Experimental determination of the activity of a 252Cf source

An important research line in nuclear physics nowadays is the study of unstable nuclei. Within this, one area of interest is the study of delayed neutron emission which is of relevance for di erent elds such as astrophysics, nuclear technology and nuclear structure. The study of di erent aspects of decay of exotic nuclei, such as half lives and neutron emission probabilities, provide information about their structure and these measurements are sometimes the only ones that can be performed in nuclei with very low yields. The work presented here aims at measuring the neutron activity of a 252Cf source. The goal is to verify the activity provided by the manufacturer and reduce its quoted uncertainty. The method used to obtain the 252Cf neutron source activity is based on the measurement of the gamma ray spectrum of the ssion products [1]. Once calibrated this source will be used to calibrate a neutron detector designed at UPC that is currently being used to measure delayed neutron emission. However that is beyond the scope of this work. The rst chapter of this document describes the theoretical concepts of delayed neutron emission; it also presents a brief summary about the UPC neutron detector prototype that we aim at calibrating, an overview of di erent types of neutron sources and the calibration method of the detector. The second chapter refers speci cally to the characteristics of 252Cf neutron source calibrated and the experimental setup. Chapters three and four detail the procedure for the determination of the activity of the 252Cf neutron source studied passing through the germanium detector calibration. The last chapter presents the conclusions of the results of this study and improvements to perform in future similar calibrations of this type

First measurement of beta-decay half-lives and neutron emission probabilities in several isotopes beyond N = 126

In this work beta-decay half-lives and neutron-emission probability values have been experimentally determined for first time in several nuclei beyond the neutron-shell closure at N=126. To this aim the accelerator complex at the GSI center for heavy ion research (Germany), in combination with the FRS fragment separator, were employed. The beta-decay detection system consisted of a charged particle detector named SIMBA, which served to detect both ion and beta-particles, surrounded by an array of He-3 based neutron counters named BELEN. The half-life values of eighteen isotopes of Au, Hg, Tl, Pb and Bi were determined, as well as the neutron-branching ratios (or upper limits) for seven nuclei. A comparison of the present results with previous half-life measurements in this mass-region shows a generally good agreement, thus reflecting the systematic validity of the decay data available in this region. Compared to theoretical models, our results show a reasonable agreement for half of the analyzed isotopes, and large discrepancies of up to a factor of 10 for the other half. The measured neutron-branching ratios represent the first set of experimental data available in this mass-region for several isotopes. Owing to the absence of previous experimental results, the values reported here can be only compared with theoretical predictions. In summary, a fair compatibility is found between FRDM+QRPA calculations, which however are underestimating by a factor of 5 the neutron-branching ratio of Tl-215, which is the most exotic nucleus measured in this work.En aquest treball s'han determinat, experimentalment i per primera vegada, vides mitjanes i valors de probabilitat d'emissió de neutrons de diversos nuclis amb més de 126 neutrons. Per tal d'obtenir les dades es va realitzar un experiment a les instal·lacions del centre d’investigació d'ions pesats GSI a (Alemanya), combinat amb el separador de fragments FRS. El sistema de detecció d'ions i desintegracions beta va consistir d'un detector de partícules carregades anomenat SIMBA, que estava envoltat per una matriu de comptadors proporcionals d’'He-3 que conformen el detector de neutrons BELEN. En total s'han determinat valors de vida mitjana de divuit isòtops d'or, mercuri, tal·li, plom i bismut, així com també la probabilitat d'emissió de neutrons (o llindars superiors) de set d'ells. Comparant els resultats amb les mesures de vides mitjanes anteriors en aquesta regió de nuclis s'observa un bon acord, reflectint la validesa de la sistemàtica de les dades existents. D’'altra banda, fent la comparació amb els models teòrics, els resultats mostren un acord raonable per la meitat dels isòtops analitzats, i grans discrepàncies, de fins a un factor 10, per l'altra meitat. Pel que fa a les probabilitats d'emissió de neutrons mesurades, essent la primera mesura experimental a la regió per a diversos nuclis, no és possible comparar amb altres els valors obtinguts. La única comparació que es pot avaluar és amb les prediccions teòriques. En resum, els resultats són compatibles amb el model FRDM + QRPA, no obstant s'observen discrepàncies considerables en alguns isòtops de fins a un factor 5, com és el cas del valor obtingut per Tl-215, que correspon al nucli més exòtic del qual s'’ha determinat la probabilitat d’'emissió de neutrons

