Track nanodosimetry of 20-MeV protons at 20 nm.

Track nanodosimetry is the theoretical and experimental research which studies the stochastic aspects of ionisation yield produced by ionising particles in nanometric target volumes, positioned at different distances from the primary particle track. The STARTRACK experimental set-up, mounted on the +50° beam line at the Tandem-Alpi particle accelerator of Legnaro National Laboratories, has been conceived to give an experimental basis to nanodosimetric calculations. STARTRACK is a detection system able to measure the ionisation cluster-size distributions in a 20 nm propane site, by counting the electrons set in motion by different ion tracks, with the resolution of one electron. The 'sensitive volume' SV can be moved at different distances from the primary particle track (different impact parameter). Distributions of 20-MeV protons have been measured and compared with Monte Carlo calculations.

The STARTRACK experiment.

STARTRACK is the acronym of an experiment that aims to measure ionisation cluster distributions in nanometric sites placed at different distances from an accelerated charged particle track. STARTRACK will first use the 20 nm wall-less detector, already used for studying the nanometric track structure of an alpha particle, and then a new detector designed for measuring ionisation clusters in 10 nm sites. The experiment is mounted on the beam line of the Tandem-Alpi accelerator facility of the Legnaro Laboratories, which supplies ion beams from hydrogen to gold up to energy ranging from 7 to 28 MeV/amu. Track nanodosimetry aims to measure ionisation clusters along and aside the ion track down to occurrence probability of 10(-5). To reach such a goal at least 10(6) events have to be collected and the cluster pile-up probability has to be reduced to less than 10(-6). By using a beam profile detector, which is sensitive to very weak currents, and an event rejector counter, such an aim is feasible.

Two miniaturised TEPCS in a single detector for BNCT microdosimetry.

Microdosimetry with tissue-equivalent proportional counters (TEPC) has proven to be an ideal dosimetry technique for mixed radiation fields as those ones used in boron neutron capture therapy (BNCT). A new counter, composed of two twin cylindrical mini TEPCs inserted in a slim titanium sleeve of 2.7 mm external diameter, has been constructed. The detector has been designed to perform dosimetry and microdosimetry in intense radiation fields. The two mini TEPCs work in gas flow mode. They have right cylinder sensitive volumes of 0.9 mm. In spite of gas line tiny sizes, the gas pressure inside the two counters is well established with <1% of uncertainty. The counter has been calibrated in a secondary standard photon fields. The mean of the effective sensitive volume sizes has been measured to be 0.86 mm. The twin TEPC acquisition system processes properly the signals up to about 30 kHz of counting rate. Therefore, twin TEPC can perform dosimetric measurements in photon field with intensities of some tens of Gy h(-1).

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.

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.

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.

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.

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.

A feasibility study of a single event spectrometer based on semiconductor devices.

The electronics employed around particle accelerators can be disturbed or damaged because of single event effects (SEE). The most likely effect is the single event upset (SEU) which may affect all memory devices. In the case of high energy accelerators, SEUs are mostly produced by secondary charged particles generated by neutron interactions. The measurement of the energy and the lineal energy distribution of these neutron-induced charged particles was proposed. As a first approach, a commercial p-i-n photodiode was employed. This device was irradiated with thermal and monoenergetic fast neutrons. Some effects limiting the use of such a detector as a SEE spectrometer were observed, giving guidelines for the design of an application specific integrated circuit (ASIC). The possibility of creating a solid state microdosemeter by coupling the ASIC with a tissue-equivalent radiator is discussed. Moreover, the p-i-n photodiode covered with a hydrogenated plastic radiator may be employed as a proton-recoil spectrometer.

Track nanodosimetry of an alpha particle.

Experimental measurements and calculations are described of ionisation distributions in propane wall-less gas cavities of about 20 nm simulated size, performed at different distances from a 244Cm alpha particle track. Ionisation events are detected one by one by collecting electrons from the sensitive volume and by separating them with a drift column. Experimental results and Monte Carlo calculations indicate that, in the delta ray cloud, conditional probability curves, average cluster size and the ratio of second moment above first moment of the cluster distribution are invariant with track distance.

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.

Stilbene compounds and stilbene synthase expression during ripening, wilting, and UV treatment in grape cv. Corvina.

The content of selected phenolic compounds including resveratrol (trans-3,5,4'-trihydroxystilbene) and its cis-isomer and glucosides (piceides) were monitored in grape (Vitis vinifera L. cv. Corvina) berry skin during ripening in the vineyard and in response to the post-harvest drying process (wilting). Four wilting conditions were compared (traditional, mixed, low-temperature, and high-temperature) to verify the eliciting effect of drying on resveratrol production. During fruit ripening the cis-piceid was the major stilbene found in berry skins, and a weak accumulation of stilbene synthase (STS) mRNA was observed, whereas UV-light irradiation greatly stimulated STS transcript of unripe berries. A time-course experiment showed the highest STS mRNA accumulation and resveratrol content (34 microg/g fresh weight at 58 days) occurring in berry skins in a mixed wilting process.