N. De Cesare

First direct measurement of the total cross-section of 12C(α,γ)16O

Abstract.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.

First direct measurement of the total cross section of 12C(alpha,gamma)16O

Abstract.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.

Dynamical effects in nuclear collisions in the fermi energy range: aligned breakup of heavy projectiles

Abstract Recent experimental results concerning heavy systems (Pb + Au, Pb + Ag, Pb + Al, Gd + C, Gd + U, Xe + Sn, …) obtained at GANIL with the INDRA and NAUTILUS 4 π arrays will be presented. The study of reaction mechanisms has shown the dominant binary and highly dissipative character of the process. The two heavy and excited fragments produced after the first stage of the interaction can decay into various decay modes from evaporation to multifragmentation including fission. However, deviations from this simple picture have been found by analyzing angular and velocity distributions of light charged particles, and fragments. Indeed, there is a certain amount of matter in excess emitted between the two primary sources suggesting either the existence of a mid-rapidity source similar to the one observed in the relativistic regime (participants) or a strong deformation induced by the dynamics of the collision (neck instability). This last possibility has been suggested by analyzing in detail the angular distributions of the fragments. More precisely, we observe an isotropic component which is compatible with the prediction of statistical models and a second one corresponding to breakup aligned with the recoil direction of the projectile like source which should be compared with the predictions of dynamical calculations based on microscopic transport models.

Off-line production of a 7Be radioactive ion beam

Abstract A 7 Be ion beam of several particle pA at 8 MeV has been produced at the TTT3 tandem of the University “Federico II” in Naples. The 7 Be nuclides were formed via the 7 Li(p,n) 7 Be reaction using a metallic Li target and an 11.4 MeV proton beam of 20 μA intensity, delivered by the cyclotron in Debrecen. Methods of hot chemistry were used to extract the 7 Be nuclides from the Li matrix and to prepare the 7 Be cathodes for the ion sputter source of the tandem. Examples of 7 Be beam applications are given.

OPTIMIZATION OF 236U AMS AT CIRCE

Actinide isotopes are present in environmental samples at ultra-trace levels (236U concentration is quoted to be on the order of pg/kg or fg/kg). Their detection requires the resolution of mass spectrometry (MS) techniques, but only accelerator mass spectrometry (AMS) has the sensitivity required. In order to perform the isotopic ratio measurements of actinides, such as 236U/238U, an upgrade of the Center for Isotopic Research on Cultural and Environmental Heritage accelerator (CIRCE) in Caserta, Italy, has been performed. The system was originally equipped for radiocarbon AMS measurements. The main difficulty of AMS measurement of 236U is the intense neighboring beam of 238U. Although most of the 238U ions are suppressed by means of magnetic and electrostatic elements, a small fraction of this intense beam can interfere with the rare isotopes. This paper reports the preliminary results of the 236U/238U isotopic ratio measurement limit <5.6 x 10^(-11)), aimed also to better understand the origin of background ions. For this purpose, a large 16-strip silicon detector providing spatial resolution has been used. In addition, calculations to assess the performance of the system obtained by adding a high-resolution time of flight-energy (TOF-E) detector are discussed.

236U AMS measurement at CIRCE

In order to measure the isotopic ratio of actinides, the upgrade of the accelerator mass spectrometry system at the Center for Isotopic Research on Cultural and Environmental heritage at the Second University of Naples, Italy, was performed. The beam emittance of 238U and the isotopic abundance sensitivity of 236U were measured on the present beam line. Utilizing a 16-strip silicon detector, the sensitivity of 236U/238U≈1×10−11 was obtained.

Uranium beam characterization at CIRCE for background and contamination determinations

The Accelerator Mass Spectrometry (AMS) is the most sensitive technique, compared either to the Inductively Coupled Plasma (ICP-MS) or Thermal Ionization (TI-MS) mass spectrometer, for the actinide (e.g. (236)U, (x)Pu isotopes) measurements. They are present in environmental samples at the ultra trace level since atmospheric tests of Nuclear Weapons (NWs) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale, and operation of Nuclear Power Plants (NPPs), on a small scale, have led to the release of a wide range of radioactive nuclides in the environment. At the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been developed and routinely operated. At CIRCE a charge state distribution as a function of terminal voltage, the beam emittance, measured in the 20° actinides dedicated beam line, as well as the energy and position validation of the U ions were performed in order to determine the best measurement conditions. A (236)U/(238)U isotopic ratio background level of about 5×10(-12) or 3×10(-13), depending on the Time of Flight-Energy (TOF-E) configurations, as well as the spatial distribution of the (235)U, (238)U interferences ions and a (236)U contamination mass of about 0.5 fg have been determined.

PIXE cross sections for some moderately toxic heavy metals

Abstract L-shell X-ray production cross sections by proton and 4 He ion impact on Hg and Tl have been measured in the energy ranges 0.3 ≤ E p ≤ 2.6 MeV and 0.7 ≤ E 4He ≤ 1.8 MeV, respectively. These elements are of great importance from the biological point of view, owing to their moderate toxicity properties. Data by 4 He ions impinging and, in the case of Hg, also by protons impinging, have been measured for the first time. A good agreement has been obtained with the few existing data from other authors on the proton induced cross sections of Tl. The experimental results are compared with the predictions of the ECPSSR (W. Brandt, G. Lapicki, Phys. Rev. A 20 (1979) 465) model. The disagreements already observed at low energy per atomic mass values for neighbouring elements clearly appear also in these cases and can be reduced by using a United Atom approximation in the treatment of the binding correction, suggested by our group (ECPSSR-UA)).

High spatial resolution HgI2 linear array based on resistive charge division

Newly designed Hg12 linear arrays based on resistive charge division, obtained by depositing a Ge surface resistive layer (with typical interstrip resistances of ≈ 4 and 6 MΩ) between the read-out Pd strips, have been fabricated. These detectors, coupled with specially designed front-end electronics, have shown a high detection efficiency over a large active detection area and an energy resolution of 20% for X-ray energy Ex = 22 keV, estimated to become 100 keV. Further, a spatial sensitivity of ≈ 10 μm and a spatial resolution of ≈ 100 μm have been obtained at 30 keV, by making use, for a fine spatial characterization of the devices, of a laser beam spot 50 μm in diameter with wavelength tuned to match the crystal band gap (582 nm). These devices could be successfully employed in basic research (for example Bragg X-ray spectrometry) and for radiological and high-energy (Ex > 100 keV) astrophysical applications.

Measurement of 3He(α, γ)7Be with ERNA Recoil Separator

The 3He(α, γ)7Be reaction plays an important role in the interpretation of the results of the solar neutrino experiments, since the estimate of the oscillation parameters relies on the solar neutrino spectrum, calculated by solar models. The high energy component in this spectrum is mainly produced by the decay of 7Be and 8B. The uncertainty in the 3He(α, γ)7Be cross section is also one of the largest contributions to the uncertainty on the predicted primordial 7Li abundance in Big Bang Nucleosynthesis calculations.Previous measurements of the 3He(α, γ)7Be cross section have been performed detecting the capture γ‐rays or, alternatively, measuring the activity of the synthesized 7Be. While the results of the two different approaches agree on the energy dependence of the astrophysical S factor, they disagree in the extrapolated S34(0) value at a 3σ level.A novel approach uses the European Recoil separator for Nuclear Astrophysics (ERNA) to detect directly the 7Be ions produced in the reaction and, additiona...