Centro Nacional De Aceleradores Research Articles

Towards a Timepix3 Radiation Monitor for the Accelerator Mixed Radiation Field: Characterisation with Protons and Alphas from 0.6 MeV to 5.6 MeV

A Timepix3 detector with a 300 μm silicon sensor has been studied as a novel radiation monitor for the mixed radiation field at the Large Hadron Collider at CERN. This work describes a test campaign carried out at Centro Nacional de Aceleradores with quasi-mono energetic protons (alphas) from 0.6 (1) to 5 (5.6) MeV, where orthogonal irradiations are used to obtain an energy calibration, and a low-energy angular scan to estimate the front dead layer thickness of the sensor. The detector is operated in hole collection mode and at a partial bias of 250 μm at 50 V, which increases the charge sharing among pixels to mitigate the signal saturation at high energy depositions. The data, supported by FLUKA Monte Carlo simulations of energy losses in the sensor, show that the Timepix3 monitor operates in a linear regime up to energy depositions of around 600 keV per pixel and 2 MeV per cluster. As a result, the detector has been found to be suitable for measuring charged particle fluxes in the LHC mixed radiation field within the linear calibration regime, with the partial exception of inelastic nuclear reaction hits (mostly from neutrons).

Continuous and pulsed fast neutron beams at the CNA HiSPANoS facility

The characteristics of the fast neutron beams produced in the HiSPANoS facility at Centro Nacional de Aceleradores (CNA) are presented. The neutrons are generated by deuteron beams from a 3 MV tandem accelerator in either continuous (5 μA) or pulsed (2 ns width, 500 kHz and 4% duty cycle) mode. In this work, the pulsed mode was used in a time-of-flight characterization of the produced neutron beams in terms of yield, flux, energy resolution, and background. The results were then validated through their comparison with previously published data.Quasi-monoenergetic neutron beams between 2 and 6 MeV are produced by means of the 2H(d,n)3He reaction, featuring a neutron yield of 106 n/sr/μC at the target, with an energy resolution of about 7% at 150 cm. Neutron beams with broad energy distributions are produced by deuteron irradiation of thick beryllium and lithium targets, resulting in maximum neutron energies of 10 and 20 MeV, respectively. In this case, the neutron yields are significantly higher, reaching 1010 n/sr/μC.On the basis of these results, we consider that the HiSPANoS facility is now fully operational for the usage of fast neutrons by internal and external users of CNA.

Performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores for the analysis of 233U at environmental levels

233U (T1/2 = 0.159 My) has aroused much interest in the last few years because of the potential of 233U/236U to inform about anthropogenic U sources. The reported 233U/238U atom ratios in general environmental samples are in the 10−12–10−6 range. We demonstrate that 233U/238U abundance sensitivities at the 5 × 10−11 level can be achieved at the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain). Unresolved 234U, 235U and 232Th molecular fragments are identified as the main233U background contributors and procedures to subtract them are proposed. 233U/238U and 236U/238U atom ratios were analysed in the IAEA reference materials coded Soil-6, 300, 385, 410, and 412 at the CNA and at the 600 kV ETH AMS system for intercomparison. 233U/238U atom ratios for samples 412 and 385 were only reported by the ETH.

Characterization of Castellani nineteenth-century gold jewellery by in situ micro-XRF spectroscopy

The material characterization of nineteenth-century artifacts is of great interest, due both to the breakthrough technological advances and to the unprecedented spread of forgeries of antiquities which took place in that period. However, this type of artifacts has been largely overlooked in the past. In this paper we present the compositional analysis of gold jewels by the Castellani, one of the most important families of goldsmiths in nineteenth-century Europe. The use of a portable micro-XRF spectrometer, specifically developed for jewellery analysis at the Centro Nacional de Aceleradores (Seville), allowed us to analyse, in a completely non-invasive way, the alloys, joining techniques and surface treatments of the jewels of the Castellani collection at the National Etruscan Museum of Villa Giulia in Rome. The addition to the spectrometer of a second X-rays detector with a zinc filter allowed us to check the possible presence of low amounts of cadmium, a metal added to gold soldering only from the nineteenth century and often used in authenticity studies. Moreover, the relative intensities of the Au X-ray lines were studied in order to check non-invasively the presence of surface enrichments in gold.

