Alpha Particle Response Research Articles

Alpha-particles Induce Preneoplastic Transformation of Rat Tracheal Epithelial Cells in Culture

To characterize the potential role of high-l.e.t. radiation in respiratory carcinogenesis, the cytotoxic and transforming potency of 5.5 Me V alpha-particles from electroplated sources of 238Pu were determined using primary cultures of rat tracheal epithelial cells. The alpha-particle response was compared to the effects of 280 kVp X-rays and of the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine. Increasing the alpha-particle dose caused an exponential decrease in survival with a D37 of 1.6 Gy. X-rays also caused a dose-dependent decrease in survival (D37 = 3.6 Gy) but the survival curve had a significant shoulder. The RBE for cell killing by alpha-particles versus X-rays varied with dose, and ranged between 4 and 1.5 for alpha doses in the range 0.2-4 Gy. At equally toxic doses (relative survival 0.18-0.2), all three agents induced similar frequencies of preneoplastic transformation. For preneoplastic transformation induced by doses of alpha- and X-radiations giving 80 per cent toxicity, an alpha RBE of 2.4 was derived. The similar RBEs for cell killing and for preneoplastic transformation suggest an association between the type or degree of radiation-induced damage responsible for both cell killing and cell transformation.

Alpha Spectrometry by Using CN85 Plastic Track Detectors

In the present study the alpha particle response which is characteristic of cellulose nitrate detectors CN85 was investigated The track diameter as a function of alpha energy was examined. With regard to the spectroscopy of alpha from track radii it was stated that the discrimination of lower alpha energies shows better results than the high energies for the present etching condition.

Destabilization of global Alfvén eigenmodes and kinetic Alfvén waves by alpha particles in a tokamak plasma

Alfvén wave instabilities in a reacting tokamak plasma are calculated both analytically and numerically. Two distinct classes of eigenmodes are considered, global Alfvén eigenmodes and kinetic Alfvén waves, each driven unstable by the free energy associated with the alpha particle density gradient. The growth rates of the global Alfvén eigenmodes are given for the first time. These are basically magnetohydrodynamic (MHD) modes, whose resonances with electrons and alpha particles are calculated using kinetic theory. The calculation of kinetic Alfvén wave growth rates is improved from earlier treatments. These modes depend on electron inertia and finite ion gyroradius for their existence and have no counterpart in MHD theory. In both sets of calculations toroidal coupling of the alpha particle response to sidebands in the poloidal mode number is fully taken into account. Global modes with small parallel phase velocity are identified as the most dangerous, both because of their substantial growth rates and the expected ineffectiveness of quasilinear stabilization. The kinetic waves, on the other hand, are likely to be stabilized easily by quasilinear flattening of the alpha particle profile. Calculations using both Maxwellian and slowing-down alpha distributions are performed, showing that, for the same alpha density and energy density, the slowing-down distribution yields somewhat larger growth rates.

Ageing effects in CR-39

Abstract The time dependence of the track response of Bristol CR-39 to alpha-particles is investigated. The behaviour of the plastic with time is of importance in low-level alpha activity applications such as lung alpha-autoradiography which requires CR-39 to be stored for long periods of time, and in neutron spectrometry where the accumulation of sufficient track statistics can necessitate lengthy exposure periods. It is shown that at room temperature within three weeks of manufacture the plastic undergoes a rapid fall-off in sensitivity as measured by VT/VB. This fading continues at a much reduced rate therafter. At freezer temperatures, -20°C, the initial fading is not as dramatic and the subsequent response appears stable on a scale of 6 months. It is shown that it is the plastic which fades and not the latent tracks, i.e. the important parameter is the age of the plastic itself and not the age of the latent track. An antioxidant is assessed for performance and is found to have little effect on the fading characteristics. It is shown that antioxidants are not suitable for use in CR-39, but that progress can be made by modifying the diethylene glycol bis (allyl carbonate) itself by eliminating the tertiary hydrogen atoms. The effect of vacuums on the alpha-particle response is also assessed and it is shown that this response is dramatically effected by the presence of vacuum. The response recovers with time, however. The effect appears to be dependent on either oxygen or water vapour present at exposure.

