Quasi-monoenergetic Neutron Beams Research Articles

Relations Between Basic Nuclear Data and Single-Event Upsets Phenomena

AbstractThis article approaches single-event upset (SEU) problems from the standpoint of experimental nuclear physics, with a focus on certain neutron experiments and neutron data essential for SEU studies. A review is given of some research programs, both basic and applied, that are strongly motivated by SEU applications. Some specific examples are presented from the The (short for Theodor) Svedberg Laboratory (TSL) in Uppsala, Sweden: First, using the quasi-monoenergetic neutron beam, SEU cross sections (of chips) are measured over the neutron energy range of 20–150 MeV. Data from the same technology generation, in general, can be fitted into a simple curve. Second, the particle origins of SEUs are discussed from the framework of neutron–nucleus spallation reactions.

Measurements of Neutron-Induced Fission Cross Sections of Pb and Bi at Intermediate Energies

Neutron-induced fission cross sections of nalPb and 209Bi have been measured relative to the 238U(n.f) cross section at energies 96 MeV for lead and 133 MeV for bismuth. The measurements were performed at the quasi-monoenergetic neutron beam facility of The Svedberg Laboratory in Uppsala using Frisch-gridded ionization chamber. The results obtained are compared with other experimental data. The present state of the Bi standard recommended by IAEA is discussed.

Cross Section Measurements for Science and Industry at Intermediate Energies

Applications involving intermediate-energy neutrons (> 20 MeV) are rapidly growing. These applications are to be found within nuclear energy research, medicine, reliability of electronics, etc. Cross section data are needed to develop these areas, and thus neutron beam facilities, as well as various spectrometers, are needed. The situation at TSL in Uppsala is used to illustrate the needs and the techniques. It is argued that a dedicated, quasi-monoenergetic neutron beam facility is well motivated in an international perspective.

High-energy neutron dosimetry with superheated drop detectors.

A systematic analysis of the response of dichlorodifluoromethane superheated drop detectors was performed in the 46-133 MeV energy range. Experiments with quasi-monoenergetic neutron beams were performed at the Université Catholique de Leuvain-la-Neuve, Belgium and the Svedberg Laboratory, Sweden, while tests in a broad field were performed at CERN. To determine the response of the detectors to the high-energy beams, the spectra of incident neutrons were folded over functions modelled after the cross sections for the production of heavy ions from the detector elements. The cross sections for fluorine and chlorine were produced in this work by means of the Monte Carlo high-energy transport code HADRON based on the cascade exciton model of nuclear interactions. The new response data permit the interpretation of measurements at high-energy accelerators and on high-altitude commercial flights, where a 30-50% under-response had been consistently recorded with respect to neutron dose equivalent. The introduction of a 1 cm lead shell around the detectors effectively compensates most of the response defect.

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 238U 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.

Measurement of neutron energy spectra from 15 to 150 MeV using stacked liquid scintillators

A multiple liquid scintillator system for measuring the energy spectrum of a neutron beam in the range 15–150 MeV is described. Two or more slabs of NE213 scintillator (13×13×7 cm 3) are stacked behind one-another and only events in which a neutron interacts in the upstream scintillator are analysed. The system is designed to minimise the escape of forward recoil protons from the detecting media. Test measurements and Monte Carlo simulations of the detector response to quasi-monoenergetic neutron beams of energies 62.5 and 97.5 MeV are presented.

Proton recoil telescopes for fluence measurement in neutron beams of 20–200 MeV energy

Two proton recoil telescopes (PRTs) for the precise determination of neutron fluences are described. The first covers the neutron energy range from 20 to 65 MeV and the second is applicable up to 200 MeV neutron energy. We report in detail on the experimental set-up and describe the response simulation using two different Monte Carlo codes. The two telescopes are compared in a 62 MeV quasi-monoenergetic neutron beam. The measurement uncertainties are discussed.

