutrons by means of (p,n) and (d,n) reactions on 7 Li, 2 H or 3H in the energy range from 35 kev to 21 MeV. Particle currents up to 50 µa can be produced leading to neutron fluxes of 10 9 neutrons/steradian/s. The neutron source may be operated in DC or fast-pulsing mode. Recently a new slow pulsing system has been installed at the Van de Graaff mono-energetic neutron source for investigating short-lived activation products, spin isomer population and fission shape isomer decay. A slow pulsing system, installed on the 0 degree beamline and called NEPTUNE (NEutron Production with TUNEable pulse structure) permits to flexibly adjust pulse frequency and duty cycle according to the specific requirements of the experiment. The maximum pulse frequency of NEPTUNE is 5 khz. The minimum pulse width is in the order of 2 µs. NEPTUNE was designed for investigating long-lived isomers and is particularly useful to monitor the neutron field in reaction cross-section measurements, where down-scattered or thermalized neutron background is critical. In addition we operate a low-level radioactivity laboratory in the 225 m deep underground facility HADES. We host a unique infrastructure for the preparation and characterization of actinide and stable targets needed for nuclear data measurements. Neutron fluence measurements at IRMM are mainly carried out as a routine support to characterize and model neutron fields for experimental activities in neutron data measurements. Experimental projects are related to investigation of fundamental material properties and initiated by demands from international organizations (like JEF - Joint European File and the OECD) as well as European Commission policies. The work programme includes basic research in nuclear physics, mainly related to neutroninduced reaction in support of nuclear applications and nuclear reaction modeling, and nuclear - 1 -

2 data measurements relevant for Generation-III and -IV reactor design and safety assessment, nuclear waste characterization and handling. Further part of the work programme of the Joint Research Centre IRMM is dealing with training and education in nuclear data measurements and data analysis as well as with giving access to the nuclear community to its neutron facilities. Trans-national Access Activity (TAA) JRC-IRMM has been at the forefront of transnational access activities in Europe. Since 2005, JRC-IRMM is being giving transnational access to the two accelerators within the frame of a direct action (NUDAME). One year later, based on the success of NUDAME, IRMM initiated another indirect action called EFNUDAT (European Facilities for nuclear data measurements) with 11 other partners (integrated infrastructure initiative combining access activities with joint research projects). When EFNUDAT ended JRC-IRMM launched the next access programme ERINDA creating a consortium with 18 partners, which finally evolved now into CHANDA. CHANDA is a running European consortium with 35 partners that coordinates the nuclear data research program and the infrastructures and capabilities in the Member States in a stable structure. In view of access the CHANDA consortium offers supplementary datataking hours to external users at the nuclear facilities of the consortium and supports the users. CHANDA and EUFRAT have close links. As JRC-IRMM could not be the project coordinator, as Commission staff cannot be coordinator of indirect actions, JRC-IRMM always handed over the lead of these projects to someone from our MS partner institutes. However, in all these projects, members from JRC- IRMM had important leading roles (member of Executive Committee, transnational access coordinator, scientific visits coordinator, work package leader ). Activities in The measurement programme was very much determined by the on-going refurbishment activities around the neutron