A track detector technique for determining ion source emission profiles

Solid state nuclear track detectors have been used to directly measure for an ion source the beam emission cross sections along the ion beam trajectory. Results are demonstrated for an ion source of the surface ionization type using solid source materials to obtain ¹⁴⁷Sm or ⁶Li isotopes. Cellulose nitrate LR 115 was used as the detector to register the alpha tracks from the radioactive decay of the implanted ¹⁴⁷Sm and from the ⁶Li (n, α) reaction induced by thermal neutrons in a nuclear reactor.     

Optimization of the steady neutron source technique for absorption cross section measurement by using an 124Sb–Be neutron source

An improved experimental approach has been developed to determine thermal neutron absorption cross sections. It uses an ¹²⁴Sb–Be neutron source which has an average neutron energy of only about 12 keV. It can be moderated in either a water tank or a paraffin filled box and can be used for aqueous or powder samples. This new design is first optimized by MCNP simulation and then benchmarked and calibrated with experiments to verify the simulations and realize the predicted improved measurement sensitivity and reproducibility. The ¹²⁴Sb–Be source device is from 1.35 to 1.71 times more sensitive than the previous method based on the use of a ²⁵²Cf source.     

Negative ion test facility ELISE—Status and first results

The new test facility ELISE (Extraction from a Large Ion Source Experiment) has been designed and installed since November 2009 at IPP Garching to support the development of the radio frequency driven negative ion source for the Neutral Beam System on ITER. The test facility is now completely assembled; all auxiliary systems have been commissioned and are operational. First plasma and beam operation is starting in October 2012.The source is designed to deliver an ion beam of 20 A of D^? ions, operating at 0.3 Pa source pressure at an electron to ion current ratio below 1. Beam extraction is limited to 60 kV for 10 s every 3 minutes, while plasma operation of the source can be performed continuously for 1 hour. The ion source and extraction system have the same width as the ITER source, but only half the height, i.e. 1 × 1 m² source area with an extraction area of 0.1 m². The aperture pattern of the extraction system and the multi driver source concept stay as close as possible to the ITER design. Easy access to the source for diagnostic tools or modifications allows to analyze and optimize the source performance. Among other possibilities many different magnetic filter field configurations inside the source can be realized to enhance the negative ion extraction and to reduce the co-extraction of electrons. Beam power and profiles are measured by calorimetry and thermography on an inertially cooled target as well as by beam emission spectroscopy. Cs evaporation into the source is done via two dispenser ovens.     

Absolute measurements of U and Pu fission cross-sections with photoneutron sources

the fission cross-sections of ²³⁵U and ²³⁹Pu for Na---Be, La---Be, Na---D and Ga---D photoneutrons have been measured absolutely. The neutron source strength was measured using a manganese bath to compare the photoneutron yield from the sources with the standard source NBS-II. Fission counts were accumulated with the source positioned symmetrically between two identical fission foils in an experiment package suspended in a low-albedo laboratory. Fission fragments passing through limited solid angle apertures were recorded on polyester track-etch films. The masses of the foil deposits were determined by microbalance weighings and confirmed by thermal neutron fission and alpha counting. After making a correction for the calculated energy distribution of the source neutrons, values of 1.471 ± 0.029, 1.274 ± 0.026, 1.162 ± 0.025 and 1.195 ± 0.026 barns were obtained for the ²³⁵U fission cross-section at the source median energies of 140, 265, 770 and 964 keV, respectively. Corresponding values of 1.469 ± 0.045, 1.515 ± 0.038, 1.670 ± 0.039 and 1.643 ± 0.038 barns were determined for ²³⁹Pu.     

