Search

The lower operation limit of common tissue equivalent proportional counters (TEPCs) is about 0.3 μm in simulated site. On the other hand, the pattern of the particle interactions at the nanometric level, which has a correlation with the radiation induced damage on the DNA, is measurable by only three instruments worldwide. In order to fill this gap, a novel TEPC capable of simulating site sizes down to 25 nm was designed and constructed. Its response was characterized with gamma, neutron and carbon beams and the capability in measuring microdosimetric spectra at 25 nm was demonstrated. The present paper aims at describing a further characterization of this TEPC by simulating with the Monte Carlo FLUKA code the microdosimetric spectra measured with a carbon beam. Since the sensitive volume of the TEPC has an unconventional shape, a study on the chord length distribution for the adopted irradiation set-up was performed and compared with the analytical one. The results show a good agreement between the experimental data and the FLUKA simulations, showing that this code is capable of reproducing microdosimetric spectra of a carbon beam down to 25 nm in simulated site.

An innovative portable detection system based on real-time spectrometry was developed for neutron field characterization and dosimetry. This system, called DIAMON (Direction-aware Isotropic and Active neutron MONitor with spectrometric capabilities), relies on a multi-detector geometry and a built-in unfolding code to provide in real time all field and operational quantities of interest. A patent pending design provides a quasi-ideal isotropic response and an optimized spectrometric performance from thermal to high energies. Furthermore, the custom signal processing and acquisition system is conceived for deriving continuously the 3D directional distribution of incoming neutrons. This work describes the characterization of DIAMON performances carried out at the neutron calibration facility of Politecnico di Milano. Neutron spectra, field quantities and dosimetric values are reported and compared with those assessed by a reference, calibrated, Bonner Sphere System. The overall variability of the DIAMON angular response and the gamma sensitivity are presented and discussed. An example of the continuous monitoring capabilities is also shown. Results demonstrate DIAMON is an all-in-one detection system able to characterize accurately all neutron field properties in real-time.

The tissue-equivalent proportional counter (TEPC) is the most accurate device for measuring the microdosimetric properties of a particle beam but, since the lower operation limit of common TEPCs is ~0.3 μm, no detailed information on the track structure of the impinging particles can be obtained. The pattern of particle interactions at the nanometric level is measured directly by only three different nanodosimeters worldwide: practical instruments are not yet available. In order to partially fill the gap between microdosimetry and track-nanodosimetry, a low-pressure avalanche-confinement TEPC was designed and constructed for simulating tissue-equivalent sites down to the nanometric region. The present paper aims at describing the response of this TEPC in the range 0.3 μm-25 nm to a 62 MeV/n 4He ion beam. The experimental results, for depths near the Bragg peak, show good agreement with FLUKA simulations and suggest that, for smaller depths, the distribution is highly influenced by secondary electrons.

The tissue equivalent proportional counter (TEPC) is the most accurate device for measuring the microdosimetric properties of a particle beam, showing to assess the relative biological effectiveness by linking the physical parameters of the radiation field with the corresponding biological response. Nevertheless, no detailed information on the track structure of the impinging particles can be obtained, since the lower operation limit of the common TEPCs is about 0.3 μm. On the other hand, the pattern of particle interactions at the nanometer level, which demonstrated to have a strong correlation with radiation-induced damages to the DNA, is measured directly by only three different nanodosimeters worldwide: practical instruments are not yet available. The gap between microdosimetry and track-nanodosimetry can be filled partially by extending the TEPC response down to the nanometric region. A feasibility study of a novel TEPC designed to simulate tissue-equivalent sites in the nanometric domain was performed. The present paper aims at describing the design, the development and the characterization of this avalanche-confinement TEPC. Irradiations with photons, fast neutrons and low-energy carbon ions demonstrated the capability of this TEPC of measuring in the range 0.3 μm–25 nm.

The design and development of a recent avalanche-confinement tissue equivalent proportional counter (TEPC) for microdosimetry and nanodosimetry applications required the selection of a proper miniaturized solid state detector (SSD) for detecting alpha particles emitted by a thick removable Cm-244 source embedded in the cylindrical TEPC chamber for characterization and calibration purposes. Since the available cavity for embedding the SSD detector is only 4.2 mm in diameter, no standard devices can be exploited. The selection of the best SSD for this application was based on the following requirements: very low size, proper energy resolution, cheapness. The performances of the finally selected SSD were assessed by exploiting a multi-peak calibration alpha source (Pu-239, Am-241, Cm-244). The measured energy resolution resulted about 25 keV FWHM. The TEPC calibration procedure, which exploits the selected SSD aligned to the built-in Cm-244 alpha source, is described in details.

The tissue equivalent proportional counter (TEPC) is the most accurate device for measuring the microdosimetric properties of a particle beam, nevertheless no detailed information on the track structure of the impinging particles can be obtained, since the lower operation limit of common TEPCs is about 0.3 μm. On the other hand, the pattern of particle interactions is measured by track-nanodosimetry, which derives the single-event distribution of ionization cluster size at the nanometric scale. Anyway, only three nanodosimeters are available worldwide. A feasibility study for extending the performances of TEPC down to the nanometric region was performed and a novel avalanche-confinement TEPC was designed and constructed. This detector is constituted by a cylindrical chamber, based on a three-electrode structure, connected to a vacuum and gas flow system to ensure a continuous replacement of the tissue equivalent gas, thus allowing to simulate different biological site sizes in the range 300-25 nm. This TEPC can be calibrated by exploiting a built-in alpha source and a miniaturized solid-state detector as a trigger. Irradiations with photons, fast neutrons and two hadron beams demonstrated the good performances of the device. A satisfactory agreement with FLUKA simulations was obtained.