External Radiation Source Research Articles

Effects of Heating Mode on Steady Axisymmetric Thermocapillary Flows in Microgravity

Steady thermocapillary flows in cylindrical containers with unit aspect ratio (radius = depth) are studied numerically and by scaling analysis in order to investigate how the velocity and thermal fields are influenced by the method of heating. Two heating modes are considered: heating by a uniform temperature cylindrical heater placed along the centerline (called the CT heating) and heating by an external radiative source (the CF heating). The steady velocity and temperature fields are computed numerically under various conditions for various Prandtl number fluids. The effects of those two types of heating on the flows are discussed. The results are also found to support the scaling laws derived herein for the characteristic velocity, length, and Nusselt number. The main thermocapillary driving force region is fixed by the heating zone area in the CF heating but it generally varies with the flow in the CT heating.

Application of pulse height spectral analysis to double-label counting of 35S− 32P

The characteristics of magnitude and shape of the liquid scintillation pulse height spectra of composite samples of 35S + 32P were studied as a function of their 32P: 35S activity ratios and fluor quenching properties. Pulse height spectra were characterized via the measurement of the spectral index of the samples (SIS). A linear relation exists between the value of the dual-label activity ratio plotted on a logarithmic scale against the SIS of the composite sample when the sample and fluor cocktail characteristics are maintained constant. This relationship was used to determine the activity ratios of composite radionuclide samples. The separate activities of 35SS and 32P of composite samples were calculated from the activity ratio and total activity. The method was tested against different mixtures of 35SS and 32P in plant matter. The mean % recovery of the calculated activities for 14 measurements of 32P and 32SS was 99.2%. The methods described are useful particularly with liquid scintillation counters not equipped with an external standard radiation source.

Paradox about quality values of dielectric resonators

The pi-phase difference that exists between the reflecting and the refracting rays from a dielectric resonator results in a suppression of the energy leakage from the resonator. If the resonator is not illuminated by an external source of radiation but is, instead, supplied by an internal source, then the reflecting ray vanishes, and the rate of energy leakage increases. An exact wave-theory analysis shows that the quality value of the resonator is approximately quartered, which is considerable in both theory and applications of current interest.

β-Backscattering: A radiochemical tool for the in-situ study of the electrochemical formation and dissolution of thin layers: Part 2. Application of external β-sources

The application of backscattering of β-radiation emitted outside an electrochemical cell to the investigation of the formation and dissolution of thin layers electrochemical cells is discussed. The backscattering of the radiation emitted by 99Tc, 36Cl and 204Tl external radiation sources was followed in during the formation of Cu, Ag and Bi layers on Au. Simultaneous changes in the energy spectra of the radiations are also demonstrated. It was shown that the method can be used to study the anodic dissolution of metal layers.

Ignition of combustible gases by radiative heating of inert particles

In this work the thermal ignition of a two-phase mixture, using a suspension comprising inert particles and hydrogen/air in slab geometry, is to be quantitatively and qualitatively analyzed. Whereas the hydrogen/air is assumed to be transparent to radiation, the solid particles are considered to actively absorbed and emit the radiation. A two-phase mixture of inert particles and hydrogen/air is contained between two transparent parallel walls. At one side, the mixture is subject to an external high temperature source of radiation. The main assumptions used in the following analysis can be summarized as follows: (1) The system is one dimensional and open. Therefore the gas expansion is neglected. (2) The uniform mixture of inert particles and hydrogen/air remains quiescent. (3) Occupied volume by particle is negligible compared with the gas suspension volume. (4) Only the particles are supposed to absorb and emit the radiation; the gas mixture is transparent to radiation.

Para-positronium annihilation induced by infrared radiation

An analysis is made of the possibility of observation of spontaneous—stimulated annihilation of a noninverted relativistic flux of para-positronium with an energy of about 80 MeV in the field of radiation of an atomic transition in a second (counterpropagating) positronium beam excited by an external source of far-infrared radiation.