Importance of the MUSE experiments for emerging ADS concepts from the nuclear data viewpoint

The current investigation, conducted in the general framework of the MUSE program (“MUltiplication avec une Source Externe”), considers the representativity of a specific configuration of its fourth phase (M4SC2), which is driven by an external D(d,n)He³ or T(d,n)He⁴ neutron source, with respect to current concepts of eXperimental Accelerator Driven Systems (XADSs) with gas (He), Na and Pb/Bi coolants. The study has been carried out from the nuclear data viewpoint, with the external source being accounted for in an appropriate manner. In this context, data sensitivity/uncertainty analyses based on first-order perturbation theory calculations have been performed using the deterministic code ERANOS (Version 2.0) in conjunction with its adjusted nuclear data library ERALIB-1.It is found that the M4SC2 configuration, independent of the external source, is quite representative of the different XADSs for actinide capture reactions at the centre of the fuel zone, relative to ²³⁹Pu fission at the same location. For the case of a threshold fission reaction, such as that in ²³⁸U, the sensitivity to the external source is significantly higher. With respect to the corresponding spectral index, M4SC2 with the D(d,n)He³ source remains quite representative of the He- and Na-cooled XADSs. For the system with Pb/Bi coolant, on the other hand, effects of uncertainties associated with the data for these two nuclides and their low content in the MUSE configuration result in significantly lower associated representativity factors. A better overall representativity of the Pb/Bi-cooled XADS is expected to be achieved by the new MUSE_Na/Pb configuration.     

An intense channeling radiation source

A non-conventional X-ray source which is based on the production of electron channeling radiation in a diamond crystal has been installed at the radiation source ELBE. The brilliant electron beam with an average current of up to 200 μA allows to reach photon rates of quasi-monochromatic channeling radiation between 10¹⁰ s⁻¹ and 10¹¹ s⁻¹ per 10% bandwidth. The photon energy can be tuned by variation of the beam energy. On-line X-ray monitoring was realised at high beam currents using a Compton spectrometer. Monochromisation of channeling radiation and bremsstrahlung background reduction has been investigated applying X-ray diffraction at a highly ordered pyrolytic graphite crystal.     

Nuclear mubeams: Realization and use as scientific tool

A nuclear mubeam is an ion beam focussed down to a spot of only a few μm in diameter. If such a beam is surrounded by equipment for elemental analysis we have the nuclear muprobe (NMP) suited for elemental analysis with μm spatial resolution and detection limits of a few ppm. The beam focus is achieved by collimation to some 10 μm and further demagnification with the help of an appropriate lens system. The need to fabricate the mechanical parts to a very high precision and to avoid slit scattering at the collimators will be demonstrated and a guide to the optimal design will be given. The different ways of realization are illustrated. Applications in different fields of science are given and the availability of NMPs throughout the world illustrated.     

Highly sensitive AMS measurements of 53Mn

Our AMS system, with the gas-filled detector system GAMS, has been optimized for measurements with ⁵³Mn. A high sensitivity has been achieved. A newly installed cesium sputter ion source yields an improved emittance, and thus a higher mass resolution. By the extraction of the manganese molecule MnF^? instead of MnO^? we can suppress the isobaric chromium background in the ion source by more than a factor of three. The GAMS system achieves an isobaric suppression factor of about 3 × 10⁸. Measurements on blank samples yielded upper limits for the ⁵³Mn/⁵⁵Mn ratios of 7 × 10^?15.     

An Adaptive Control Concept of Reactor Power Distribution

A new method has been developed for obtaining the β-ray self-absorption correction factor of a Au-foil with uniformly distributed A-ray source. The method is essentially to average the β-ray self-absorption correction factor of Au-foil packs composed of non-activated Au-layers and an activated Au-layer placed at the various depths.

The β-ray self-absorption correction factors of the Au-foil with thicknesses ranging 0.15–80mg/cm² were measured within an experimental error of less than 0.5%. Between the thicknesses of 0 and 10mg/cm², a sharp decrease was observed. In the range of thickness below 45mg/cm² the present experimental results diverge from the currently used formula (f _a = (l–e ^μt)/μt), but are in good agreement with a semi-empirical expression (f _a = (l/2–E ₃(^μt)/μt), formulated on the assumption of isotropic penetration of β-rays.

The escape probability of β-rays emitted from a certain depth of Au-foil was also measured as a function of source depth. By using this escape probability it is possible to obtain the β-ray self-absorption correction factors for any concave source distribution through the thickness of a foil, a situation commonly encountered especially in the foil irradiated with epi-thermal neutrons.     

