Clarifying the radiative decay of the Hoyle state with charged-particle spectroscopy.

A detailed knowledge of the decay properties of the so called Hoyle state in the 12 C nucleus ( E x = 7.654 MeV, 0 + ) is required to calculate the rate at which carbon is forged in typical red-giant stars. This paper reports on a new almost background-free measurement of the radiative decay branching ratio of the Hoyle state using advanced charged particle coincidence techniques. The exploitation, for the first time in a similar experiment, of a bidimensional map of the coincidence efficiency allows to reach an unitary value and, consequently, to strongly reduce sources of systematic uncertainties. The present results suggest a value of the radiative branching ratio of Γ rad / Γ tot = 4.4 ( 6 ) · 10 - 4 . This finding helps to resolve the tension between recent data published in the literature.

Study of the radionuclide deposition in the radioactive ion line of the Selective Production of Exotic Species (SPES) facility.

SPES (Selective Production of Exotic Species) is a second generation facility for the production of radioactive ion beams that is going to be commissioned at the Laboratori Nazionali di Legnaro of INFN at Legnaro, Padua, Italy. Radioactive neutron-rich isotopes are expected to be produced by nuclear fission induced by a 40 MeV, 200 µA primary proton beam impinging on a 238UCx target. The expected reaction rate is about 1013 fission/s. Radioactive ion beams are produced using the isotope separation on-line technique. The production of such an amount of radioactive species raises radiological issues throughout the life cycle of the facility. A study of the radioactive contamination of the components of the radioactive ion beam line is performed with the FLUKA Monte Carlo simulation code, under realistic hypotheses for the produced isobaric beams. The present results complete previous studies focused on the radiological impact of the production target irradiation, the residual activation of the primary proton beam line and the radioactive contamination of the ion source complex. The overall ambient dose equivalent rate due to the different radiation sources is calculated at several positions inside the production bunker and at different times after a typical one-year operating period of the facility with the 238UCx target at full power. The obtained results and the developed methodology provide the guidelines and the needed tools to plan ordinary and extraordinary interventions as well as final decommissioning of the SPES facility.

Optical properties and pulse shape discrimination in siloxane-based scintillation detectors.

The possibility to detect fast neutrons as a distinct signal from that one of γ-rays background is surely of great importance for several topics, spanning from homeland security to radiation monitoring in nuclear physics research plants. Nowadays, Helium-3 based detectors are extremely expensive, while the use of large volume liquid scintillators presents serious concerns related to spillage risks and waste disposal. A very attractive alternative is the use of commercially available solid scintillators, which exploits an aromatic polymer matrix entrapping very high loadings of primary dye, thereby enabling the use of pulse shape analysis (PSA) to discriminate between fast neutrons and γ-rays. In this work, we analyse in detail the optical features of a solid scintillator composed by polymethylphenylsiloxane (PMPS) as base polymer loaded with moderate amounts of 2,5-diphenyloxazole (PPO). Furthermore, fluorescence decay kinetics have been correlated to the observed pulse shape discrimination capabilities of this radiation and thermally resistant scintillator, whose performances have been discussed in terms of conformational features and excimers formation revealed by the optical analyses.

Possible effects of clustering structure in the competition between fast emission processes and compound nucleus decay / Posibles efectos de estructura de agrupamiento en la competencia entre los procesos de emisión rápida y desintegración del núcleo compuesto

Abstract The attention to nuclear clustering has been renewed due to the study of weakly bound nuclei at the drip lines. In particular, clustering structural properties in medium-mass systems have been studied by looking at the competition between the evaporation and pre-equilibrium particle emission in central collisions. Although for light nuclei at an excitation energy close to the particle separation value there are experimental evidence of such structure effects, this is still not the case for heavier systems since the determination of pre-formed clusters within nuclear matter is less obvious. Two systems, leading to the same 81Rb* compound nucleus, have been studied at the same beam velocity 16 AMeV: 16O + 65Cu and 19F + 62Ni. The experiment has been performed using the GARFIELD + RCo detection system installed at the Legnaro National Laboratories.Light charged particles energy distributions and multiplicities have been compared with different statistical and dynamical model calculations. From the first comparison between the two systems a difference in the fast α-decay channel has been evidenced, which can be related to the difference in the projectile structure. Recent data analysis results and comparisons with model calculations are presented in this contribution.