facilities. The refurbishment/reconstruction of the measurement cabins on the flight-path area at the GELINA neutron time-of-flight facility could be carried in two phases for the north and the south side areas, the measurement programme and the TAA activities were slowed down, but were taken up again without further delay. The refurbishment of the Van-de-Graaff building, started in early 2012, caused a total stop of all measurement activities for almost two years. Damage to the accelerator infrastructure during the refurbishment caused an extended down time of the neutron source by another year. The age of the Van-de-Graff accelerator, about 40 years, led to severe start-up problems, leaving the performance of the neutron source way behind expectations. As a consequence of the increasing problems in getting spare parts, e.g. new belts are no longer fabricated, we decided to apply for a new 4 MV tandem accelerator. The accelerator will be delivered in mid 2016 and fully operational in early Despite the perturbations the following measurement campaigns were conducted in the reporting years: - 2 -

3 1. Measurement of the neutron-induced fission cross-section of 240,242 Pu in the incident neutron energy range from 0.5 MeV (0.3 MeV) to 3 MeV: The measurements were performed in response to a high-priority data request from the OECD/NEA (H:37, H:38), which requires a reduction of the point-wise uncertainty from 20% to below 7%. The high-purity targets (uncertainty on the isotope content < 0.001% (σ)) were produced in the Sample-preparation Group of IRMM. The uncertainty on the sample mass was 0.9% (σ). 2. Neutron activation cross-section measurement by spectrum unfolding (NAXSUN): This is a follow up of an activity published in 2007 (for details about the method the reader is referred to NIM A580). The method aims at the fast determination of the energy dependence of (n,n ), (n,2n) and (n,x) reaction cross-sections by irradiating a small number of samples with distorted, overlapping neutron beams with subsequent unfolding of the cross-section shape. The spectrum unfolding is done with either the GRAVEL or the MAXED code for spectrum unfolding. After the first measurement campaign on 113 Ir(n,n ) 113m Ir and 115 Ir(n,n ) 115m Ir published in NIM A we put a focus on the determination of the default curve for the unfolding procedure, as this is the essential ingredient for the successful solution of an underdetermined system of equations. The proposed solution was to symmetrize the system of equations, i.e. calculating the average cross-section at an average neutron energy corresponding to the mean of the distorted neutron beam during irradiation of each of the 8 samples. A linear interpolation between the average cross section values is then used as default function in the spectrum unfolding. The work is published in NIM A739 [13]. We investigated the reactions 185 Re(n,2n) 184 Re, 187 (Re(n,2n) 186 Re and 187 Re(n,α) 184 Re, where the existing discrepancy between different evaluated data files and EXFOR data may, at present, exceed 200%. We performed measurements with the NAXSUN method and determined the method of default function determination. The data analysis is ongoing, but preliminary results are very promising to eventually help benchmarking existing evaluations. 3. Measurement of the neutron-induced fission cross-section of 242 Pu in the energy range between 15 and 19 MeV relative to reaction 238 U(n,f): data analysis is ongoing. In collaboration with the Institut de Physique Nucléaire in Orsay a cinematically focused neutron beam, LICORNE, was installed at the 15MV tandem accelerator in Based on the reaction p( 7 Li,n) 7 Be neutrons with energies from 0.5 to 3.5 MeV are produced into a narrow cone, which allows performing measurements with large arrays of high-resolution gamma-detectors, e.g. ORGAM, MINIBALL, or neutron detectors [25]. In fall 2014 a hydrogen-gas target was successfully commissioned to avoid any isotropic neutron production by fusion-evaporation reactions on carbon and other low-z material. Outlook The installation of the new 4MV tandem accelerator will be accompanied by a complete redesign of the experiment area. We will keep only one beam line with standard - 3 -