Present and future trends for neutron source calibrations at the National Institute of Standards and Technology

The neutron source calibration facility operated by the United States National Institute of Standards and Technology (NIST) is a world-class calibration laboratory providing neutron source calibration services for radioisotopic sources with neutron emission rates ranging from 5 × 10⁵ to 1 × 10¹⁰ s⁻¹. Calibrations are performed using the manganous sulfate bath technique with a relative expanded uncertainty of approximately 3.5% (2σ). Recently, an improvement to the calibration procedure has been implemented whereby sources are regularly cross-calibrated against the national standard neutron source as well as one of three (international) standard sources formerly maintained by the Bureau International des Poids et Mesures. This feature helps ensure that the fidelity of NIST neutron source calibrations is maintained at the highest level. In addition to the Institute’s external customers, NIST’s neutron source calibration facility also provides important contributions to other neutron irradiation and calibration services provided by the Institute, as well as to NIST’s intramural research programs in neutron metrology, nuclear reactor pressure-vessel dosimetry, and fundamental neutron physics.     

Source efficiency as function of fuel and coolant in accelerator-driven systems

We have studied the efficiency of spallation neutron sources for different combinations of coolant and fuel in 80 MW_th, sub-critical, cores. It has been found that the proton source efficiency, ψ^∗, is reduced by 10% when switching coolant from helium to lead–bismuth eutectic. Substituting MOX fuel with an americium based fuel, results in another 10% reduction of ψ^∗. The relatively high source efficiencies found for prototype accelerator-driven systems, using standard MOX fuel and helium coolant, may thus be difficult to achieve in future systems dedicated to the transmutation of higher actinides. Our results are in agreement with previous investigations of the dependence of the source efficiency on the selection of coolant.     

Characteristics of Neutron Guide Tubes in Upgraded JRR-3

Abstract

The JRR-3 has been upgraded to be a new high performance research reactor JRR-3M with neutron guide tubes on a large scale and a cold neutron source. The neutron fluxes and spectra were measured at the end of the two thermal and three cold neutron guide tubes. The gain of the cold neutron source is also found from these spectra. The neutron fluxes of thermal neutron guide tubes with characteristic wavelength 2 Å are 1.2x10⁸ n/cm².s at a reactor power of 20 MW. The neutron fluxes of cold guide tubes are 2.0x 10⁸ n/cm².s with characteristic wavelength 4 Å and 1.4x10⁸ n/cm².s with 6 A when the cold neutron source is operated. The neutron spectra measured by the time-of-flight method agree well with their designed ones. The gains of the cold neutron source are 8 for 4 Å and 20 for 6 Å at a reactor power of 20 MW.     

Prospects for the development of neutron-activation analytical facilities based on powerful antimony-beryllium sources

Conclusions When using antimony-beryllium neutron sources for activation analysis of the composition of a substance, the problem of the analytical monitoring of many elements can be solved with a limit of determination of 10^–3–10^–5%. Based on the data obtained by the authors concerning the spatial distribution of the neutrons from a¹²⁴Sb–Be-source in different moderators, a beryllium-graphite assembly with a powerful¹²⁴Sb source has been designed, manufactured, and introduced into operation, for neutron-activation analysis.As applicable to the¹²⁴Sb–Be-graphite assembly, a procedure has been developed for the neutron-activation determination of gold, with a limit of determination of 2·10^–5%. The possible limits of the neutron-activation determination of certain other elements have been estimated. In order to ensure operation of the facility with recharging of the source once in 6 months, it is advisable to carry out the preparation of a source in a neutron flux with a density of 3·10^–13 neutrons/ (cm²·sec) during 30–50 days (for a mass of metallic antimony of 500 g) with subsequent two-week cooling in order to reduce the¹²²Sb activity. Initial data have been obtained for the design of a transportation container for powerful¹²⁴Sb sources.Translated from Atomnaya Énergiya, Vol. 53, No. 4, pp. 255–260, October, 1982.     

Source term evaluation for the upgraded LEU Pakistan Research Reactor-1 under severe accidents

Evaluation of source term has been carried out for the upgraded LEU PARR-I system taken as a typical material test reactor (MTR). The modeling and simulation of release of radioactivity has been carried out by developing a Matlab based computer program which uses the ORIGEN2 code for core inventory calculations. For post 180 full-power days continuous operation, various accident scenarios, with instantaneous release of radioactivity to containment, have been considered including the startup, fuel loading, and loss-of-coolant accidents. For noble gases, iodine and for aerosols, the release rate studies have been carried out for the normal, emergency and for the isolation states of containment. The values of source term as well as that of containment retention factor show rapid increase followed by an approach towards saturation values as the exhaust rate values are increased. The isotope-dependency of the containment retention factor has been studied and the results indicate strong sensitivity for ⁸⁵Kr, ¹³⁷Xe, ¹³⁸Xe and ¹³⁸Cs towards exhaust rate values.     

