Radiation Path Length Research Articles

A study of decay chains of radioactive actinium isotopes

In this paper, we systematically studied half-lives of the different decay modes using various theoretical models such as the unified fission model (UFM) and the effective liquid drop model. Beta-decay half-lives were evaluated using semi-empirical formulae available in the literature. We compared half-lives of all the studied decay modes and identified shorter half-lives among the same in [Formula: see text]Ac nuclei. We investigated the actinium series which is similar to the thorium series. Among these decay series, alpha-emitting isotopes show great promise for cancer treatment because of their short path length and high-energy transfer of radiation. Furthermore, we predicted the decay chains of the actinium isotopes. All the decay series of actinium ends with the formation of stable nuclei or with longer half-lives. The predicted decay series and new isotopes during the decay process are helpful in the field of medicine and radiotherapy.

Calibration of cylindrical NaI(Tl) gamma-ray detector intended for truncated conical radioactive source

The computation of the solid angle and the detector efficiency is considering to be one of the most important factors during the measuring process for the radioactivity, especially the cylindrical γ-ray NaI(Tl) detectors nowadays have applications in several fields such as industry, hazardous for health, the gamma-ray radiation detectors grow to be the main essential instruments in radiation protection sector. In the present work, a generic numerical simulation method (NSM) for calculating the efficiency of the γ-ray spectrometry setup is established. The formulas are suitable for any type of source-to-detector shape and can be valuable to determine the full-energy peak and the total efficiencies and P/T ratio of cylindrical γ-ray NaI(Tl) detector setup concerning the truncated conical radioactive source. This methodology is based on estimate the path length of γ-ray radiation inside the detector active medium, inside the source itself, and the self-attenuation correction factors, which typically use to correct the sample attenuation of the original geometry source. The calculations can be completed in general by using extra reasonable and complicate analytical and numerical techniques than the standard models; especially the effective solid angle, and the detector efficiency have to be calculated in case of the truncated conical radioactive source studied condition. Moreover, the (NSM) can be used for the straight calculations of the γ-ray detector efficiency after the computation of improvement that need in the case of γ-γ coincidence summing (CS). The (NSM) confirmation of the development created by the efficiency transfer method has been achieved by comparing the results of the measuring truncated conical radioactive source with certified nuclide activities with the γ-ray NaI(Tl) detector, and a good agreement was obtained after corrections of (CS). The methodology can be unlimited to find the theoretical efficiencies and modifications equivalent to any geometry by essential sufficiently the physical selective considered situation.

Small field depth dose profile of 6 MV photon beam in a simple air-water heterogeneity combination: A comparison between anisotropic analytical algorithm dose estimation with thermoluminescent dosimeter dose measurement.

To establish trends of estimation error of dose calculation by anisotropic analytical algorithm (AAA) with respect to dose measured by thermoluminescent dosimeters (TLDs) in air-water heterogeneity for small field size photon. TLDs were irradiated along the central axis of the photon beam in four different solid water phantom geometries using three small field size single beams. The depth dose profiles were estimated using AAA calculation model for each field sizes. The estimated and measured depth dose profiles were compared. The over estimation (OE) within air cavity were dependent on field size (f) and distance (x) from solid water-air interface and formulated as OE = - (0.63 f + 9.40) x2+ (-2.73 f + 58.11) x + (0.06 f2 - 1.42 f + 15.67). In postcavity adjacent point and distal points from the interface have dependence on field size (f) and equations are OE = 0.42 f2 - 8.17 f + 71.63, OE = 0.84 f2 - 1.56 f + 17.57, respectively. The trend of estimation error of AAA dose calculation algorithm with respect to measured value have been formulated throughout the radiation path length along the central axis of 6 MV photon beam in air-water heterogeneity combination for small field size photon beam generated from a 6 MV linear accelerator.

A method of providing directionality for ionising radiation detectors — RadICAL

A novel method for providing directionality for radiation detection is presented. The idea is based upon the fact that detector response depends upon two properties of the active component in the detector: the radiation pathlength and the area presented to a particle flux. Thus a rotating slab of detector gives a characteristic temporal response that can be used to identify the direction of the photon flux. A model of the detector system is used to design and build a detector which is then evaluated. It is shown that a rotating detector of this nature can produce a characteristic curve which can be used to determine the location of a single stationary point source.