Monoenergetic neutron sources below 100 MeV

Monoenergetic neutron sources are essential for fundamental studies in radiobiology and dosimetry, for measurement of cross sections and kerma coefficients, for calibration of detectors, for activation analysis and for fusion research. Monoenergetic neutrons below energies of 20 MeV are most conveniently produced by reactions between the hydrogen isotopes or between protons and 7Li. By proper choice of reaction type monoenergetic neutrons up to 20 MeV can be produced with negligible secondary background radiation. These reactions cannot provide monoenergetic beams between about 8 and 14 MeV and in this “gap” region inverse reactions are most favourable. The most practical way of producing quasi-monoenergetic neutron beams in the energy range from 20 to 100 MeV is by the bombardment of light elements with protons. Because of the relative simplicity of manufacturing suitable isotopically-pure targets and the large 0° cross section, the 7Li(p,n) 7Be reaction is a convenient source of quasi-monoenergetic neutrons over this range of energies, although the 9Be(p,n) 9B reaction is also used.

Advances in cross section measurements at low energies

A systematic study was made to measure many cross sections for relevant neutron-induced reactions. This study was motivated by the need to better understand cosmic ray interactions with extraterrestrial materials. The major constituents of meteorites and lunar rocks include oxygen, silicon, and aluminum. The primary aim was to measure cross sections for neutron-induced reactions producing long-lived radionuclides (e.g. 14C) and stable isotopes (e.g. Ne isotopes) but the irradiation conditions allowed cross sections for many reactions producing relatively short-lived radionuclides (e.g. 22Na) to be well measured. Monitor foils used in the irradiations included C, Al, and Au. Quasi-monoenergetic neutron beams were produced by bombarding Be targets with 80, 120 and 160 MeV proton beams at iThemba LABS, South Africa. Two identical target stacks were irradiated in beam lines at 0° and 16° to the incident proton beam direction. The yield at an unique neutron energy was obtained by subtracting the yield measured at 16° (after suitable normalization) from that measured at 0°. The cross sections for the following reactions: 27Al(n,x)22,24Na; natC(n,x)7Be; 197Au(n,x)194,196Au; SiO2(n,x)22Na and natSi(n,x)24Na are reported.

Performance of a plasma window for a high pressure differentially pumped deuterium gas target for mono-energetic fast neutron production – Preliminary results

The reactions D(d,n) 3He and T(d,n) 4He are frequently used for production of the mono-energetic or quasi mono-energetic neutron beams but successful applications are often limited by the intensity of the generated neutron beams. The development of a suitable neutron source for such applications as studies of resonance phenomena, fast neutron radiography, selective fast neutron activation, explosives and contraband detection and others, depends on the output ion current of the accelerator and the design of the target system. A practical solution for a high pressure gas target was previously developed and successfully implemented at De Beers Diamond Research Laboratory in Johannesburg (Guzek et al., 1999), but it is limited to applications using low (<20%) duty cycle accelerators. The concept of a plasma window for the separation of a high pressure gas target region and accelerator vacuum, that was originally developed by Hershcovitch (1995) for electron welding applications, may be suitable for operation with continuous wave accelerators at high particle current output. Preliminary test results, which have been performed with various gases (argon, helium and deuterium), indicate that implementation of the plasma window into a gas target system, for the production of intense mono-energetic fast neutron beams will be achievable.

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 Université 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 238U fission ionisation chamber. The results obtained with the different methods are in agreement within the respective uncertainties.

Measurements with the PTB 'C' Bonner Sphere Spectrometer in the PSI Villigen 55 MeV Neutron Field for Spectrometry and Calibration Purposes

The PTB Bonner sphere spectrometer was used for measurements in the 55 MeV quasi-monoenergetic neutron beam at PSI, Villigen. The spectral fluence of the neutron background was determined using the fluence response matrix well specified for energies below 20 MeV. The spectral fluence of the neutron beam was analysed, with the background subtracted, but testing five different high energy extensions of the existing response matrix, and compared with time-of-flight spectral and telescope integral fluence measurements taken as reference. The high energy response shapes which agreed best with the references were used to extend our response matrix.