Resumen La atención a la agrupación nuclear se ha renovado debido al estudio de núcleos débilmente unidos en las líneas de goteo. En particular, se han estudiado las propiedades estructurales del agrupamiento en sistemas de masa media al observar la competencia entre la evaporación y la emisión de partículas de preequilibrio en colisiones centrales. Aunque para núcleos ligeros a una energía de excitación cercana al valor de separación de la partícula hay evidencia experimental de tales efectos de estructura, este no es el caso para sistemas más pesados ya que la determinación de agrupamientos preformados dentro de la materia nuclear es menos obvia. Se han estudiado dos sistemas, que conducen al mismo núcleo compuesto 81Rb *, a la misma velocidad de haz 16 AMeV: 16O + 65Cu y 19F + 62Ni. El experimento se ha realizado utilizando el sistema de detección GARFIELD + RCo instalado en los Laboratorios Nacionales Legnaro. Las distribuciones de energía y las multiplicidades de partículas de carga ligera se han comparado con diferentes cálculos de modelos estadísticos y dinámicos. Desde la primera comparación entre los dos sistemas, se ha evidenciado una diferencia en el canal de desintegración α rápida, que se puede relacionar con la diferencia en la estructura del proyectil. En esta contribución se presentan los resultados del análisis de datos recientes y las comparaciones con los cálculos del modelo.

Response function of single crystal synthetic diamond detectors to 1-4 MeV neutrons for spectroscopy of D plasmas.

A Single-crystal Diamond (SD) detector prototype was installed at Joint European Torus (JET) in 2013 and the achieved results have shown its spectroscopic capability of measuring 2.5 MeV neutrons from deuterium plasmas. This paper presents measurements of the SD response function to monoenergetic neutrons, which is a key point for the development of a neutron spectrometer based on SDs and compares them with Monte Carlo simulations. The analysis procedure allows for a good reconstruction of the experimental results. The good pulse height energy resolution (equivalent FWHM of 80 keV at 2.5 MeV), gain stability, insensitivity to magnetic field, and compact size make SDs attractive as compact neutron spectrometers of high flux deuterium plasmas, such as for instance those needed for the ITER neutron camera.

Quadrupole transition strength in the (74)Ni nucleus and core polarization effects in the neutron-rich Ni isotopes.

The reduced transition probability B(E2;0(+)→2(+)) has been measured for the neutron-rich nucleus (74)Ni in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained B(E2;0(+)→2(+))=642(-226)(+216) e(2) fm(4) value defines a trend which is unexpectedly small if referred to (70)Ni and to a previous indirect determination of the transition strength in (74)Ni. This indicates a reduced polarization of the Z=28 core by the valence neutrons. Calculations in the pfgd model space reproduce well the experimental result indicating that the B(E2) strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.

X-ray fluorescence from the element with atomic number Z=120.

An atomic clock based on x-ray fluorescence yields has been used to estimate the mean characteristic time for fusion followed by fission in reactions 238U + 64Ni at 6.6 MeV/A. Inner shell vacancies are created during the collisions in the electronic structure of the possibly formed Z=120 compound nuclei. The filling of these vacancies accompanied by a x-ray emission with energies characteristic of Z=120 can take place only if the atomic transitions occur before nuclear fission. Therefore, the x-ray yield characteristic of the united atom with 120 protons is strongly related to the fission time and to the vacancy lifetimes. K x rays from the element with Z=120 have been unambiguously identified from a coupled analysis of the involved nuclear reaction mechanisms and of the measured photon spectra. A minimum mean fission time τ(f)=2.5×10(-18) s has been deduced for Z=120 from the measured x-ray multiplicity.