Radiation-Associated Lung Cancer: A Comparison of the Histology of Lung Cancers in Uranium Miners and Survivors of the Atomic Bombings of Hiroshima and Nagasaki

A binational panel of Japanese and American pulmonary pathologists reviewed tissue slides of lung cancer cases diagnosed among Japanese A-bomb survivors and American uranium miners and classified the cases according to histological subtype. Blind reviews were completed on slides from 92 uranium miners and 108 A-bomb survivors, without knowledge of population, sex, age, smoking history, or level of radiation exposure. Consensus diagnoses were obtained with respect to principal subtype, including squamous-cell cancer, small-cell cancer, adenocarcinoma, and less frequent subtypes. The results were analyzed in terms of population, radiation dose, and smoking history. As expected, the proportion of squamous-cell cancer was positively related to smoking history in both populations. The relative frequencies of small-cell cancer and adenocarcinoma were very different in the two populations, but this difference was accounted for adequately by differences in radiation dose or, more specifically, dose-based relative risk estimates based on published data. Radiation-induced cancers appeared more likely to be of the small-cell subtype, and less likely to be adenocarcinomas, in both populations. The data appeared to require no additional explanation in terms of radiation quality (alpha particles vs gamma rays), uniform or local irradiation, inhaled vs external radiation source, or other population difference.

Feasibility study of an electric dosimetry technique

Characteristics of a radiation charged electret dosimeter are described. The dosimeter is based on a parallel-plate ionization chamber with the exception that the collecting electrode is covered by a thin polymer, Teflon or Mylar. During the charging of the dosimeter, ions produced in the sensitive volume by an external radiation source drift in the externally applied electric field and become trapped on the polymer surface forming an electret. Once the external supply is removed, a field across the sensitive volume is produced by the electret charge, such that during any subsequent irradiation, ions opposite in sign to those on the electret surface are attracted to the electret and deplete the charge layer in an amount proportional to the air kerma. Calibration, energy dependence, air kerma range, and reproducibility are discussed, and guard-ring effects on the linearity of the chamber are presented. Measurements of natural charge decay on the electrets are introduced.

Medical applications of synchrotron radiation

Abstract Ever since the first diagnostic X-ray was done in the United States on February 3, 1896, the application of ionizing radiation to the field of medicine has become increasingly important. Both in clinical medicine and basic research the use of X-rays for diagnostic imaging and radiotheraphy is now widespread. Radiography, angiography, CAT and PETT scanning, mammography, and nuclear medicine are all examples of technologies developed to image the human anatomy. In therapeutic applications, both external and internal sources of radiation are applied to the battle against cancer. The development of dedicated synchrotron radiation sources has allowed exciting advances to take place in many of these applications. The new sources provide tunable, high-intensity monochromatic beams over a wide range of energies which can be tailored to specific programmatc needs. This paper surveys those areas of medical research in which synchrotron radiation facilities are actively involved.

Anomalous on-orbit behaviour of the NASA Cosmic Background Explorer (COBE) Dewar

The cryogenic operation of NASA's Cosmic Background Explorer (COBE) ended on September 21, 1990, with the depletion of the liquid helium cryogen, after COBE had completed more than 10 months of successful Dewar and instrument operation. In this report we provide a brief summary of the nominal cryogenic performance of the Dewar (for more detail consult Reference 1). We present in detail several aspects of the helium and spacecraft dynamical behaviour. We discuss the occurrence of temperature and pressure oscillations in the Dewar porous plug. We review the impact of internal instrument malfunctions and of external radiation sources on the performance of the Dewar and of the instruments. From measurements of the COBE spacecraft spin rate we are able to monitor the spin coupling of the liquid helium to the walls of the Dewar. We analyse the spin measurements and present a model for the coupling. Finally, we review a number of helium Dewar ‘lessons learned’ from the COBE mission, and remark on the applicability of these lessons to future missions involving cryogenic payloads.

How to Measure the New ICRU Operational Quantities with Individual Dosemeters

Since the ICRU Report 39 in 1985 on Determination of Dose Equivalent Resulting from External Radiation Sources, a number of Reports have been published dealing with various aspects of ionising radiation. Measurement of these quantities is agreed by many to be the aim of personnel dosimetry. They are, however, sufficiently new, and their detailed interpretation sufficiently subtle, to warrant frequent and continued exposition and examination. Those who are involved in routine personnel and environmental monitoring services would therefore like to know in simple terms : i) how to measure the new ICRU quantities and whether the present dosemeters (or instruments) can be used for this purpose or wheter any major modification in their design will be needed

A unified approach to the optimization of brachytherapy and external beam dosimetry

Semi-automated optimization of dose distributions is possible using techniques borrowed from imaging science. The ideal distribution of dose is first deconvolved by a convolution kernel yielding an ideal weighting distribution in the patient. The weighting distribution describes the total energy released per unit mass of the irradiated medium. For internal and external radiation sources, this is directly related to the amount and distribution of radioactivity and energy fluence in the medium, respectively. For external sources, the exponential Radon transform is used to obtain ideal fluence projections incident on the patient. In both instances negative values are produced, which when set to zero result in perturbed dose distributions. This may necessitate iterative techniques to reduce the ‘residual dose’ produced by the zeroing process. Application of the approach is presented for the optimization of 2-dimensional dose distributions in external beam therapy, radioimmunotherapy, and brachytherapy sources.

