F. Pino

The light output and the detection efficiency of the liquid scintillator EJ-309

The light output response and the neutron and gamma-ray detection efficiency are determined for liquid scintillator EJ-309. The light output function is compared to those of previous studies. Experimental efficiency results are compared to predictions from GEANT4, MCNPX and PENELOPE Monte Carlo simulations. The differences associated with the use of different light output functions are discussed.

Detecting fast and thermal neutrons with a boron loaded liquid scintillator, EJ-339A.

A commercial boron-loaded liquid scintillator EJ-339 A was studied, using a (252)Cf source with/without polyethylene moderator, to examine the possibility of discriminating slow-neutron induced events in (10)B from fast-neutron events, resulting from proton recoils, and gamma-ray events. Despite the strong light quenching associated with neutron induced events in (10)B, correct classification of these events is shown to be possible with the aid of digital signal processing.

A new facility for non-destructive assay using a 252Cf source.

A new laboratory facility for non-destructive analysis (NDA) using a time-tagged (252)Cf source is presented. The system is designed to analyze samples having maximum size of about 20 × 25 cm(2), the material recognition being obtained by measuring simultaneously total and energy dependent transmission of neutrons and gamma rays. The equipment technical characteristics and performances of the NDA system are presented, exploring also limits due to the sample thickness. Some recent applications in the field of cultural heritage are presented.

Study of the thermal neutron detector ZnS(Ag)/LiF response using digital pulse processing

The neutron and gamma responses of a commercial 6Li loaded ZnS(Ag) detector (EJ-420) have been studied using a moderated 252Cf source and a set of pure gamma ray sources (137Cs and 241Am). Digital pulse processing was used to implement the pulse shape discrimination technique in order to well-separate neutrons from gamma-induced events. It was found that in case of a mixed neutron/gamma radiation field (252Cf) pulse-height discrimination technique works quite good for the measurement of the neutron field, but if one desires to reach a gamma-to-neutron sensitivity ratio lower than 0.7% pulse shape discrimination technique must be implemented. The decay time of the scintillation components of ZnS(Ag)/6LiF were determined by following the so called ``peeling off method. The results were compared with some reported values. In order to better understand the shape of the neutron-induced pulses produced by the EJ-420 detector, a measurement with an EJ-440 detector of an alpha source (210Po) was performed. The response of both detectors must be very similar because these are based in ZnS(Ag) scintillator. It seems that for neutron detection with the EJ-420, the slow component of the scintillation yield produced by the tritium is higher than the one produced by the alpha particle. Finally, the neutron efficiency and some experimental features of the EJ-420 detector were determined and reproduced respectively by Monte Carlo simulations (GEANT4 9.6).

k0-INAA of Venezuelan ceramics and complete statistical analysis to establish their provenance

A group of 46 archaeological figurines samples (ad 1300 and 1500) from Venezuelan mainland and northern island were analyzed by k0-instrumental neutron activation analysis (k0-INAA) to obtain their elemental content and give a step ahead to establish the provenance of the island figurines. In total 37 elemental concentrations were measured with uncertainties between 3 and 20xa0%. To make the study of provenance, a complete statistical analysis was achieved; Fisher linear discriminant, principal component analysis, hierarchical clustering and the Hotelling T2 test were used to this end. Furthermore, not only the 46 samples analyzed in this work by k0-INAA were used, but also 40 samples analyzed by PGNAA and reported by Sajo-Bohus et al. (JRNC 265(2):247–256, 2005) were included in the statistical analysis. It was done in order to increase the size of the data set, and then to obtain from the statistical techniques more reliable results. It was found that a very good differentiation exits between the figurines from the island and from the mainland supporting the idea that the raw materials of the figurines come from different places.

Quality Control of Pavements and Tarmacs Using (137Cs) γ Compton Scattering

The γ Compton scattering over a volume of concrete has been studied in order to design an instrument for density measurements. It will be used for the quality control in road construction, where large surfaces must be monitored. The experimental results and Monte Carlo simulations of the γ Compton scattering over homogeneous and inhomogeneous volumes of concrete are shown. MC simulations have been useful to optimize the values of several parameters to improve the experimental set up and to estimate the extension of the explored volume.

Search of Explosives in Vehicles by Using Tagged Neutrons

The search for explosives hidden in vehicles is one of the tasks of counterterrorism application. This task requires the detection of explosive material in car or truck bombs as well as illicit transport of such items. Liquid explosives, especially home made (HME) ones, have been used in terrorist attacks and are thus of great importance in this field. The detection of HME liquid explosives in trucks by using a neutron-in/gamma-out system as the EURITRACK portal is discussed. Moreover the possibility of material recognition by transmission measurements with a tagged 252Cf source is also presented. The latter system might find application in car inspections or in small parcel scanning systems.

Target Design for a Thorium Accelerator-Driven Molten Salt Reactor (AD-MSR)

Th–FLiBe fluid target design is proposed for a 1 GeV, 1 mA proton accelerator-driven molten salt reactor (AD-MSR). Simulations are carried out by FLUKA. The core of the system is an assembly with EURISOL target geometry. Results are presented for the geometrical distribution of neutron fluencies, the energy produced and fission density distribution, as well as neutron spectra in fuel, graphite moderator, reflector and concrete shielding. It is forecast to produce 10 MWth power, neutron fluence of 1022 n/cm2/GeV/mA produced by the spallation source and induced fission in FLiBe fuel.

Th and U fuel photofission study by NTD for AD-MSR subcritical assembly

During the last decade a considerable effort has been devoted for developing energy generating systems based on advanced nuclear technology within the design concepts of GEN-IV. Thorium base fuel systems such as accelerator driven nuclear reactors are one of the often mentioned attractive and affordable options. Several radiotherapy linear accelerators are on the market and due to their reliability, they could be employed as drivers for subcritical liquid fuel assemblies. Bremsstrahlung photons with energies above 5.5MeV, induce (γ,n) and (e,e’n) reactions in the W-target. Resulting gamma radiation and photo or fission neutrons may be absorbed in target materials such as thorium and uranium isotopes to induce sustained fission or nuclear transmutation in waste radioactive materials. Relevant photo driven and photo-fission reaction cross sections are important for actinides 232Th, 238U and 237Np in the radiotherapy machines energy range of 10-20 MV. In this study we employ passive nuclear track detectors (...

Determination of Multiple Compton Scattering Fractions in Gamma Densitometry by Monte Carlo Simulation

A method, based on Monte Carlo simulations, is given with the purpose of studying physical aspects on a Compton scattering densitometer. The energy spectrum of the scattered photons was determined by PENELOPE 2008 code to validate the physical model. A method to determine the single and multiple Compton scattering fractions is included to highlight physical aspects useful for response interpretation in cases where the main aim is to find zones with reduced continuity. By Monte Carlo simulations, we reproduced and improved empirical results related to the bulk density determination. Results related to the size of the volume explored in a semi-infinite concrete volume are given. Important advancement in densitometry applications were achieved in identifying nonhomogeneous zones by analyzing the scattered photons spectrum shape.