R. Nolte

Characterization of the ANITA Neutron Source for Accelerated SEE Testing at the Svedberg Laboratory

ANITA ( Atmospheric-like Neutrons from thIck TArget), a new neutron facility for accelerated testing of components and systems for single event effects, has been put into operation at The Svedberg Laboratory in Uppsala, Sweden. Results of beam characterization measurements are reported.

Quasi-monoenergetic neutron beams with energies from 25 to 70 MeV

Quasi-monoenergetic neutron beams in the energy range from about 25 to 70 MeV have been produced and accurately characterised at the accelerator facility of the Universite Catholique de Louvain (UCL), Belgium. The neutron fluence was determined with a proton recoil telescope and a liquid scintillation detector (NE213). The spectral fluence was measured employing the time-of-flight method with the NE213 detector and a U-238 fission ionisation chamber. The results obtained with the different methods are in agreement within the respective uncertainties

High-energy neutron reference fields for the calibration of detectors used in neutron spectrometry

Quasi-monoenergetic reference neutron beams in the energy range between 20 and 100 MeV have been produced and characterized with a proton recoil telescope, a scintillation spectrometer, a U-238 fission chamber and a Bonner sphere spectrometer. The beams are well suited for the calibration of detectors used in neutron spectrometry. A new method is described which reduces the correction for the contribution from low-energy neutrons present in the beams

Characterization of liquid scintillation detectors

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.

Results from the commissioning of the n_TOF spallation neutron source at CERN

Abstract The new neutron time-of-flight facility (n_TOF) has been built at CERN and is now operational. The facility is intended for the measurement of neutron induced cross-sections of relevance to Accelerator Driven Systems (ADS) and to fundamental physics. Neutrons are produced by spallation of the 20 GeV /c proton beam, delivered by the Proton Synchrotron (PS), on a massive target of pure lead. A measuring station is placed at ≈185 m from the neutron producing target, allowing high-resolution measurements. The facility was successfully commissioned with two campaigns of measurements, in November 2000 and April 2001. The main interest was concentrated in the physical parameters of the installation (neutron fluence and resolution function), along with the target behavior and various safety-related aspects. These measurements confirmed the expectations from Monte Carlo simulations of the facility, thus allowing to initiate the foreseen physics program.

Cross sections for neutron-induced fission of U-235, U-238, Bi-209, and Pb-nat in the energy range from 33 to 200 MeV measured relative to n-p scattering

Abstract The cross sections for neutron-induced fission of 235U, 238U, 209Bi, and natPb in the intermediate-energy region were measured using parallel plate fission ionization chambers. The experiments were carried out relative to the differential n-p scattering cross section using quasi-monoenergetic neutron beams with peak energies ranging from 33 to 200 MeV. The experimental cross sections were compared to International Nuclear Data Committee reference fission cross sections, to results of nuclear model calculations, and to cross sections calculated with the nuclear models implemented in the radiation transport code MCNPX. The experimental results for 235U and 209Bi are consistent with the available reference cross sections and theoretical data while the 238U(n,f) cross section exceeds the reference cross section systematically by ˜7% between 30 and 60 MeV. The experimental results for natPb agree with a parameterization of other experimental data for natPb(n,f).

Quasi-monoenergetic high-energy neutron standards above 20???MeV

This paper provides an overview of high-energy quasi-monoenergetic neutron sources and facilities above 20 MeV around the world. Various technical matters are discussed which are required in characterizing the neutron fields by spectrometry, fluence and beam profile measurements. Important topics regarding the calibration of neutron detectors are also introduced with emphasis on beam monitoring, tail correction, background subtraction and fluence-to-dose conversion. Efforts to standardize the high-energy neutron fluence in Japan and by the German national metrology institute in collaboration with Belgian and South African institutions are also presented.

A Model for Photon Detection and Dosimetry with Superheated Emulsions

A model is presented for the analysis and prediction of the photon response of detectors based on superheated emulsions of light halocarbons in tissue equivalent gels. It is shown that on the basis of a nondimensional thermodynamic quantity, called reduced superheat, it is possible to identify the degree of superheat, or the operating temperature, corresponding to the photon sensitization of the emulsions. Moreover, on the basis of the mass energy absorption coefficients, it is possible to determine the energy dependence of the photon response. The vaporization energy necessary for bubble nucleation is estimated by means of the thermal spike theory developed for bubble chambers. The energy deposition requirements are consistent with the energy transferred by secondary electrons at the end of their range in the halocarbons. These findings provide design criteria for photon detectors based on superheated emulsions. It is shown that light halocarbons of low effective atomic numbers present the best dosimetric properties. In particular, by manufacturing superheated emulsions with octafluoropropane, or halocarbon R-218, photon sensitivity is achieved at room temperature along with a fairly constant air-kerma response.

HINDAS A European Nuclear Data Program for Accelerator-Driven Systems

In the HINDAS program, nuclear data in the 20-2000 MeV range are evaluated by means of a combination of nuclear tmodels and well-selected intermediate- and high-energy experiments. A panoply of European accelerators is utilized to provide complete sets of experimental data for iron, lead and uranium over a large energy range. Nuclear model codes are being improved and validated against these new experimental data. This should result in enhanced ENDF-formatted data libraries up to 200 MeV, and cross sections for high-energy transport codes above 200 MeV. The impact of the new data libraries and high-energy models will be directly tested on some important parameters of an accelerator-driven system (ADS). Here, we report the recent progress of the various experimental and theoretical activities in HINDAS.

International Key Comparison of Neutron Fluence Measurements in Monoenergetic Neutron Fields - CCRI(III)-K11

To ensure the validity of their national standards, National Metrology Institutes, NMIs, participate regularly in international comparisons. In the area of neutron metrology, Section III of the Consultative Committee for Ionizing Radiation is in charge of the organization of these comparisons. From September 2011 to October 2012, the eleventh key comparison, named CCRI(III)-K11, took place at the AMANDE facility of the LNE-IRSN, in France. Participants from nine NMIs came with their own primary reference instruments, or instruments traceable to primary standards, with the aim of determining the neutron fluence, at 1 m distance from the target in vacuum, per monitor count at four monoenergetic neutron fields: 27 keV, 565 keV, 2.5 MeV and 17 MeV. The key comparison reference values (KCRV) were evaluated as the weighted mean values of the results provided by seven participants. The uncertainties of each KCRV are between 0.9 % and 1.7 %. The degree of equivalence (DoE), defined as the deviation of the result reported by the laboratories for each energy from the corresponding KCRV, and the associated expanded uncertainty are also reported and discussed.