Research facilities and highlights at the Centro Nacional de Aceleradores (CNA)

The Centro Nacional de Aceleradores is a user-oriented accelerator facility in Seville, Spain. Its main facilities are a 3 MV tandem accelerator, an 18 MeV proton Cyclotron, a tandetron used for AMS, a compact accelerator used for radiocarbon measurements, a ^{60}Co irradiator and a PET/CT scanner. The technical specifications and research applications of these facilities are described. A neutron beam line associated to a charged pulsed beam in the tandem allows for time of flight measurements which determine the neutron energy. The use of an adequate stripper gas in the AMS tandetron permits to measure heavy radionuclides with very low detection levels, allowing to perform environmental studies using these radionuclides as tracers. The use of the microbeam in the tandem accelerator allows to apply the ion beam-induced current technique to investigate the spectroscopic properties and radiation hardness of different semiconductor detectors.

HiSPANoS facility and the new neutron beam line for TOF measurements at the Spanish National Accelerator Lab (CNA)

HiSPANoS (HiSPAlis Neutron Source) is the first accelerator-based neutron facility in Spain, installed at the Centro Nacional de Aceleradores (CNA), where different experiments have been performed related to nuclear astrophysics, detector characterization, electronic devices irradiation, imaging, etc. An upgrade of the neutron facility has been carried out recently, installing a pulsing system at the 3 MV tandem accelerator at CNA. Such system, composed by a chopper and buncher unit, can provide nanosecond proton and deuteron pulsed beams. A new experimental line dedicated to neutron time-of-flight (n-TOF) technique has been installed at the tandem accelerator. Proton and deuterium pulse width of 1 ns have been measured with a repetition rate in the range of 62.5 kHz to 2 MHz. The commissioning of the n-TOF line has consisted of the measurement of the neutron field generated by 7Li(p,n) reaction with proton energy of 1912 keV.

Accelerator Mass Spectrometry of 237Np, 239Pu and 240Pu for environmental studies at the Centro Nacional de Aceleradores

Low-energy Accelerator Mass Spectrometry (AMS) systems (i.e. working with 1 MV terminal voltages and below) have demonstrated in the past their capability for the ultra-trace analyses of 236U and 239,240Pu in different field studies. The situation for 237Np has been different, mostly due to the constraints imposed by the lack of a Np isotopic tracer. Here, it is presented a comprehensive study on the performance of the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) for: i) the determination of 237Np using 242Pu as the AMS normalisation isotope and, ii) the efficient analysis of 239Pu, 240Pu and 237Np when they coexist in the same cathode with traces of natural uranium. Working procedures to analyse 237Np and 239Pu on one hand, and 240Pu on the other, are developed in order to meet competitive 238U suppression factors and counting efficiencies for every radionuclide. It is demonstrated that the sputtering-process-based temporal trend in the 237Np/242Pu AMS ratios show a coherent behaviour between the different studied matrixes, demonstrating the reliability of the necessary standard correction procedure in AMS. It is proved that 237Np and 239Pu concentrations at the 1 fg level and 240Pu concentrations at the 0.1 fg level can be quantified in samples containing 238U traces. The technique is applied to the 239,240Pu and 237Np analysis of a seawater reference sample supplied by the International Atomic Energy Agency (IAEA): IAEA-443.

Cultural heritage science at CNA (seville, Spain): Applications of XRF and IBA techniques to art and archaeological objects.

The use of nuclear analytical techniques has experienced an extraordinary growth in recent decades in the field of cultural heritage. Nowadays, their use in the study of objects of interest in heritage has become essential. An important effort has been made since the 90s by the archaeometry research group of the Centro Nacional de Aceleradores, CNA (Sevilla, Spain) to develop different non-destructive analytical techniques for the study of art and archeological objects. These efforts were initially focused on the use of Ion Beam techniques (IBA) and lately in the development of portable X-Ray Fluorescence (XRF) equipment, including microbeam versions with the implementation of polycapillary lenses (μXRF and confocal XRF).The different methods and instrumentation developed in the past years at CNA are presented in this work and several applications illustrate the capabilities for the analysis of different types of objects: jewelry, coins, paintings, ceramics, etc. Advantages and limitations of the different techniques are shown together with examples of how the combination of several of those methods can overcome some of the limitations are presented.