4 instrumentation in a modular system. This will reduce the workload on a steadily decreasing number of staff and enable the rapid change of measurement set-ups for the different experiment campaigns. Also the entire neutron monitoring will be reconfigured and modernized. The main focus will be put on trans-national access activity (TAA) in the framework of the EUFRAT initiative at IRMM. An internal panel of experts is being evaluating experiment proposals two times a year. Proposals may be submitted at any time of the year. For details about the application and submission deadlines the reader is referred to

5 List of publications (co-)authored by the European Commission Joint Research Centre IRMM 1) Radiopurity of a CeBr 3 crystal used as scintillation detector, Guillaume Lutter, Mikael Hult, Robert Billnert, Andreas Oberstedt, Stephan Oberstedt, Erica Andreotti, Gerd Marissens, Ulf Rosengård, Faidra Tzika, Nucl. Instr. Meth. A703 (2013) ) New prompt spectral gamma-ray data from the reaction 252 Cf(SF) and its implication on present evaluated nuclear data files, R. Billnert, F.-J. Hambsch, A. Oberstedt, S. Oberstedt, Phys. Rev. C87, (2013) 3) Neutron measurements with lanthanum-bromide scintillation detectors - a first approach, A. Oberstedt, R. Billnert, S. Oberstedt, Nucl. Instr. Meth. A708 (2013) ) Artificial diamonds as radiation-hard detectors for ultra-fast fission-fragment tim- ing S. Oberstedt, R. Borcea, T. Bryś, Th. Gamboni, W. Geerts, F.-J. Hambsch, A. Oberstedt, and M. Vidali, Nucl. Instr. Meth. A714 (2013) ) Improved values for prompt fission γ-ray spectra characteristics from the reaction 235 U(n th, f) A. Oberstedt, T. Belgya, R. Billnert, R. Borcea, T. Bry`s, W. Geerts, A. Göök, F.-J. Hambsch, Z. Kis, T. Martinez, S. Oberstedt, L. Szentmiklosi, K. Takács, and M. Vidali, Phys. Rev. C87, (R) (2013) 6) 234 U(n, f) model description of sub-barrier fission cross-section resonances and calculation of prompt neutron emission data A. Tudora, F.-J. Hambsch, S. Oberstedt, Phys. Procedia 47 (2013) ) Corrections of prompt-neutron emission in fission-fragment experiments A. Al-Adili, F.-J. Hambsch, S. Pomp, S. Oberstedt, Phys. Procedia 47 (2013) ) Measurement of the 240,242 Pu neutron-induced fission cross sections, P. Salvador- Castiñeira, R. Bevilacqua, T. Bry ś, F.-J. Hambsch, S. Oberstedt, C. Pretel, M. Vidali, Phys. Procedia 47 (2013) ) New prompt fission γ-ray spectral data and its implication on present evaluated nuclear data files, A. Oberstedt, T. Belgya, R. Billnert, F.-J. Hambsch, Z. Kis, T. Martinez Perez, S. Oberstedt, L. Szentmiklosi, K. Takács, M. Vidali, Phys. Procedia 47 (2013) ) Prompt fission neutron emission calculations and description of sub-barrier fission cross section resonances for 234 U(n, f) A. Tudora, F.-J. Hambsch, S. Oberstedt, Nucl. Phys. A917 (2013) ) Highly accurate measurements of the spontaneous fission half-life of 240,242 Pu, P. Salvador Castiñiera, T. Bryś, R. Eykens, F.