Pulsed plasma ion source to create Si nanocrystals in SiO2 substrates

A pulsed KrF excimer laser of irradiance of about 10⁸ W/cm² was utilized to synthesize Si nanocrystals on SiO₂/Si substrates. The results were compared with that ones obtained by applying low bias voltage to Si(1 0 0) target in order to control the kinetic energy of plasma ions. Glancing incidence X-ray diffraction spectra indicate the presence of silicon crystalline phases, i.e. (1 1 1) and (2 2 0), on SiO₂/Si substrates. The average Si nanocrystal size was estimated to be about 45 nm by using the Debye-Scherrer formula. Scanning electron microscopy and atomic force microscopy images showed the presence of nanoparticles of different size and shape. Their distribution exhibits a maximum concentration at 49 nm and a fraction of 14% at 15 nm.     

Molecular technology and the recombinant TSH have changed diagnostics of thyroid carcinoma with positive I-131 whole body scan but low serum thyroglobulin

The early detection of recurrent differentiated thyroid carcinoma (DTC) cells in the post surgery DTC patients relies on the sensitivity of measuring both the level of thyroglobulin (Tg) and 131-Iodine distribution by Whole Body Scan (WBS). Undetectable level of Tg associated with negative WBS or elevated levels of Tg associated with positive WBS ("concordant") is ordinarily indicative of either absence or presence of disease. At times, elevated level of Tg with negative WBS or low levels of Tg with positive WBS ("discordant") could also occur. In the present study, we retrospectively reviewed series of 573 patients with DTC followed in the Diagnostic Imaging and Radiotherapy of the University "Federico II" of Naples between 1993 and 1997. We focused on 9 out of 573 patients (1.56%) who had a discordant pattern with low level of Tg/positive WBS in the post-surgical follow-up. Four patients were metastatic at presentation while 5 patients with metastasis during follow-up still remained in persistently low levels of Tg (<5 ng/mL). This result does point to some flaw in the evaluation of "discordant" cases. Reviewing data previously described series by resetting cut-off values of Tg <1 ng/ml as undetectable changed the apparent "discordant" subgroup of patients into "concordant". Recent introduction of recombinant human TSH (rhTSH) to enhance the expression level of Tg brought significant increase in the sensitivity of diagnostic evaluation of thyroid cancer patients. The role of burdensome WBS in the follow up evaluation of DTC patients is significantly reduced over time especially in low-risk patients while the relevance of Tg assay is steadily increased. Sensitive Tg assays, significantly improved our ability to assess disease status in follow-up of DTC. Given the possibility of late disease relapses, the need for long-term follow-up, and reduced delay in treatment of persistent disease, there is still need for greater sensitive diagnostic tools for DTC.     

Measurement of the total proton-proton cross-section at the ISR

We present the first results of a measurement of the total cross-section σ_T in proton-proton collisions at equivalent laboratory momenta between 291 and 1480 GeV/c at the CERN Intersecting Storage Rings (ISR). The method is based on the measurement of the ratio of the total interaction rate and the machine luminosity. The data show an increase of about 10% in σ_T in this energy interval.     

Thermal treatments and characterizations of pellets for SPES direct target

In this work targets of graphite-rich lanthanum dicarbide have been produced through carburization and sintering of suitable precursor pellets obtained by mixing and pressing lanthanum oxide and graphite powders. The results about the control of the production process and the investigation of the physical properties of the pellets, performed respectively through thermal analyses (TG/DTA) and X-ray diffraction (XRD), are reported and discussed.     

The SPES direct UCx target

A possible solution for a target system aimed at the production of exotic nuclei as a result of high energy fissions in ²³⁸U compounds has been analyzed. The proposed configuration is constituted by a primary proton beam (40 MeV, 0.2 mA) directly impinging on uranium carbide disks inserted within a cylindrical carbon box. This system has been conceived to obtain both a high number of neutron rich atoms (originated from about 10¹³ fissions/s) and a low power deposition in the target. In order to extract the fission fragments, the box has to be hold at 2000^○C. The thermal analysis shows the capability of the thermal radiation to cool the disks with a reasonable margin below the material melting point. Moreover, the analyses of the thermo-mechanical behaviour and of the effusion times confirm the promising features of this target configuration.     

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

Light charged particle (LCP) emission in the evaporation residue (ER) and fusion fission (FF) channels have been studied for the 200 MeV ³²S + ¹⁰⁰Mo reaction, leading to ¹³²Ce composite nuclei at E _x =122 MeV. The main goal was to study the decay of ¹³² Ce on the basis of an extended set of observables, to get insights on the fission dynamics. The proton and alpha particle energy spectra, their multiplicities, ER-LCP angular correlations, ER and FF angular distributions, and ER and FF cross-sections were measured. The measured observables were compared with the Statistical Model (SM). Using standard parameters, the model was able to reproduce only the pre-scission multiplicities and the FF and ER cross-sections. The calculation was observed to strongly overestimate the proton and alpha particle multiplicities in the ER channel. Disagreements were also observed for the ER-LCP correlations, the LCP energy spectra and the ER angular distribution. By varying the SM input parameters over a wide range of values, it is shown that it is not possible to reproduce all the observables simultaneously with a unique set of parameters. The inadequacy of the model in reproducing the ER particle multiplicities is also observed analysing data from the literature for other systems in the A ≈ 150 and E _x ≈ 100?200 MeV region. These results indicate serious limitations about the use of the SM in extracting information on fission dynamics.     

Tunable hot-electron transfer within a single core-shell nanowire

We report the hot photoexcited electron transfer across the coaxial interface of a cylindrical core-shell nanowire. Modulation of the transfer rates, manifested as a large tunability of the voltage onset of negative differential resistance and of voltage-current phase, is achieved using three different modes. The coupling of electrostatic gating, incident photon energy, and the incident photon intensity to transfer rates is facilitated by the combined influences of geometric confinement and heterojunction shape on hot-electron transfer, and by electron-electron scattering rates that can be altered by varying the incident photon flux, with evidence of weak electron-phonon scattering. Dynamic manipulation of this transfer rate permits the introduction and control of a continuously adjustable phase delay of up to ～130° within a single nanometer-scale device element.     

Experimental determination of in-medium cluster binding energies and Mott points in nuclear matter

In-medium binding energies and Mott points for d, t, 3He and α clusters in low-density nuclear matter have been determined at specific combinations of temperature and density in low-density nuclear matter produced in collisions of 47A MeV 40Ar and 64Zn projectiles with 112Sn and 124Sn target nuclei. The experimentally derived values of the in-medium modified binding energies are in good agreement with recent theoretical predictions based upon the implementation of Pauli blocking effects in a quantum statistical approach.