Radiocarbon measurements of foraminifera with the mini carbon dating system (MICADAS) at the Centro Nacional de Aceleradores

Radiocarbon (14C) measurements of foraminifera are often challenging as their reliability and accuracy can be biased by several complicating factors. In this work, at the Centro Nacional de Aceleradores (CNA) in Seville, an automated setup with a Carbonate Handling System coupled with an automated graphitization system has been tested to investigate the potential for running samples of foraminiferal carbonate for AMS 14C dating of marine archives. The reproducibility of 14C ages for blanks and standard materials indicates that reliable 14C analyses are possible for carbonate samples with a 14C age up to 50,000 yr BP. With this automated procedure we were able to date monospecific planktonic foraminifera younger than 1000 yr BP. Biological mixing and high sedimentation are potentially complicating mechanisms resulting in anomalous young 14C ages in planktonic foraminifera from the deep Mediterranean Sea.

Palladium analysis in gold items from Punic jewellery (Cádiz, Spain)

Some years ago a group of jewels from the Museum of Cádiz (South Spain) was analysed by micro-PIXE (Particle Induced X-ray Emission) at Centro Nacional de Aceleradores (Sevilla). During this work two similar spiral earrings happened to have significant amounts of palladium in their composition, up to 0.7 wt%, and some hypotheses about the provenance of this palladium-bearing gold were exposed.Many similar gold earrings from the same location and time are kept in the museum, some of them permanently exhibited in the showcases. Now, by means of a portable X-ray spectrometer device, especially designed for the analysis of gold jewels, a second campaign has been accomplished to study the rest of the jewels kept at the museum. This time the equipment was moved to the museum instead of taking the gold items to the laboratory, facilitating the analysis of the samples in the showcases and reducing the costs.A total of 94 jewels have been studied and 24 of them contained palladium up to 1.1 wt%. Copper content was below 2.5 wt% in most of the cases. X Ray Fluorescence technique was employed for this study. A filter of 20 μm of Zn was used in the detector to enhance the detection of palladium, and other potential platinum group elements, by absorbing the Au-Lα emission line. The effects of this method in the quantification was also compared in this work, finding higher uncertainties with the use of the filter, but demonstrating the convenience of its use to discriminate the Pd-Kα line from the sum peaks of the very intense gold lines.

Meteoric 10Be in aerosol filters in the city of Seville

Cosmogenic radionuclides in the one-million-year half-life range, like 10Be, find application fields in several Sciences. They are powerful tools in Geology and Geochronology, as they are very important tracers on the Earth, being utilized as chronometer. Meteoric 10Be (T1/2 = 1.39 × 106 y) associated to aerosols can be used as a tracer of atmospheric processes and specifically as indicators of the cosmogenic interactions in lower Stratosphere, upper Troposphere, the air exchange between both and deposition processes on the Earth surface. The applications of 10Be are even more relevant when combined with other radionuclides such as 26Al. In order to provide new data about concentration 10Be in this type of samples, the first atmospheric air filters in Spain have been analysed. Values around 104 at/m3 (atoms per cubic meter of air) for 10Be have been obtained. Due to the location and the features of the sampling site (urban area, at sea level and mid latitude), a new radiochemical procedure was designed and developed in our laboratory for the Accelerator Mass Spectrometry (AMS) measurement of 10Be in this kind of samples. The samples were measured in SARA, the 1 MV AMS system at Centro Nacional de Aceleradores (CNA).

10Be low-energy AMS with the passive absorber technique

The passive absorber technique is one of the most common ways to suppress the 10B interference during 10Be measurements at facilities working with beam energies above 7 MeV. At lower energies, the range straggling complicates the application of absorbers, so that other suppression techniques are normally preferred. Several experiments were conducted at the SARA (hosted at Centro Nacional de Aceleradores, Seville, Spain) and VERA (Faculty of Physics, University of Vienna, Austria) AMS facilities to demonstrate the potential of the passive absorber technique also at and below 2.4 MeV. Two different absorber setups were installed and tested. For the detection of the rare isotopes both facilities used a gas ionization chamber optimized for light ions detection based on the same design. The absorber installed at the SARA facility was a combination of SiN foils and an isobutane gas volume, whereas VERA was equipped with an absorber constituted of a stack of SiN foils. In both cases, 10Be could be clearly separated from 10B and the use of a passive absorber at the entrance of the detector gave higher transmission compared to the degrader method.Depending on the absorber design, different background contributions could be identified: Rutherford scattering of 10B on the protons contained in the SiN foils and isobutane gas was responsible of a severe background at SARA, and fragments from 9Be1H molecules surviving the stripping process resulted in events partially overlapping the 10Be gate at VERA. The measured transmissions and background levels will be presented for the tested setups, as well as the advantages and disadvantages of each absorber design.