β-decay half-lives and β-delayed neutron emission probabilities for several isotopes of Au, Hg, Tl, Pb, and Bi, beyond N = 126

Background: There have been measurements on roughly 230 nuclei that are β-delayed neutron emitters. They range from 8 He up to 150La. Apart from 210Tl, with a branching ratio of only 0.007%, no other neutron emitter has been measured beyond A = 150. Therefore, new data are needed, particularly in the region of heavy nuclei around N = 126, in order to guide theoretical models and help understand the formation of the third r-process peak at A ∼ 195. Purpose: To measure both β-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl, Pb, and Bi isotopes beyond N = 126. Method: Ions of interest were produced by fragmentation of a 238U beam, selected and identified via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) was used to measure ion implants and β decays. An array of 30 3 He tubes embedded in a polyethylene matrix (BELEN) was used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time correlations. The latter were analyzed with an analytical model and results for the half-lives and neutron-branching ratios were derived by using the binned maximum-likelihood method. Results: Twenty new β-decay half-lives are reported for 204−206Au, 208–211Hg, 211–216Tl, 215–218Pb, and 218–220Bi, nine of them for the first time. Neutron emission probabilities are reported for 210,211Hg and 211–216Tl. Conclusions: The new β-decay half-lives are in good agreement with previous measurements on nuclei in this region. The measured neutron emission probabilities are comparable to or smaller than values predicted by global models such as relativistic Hartree Bogoliubov plus the relativistic quasi-particle random phase approximation (RHB + RQRPA).Spanish Ministerio de Economía y Competitividad-FPA2011- 28770-C03-03, FPA2008-04972-C03-3, AIC-D2011-0705, FPA2011-24553, FPA2008-6419, FPA2010-17142, FPA2014-52823-C2-1-P, FPA2014- 52823-C2-2-P, and CPAN CSD-2007-00042 (Ingenio2010)Program Severo Ochoa-SEV-2014-0398German Helmholtz Association (Young Investigators)-VH-NG 627 (LISA-Lifetime Spectroscopy for Astrophysics)Nuclear Astrophysics Virtual Institute-VH-VI-417German Bundesministerium für Bildung und Forschung-06MT7178 / 05P12WOFNFSpanish Nuclear Security Council (CSN)-Catedra ArgosUK Science & Technology Facilities Council (STFC)-ST/F012012/

Prevención, seguimiento y evaluación de la descontaminación de percloroetileno en suelo y aguas subterráneas en un terreno industrial

