Biomedical subjects

L De Nardo

Publications and source records attributed to L De Nardo.

At least 19 recordsLinked to original sources

PubMed2007

Bayesian reconstruction of nanodosimetric cluster distributions at 100% detection efficiency.

Ionisation spectra in nanometric volumes at a given distance from a charged particle track are obtained by using electron (or ion) gas detectors, having non-uniformly distributed detection efficiency. Therefore, such spectra should be properly processed in order to reconstruct the frequency distribution of clusters really produced in the detector gas. A Bayesian unfolding has been applied to ionisation distributions due to 5.4 MeV alpha particles in a 20-nm site obtained by Monte Carlo simulations, taking into account different detection efficiency conditions. It will be shown that Bayesian analysis provides a valid tool for reconstructing the true ionisation distributions, well beyond the maximum measured cluster size.

Bayes Theorem↗

PubMed2006

Simulation of the measured ionisation-cluster distributions of alpha-particles in nanometric volumes of propane.

In the last years, the probability of the formation of ionisation clusters by primary alpha particles at 5.4 MeV in nanometric volumes of propane (20.6 and 24.0 nm in a material of density 1.0 g cm(-3)) was studied experimentally and by Monte Carlo simulation. Calculations were performed taking into account the single electron detection efficiency of the track-nanodosimetric counter, which was estimated on the base of Monte Carlo calculations of electron transport inside the detector. Now a new evaluation of the efficiency has been performed, pointing out a value lower than previously estimated. Besides, the efficiency of the counter in resolving temporally the collected electrons has been calculated, together with its effect on the measured distribution. On the base of these evaluations, a new comparison has been performed between measurements and calculations, pointing out a better agreement than previously reported.

Alpha Particles↗

PubMed2006

Double-hadron leptoproduction in the nuclear medium.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

Journal Article↗

PubMed2005

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

Journal Article↗

PubMed2005

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target.

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

Journal Article↗

PubMed2004

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Journal Article↗

PubMed2004

Mini-TEPCs for radiation therapy.

A mini-tissue-equivalent proportional-counter (TEPC) has been constructed to study the possibility to manufacture mini-counters without field-shaping tubes for radiation therapy. The mini-TEPC can be assembled with and without field-shaping tubes. It can be equipped with a mini-alpha source for a precise lineal energy calibration. After the positive conclusions of this study, a slim TEPC has been designed and constructed. The slim TEPC has an external diameter of only 2.7 mm. It has been tested with therapeutic proton beams and gamma ray sources.

Equipment Design↗

PubMed2004

Microdosimetric investigation at the therapeutic proton beam facility of CATANA.

Proton beams (62 Mev) are used by the Laboratori Nazionali del Sud of the Italian Institute of Nuclear Physics to treat eye melanoma tumours at the therapeutic facility called CATANA. A cylindrical slim tissue-equivalent proportional counter (TEPC) of 2.7 mm external diameter has been used to compare the radiation quality of two spread-out Bragg peaks (SOBP) at the CATANA proton beam.

Algorithms↗

PubMed2004

Design of a 10 nm electron collector for a track-nanodosimetric counter.

Recently we have developed a track-nanodosimetric counter, which is a gas detector that measures the distributions of electrons induced by a charged particle in nanometric volumes of tissue equivalent matter, positioned at different distances from the track. Sites equivalent to 20 and 24 nm were defined by means of an electron collector, which is a system of electrodes enclosing an almost wall-less cylindrical volume. In this paper, we present the design of a new electron collector that is able to simulate a volume as small as 10 nm in diameter.

Algorithms↗

PubMed2004

Reconstruction of cluster distributions at 100% detection efficiency for a track-nanodosimetric counter through a Bayesian analysis.

A Bayesian unfolding has been applied to ionisation distributions due to 5.4 MeV alpha particles in a 20-nm site obtained using Monte Carlo simulations, taking into account different detection efficiency conditions. The ideal case of a target volume with uniform efficiency has been investigated to study the dependence of the reconstruction on prior distributions. A simplified approach has been used to treat the case of a target volume with non-uniformly distributed efficiency, like the sensitive volume of the track-nanodosimetric counter. Our results point out that Bayesian analysis provides a effective tool for reconstructing the true ionisation distributions, well beyond the maximum measured cluster size.

Algorithms↗

PubMed2004

First microdosimetric measurements with a TEPC based on a GEM.