-J. Hambsch, A. Moens, S. Oberstedt, G. Sibbens, D. Vanleeuw, and M. Vidali, Phys. Rev. C88, (2013) 12) Development of a kinematically focused neutron source with the p( 7 Li, n) 7 Be inverse reaction, M.Lebois, J.N. Wilson, P. Halipré, B. Leniau, I. Matea, A. Oberstedt, S. Oberstedt, D.Verney, Nucl. Instr. Meth. A735 (2014) ) Determination of the default curve for the unfolding procedure in the measurement of threshold neutron excitation functions Nikola Jovancevic, Laura Daraban, Stephan Oberstedt, Nucl. Inst. Meth. A739 (2014) ) Physical vapour deposition of metallic lithium D. Vanleeuw, D. Sapundjiev, G. Sibbens, S. Oberstedt and P. Salvador Castiñeira, J. Radioanal. Nucl. Chem. 299 (2014) ) Multi-layer 235 UF 4-6 LiF-Au targets for high-resolution fission fragment measurements G. Sibbens, D. Vanleeuw, R. Eykens, S. Oberstedt, Appl. Rad. Isot. 87 (2014) ) International Key Comparison of Neutron Fluence Measurements in Monoener- getic Neutron Fields CCRI(III)-K11, V. Gressier, A.C. Bonaldi, M.S.Dewey, D.M. Gilliam, H.Harano, A. Masuda, T. Matsumoto, N.Moiseev, J.S. Nico, R.Nolte, S. Oberstedt, N.J. Roberts, S.Ro ẗtger, D.J. Thomas, Metrologia 51 (2014) Tech. Supp. Series

6 17) Fission Fragment Yield, Cross Section and Prompt Neutron and Gamma Emis- sion Data from Actinide Isotopes, F.-J. Hambsch, S. Oberstedt, A. Al-Adili, T. Bryś, R. Billnert, C. Matei, A. Ober- stedt, P. Salvador-Castiñiera, A. Tudora, and M. Vidali, Nucl. Data Sheets 119 (2014) 38 18) Neutron-induced Fission Cross Section of 240,242 Pu up to E n = 3 MeV, P. Salvador- Castiñiera, T. Bryś, F.-J. Hambsch, S. Oberstedt, C. Pretel, and M. Vidali, Nucl. Data Sheets 119 (2014) 55 19) New Prompt Fission γ-ray Data in Response to the OECD/NEA High Priority Request S. Oberstedt, R. Billnert, T. Belgya, R. Borcea, T. Bryś, W. Geerts, A. Göök, F.-J. Hambsch, Z. Kish, T. Martinez Perez, A. Oberstedt, L. Szentmiklosi, and M. Vidali, Nucl. Data Sheets 119 (2014) ) Sensitivity of Measured Fission Yields on Prompt-neutron Corrections, A. Al-Adili, F.-J. Hambsch, S. Pomp, and S. Oberstedt, Nucl. Data Sheets 119 (2014) ) The Neutrons for Science Facility at SPIRAL-2, X. Ledoux, M. Aïche, M. Avrigeanu, V. Avrigeanu, L. Audouin, E. Balanzat,..., J. Novak, S. Oberstedt, A. Oberstedt,..., and C. Varignon, Nucl. Data Sheets 119 (2014) ) High precision prompt γ-ray spectral data from the reaction 241 Pu(n th, f), S. Oberstedt, R. Billnert, T. Belgya, T. Bryś, W. Geerts, C. Guerrero, F.-J. Hambsch, Z. Kis, A. Moens, A. Oberstedt, G. Sibbens, L. Szentmiklosi, D. Vanleeuw, and M. Vidali, Phys. Rev. C90, (2014) 23) Prompt gamma-ray spectral data from 252 Cf, 235 U(n th, f) and 241 Pu(n th, f), R. Billnert, A. Oberstedt, S. Oberstedt, Phys. Procedia 59 (2014) 17 24) Systematics on prompt fission gamma-ray spectra characteristics, R. Billnert, A. Oberstedt, S. Oberstedt, Phys. Procedia 59 (2014) 24 25) The LICORNE neutron source and measurements of prompt γ-rays emitted in fission, J.N. Wilson, M. Lebois, P. Halipré, S. Oberstedt, A. Oberstedt, Phys. Procedia 59 (2014) 31 26) Prompt γ-rays from the fast neutron induced fission on 235,238 U and 232 Th, M. Lebois, J.N. Wilson, P. Halipré, B. Leniau, I. Matea, A. Oberstedt, S. Oberstedt, D. Verney, Phys. Procedia 59 (2014) 37 27) Photofission fragment characteristics of 234,238 U and 232 Th in the barrier region A. Göök, M. Freudenberger, J. Enders, C. Eckardt, A. Oberstedt, S. Oberstedt, Phys. Procedia 59 (2014) 42 28) Correlation between the prompt neutron multiplicity and prompt gamma-ray energy in the frame of the point-by-point model, A. Tudora, F.-J. Hambsch, S. Oberstedt, G. Guibega, I. Visan, Phys. Procedia 59 (2014) 95 29) A multi-detector NaI(Tl) gamma-ray spectrometry system for investigation of neutron induced capture and fission reactions, I. Ruskov, Yu.N. Kopach, V. Skoy, F.-J. Hambsch, S. Oberstedt, Phys. Procedia 59 (2014) ) Shape isomer studies with resonance neutron capture, A. Dragić, G. Nyman, A. Oberstedt, S. Oberstedt, Phys. Procedia 59 (2014) ) Analysis of threshold neutron excitation function measurements using wide energy neutron beams, L. Daraban, N. Jovančević, S. Oberstedt, F.-J. Hambsch, Phys. Procedia 59 (2014) ) Measurement of the neutron spectrum using the activation method, N. Jovančević, L. Daraban, S. Oberstedt, F.-J. Hambsch, M. Hult, G. Lutter, G. Marissens, Phys. Procedia 59 (2014) 154