[en] Radiation shielding for proton radiation therapy facilities is determined by energetic secondary neutrons produced by proton bombardment of accelerator components and patients. Because of the scarcity of data describing neutron production, attenuation, dose, and dose equivalent values, the authors have measured these parameters for several target materials and for bulk concrete shielding. Preliminary results showing the microdosimetric event size spectra as well as absorbed dose and dose equivalent values derived from these spectra were deduced. Attenuation lengths determined from these spectra were deduced. Attenuation lengths determined form these measurements are presented and compared with Monte Carlo calculations

[en] Short communication

[en] We report a series of measurements directed to assess the suitability of alanine as a mailable dosimeter for dosimetry quality assurance of proton radiation therapy beams. These measurements include dose-response of alanine at 140 MeV, and comparison of response vs energy with a parallel plate ionization chamber. All irradiations were made at the Harvard Cyclotron Laboratory, and the dosimeters were read at NIST. The results encourage us that alanine could be expected to serve as a mailable dosimeter with systematic error due to differential energy response no greater than 3% when doses of 25 Gy are used. (Author)

[en] Shape-memory polymers (SMPs) are being increasingly proposed for use in biomedical devices. This paper investigates the cytotoxicity, surface characteristics and thermomechanics of two acrylate-based SMP networks as a function of sterilization using a minimal essential media elution test, FTIR-ATR and dynamic mechanical analysis (DMA). Networks sterilized by low-temperature plasma elicited a cytotoxic response and are shown to completely destroy the cell monolayer. FTIR-ATR analysis showed evidence of surface oxidation with an increase and broadening of the absorbance peak from ∼3500 to 3100 cm^-1, which is associated with an increase in hydroxyl groups. DMA revealed small, but statistically significant, differences in reduction of the glass transition temperatures of both networks when sterilized with gamma irradiation. One network showed an increase in rubbery modulus, which is an indication of crosslink density, after gamma irradiation. Lastly, practical sterilization concerns of SMP devices are discussed in light of the different methods

[en] The preliminary results are presented of a series of measurements performed at the Centre de Protontherapie d'Orsay to evaluate the neutron yield when a 200 MeV proton beam interacts with aluminium and water, the attenuation of different thicknesses of concrete at different angles and the response of different detectors. The effect of shielding has been fitted to exponential functions with first estimations of attenuation lengths for both targets and angles from 0^o to 90^o. The attenuation length for aluminium changes from 900 kg.m^-2 at 0^o to 680^okg.m^-2 at 90^o, in agreement with published data. Similar values have been obtained for water targets. The source term seems to be underestimated, in spite of using an extended range rem counter. Microdosimetric spectra have been obtained simulating the conditions used to extend the energy range or rem counters. (author)

[en] Background and purpose: Methods for determining absorbed dose in clinical proton beams are based on dosimetry protocols provided by the AAPM and the ECHED. Both groups recommend the use of air-filled ionization chambers calibrated in terms of exposure or air kerma in a ⁶⁰Co beam when a calorimeter or Faraday cup dosimeter is not available. The set of input data used in the AAPM and the ECHED protocols, especially proton stopping powers and w-value is different. In order to verify inter-institutional uniformity of proton beam calibration, the AAPM and the ECHED recommend periodic dosimetry intercomparisons. In this paper we report the results of an international proton dosimetry intercomparison which was held at Loma Linda University Medical Center. The goal of the intercomparison was two-fold: first, to estimate the consistency of absorbed dose delivered to patients among the participating facilities, and second, to evaluate the differences in absorbed dose determination due to differences in ⁶⁰Co-based ionization chamber calibration protocols. Materials and methods: Thirteen institutions participated in an international proton dosimetry intercomparison. The measurements were performed in a 15-cm square field at a depth of 10 cm in both an unmodulated beam (nominal accelerator energy of 250 MeV) and a 6-cm modulated beam (nominal accelerator energy of 155 MeV), and also in a circular field of diameter 2.6 cm at a depth of 1.14 cm in a beam with 2.4 cm modulation (nominal accelerator energy of 100 MeV). Results: The results of the intercomparison have shown that using ionization chambers with ⁶⁰Co calibration factors traceable to standard laboratories, and institution-specific conversion factors and dose protocols, the absorbed dose specified to the patient would fall within 3% of the mean value. A single measurement using an ionization chamber with a proton chamber factor determined with a Faraday cup calibration differed from the mean by 8%. Conclusion: The adoption of a single ionization chamber dosimetry protocol and uniform conversion factors will establish agreement on proton absorbed dose to approximately 1.5%, consistent with that which has been observed in high-energy photon and electron dosimetry

[en] Influence of dispersed particles of Ti₃Ni₄ on the shape memory effect and superplasticity was studied using Ti-51 at.% Ni monocrystals oriented for extension along <111>. It was shown experimentally that aging according to the following conditions: 823 K, 1.5 h; 773 K, 1 h; 673 K, 1 h - results in isolation of four crystallographically equivalent variants of dispersed particles. It was ascertained that by regulating the number and size of Ti₃Ni₄ particles that do not experience martensitic transformation one can control the shape memory effect, temperature range of superplasticity and mechanical hysteresis value

[en] This paper presents experimental investigation of nanoscale indentation formation in shape memory polymers. The polymers were synthesized by photopolymerizing a tert-butyl acrylate (tBA) monomer with a poly(ethylene glycol dimethacrylate) (PEGDMA) crosslinker. The concentration and the molecular weight of the crosslinker were varied to produce five polymers with tailored properties. Nanoscale indentations were formed on the polymer surfaces by using a heated atomic force microscope (AFM) cantilever at various temperatures near or above the glass transition (between 84 and 215 deg. C) and a range of heating durations from 100 μs to 8 ms. The images of the indents were obtained with the same probe tip at room temperature. The contact pressure, a measure of transient hardness, was derived from the indentation height data as a function of time and temperature for different polymers. With increasing crosslinker molecular weight and decreasing crosslinker concentration, the contact pressures decreased at a fixed maximum load due to increased crosslink spacing in the polymer system. The results provide insight into the nanoscale response of these novel materials