Spallation neutron spectra measurements Part I: Time-of-flight technique

We present an experimental method based on a time-of-flight technique between the tagged incident particles and a thick liquid NE213 scintillator to measure neutron energy spectra from 3 to 400 MeV at the Saturne synchrotron of Saclay. Efficiency measurements are made using a pulsed neutron source from the Tandem Van de Graaff of Bruyères-le-Châtel at low energies and a quasi-monoenergetic neutron beam at Saturne up to 50 MeV.

Spallation neutron spectra measurements Part II: Proton recoil spectrometer

We present the experimental method conceived to measure high energy neutrons in the range (200 ≤ E ≤ 1600 MeV). The neutrons produce recoil protons in a liquid hydrogen converter. Momentum evaluation and identification of these protons are made by using a magnetic spectrometer equipped with plastic scintillators and three double-plane ( X- Y) wire chambers. The response functions of the apparatus are determined using quasi-monoenergetic neutron beams produced by the break-up of deuterons or 3He on a Be target. The performance of the apparatus is illustrated in the form of a preliminary neutron spectrum.

Total cross sections, elastic scattering observables and direct reconstruction of scattering matrix in np Interactions between 0.8 and 1.1 GeV at SATURNE II

Neutron-proton total cross section differences with the beam and target polarizations orientated either transversally or longitudinally with respect to the beam direction, as well as 11 spin dependent elastic scattering observables measured at SATURNE II as a function of energy and angle are presented. A major part of results was measured using the quasimonoenergetic polarized neutron beam and/or the polarized proton target. A small part of data was obtained using a polarized deuteron beam considered as a beam of quasifree neutrons and protons. The present paper represents a review of measured observables. Several sets of present data are compared with results obtained in other laboratories below 0.8 GeV. Imaginary parts of spin dependent forward amplitudes for np scattering and for the isospin stateI=0 were determined. First direct reconstruction of the np scattering matrix at 0.84 GeV is shown.

Time-Resolved Microdosimetry in a Quasi-Monoenergetic Neutron Beam

Timing characteristics of commercial Rossi-type proportional counters operating at low gas pressures were studied in a pulsed neutron beam of nominal energy 63 MeV. The correlation between electron drift and counter dimensions is demonstrated from TOF measurements performed in normal and helix modes. By identifying each registered pulse height event with its own time-of-flight, it is shown that the timing response is masked by amplitude walk derived in the time pick-off. The inherent response of the counter in helix mode is revealed after accounting for time slewing and compares favourably with that of an NE213 liquid scintillator. Distinct structure associated with the incident energy spectrum is discernible and enables the unambiguous selection of energy deposition events resulting from neutrons of the nominal energy.

Time-Resolved Microdosimetry in a Quasi-Monoenergetic Neutron Beam

Time-Resolved Microdosimetry in a Quasi-Monoenergetic Neutron Beam

The 1H( 7Li, n) 7Be reaction as an intense MeV neutron source

Heavy ion bombardment of hydrogen provides a number of new possibilities for mono-energetic and quasi mono-energetic neutron beam production. Close to the threshold, the strong kinematic focussing for negative Q-value reactions gives rise to intense well-collimated beams of MeV neutrons. An experimental study of 0° neutron production in the 1H( 7Li, n) reaction ( Q = −1.64 MeV) has been carried out from the threshold energy, 13.15 MeV, up to 22 MeV. Measured cross sections are compared to prediction based on known 7Li(p, n) cross sections. At 13.5 MeV the effective cross section reaches 4 b/sr, and the neutrons are confined within a cone of half angle 9°. Cross section predictions for 9Be, 11B and 13C bombardment of hydrogen are also presented.