Dosimetry and Radiobiological Studies of Automated Alpha-Particle Irradiator

Understanding the effect of alpha radiation on biological systems is an important component of radiation risk assessment and associated health consequences. However, due to the short path length of alpha radiation in the atmosphere, in vitro radiobiological experiments cannot be performed with accuracy in terms of dose and specified exposure time. The present paper describes the design and dosimetry of an automated alpha-particle irradiator named 'BARC BioAlpha', which is suitable for in vitro radiobiological studies. Compared to alpha irradiators developed in other laboratories, BARC BioAlpha has integrated computer-controlled movement of the alpha-particle source, collimator, and electronic shutter. The diaphragm blades of the electronic shutter can control the area (diameter) of irradiation without any additional shielding, which is suitable for radiobiological bystander studies. To avoid irradiation with incorrect parameters, a software interlock is provided to prevent shutter opening, unless the user-specified speed of the source and collimator are achieved. The dosimetry of the alpha irradiator using CR-39 and silicon surface barrier detectors showed that ~4 MeV energy of the alpha particle reached the cells on the irradiation dish. The alpha irradiation was also demonstrated by the evaluation of DNA double-strand breaks in human cells. In conclusion, 'BARC BioAlpha' provides a user-friendly alpha irradiation system for radiobiological experiments with a novel automation mechanism for better accuracy of dose and exposure time.

A new mathematical approximation of sunlight attenuation in rocks for surface luminescence dating

The attenuation of sunlight through different rock surfaces and the thermoluminescence (TL) or Optical stimulated luminescence (OSL) residuals clock resetting derived from sunlight induced eviction of electrons from electron traps, is a prerequisite criterion for potential dating. The modeling of change of residual luminescence as a function of two variables, the solar radiation path length (or depth) and exposure time offers further insight into the dating concept. The double exponential function modeling based on the Lambert–Beer law, valid under certain assumptions, constructed by a quasi-manual equation fails to offer a general and statistically sound expression of the best fit for most rock types. A cumulative log-normal distribution fitting provides a most satisfactory mathematical approximation for marbles, marble schists and granites, where absorption coefficient and residual luminescence parameters are defined per each type of rock or marble quarry. The new model is applied on available data and age determination tests.

The analysis of solar UVB radiation as a function of solar global radiation, ozone layer thickness and aerosol optical density

Incident solar radiation (insolation) is attenuated by two different phenomena, (i) atmospheric scattering by air molecules, water vapor and aerosols, and (ii) atmospheric absorption by ozone, water and carbon dioxide. The degree of terrestrial solar radiation attenuation is a function of its optical path length, i.e., the distance the Sun’s ray traverse through the Earth’s atmosphere prior to being incident on the its surface. The attenuation by atmospheric scattering, irrespective of source, is an inverse function of the wavelength. Absorption of insolation in the atmosphere is due mainly to ozone in the ultraviolet range and water vapor in the infrared range of the solar spectrum. Ozone absorption decreases with increasing wavelength and above 350 nm there is no absorption. Thus, a priori, any changes in either the ozone layer thickness (OLT) and/or aerosol optical density (AOD) will have a greater effect on ultraviolet radiation, in general, and on UVB in particular. An empirical correlation that determines the UVB radiation intensity as a function of solar global radiation, OLT, AOD and optical path length as represented by the air mass is presented and validated by an independent database. In addition, a parameter sensitivity study was performed on the empirical correlation using two different methods. The application of the empirical correlation as a function of hour type (i.e., clear, partially cloudy and cloudy) was also investigated.

Light Trapping in Silicon Nanowire Solar Cells

Thin-film structures can reduce the cost of solar power by using inexpensive substrates and a lower quantity and quality of semiconductor material. However, the resulting short optical path length and minority carrier diffusion length necessitates either a high absorption coefficient or excellent light trapping. Semiconducting nanowire arrays have already been shown to have low reflective losses compared to planar semiconductors, but their light-trapping properties have not been measured. Using optical transmission and photocurrent measurements on thin silicon films, we demonstrate that ordered arrays of silicon nanowires increase the path length of incident solar radiation by up to a factor of 73. This extraordinary light-trapping path length enhancement factor is above the randomized scattering (Lambertian) limit (2n(2) approximately 25 without a back reflector) and is superior to other light-trapping methods. By changing the silicon film thickness and nanowire length, we show that there is a competition between improved absorption and increased surface recombination; for nanowire arrays fabricated from 8 mum thick silicon films, the enhanced absorption can dominate over surface recombination, even without any surface passivation. These nanowire devices give efficiencies above 5%, with short-circuit photocurrents higher than planar control samples.