The effect of gamma dose on the alpha response of CR-39

Abstract The effect of gamma irradiation on the alpha-particle track response of CR-39 is investigated. The effects are dramatic above doses of 500Krad. The alpha-particle tracks in highly dosed plastic exhibit a ‘threshold’ residual range below which the track etching appears to saturate. The effects can be simulated by the use of a suitable VT(R) vs range curve and is therefore not a ‘skin’ effect. The effects appear to be due to the addition of the two doses, the effects being present for alpha dose + gamma dose and gamma dose + alpha dose. The average track etch rates VT/VB, remain constant up to 500Krad but then exhibit a fall-off at higher doses. The observations have relevance for neutron spectrometry and dosimetry measurements where large gamma fields may be present. The bulk etching behaviour is also investigated. The change in bulk etching rate is too small to be of any value in a gamma dosemeter for doses below 100Krad.

Imaging of fast neutron sources using solid state track recorder pinhole radiography

Pinhole imaging methods are being developed and tested for potential future use in imaging the intense neutron source of the Fusion Materials Irradiation Test (FMIT) Facility. Previously reported, extensive calibration measurements of the proton, neutron, and alpha particle response characteristics of CR-39 polymer solid state track recorders (SSTRs) are being used to interpret the results of imaging experiments using both charged particle and neutron pinhole collimators. High resolution, neutron pinhole images of a 252Cf source have been obtained in the form of neutron induced proton recoil tracks in CR-39 polymer SSTR. These imaging experiments are described as well as their potential future applications to FMIT.

Degradation Characteristics of Au-Si Nuclear Detectors by a Few MeV Charged Particle Irradiation

It is found that a Si surface barrier detector has been degraded after 3.2 MeV protons or 3.5 MeV 3He particle irradiation with low doses ranging from 1011 to 1012 cm-2. The degradation characteristics have been investigated through the changes in the reverse current, capacitance, alpha-particle counting response and DLTS measurements. 3He particle irradiation produces a change of the capacitance at lower reverse bias compared to that of proton irradiation, indicating the defect creation at the short penetration depth of 3He particles. Capacitance-voltage characteristics of the irradiated detectors can be simply analysed using Poisson's equation with an assumption that the charge defects are created within the depletion layers. Such kinds of defects are considered as electron traps at 0.36, 0.45 and 0.51 eV from the conduction band.

Response of solid state track recorders to neutrons: I. Experimental results

Experimental results are presented from a detailed study of CA80-15, Makrofol KG and CR-39 SSTRs for fast neutron measurements in the presence of a high flux of γ-rays. For a fission neutron source, the efficiency in CA80-15 is ∼ 1.4 × 10 − tracks per neutron. These results are in agreement to within ± 15% of the theoretical results. Proton, alpha and recoil particle response characteristics of CR-39 SSTR have also been investigated, showing its excellent proton energy resolution. The large energy range for proton registration and smooth surface of excellent optical quality suggest CR-39 as a suitable material for fast neutron dosimetry using recoil proton tracks.

Response curves of alkali halide scintillators with special reference to the Li 6(n,α) reaction in lithium iodide

Proton and gamma-ray responses of the alkali halide scintillators, NaI, KI, CsI, LiI and Li 6I have been obtained and the response of a 5-MeV proton was found to be approximately equivalent to the response of a 7-MeV electron for all five scintillators. Special emphasis was given to the responses of LiI and Li 6I in an attempt to clarify various anomalies which have arisen in the course of neutron energy measurements with LiI by means of the Li 6(n,α) reaction. From an estimate of the triton response of LiI and Li 6I, which was derived from the proton and gamma-ray data in conjuntion with the alpha-particle response and measurements of the pulse height of the Li 6(n,α) group, it has been shown that energy calibration of the Li 6(n,α) group with gamma rays is unsatisfactory.