La contaminación de suelos y aguas subterráneas es uno de los problemas ambientales más extendidos en gran parte de los terrenos industriales de Cataluña. En este proyecto se ha analizado el proceso de gestión de la contaminación: caracterización, remediación y seguimiento de la descontaminación en suelos y aguas subterráneas por un caso de afección por organoclorados (percloroetileno) y otros contaminantes (hidrocarburos, selenio y cromo) en un emplazamiento industrial situado en una zona agroforestal (superficie de 81.462 m2). A partir de la implantación en la empresa del sistema de gestión ISO 14.001 en 1.996, se abrieron diferentes proyectos de gestión para los posibles contaminantes. Por las mismas fechas, también se detectó una afección por selenio en aguas subterráneas, ajena a la empresa de estudio. Por el momento, el único contaminante que ha requerido de un proceso de descontaminación ha sido el percloroetileno. En suelos se emplea el método "soil vapor extraction" y en aguas subterráneas el método "airstripping". Finalmente, se ha llevado a cabo una comparación de los costes reales derivados del proceso de descontaminación del percloroetileno en contra de los costes que se hubiesen derivado la implantación de medidas de prevención de la contaminación. El resultado de la valoración indica que la descontaminación de éste compuesto requiere de una inversión económica importante, unas 10 veces más elevada que los costes derivados de las medidas de prevención.La contaminació de sòls i aigües subterrànies és un dels problemes ambientals més extesos a gran part dels terrenys industrials de Catalunya. En aquest projecte s'ha analitzat el procés de gestió de la contaminació: caracterització, remediació i seguiment de la descontaminació de sòls i aigües subterránies per un cas d'afecció per organoclorats (Percloroetilè) i altres contaminants (hidrocarburs, seleni i crom)en un emplaçament industrial situat a una zona agroforestal (superfície de 81.462 m2). A partir de la implantació a la empresa del sistema de gestió ISO 14.001 al 1.996, es van obrir diferents projectes de gestió per als possibles contaminants. Per les mateixes dates, també es va detectar una afecció per seleni a les aigües subterrànies, aliena a l'empresa d'estudi. Pel moment, l'únic contaminant que ha calgut d'un procés de descontaminació ha estat el percloroetilè. En sòls es va emprà el mètode "soil vapor extraction" i a les aigües subterrànies el mètode "air-stripping". Finalment, s'ha portat a terme una comparació dels costos reals derivats del procés de gestió de la contaminació per percloroetilè en contra dels costos que s'haguessin gastat en la implantació de mesures de prevenció de la contaminació. El resultat de la valoració indica que la descontaminació d'aquest compost, requereix d'una inversió econòmica important, unes 10 vegades més elevada que els costos de les mesures de prevenció.Soil and groundwater pollution is one of the main environmental issues in a important proportion of the industrial areas of Catalonia In this project we have analysed the contamination management process: characterization, remediation and monitoring for a case of affection for organochloride (perchloroethylene) and another contaminants (mineral oils, selenium and chromium) in an industrial site located in an agroforestry zone (surface of 81,462 m2). Since the company implementations of norm ISO 14,001 in 1996, different management projects for potential contaminants have been opened. At the same time a selenium affection in groundwater outside the research company was detected. At the moment, the only contaminant that has required a decontamination process has been perchloroethylene. In soils, the Soil Vapor Extraction method was used, and the Air-Stripping method was used for groundwater. Finally, a comparison between real costs of the management process of perchloroethylene pollution and potential costs for the implementation of measures to prevent pollution, was made. The outcome of this comparison indicates that the remediation of this compound requires a major investment, about 10 times higher than the costs of preventive measures

Monte Carlo simulations for the study of a moderated neutron detector

This work presents the Monte Carlo simulations performed with the MCNPX and GEANT4 codes for the design of a BEta deLayEd Neutron detector, BELEN-20. This detector will be used for the study of beta delayed neutron emission and consists of a block of polyethylene with dimensions 90x90x80 cm3 and 20 cylindrical 3He gas counters. The results of these simulations have been validated experimentally with a 252Cf source in the laboratory at UPC, Barcelona. Also the first experiment with this detector has been carried out in November 2009 in JYFL, Finland. In this experiment the neutron emission probability after beta decay of the fission products 88Br, 94;95Rb, and 138I has been measured; this data is still under analysis. Simulations with MCNPX and GEANT4 have been performed in order to obtain the efficiency of the BELEN-20 detector for each of the above nuclei using the neutron energy distribution corresponding to each nucleus.Peer ReviewedPostprint (published version

Assessment of an enhanced program for depression management in primary care: a cluster randomized controlled trial. The INDI project (Interventions for Depression Improvement)

