[en] We study the effect of tempering on a martensitic steel containing 1.23 wt.% carbon, in the temperature range 300-800 K, correlating the results obtained by measurements of thermoelectric power (TEP), Young's modulus, calorimetry, nanoindentation, and the observations by transmission electron microscopy (TEM). Two tempering stages are observed, one between 350 and 430 K, and the other between 470 and 550 K. They are attributed to two stages of carbon precipitation. The evolution of Young's modulus, TEP, and hardness is mainly attributed to the change of the amount of interstitial carbon in iron

[en] The in vivo colony method used to generate survival curves following exposure to ionizing irradiation allows to score large clones, representing surviving cells, and small colonies, representing late reproductive death. By subtraction, early-dying cells can be estimated. In the three human tumour cell lines examined, we have observed that early cell death is a major mode of action of irradiation. The contribution of early cell death to total mortality increases as the dose increases. Moreover, repair due to dose-splitting and delayed plating in densely-inhibited cells is not observed in early-dying cells. (authors)

[en] Full text: Composites made of zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (CNTs) were processed by spark plasma sintering with various amounts of CNTs (3Y-TZP/X wt% CNT, X=0, 0.5, 1.5, 3 and 5). High temperature mechanical properties were investigated using mechanical spectroscopy and low stress (8 MPa) creep. The general mechanical loss spectrum consists of a mechanical loss peak at a frequency of about 0.1 Hz, which is superimposed on an exponential increase at low frequency. The absence of a well-marked peak in monolithic 3Y-TZP is justified considering that the restoring force due to the elasticity of neighboring grains decreases at low frequencies or high temperatures. However, with CNT additions the mechanical loss and creep rate decreases and a better resolved peak was observed. These results can be interpreted by the pinning effect of CNTs, which can hinder grain boundary sliding at high temperatures, resulting in a creep resistance improvement. (author)

[en] The paper describes an optical interferometer realized at INRiM, which works as pressure standard based on a well-known phenomenon of light-matter interaction: the dependence of refractive index with pressure (density) of a gas. The realization of a pressure standard via optical method requires a combined approach of high accurate refractive index measurements (sub-nanometer and sub-millikelvin metrology) with ab-initio quantum calculation of molar refractivity, paving the way for a quantum-based standard.

The paper reports recent development concerning a new layout of the system, currently focused to improve the temperature measurement and stability.

The developed system is a preliminary achievement towards a quantum-based pressure standard in the range between 100 Pa and 150 kPa. (paper)

[en] V 79 cells were exposed to fast neutrons generated by 60 MeV p -> Be produced by the cyclotron Medicyc at four different depths: 1.3, 25.8, 72.2 and 116.8 mm. Survival was assessed by the in vitro colony method. Mean inactivation doses (MID) were significantly different among the four points. The ratio of MID was used to determine the relative efficiency of the neutron beam at these points. Compared to 25.8 mm depth, a 40 % increase in biological effect was observed at the superficial point versus a 14 to 16 % decrease in effect for the deeper points. This is ascribed to absorption of low energy neutrons near the surface and to beam hardening with depth. Taking in consideration the relative physical dose delivered, these findings suggest that skin-sparing may be markedly reduced and that the lower effectiveness with depth should be kept in mind when dealing with deep tumours. (author)

[en] The aim of this study was to measure the biological efficiency of a low-energy argon beam (E=7.1 MeV/nucleon, LET=1590 keV/μm) on a human melanoma cell line (CAL4) established in our Institute. Two different methods were used: the micronucleus (MN) test and the colony-forming assay. MN are scored in binucleate cells (BNC) and are formed from acentric fragments or whole chromosomes that have not been incorporated into daughter nuclei at mitosis. The colony-forming assay quantifies reproductive death. Parallel experiments were run with cobalt gamma-rays for comparison. After Co irradiation, the MN-free BNC dose-response curve coincided with that of the loss of colony-forming ability, suggesting the potential of the former as a predictive test of cell killing. After Ar irradiation, there was a dissociation between the two effects, especially at high doses: cell death was greater than the frequency of BNC with MN. The inactivation cross-section was 74 μm²; it was 39 μm² for MN yield. Therefore, the relative biological effectiveness (RBE) was higher for cell killing than for MN yield (0.8 and 0.5, respectively, at a Co dose of 3 Gy). The total MN count in BNC followed the same pattern of response as the fraction of BNC with MN. However, multiple (>2) MN in BNC were more frequently observed after low-dose Ar irradiation than after gamma-ray exposure (RBE > 1). Moreover, the frequency of multiple MN induction exceeded that expected from a Poisson distribution at all dose levels of Ar irradiation. (orig.)