A new type of mini multi-element tissue-equivalent proportional counter (TEPC) based on a gas electron multiplier (GEM) has been designed and constructed. This counter is in particular suitable to be constructed with a small sensitive volume so that it can be used for microdosimetry in intense pulsed radiation fields to measure the microdosimetric spectrum in the beam of, for instance, a clinical linear accelerator. The concept lends itself also for a mini multi-element version of the counter to be used for applications in which a high sensitivity is required. In this paper, we present the first microdosimetric measurements of this novel counter exposed to a 14 MeV monoenergetic neutron beam and a californium (252Cf) source for a counter cavity diameter of 1.8 mm simulating 1.0 microm tissue site size. The measured spectra showed an excellent agreement with spectra from the literature. The specific advantages of the TEPC-GEM are discussed.

Algorithms↗

PubMed2004

Experimental equivalent cluster-size distributions in nanometric volumes of liquid water.

Ionisation cluster-size distributions in nanometric volumes of liquid water were determined for alpha particles at 4.6 and 5.4 MeV by measuring cluster-size frequencies in small gaseous volumes of nitrogen or propane at low gas pressure as well as by applying a suitable scaling procedure. This scaling procedure was based on the mean free ionisation lengths of alpha particles in water and in the gases measured. For validation, the measurements of cluster sizes in gaseous volumes and the cluster-size formation in volumes of liquid water of equivalent size were simulated by Monte Carlo methods. The experimental water-equivalent cluster-size distributions in nitrogen and propane are compared with those in liquid water and show that cluster-size formation by alpha particles in nitrogen or propane can directly be related to those in liquid water.

Algorithms↗

PubMed2004

BNCT microdosimetry at the tapiro reactor thermal column.

A thermal column is available for dosimetric and radiobiological studies by the fast reactor TAPIRO, located at the ENEA research centre Casaccia. The TAPIRO neutron field has been studied (in the frame of LNL BNCT project) with a tissue-equivalent proportional counter, which has worked alternatively with an ordinary tissue-equivalent cathode and with a boron-enriched cathode. Measurements have been performed with polyethylene caps of different thickness. Both the absorbed dose and the microdosimetric-calculated biological effective dose show a maximum at approximately 0.5 mg cm(-2) of depth. The different dose components have been calculated and the results are discussed.

Body Burden↗

PubMed2003

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

Journal Article↗

PubMed2003

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

Journal Article↗

PubMed2003

Bayesian analysis of data: reconstruction of track structure at 100% detection efficiency for a track-nanodosimetric counter.

An algorithmic reconstruction of the probability distribution of ionisation cluster-size formation from measurements performed with detectors having a non-uniform sensitive volume is presented. From such a data analysis, ionisation spectra, which correspond to a detection efficiency of 100% are extracted for the track-nanodosimetric counter at L.N.L.-I.N.F.N.

Algorithms↗

PubMed2002

Ionization-cluster distributions of alpha-particles in nanometric volumes of propane: measurement and calculation.

The probability of the formation of ionization clusters by primary alpha-particles at 5.4 MeV in nanometric volumes of propane was studied experimentally and by Monte Carlo simulation, as a function of the distance between the center line of the particle beam and the center of the target volume. The volumes were of cylindrical shape, 3.7 mm in diameter and height. As the investigations were performed at gas pressures of 300 Pa and 350 Pa, the dimensions of the target volume were equivalent to 20.6 nm or 24.0 nm in a material of density 1.0 g/cm(3). The dependence of ionization-cluster formation on distance was studied up to values equivalent to about 70 nm. To validate the measurements, a Monte Carlo model was developed which allows the experimental arrangement and the interactions of alpha-particles and secondary electrons in the counter gas to be properly simulated. This model is supplemented by a mathematical formulation of cluster size formation in nanometric targets. The main results of our study are (i) that the mean ionization-cluster size in the delta-electron cloud of an alpha-particle track segment, decreases as a function of the distance between the center line of the alpha-particle beam and the center of the sensitive target volume to the power of 2.6, and (ii) that the mean cluster size in critical volumes and the relative variance of mean cluster size due to delta-electrons are invariant at distances greater than about 20 nm. We could imagine that the ionization-cluster formation in nanometric volumes might in future provide the physical basis for a redefinition of radiation quality.

Biophysics↗

PubMed2002

Nanodosimetric measurements with an avalanche confinement TEPC.

This paper illustrates a tissue-equivalent proportional counter designed to have high gas gain and good energy resolution at nanometric simulated site sizes. Microdosimetric neutron and gamma spectra were measured in dimethyl ether and in propane-based tissue-equivalent gas mixture down to 35 nm. The comparison of experimental data with the results of Monte Carlo calculations shows a satisfactory agreement.

Dose-Response Relationship, Radiation↗