<p>Abstract</p> <p>Background</p> <p>Most depressed patients are attended at primary care. However, there are significant shortcomings in the diagnosis, management and outcomes of these patients. The aim of this study is to determine whether the implementation of a structured programme for managing depression will provide better health outcomes than usual management.</p> <p>Methods/Design</p> <p><it>Design</it>: A cluster-randomized controlled trial involving two groups, one of which is the control group consisting of patients who are treated for depression in the usual way and the other is the intervention group consisting of patients on a structured programme for treating depression.</p> <p><it>Setting</it>: 20 primary care centres in the province of Tarragona (Spain)</p> <p><it>Sample</it>: 400 patients over 18 years of age who have experienced an episode of major depression (DSM-IV) and who need to initiate antidepressant treatment</p> <p><it>Intervention</it>: A multi-component programme with clinical, educational and organisational procedures that includes training for the health care provider and evidence-based clinical guidelines. It also includes primary care nurses working as care-managers who provide educational and emotional support for the patients and who are responsible for active and systematic clinical monitoring. The programme aims to improve the primary care/specialized level interface.</p> <p><it>Measurements</it>: The patients will be monitored by telephone interviews. The interviewer will not know which group the patient belongs to (blind trial). These interviews will be given at 0, 3, 6 and 12 months.</p> <p><it>Main variables</it>: Severity of the depressive symptoms, response rate and remission rate.</p> <p><it>Analysis</it>: Outcomes will be analyzed on an intent-to-treat basis and the unit of analysis will be the individual patient. This analysis will take into account the effect of study design on potential lack of independence between observations within the same cluster.</p> <p>Discussion</p> <p>The effectiveness of caring for depression in primary care can be improved by various strategies. The most effective models involve organisational changes and a greater role of nurses. However, these models are almost exclusively from the USA, and this randomized clinical trial will determine if this approach could be effective to improve the outcomes of depression in primary care in the Spanish health care system.</p> <p>Trial registration</p> <p>ISRCTN16384353</p

First determination of ß -delayed multiple neutron emission beyond A=100 through direct neutron measurement: the P2n value of Sb 136

Background: ß-delayed multiple neutron emission has been observed for some nuclei with A=100, being the 100Rb the heaviest ß2n emitter measured to date. So far, only 25P2n values have been determined for the ˜300 nuclei that may decay in this way. Accordingly, it is of interest to measure P2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A>100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes, such as the r-process, and safety inputs for nuclear reactors.Postprint (published version

Half-lives of neutron-rich Cd 128-130

R. Dunlop et al. ; 6 págs.; 7 figs.; 1 tab. ; Rapid CommunicationsThe β-decay half-lives of Cd128-130 have been measured with the newly commissioned GRIFFIN γ-ray spectrometer at the TRIUMF-ISAC facility. The time structures of the most intense γ rays emitted following the β decay were used to determine the half-lives of Cd128 and Cd130 to be T1/2=246.2(21) ms and T1/2=126(4) ms, respectively. The half-lives of the 3/2+ and 11/2- states of Cd129 were measured to be T1/2(3/2+)=157(8) ms and T1/2(11/2-)=147(3) ms. The half-lives of the Cd isotopes around the N=82 shell closure are an important ingredient in astrophysical simulations to derive the magnitude of the second r-process abundance peak in the A∼130 region. Our new results are compared with recent literature values and theoretical calculations. ©2016 American Physical SocietyThis work has been partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Research Chairs Program. I.D. and R.C.-F. are supported by NSERC Discovery Grants SAPIN-2014-00028 and RGPAS 462257-2014. A.J. acknowledges financial support by the Spanish Ministerio de Ciencia e Innovación under contract FPA2011-29854-C04 and the Spanish Ministerio de Economía y Competitividad under contract FPA2014- 57196-C5-4-P. S.L.T acknowledges financial support from the U.S. National Science Foundation under contract NSF- 14-01574. E.P.-R. acknowledges financial support from the DGAPA-UNAM under the PASPA program. The GRIFFIN spectrometer was funded by the Canada Foundation for Innovation, TRIUMF, and the University of Guelph. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada.Peer Reviewe

In-beam internal conversion electron spectroscopy with the SPICE detector

The SPectrometer for Internal Conversion Electrons (SPICE) has been commissioned for use in conjunction with the TIGRESS $\gamma$-ray spectrometer at TRIUMF's ISAC-II facility. SPICE features a permanent rare-earth magnetic lens to collect and direct internal conversion electrons emitted from nuclear reactions to a thick, highly segmented, lithium-drifted silicon detector. This arrangement, combined with TIGRESS, enables in-beam $\gamma$-ray and internal conversion electron spectroscopy to be performed with stable and radioactive ion beams. Technical aspects of the device, capabilities, and initial performance are presented