Theory of fiber optic radiometry, emissivity of fibers, and distributed thermal sensors

This paper formulates a general radiometric theory of multimode step index fibers, covering in particular the region of mid- and far IR fibers. The optical fiber is treated both as a passive waveguide, guiding the external radiation injected into it, as well as an active waveguide, generating internal thermal radiation which is guided to both fiber endfaces. Several fiber absorption profiles are considered. In other words, the thermal radiation sources coupling radiation into the guided modes of the fiber are in one case considered to be distributed in the core, and in another, to be distributed in the cladding. The model is based on 3-D optical geometry of bounded and tunneling skew rays and yields an analytical expression for the angular power distribution along the length of the fiber. The radiation emissivity of multimode fibers is formulated. Based on the model, the theory of a new fiber optic distributed thermal sensor is presented. This sensor needs no external source of radiation for its operation and is based on the self-generation of thermal radiation in a modified IR fiber. Such a sensor can be produced by deliberately inducing surface or bulk absorption in the fiber core or coating (cladding) a bare fiber core with an IR absorbing material.

Numerical model of ignition processes of polymeric materials including gas-phase absorption of radiation

A one-dimensional unsteady mathematical model of solid fuel ignition is presented. The solid fuel is heated by an external radiative heat source. Some radiation is absorbed in depth by the solid fuel and some by the decomposition products in the gas phase. Solid fuel degradation occurs according to a zero-order Arrhenius pyrolysis reaction and gas-phase combustion according to a second-order Arrhenius reaction. Gas-phase heat and mass transfer and solid phase heat transfer are described by differential balance equations that are coupled through the boundary conditions at the interface. The solution is computed numerically by an implicit finite difference method. PMMA radiative ignition is simulated by varying the intensity of the radiative heat flux and predictions show quite good agreement with experiments. The ignition process oceurs in the gas phase in a premixed fashion, rapidly followed by the transition to a diffusion flame. As the radiative heat flux is increased, higher surface temperatures and pyrolysis mass fluxes are reached, ignition occurs closer and closer to the fuel surface, and ignition delay times decrease. Gas-phase absorption of radiation plays a fundamental role in the predicted ignition phenomenon and ignition delay times. In particular, with realistic data and no absorption of radiation in the gas phase, ignition does not occur at all. Finally, a parametric study is performed in order to analyze the dependence of the predicted ignition phenomenon on key parameters used to model degradation and combustion processes, such as preexponential factors and activation energies of the reactions.

Ignition in enclosed volumes of condensed materials heated by external radiation sources

Ignition in enclosed volumes of condensed materials heated by external radiation sources

Eds Of Radioactive Particles By Self-Induced Fluorescence

The elemental composition of individual particles is commonly measured by using energydispersive spectroscopic microanalysis (EDS) of samples excited with electron beam irradiation. Similarly, several investigators have characterized particles by using external monochromatic X-irradiation rather than electrons. However, there is little available information describing measurements of particulate characteristic X rays produced not from external sources of radiation, but rather from internal radiation contained within the particle itself. Here, we describe the low-energy (< 20 KeV) characteristic X-ray spectra produced by internal radiation self-excitation of two general types of particulate samples; individual radioactive particles produced during the Chernobyl nuclear reactor accident and radioactive fused aluminosilicate particles (FAP). In addition, we compare these spectra with those generated by conventional EDS.Approximately thirty radioactive particle samples from the Chernobyl accident were on a sample of wood that was near the reactor when the accident occurred. Individual particles still on the wood were microdissected from the bulk matrix after bulk autoradiography.

Study of heat and mass transfer in a chemical moving bed reactor for gasification of carbon using an external radiative source

A theoretical model of a chemical moving bed reactor for gasifying carbon with CO 2 using an external radiative source (concentrated solar radiation) is proposed. It permits the determination of the temperature profile for gas and solid and the concentration profile in the gas as a function of control parameters: gas flow rate, warm surface temperature, diameter of particles. Comparison of model results with experiment gives satisfactory agreement.

ICRU, Determination of Dose Equivalents Resulting from External Radiation Sources

ICRU, Determination of Dose Equivalents Resulting from External Radiation Sources

Determination of Dose Equivalents from External Radiation Sources.Pt 2, no. 4

<b>Determination of Dose Equivalents from External Radiation Sources.</b>Pt 2, no. 4

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.