Accelerator mass spectrometry of 236U with He stripping at the Centro Nacional de Aceleradores

In January 2015, the 1 MV AMS facility at the Centro Nacional de Aceleradores (CNA, Seville, Spain) was upgraded with He stripping. In this work, we present a comprehensive study of the uranium transmission through the accelerator together with the background sources that limit the current sensitivity of our system to measure the 236U/238U atom ratio. In addition to the well-known background caused by scattered 235U3+ molecular fragments, we identify an additional component, not observed with Ar gas, that we relate to scattered 238U3+ molecular fragments. Stripper gas pressures below the one corresponding to the equilibrium charge state distribution are used to minimize the resulting overall background, which is in the (0.8–1.3) × 10−10 range. This is at least a factor of 3 higher than the background obtained with Ar gas. On the other hand, new information on the stripping process of U on He gas at the 400–1000 keV stripping energy range is presented. A maximum transmission of 45% for U3+ is achieved at about 650 keV, which correspond to a stripping yield of about 50%. This is the maximum yield that can be actually obtained working with He gas at low energies according to previous results.

CHARACTERIZATION OF THE EPITHERMAL NEUTRON FIELD PRODUCED BY p+7Li REACTION IN A TANDEM ACCELERATOR USING A BONNER SPHERE SPECTROMETER.

The proton beam produced in the Nuclear Physics line of the tandem accelerator of the Centro Nacional de Aceleradores was used to generate a neutron field. In particular, 1.912 MeV protons were used to produce well-known epithermal neutrons through the p+7Li → n+7Be reaction. The aim of the work was to characterize this field while testing the performance of a Bonner sphere spectrometer in the epithermal range. Measurements were performed in four locations at different angle (0°, 30°, 60° and 90°) from beam incidence direction in order to study the angular dependence of the field. Both a parametric and numerical unfolding methods were tested to process the counts of the central detectors and obtain the energy distribution of the neutron fluence. In addition, a Monte Carlo simulation was carried out to complete the study and provide a guess spectrum for numerical unfolding. It was found that the fluence rate and mean energy decrease as the angle from beam direction increases. Total fluence was 2.75, 1.36, 0.366 and 0.216 cm-2 per charge collected in the target at 0°, 30°, 60° and 90°, respectively. Mean energy of the field ranges from 46 to 17 keV at 0° and 60°, respectively. In all cases, given that the irradiation room is so large, the contribution of thermal neutrons to the field is small. Regarding the unfolding, the total fluences estimated by all methods were in agreement within the uncertainties.

41 Ca measurements on the 1 MV AMS facility at the Centro Nacional de Aceleradores (CNA, Spain)

We present a detailed study of the performance parameters for 41Ca measurements at the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) in Seville. Mixing CaF2 with Ag, we get stable (40CaF3)− currents between 50 and 100 nA. Transmission of the 2+ state in the He stripper is 41%, while optical transmission in the HE sector is typically higher than 95%. At low energies we cannot separate 41Ca from the isobar 41K at the detector, but the interference is reduced by using (41CaF3)− ions. The remaining contribution is corrected by measurement of the other stable isotope of potassium, 39K, to estimate this interference (K-correction). After this correction, we reach a 41Ca/40Ca background level between 5 × 10−12 and 8 × 10−12, making possible measurements of 41Ca/40Ca ratios higher than 4 × 10−11. Intercomparisons with the 0.6 MV AMS system at ETH Zurich show a quite good correlation.

Non-destructive micro-analytical system for the study of the manufacturing processes of a group of gold jewels from “El Carambolo” treasure

The impressive gold treasure of El Carambolo, representative of the Tartesic culture and dated from the 8th to 6th century BCE, constitutes a typological and stylistic unity unparalleled in the archeological field. Due to the importance of this treasure and the interest in studying it in depth, a new micro X-ray fluorescence (micro-XRF) portable system has been developed at the Centro Nacional de Aceleradores (Sevilla, Spain). Eleven jewels of El Carambolo treasure have been analyzed in order to characterize the composition of the employed alloys, to identify the manufacturing processes and to discuss hypothesis about the production workshop of the treasure. Besides, the application of the new micro-XRF instrumentation allowed the analysis of small details like decoration elements and joining areas. This study permits the characterization of the joining methods and manufacturing procedures, thus, the construction stages of these highly complex jewels can be inferred. Many archeological and historical studies of the treasure have been performed during the last years but very few analytical results have been published. Furthermore, the results demonstrate the capability of the new developed portable micro-XRF setup to substitute satisfactorily other micro-analytical techniques, such as micro-PIXE (Particle Induced X-ray Emission), when the sample cannot be brought to a laboratory.