Novel polysiloxane-based scintillators for neutron detection.

Polysiloxane-based scintillators are promising for employment in harsh environments, owing to their outstanding radiation resistance and thermal properties over the traditional plastics (polyvinyltoluene and polystyrene). In this work, cross-linked polydimethyl-co-diphenylsiloxane (PMPS) scintillators with 22% molar percentage of diphenylsiloxane units have been synthesised. 2,5-Diphenyloxazole and Lumogen Violet (BASF) were employed as primary and secondary fluor, respectively. Thermal neutrons sensitivity was achieved through the addition of 3% wt of ortho-carborane. Scintillation yield measurements were made by exciting with (241)Am alpha source samples with different concentrations of dye molecules. PMPS-based scintillators with ∼50% light yield as compared with the commercial plastic scintillator EJ212 were produced. The scintillation yield of the B-loaded samples under thermal neutrons was tested with a moderated Am-Be source and compared with the commercially available EJ254 (5% wt B). 2.2 MeV neutrons were produced by irradiating with a 4.0 MeV proton beam an LiF target, thus exploiting the reaction (7)Li(p,n)(7)Be. Time-of-flight measurements were performed to distinguish pulses due to neutrons or gamma. A similar test was performed with an EJ254 commercial scintillator for comparison. Using the same set-up, polyethylene bricks were used as a moderator to produce low-energy neutrons for testing B-loaded samples.

[Cervical disorders in a group of male workers not exposed to physical ergonomic risk]. / Disturbi cervicali in un gruppo maschile di lavoratori non esposti a rischi ergonomici fisici.

OBJECTIVES: The aim of our study was to assess the prevalence of neck pain in the working population not exposed to ergonomic risks. METHODS: A total of 373 male workers were recruited in the Venice area of Italy. The inclusion criterion was the absence of exposure to ergonomic risk factors at the workplace. We collected the data via interviews between March 2004 and December 2006 conducted by properly trained operators. The prevalence of neck pain episodes was calculated after selecting 347 subjects without functional outcomes for severe trauma or genetic and degenerative diseases involving the same anatomical area. The strength of the association of neck pain with the collected variables was tested by means of logistic regression analysis. RESULTS: The group had a good attitude to doing physical activity in their free time. Exposure to high stress at work involved 12% of the sample. Multivariate analysis suggested a more than 3-fold level of risk among individuals with high levels of stress at work. The O.R. was 3.51 for those suffering from back pain at the same time and 6.85 for those who reported shoulder pain. CONCLUSIONS: Our study, in agreement with the scientific literature, showed evidence of increased risk of neck pain in subjects exposed to stress. There was a clear association with neck pain and joint disorders of other areas of the spine and shoulder. The results showed that the quantification of painful joint disorders, considering the numerical importance and the brief latency, is well suited to models of cross sectional studies.

[Epidemiology of work-related diseases in ULSS 12 Venice (Italy)]. / Epidemiologia delle malattie professionali nella ULSS 12 Veneziana.

In Veneto, like in Italy, in the last years the course of the professional diseases shown a trend in reduction. This trend has had to the difficulty to recognize the professional aetiology of multifactorial diseases. In the Venice the analysis of the course of the professional diseases in last the 4-5 years has demonstrated an increase of the communications of diseases from the doctors who operate in hospital to the SPISAL for the active search for pathologies asbestos and CVM correlated; moreover it has been a reduction of the hearing loss from noise from 2000 and it has been increment of cancer of lung and mesothelioma from 2001. Emergent diseases, like the allergy, the back diseases and those tied to the organizational constriction, are sottostimate. They have been a collaboration with the doctors of hospital, the doctors of factories, the INAIL and the court.