Electron emission from carbon induced by the ions C, O, CO and

The secondary electron yield from carbon induced by the ions C⁺, O⁺, CO⁺ and has been measured as a function of ion energy in the range of 2 to 20 keV. It has been observed that electron yield from carbon increases with projectile energy. By comparing electron yields induced by equally fast atomic and molecular projectiles, a molecular effect as a yield reduction has been observed. The measured molecular effect was stronger than the predictions of sweeping-out-electron model.     

Production of 16N and obtaining of its gamma spectrum in order to calibrate detectors or determination of fluorine in geological specimens

In this paper, we show a procedure for producing ¹⁶N and a method to obtain its gamma spectrum with a NaI(Tl) detector. We also demonstrate the interest of this radioactive element for the purpose of NaI(Tl) detector calibration and for the determination of fluorine in geological specimens using an Alpha Beryllium neutron source.This work consists of a theoretical study which analyzes the characteristics of ¹⁶N and nuclear reactions that originate from an Americium Beryllium source of 1Ci activity. We justify our choice of reaction ¹⁹F(n,α)¹⁶N and the use of fluorspar as a source of fluorine.The mathematical procedure followed to obtain the gamma rays spectrum produced by ¹⁶N in a NaI(Tl) detector is shown.     

On the Cf primary and secondary gamma rays and epithermal neutron flux for BNCT

Monte Carlo simulation has been used to calculate the different components of neutrons and secondary gamma rays originated by ²⁵²Cf fission and also the primary gamma rays emitted directly by the ²⁵²Cf source at the exit face of a compact system designed for the BNCT. The system consists of a ²⁵²Cf source and a moderator/reflector/filter assembly. To study the material properties and configuration possibilities, the MCNP code has been used. The moderator/reflector/filter arrangement is optimised to moderate neutrons to epithermal energy and, as far as possible, to get rid of fast and thermal neutrons and photons from the therapeutic beam. To reduce the total gamma contamination and to have a sufficiently high epithermal neutron flux we have used different photon filters of different thickness. Our analysis showed that the use of an appropriate filter leads to a gamma ray flux reduction without affecting the epithermal neutron beam quality at the exit face of the system.     

An expanded radiocarbon age calibration procedure to correct for the marine reservoir effect in mixed marine and terrestrial samples

Recently, the importance of statistical and probabilistic analysis to derive accurate ¹⁴C data has been recognized. This paper discusses a ¹⁴C calibration procedure to correct marine reservoir effect using the marine source contribution estimated as a probability distribution. In addition, we also developed the marine source estimation with δ¹³C and δ¹⁵N for the ¹⁴C calibration in order to cover a complex mixture of terrestrial and marine carbon such as a human. In our calibration procedure, the ¹⁴C date is weighted with the probability distribution of marine source contribution and the calibrated date depended on the marine ¹⁴C intake can be evaluated. The age range calibrated by our procedure can be also reduced more than by conventional calibration methods. We illustrated the character of our calibration procedure by the example of human bones found from the archaeological shell mounds in Japan.     

The spatial distribution in water of multiply scattered gamma-quanta from unidirectional Au198, Co60, and Na24 sources

We have measured the spatial distribution of the dose of -radiation from collimated Au¹⁹⁸, Co⁶⁰, and Na²⁴ sources, where the radiation had been multiply scattered in an infinite aqueous medium. To show the use of a unidirectional source based on the obtained data we have plotted the attenuation in water of -rays with energies of 2.76, 2.07, 1.25, and 0.411 Mev for a point isotropic source and with an energy of 1.25 Mev for a plane unidirectional source. The results are in good agreement with the data of [1] except for -rays with an energy of 0.411 Mev. We have also given the empirical dependences of the angular distribution of the dose on the initial energies of the -rays and the distance between the source and the detector.In conclusion the authors would like to thank S. G. Tsypin for discussing the method of the measurements and their results.