Recent developments of the 1 MV AMS facility at the Centro Nacional de Aceleradores

The Centro Nacional de Aceleradores (CNA) hosts a 1MV accelerator mass spectrometry (AMS) apparatus since September 2005. In order to improve its overall performance, several updates have been made on the existing facility during the last 10years of operation. In this paper, two modifications conducted in 2015 will be described.To increase the transmission of the ions through the accelerator, the stripping gas on the 1MV CNA machine was changed from Ar to He. The measured maximum transmission for almost every isotope results to be higher, especially for heavy masses: for instance, in the case of uranium in the 3+ charge state, the transmission increased from 11% with Ar gas to about 38% with He gas.The second advance consisted of the substitution of the existing gas ionization chamber with a new one provided by ETH Zurich. The ETH detector features with its miniaturized design and is optimized for low energy AMS (i.e. very low electronic noise and efficient charge collection). As the electronic noise is the most important contribution to the resolution for light ions, the total energy resolution has been reduced by 15% in the case of 10Be, allowing a better discrimination against its isobar, 10B. For the heaviest radionuclides where the quality of the spectra is determined by the charge carrier production in the gas, the resolution for 2.7MeV uranium ions was improved by 30%, probably due to a more efficient charge collection.

Characterization of the new mobile confocal micro X-ray fluorescence (CXRF) system for in situ non-destructive cultural heritage analysis at the CNA: μXRF-CONCHA

Confocal micro X-ray fluorescence (CXRF) is gaining considerable interest due to its ability to provide compositional and spatial information that are typically obtained using standard micro-invasive and/or micro-destructive techniques (e.g., SEM-EDX), without the need of sampling. In this work, the specifics of the new CXRF device named μXRF-CONCHA from the Centro Nacional de Aceleradores of the University of Seville will be presented. The development of this equipment is intended to the study in situ of paintings in order to obtain depth profiles of pictorial layers by a no-destructive way. This investigation consists in studying the viability of this device for the study of pictorial layers of old paintings. The challenge consists in determining if the results obtained allow distinguishing the sequence of the paint layer and their composition. Several experimental paint multilayers have been analyzed to evaluate this setup. This paper shows that μXRF-CONCHA will be able to provide important information in order to understand and interpret the choice, palette, and technique of painters from the past.

Measurement of 236U on the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA)

In this paper we present the first comprehensive analysis of the 1MV AMS system at the Centro Nacional de Aceleradores (CNA, Seville, Spain) for 236U studies in environmental samples. In the last years, this radionuclide has become key in the AMS community, due to the very demanding 236U/238U abundance sensitivities required for general applications. As we demonstrate, the AMS system at the CNA is able to achieve sensitivity for the 236U/238U ratio of about 3×10−11 despite its compact design. The use of “239Pu”/238U ratio as a proxy for “236U”/235U background correction is proposed and tested with natural samples that were also studied on the 600kV Tandy AMS system at the ETH Zürich. This correction is significant in the CNA case, due to the low mass resolving power of the low-energy spectrometer and to the lack of a third filter on the high-energy side. With the measurement of reference solutions supplied by the Institute for Reference Materials and Methods (IRMM-075), and reference natural matrixes provided by the International Atomic Energy Agency (IAEA-Soil-6, IAEA-375; 384; 386 and IAEA-RGU), we show that the 1MV AMS system at the CNA can be routinely used for determinations of anthropogenic 236U at environmental levels.

14C SIRI samples at CNA: Measurements at 200 kV and 1000 kV

The Sixth International Radiocarbon Intercomparison (SIRI) exercise has taken place during late 2013 and 2014. 13 samples were distributed for AMS (Accelerator Mass Spectrometry) and 5 for radiometric laboratories, including one sample exclusively for radiometric laboratories. Being the first opportunity for our laboratory to participate actively in an intercomparison exercise, we have prepared and measured the samples in the two existing AMS dedicated facilities at the Centro Nacional de Aceleradores (CNA): SARA (Spanish Accelerator for Radionuclide Analysis), a 1 MV multielemental AMS system from HVEE, and Micadas, a 200kV radiocarbon dating system designed by ETH. Results are presented for the two systems, together with a description of both the sample preparation and measurement procedures.