Radiation quality of tritium

Tritium occurs from both natural and manufactured processes. In the environment, tritium can exist in the form of tritiated water (HTO) and in an organic form known as organically-bound tritium (OBT). Although, the concentrations of environmental OBT are relatively low, there is concern that current risk factors may underestimate the risk from OBT. Because tritium poses an internal hazard at cellular levels, microdosimetric techniques provide suitable tools for the study of radiation quality of tritium. In this study, microdosimetric simulations are performed for tritium uniformly distributed in a medium, and for tritium bound to biologically critical sites of dimensions from 10 nm to 2 microm. Results of local energy density are different for these two cases in microscopic regions. Based on the spatial distribution of energy deposition, dose mean lineal energies are calculated for tritium in forms of HTO and OBT. The dose mean lineal energies of OBT are about a factor of 1.7 higher than those of HTO in a wide range of target dimensions of biological interest. The results are consistent with radiobiological findings that OBT is about twice as effective as that of HTO.     

Radiation safety and quality control in the cyclotron laboratory

Radiation safety was determined to maintain quality control in the cyclotron laboratory. Based on the results of 438 runs in the Faraday cup (20 microA for 10 min), 20 runs on 18O-water target (40 microA for 2 h) and 10 runs on 18O-gas targets (30 microA for 45 min), we have established that occupationally exposed workers remain 10 +/- 5 times below federal regulatory limits (FRLs) in the cyclotron vault, 30 +/- 8 times below FRL in the radiochemistry laboratory and 200 +/- 10 times below the FRL outside the cyclotron laboratory during beam operation. (The FRL for unrestricted area are <20 microSv in 1 h.) The non-occupationally exposed workers serving in offices in the vicinity of the cyclotron vault within 100 m distance remained 200 times below the FRL irrespective of beam being on or off, suggesting that routine beam operation of 40 microA for 2 h once a day during office hours is safe provided quality control and system performance measures as discussed in this report are strictly maintained.     

Spectra of scattered photons in large absorbers and their importance for the values of radiation weighting factor wR

In its review of the present values of radiation weighting factor w(R) and of possible revisions of this factor, the German Radiation Protection Commission has recommended to maintain the approach of ICRP 60 to base the selection of the w(R) value for a given radiation (e.g. fission neutrons) on observed values of the relative biological effectiveness (RBE) of this radiation 'regardless of whether the reference radiation is X rays or gamma rays'. The physical background of the German recommendation is the buildup of a strong field of energy-degraded Compton scattered photons in the human body if exposed to an external field of high-energy photons, so that the total radiation field inside the body is a mixture comprising low and high photon energies. Therefore, it is appropriate that the selection of the w(R) value of the given radiation is guided by RBE values averaged over X rays and gamma rays as the reference radiations. In support of this rationale, the present paper provides a sample of Monte Carlo calculated scattered photon spectra in large absorbers exposed to high-energy photons. Depth-dependent fractional dose contributions of the scattered photons are tabulated for incident energies from 1 to 10 MeV, and estimates of the influence of their degraded energies on the biological effectiveness of the incoming radiation are presented. Accordingly, we point out that it is appropriate to use, for the purposes of 'risk projection', RBE values averaged over X and gamma reference radiations.     

The comparison of calculated and experimental microdosimetric distributions for carbon ions

The aim of this work is to present microdosimetric characteristics of 400 MeV amu(-1) and 500 MeV amu(-1) carbon ions obtained by theoretical calculations and to analyse them with respect to experimental data obtained by tissue-equivalent proportional counter in a scope of project ICCHIBAN and by etched track detector CR 39 Page irradiated by LHE nuclotron at JINR, Dubna, Russia. Track structures provided by Monte Carlo code TRIOL are used as an input data for calculations of energy distributions. The calculations of frequency f(y) and dose d(y) distributions are performed using own developed programs.     

Isogeometric analysis for flexural behavior of composite plates considering large deformation with small rotations

A large deformation theory, so-called Green strains with small rotations, is proposed and employed for flexural analysis of composite plates. Isogeometric analysis cooperated with first-order shear deformation theory is used to derive finite element models. Strain-displacement relations in the sense of von-Kármán theory and the proposed theory are formulated. Shear locking phenomenon is avoided by using reduced integration technique. Newton–Raphson method is employed for nonlinear analysis procedure. Numerical examples, including isotropic and laminated composite plates under different boundary conditions, are investigated. The results have been verified with those available in the literature and show the advantages of the proposed strain theory.     