[en] In an effort to clarify the relationship between sensitivity of human tumour cells to low-LET and to fast neutron irradiation, 10 human tumour cell lines were exposed to cobalt gamma-rays and to 60 MeV (p→Be⁺) neutron beam. The data were pooled with results of 31 human tumour cell lines previously published. The analysis of data using the linear-quadratic model indicated that not only α values increased after neutron irradiation, but so did β values too, although to a lesser extent. The mean inactivation dose (MID) was derived for each cell line from the linear-quadratic parameters after low-LET and high-LET exposure. MID values following neutron irradiation were closely correlated to those after gamma-ray irradiation. In these 41 cell lines, the extreme values of RBE derived by the ratio of MID varied by a factor of 3 among the cell lines. RBE was positively correlated to photon MID, meaning that intrinsically radiation resistant tumour cells have a higher neutron RBE, on average. Similar findings were observed if α ratios were used instead of MID ratios. In addition, the RBE/dose variations were more marked in cells with the higher RBE. Taken together, these data suggest that, although considerable variations exist among human tumour cell lines, intrinsically radioresistant cells are relatively more sensitized when exposed to high LET beams than radioresponsive tumours. An 'intrinsic gain factor' may thus be expected in irradiating radiation resistant tumours with fast neutrons, in addition to the hypoxic or kinetic gain factors. Because the quadratic component is still present after neutron irradiation, we suggest using MID ratio as a reference RBE when comparing survival curves of cells exposed to radiations of different qualities. (orig.)

[en] Calorimetry and internal friction were used to study the martensitic phase transformation of shape-memory metal matrix composites consisting of nearly equiatomic NiTi with up to 20 vol.% TiC particles. The start and final temperatures for the austenite-martensite transformation (M_s, M_f) and martensite-austenite transformation (A_s, A_f) are lower when measured by internal friction than when measured by calorimetry. In composites, TiC particles lower M_f and A_s but do not affect M_s and A_f. It is concluded that dissipative work due to twinning takes place to accommodate internal stresses. (orig.)

[en] It is well known that the properties of high-Tc superconducting materials depend strongly on the oxygen atoms (concentration and structural configuration). Consequently, understanding the oxygen mobility on an atomic scale becomes very important. This work presents the study of the oxygen mobility by means of internal friction measurements. Two energy dissipation peaks, which are closely related to the oxygen concentration, have been observed at 115 K (in the kilohertz frequency) and 510 K (in the low frequency range) respectively. Both of them are relaxation peaks. The first, at low temperature, (P_L) has an activation energy H_L = 0.17 ev. The second, at high temperature, (P_H) has an activation energy H_H = 1.10 ev. Both have frequency factors in the order of ∼ 10¹² sec^-1. Annealing the specimen in vacuum shows that the heights of both peaks decrease continuously as the annealing temperature is increased. This study of the relaxation strength reduction during annealing has been compared with measurements of oxygen loss (by weighing the specimen), electrical resistivity, and X-ray diffraction. Peak relaxation strengths are well correlated with the oxygen loss. Two relaxation models, which are both due to oxygen atoms movement within the basal Cu-O plane, could explain these two internal friction peaks. (orig.)

[en] Neutron diffraction measurements of internal elastic strains and texture were performed during uniaxial compressive deformation of martensitic NiTi. Rietveld refinement of the diffraction spectra was performed in order to obtain lattice parameter variations and preferred orientation of martensitic variants during deformation. The elastic internal strain is proportional to the externally applied stress but strongly dependent on crystallographic orientation. Plastic deformation by matrix twinning is consistent with Type I (1-1-1) twinning, whereby (100) and (011) planes tend to align perpendicular and parallel to the load axis, respectively. The preferred orientation ratio according to the model by March and Dollase is found to be proportional to the macroscopic plastic strain for (100) and (011) planes for loading, unloading and shape-memory recovery. To the best of our knowledge, this is the first in situ bulk measurement of reversible twinning in NiTi. Finally, shape-memory recovery results in a marked change of NiTi cell parameters. (orig.)