Radiation quality dependence of DNA damage induction

Analysis of DNA fragmentation and repair in relation to radiation quality may give important information about the role of break complexity and correlated double strand breaks (DSBs). DNA fragment analysis was performed by pulsed-field gel electrophoresis after exposure to different radiation qualities. Normal human fibroblasts were irradiated with boron ions (40, 80 and 160 keV.micron-1), nitrogen ions (80, 125, 175 and 225 keV.micron-1) and neon ions (225 and 300 keV.micron-1). The amount of DNA less than 1.1 Mbp decreased with increasing linear energy transfer (LET) for all three ions. When theoretical random distributions were subtracted from the experimental data for 225 keV.micron-1 nitrogen ions in all size intervals (5-5700 kbp), there was a significant non-random distribution of DSBs for sizes up to 1-3 Mbp. This non-random distribution of breaks, probably produced by intra-track correlated DSBs, may constitute a substantial portion of the high-LET induced DSBs.     

The test measurements of TOF in small and large scintillation counters

We tested the time resolution of “small” scintillation counters (0.8 (height) × 2.6 (width) cm² and 0.7 (height) × 2.1 (width) cm², with 1.0 cm thickness) and of a “large” counter (21 (height) × 96 (width) cm² with 2 cm thickness). The time walk correction using software (off-line) was compared with that using hardware (constant fraction discriminator). It was found that the two methods gave nearly equal time resolution. Intrinsic time resolutions of 155 and 370 ps fwhm were obtained for the small and the large counters, respectively.     

Confined laminar wakes at small and large Reynolds number

Summary The development of the wake flowfield behind a symmetric cascade of finite-thickness flat plates in steady two-dimensional laminar incompressible flow is investigated for a wide range of Reynolds number. A spectral method is used to obtain the solution to a low-Reynolds-number expansion of the Navier-Stokes equations as well as a second approximation to the Oseen equations. Comparisons to the results of the second Oseen approximation are made with previously obtained solutions to the slender-channel equations for large Reynolds number as well as with solutions to the low-Reynolds-number expansion.     

Uniform asymptotic solutions for small and large sessile drops

Summary The problem of determining the equilibrium shape of either a small or large sessile drop is studied. By the correspondence principle, the problem of approximating the static meniscus in a vertical right circular cylinder is also solved. A parameter is introduced which is ratio of the physical length scale to the capillary length scale. Perturbation solutions, which are uniformly valid over the entire surface of the drop, are obtained for either small or large values of using the method of successive substitutions. Comparisons of the results with solutions obtained by other approximate methods are presented and discussed. The solutions for small and large values of are then combined using an ad hoc, but straightforward, technique, resulting in an approximate solution which is valid for all positive values of the parameter .     

Second-order statistics of integrated intensities and detected photons,the exact analysis I. Theory

Abstract

We express the exact probability density distribution function as the product of a gamma distribution and a series of associated Laguerre polynomials, with the expansion coefficients determined by moments of the integrated intensity. Orthogonal polynomials with respect to the exact probability distribution function are then expanded in similar fashion. These polynomials are then used to construct an expansion of the joint probability distribution function in the second-order photoelectron statistics. Since the polynomials are identical with the corresponding Laguerre polynomials when the exact probability distribution function is the gamma distribution, the new polynomials are generalized versions of the associated Laguerre polynomials. The joint photoelectron statistics may be studied with these new polynomials.     

Propagation of small disturbances on large deformations in a viscoelastic fluid

Summary The propagation characteristics (i.e., wave velocity & amplitude strength) of small disturbances existing in a large base motion of a BKZ viscoelastic liquid are considered. A small motion superposed on a large deformation is taken to be a wave of small amplitude propagating across a base flow. The analysis treats a wave as a singular surface across which there is a jump discontinuity of a kinematical variable. Specific attention is directed to second order waves where the perturbed displacement and its first derivatives are continuous but higher order derivatives are not. The growth and decay of amplitude of small plane second order shear waves propagating across steady simple shearing flow is studied in detail. Using the Zapas form for the BKZ material function, it is found that the amplitude of these shear waves will always decay. The rate of decay is dependent on the rate of shear of the base flow.

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Die Ausbreitung von endlichen Verformungen überlagerten kleinen Störungen in einer viskoelastischen Flüssigkeit

Zusammenfassung Die Ausbreitungseigenschaften (d.h. Wellengeschwindigkeit und Amplitude) von kleinen, einer endlichen Grundbewegung überlagerten Störungen in einer viskoelastischen Flüssigkeit werden betrachtet. Die kleine Störung wird als eine der Grundströmung überlagerte Welle von kleiner Amplitude angenommen. In der Untersuchung wird die Welle als eine singuläre Fläche mit einer Unstetigkeit in einer kinematischen Größe behandelt. Besondere Beachtung gilt Wellen 2. Ordnung, mit stetiger Verschiebung und deren 1. Ableitung, aber nicht stetigen höheren Ableitungen. Wachstum und Abklingen der Amplitude von einfachen stationären Scherströmungen überlagerten ebenen Scherwellen 2. Ordnung werden im Detail untersucht. Bei Verwendung der von Zapas angegebenen Form der BKZ-Werkstoffunktion zeigt sich, daß die Amplitude dieser Scherwellen stets abklingt.Die Abklinggeschwindigkeit hängt von der Schergeschwindigkeit der Grundströmung ab.

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With 7 Figures     

Radiation pattern of fluorescence from molecules embedded in small particles: general case

A method is presented for calculating and analyzing the angular distribution of fluorescent emission from randomly oriented anisotropic molecules embedded in small dielectric particles with the nonzero reorientation angle between absorption and emission moments suggested by physical considerations now taken into account. Calculations performed on the basis of this method are compared with some of the available experimental data for fluorescent dye molecules embedded in microspheres, and good quantitative agreement is found. It is shown how fitting the computed results to experimental data determines an effective reorientation angle between absorption and emission transition moments. A more definitive test to which the model could be subjected is described.     

Molecular computational elements encode large populations of small objects

Since the introduction of molecular computation, experimental molecular computational elements have grown to encompass small-scale integration, arithmetic and games, among others. However, the need for a practical application has been pressing. Here we present molecular computational identification (MCID), a demonstration that molecular logic and computation can be applied to a widely relevant issue. Examples of populations that need encoding in the microscopic world are cells in diagnostics or beads in combinatorial chemistry (tags). Taking advantage of the small size (about 1 nm) and large 'on/off' output ratios of molecular logic gates and using the great variety of logic types, input chemical combinations, switching thresholds and even gate arrays in addition to colours, we produce unique identifiers for members of populations of small polymer beads (about 100 microm) used for synthesis of combinatorial libraries. Many millions of distinguishable tags become available. This method should be extensible to far smaller objects, with the only requirement being a 'wash and watch' protocol. Our focus on converting molecular science into technology concerning analog sensors, turns to digital logic devices in the present work.     

The melting of fullerites from small or large fullerenes

The physical limits are studied theoretically for a mass of fullerenes which may be used to produce a stable crystal, i.e., fullerite. The dependence of the parameters of interfullerene interaction on the mass of fullerene C _nc is used to study the evolution of the properties of fullerite as a result of variation of the number of carbon atoms nc in fullerene C _nc . The dependences of the energy of activation process and surface energy are calculated for different values of temperature and pressure in the 15 ≤ nc ≤ 147 range. It is demonstrated that fullerite becomes unstable at nc < 20, because small-sized light fullerenes cannot be localized due to weak Van der Waals forces. At the same time, fullerites with nc ≥ 110 exhibit abnormally low values of surface energy; this must bring about the fragmentation of nanoclusters of hollow spherical C _nc molecules of such a large size. Four empirical equations are used to estimate the dependence of the melting temperature of fullerite on nc. It is demonstrated that the melting temperature in the case of fullerites from small or large fullerenes is lower than that in the case of fullerites at 50 < nc < 90. It is inferred that the 30 < nc < 100 range is optimal for the formation of stable fullerite.     

The microdosimetry of low-energy photons in radiotherapy

Low energy photons are more and more in use in clinical practice, for treatment in radiotherapy as well as for imaging purposes. Their relative biological effectiveness is however still debated. In this paper, some microdosimetric parameters have been calculated for different sources: (125)I, (103)Pd, (131)Cs, an electronic brachytherapy source and various clinical mammography X-ray qualities. These parameters have been used to deduce the quality factors as defined in ICRU 40.     

Radiation safety assessment of a system of small reactors for distributed energy

A passively safe small reactor for a distributed energy system, PSRD, is an integral type of light-water reactor with a thermal output of 100 or 300 MW aimed to be used for supplying district heat, electricity to small grids, and so on. Candidate locations for the PSRD as a distributed energy source are on-ground, deep underground, and in a seaside pit in the vicinity of the energy consumption area. Assessments of the radiation safety of a PSRD were carried out for three cases corresponding to normal operation, shutdown and a hypothetical postulated accident for several siting candidates. Results of the radiation safety assessment indicate that the PSRD design has sufficient shielding performance and capability and that the exposure to the general public is very low in the case of a hypothetical accident.     

The shape of a sessile drop for small and large surface tension

Asymptotic solutions for large and small surface tension are developed for the profile of a symmetric sessile drop. The problem for large surface tension (i.e., small Bond number) is a regular perturbation problem, where the solution may be written as a uniformly valid asymptotic expansion. The problem for small surface tension (i.e., large Bond number) is a singular perturbation problem with boundary-layer behaviour in the edge region. The solution is a matched asymptotic expansion, where some care is to be taken for the matching. The respective ranges of validity are established by comparing the asymptotic results with solutions obtained by numerical integration of the full equations.