Personal UV exposure in high albedo alpine sites

Abstract. Mountain sites experience enhanced UV radiation levels due to the concurrent effects of shorter radiation path-length, low aerosol load and high reflectivity of the snow surfaces. This study was encouraged by the possibility to collect original data of personal dose on a specific anatomical site (erythemally effective UV dose on the forehead) of two groups of volunteers (ski instructors and skiers) in the mountainous areas of Italy (the Alpine site of La Thuile-Les Suches in Valle d'Aosta region). Personal doses were assessed using polysulphone dosimetry. Exposure Ratio (ER), defined as the ratio between the personal dose and the corresponding ambient dose (i.e. erythemally weighted dose received by a horizontal surface) during the same exposure period was taken into account. In addition measuring skin colours as biological markers of individual response to UV exposure, was also carried out on the forearm and cheek of each volunteer before and after exposure. The median ER, taking into account the whole sample, is 0.60 in winter, with a range of 0.29 to 1.46, and 1.02 in spring, ranging from 0.46 to 1.72. No differences in ERs were found between skiers and instructors in spring while in winter skiers experienced lower values. Regarding skin colorimetric parameters the main result was that both skiers and instructors had on average significantly lower values of luminance after exposure i.e.~they became darker. It was found that the use of sunscreen and individual skin photo-type did not produce significant variations in ER across instructor/skier group by day and by seasons (p>0.05). It seems that sunscreen use only at the beginning of the exposure or in a few cases a couple of times during exposure (at difference with the specific instructions sheets), was not sufficient to change significantly skin colorimetric parameters across participants. In conclusion UV personal doses on the ski-fields are often significantly higher than those on horizontal surfaces and consistently more intense respect to personal doses received by sunbathers on the beach in central Italy (ER range: 0.09–0.42). Given the high levels of exposure observed in the present study, specific public health warnings with regards to the efficacy of sun-protection behaviours (proper application and re-application of sunscreen and protective measures such as hats and sun glasses) should be adopted.

Effects of tissue outside of arterial blood vessels in pulse oximetry: a model of two-dimensional pulsation

We describe a new model of pulse oximetry that addresses the disagreement between theoretical calibration curves based on Beer-Lambert's Law and test results based on human test subjects. Sources of this discrepancy include variability among human subjects, experimental conditions and the effect of optical radiation propagating in tissue surrounding arteries. Unlike the conventional model, our model considers the change in the relative proportion of light that does or does not pass through blood in pulsating vessels in addition to the change in the path length of optical radiation through the blood. Theoretical calibration curves based on this model agree with human test results and help to explain the variability between in vitro and in vivo test conditions.

Improved treatment planning for COMS eye plaques

A recent reanalysis of the Collaborative Ocular Melanoma Study (COMS) medium tumor trial concluded that incorporating factors to account for anisotropy, line source approximation, the gold plaque, and attenuation in the Silastic seed carrier into the dose calculations resulted in a significant and consistent reduction of calculated doses to structures of interest within the eye. The authors concluded that future eye plaque dosimetry should be "performed using the most up-to-date parameters available." The reason these factors are important is attributable to the low energy (125)I radiation (approximately 28 keV) that is primarily absorbed by the photoelectric process. Photoelectric absorption is quite dependent on the atomic composition of the absorbing material. Being 40% silicon by weight, the effective atomic number of Silastic is significantly greater than that of water. Although the AAPM TG43 brachytherapy formalism inherently addresses the issues of source anisotropy and geometry, its parameter that accounts for scatter and attenuation, the radial dose function g(r), assumes that the source is immersed in infinite homogeneous water. In this work, factors are proposed for (125)I that correct for attenuation in the Silastic carrier and scatter deficits resulting from the gold plaque and nearby air. The implications of using (103)Pd seeds in COMS plaques are also discussed. An existing TG43-based ophthalmic plaque planning system was modified to incorporate additional scatter and attenuation correction factors that better account for the path length of primary radiation in the Silastic seed carrier and the distance between the dose calculation point and the eye-air interface. Compared with homogeneous water, the dose-modifying effects of the Silastic and gold are greatest near the plaque surface and immediately adjacent to the plaque, while being least near the center of the eye. The calculated dose distribution surrounding a single (125)I seed centered in a COMS 20 mm plaque was found to be consistent with previously published examples that used thermoluminescent dosimetry measurements and Monte Carlo methods. For fully loaded 12 and 20 mm plaques, calculated dose to critical ocular structures ranged from 16%-50% less than would have been reported using the standard COMS dose calculation protocol. Treatment planning for COMS eye plaques that accurately accounts for the presence of the gold, Silastic and extraocular air is both possible and practical.

Attenuation of spectral actinic flux and photolysis frequencies at the surface through homogenous cloud fields

The effect of clouds on derived photolysis rates has been investigated using actinic flux spectra measured from a 2π sr diode‐array spectral radiometer deployed in a series of differing field campaigns. Homogenously cloudy and clear days were selected, and ratios of cloudy‐to‐clear actinic flux spectra were used to derive a cloud transmittance slope (CTS), which is calculated as the gradient of the cloudy/clear ratio plot at 340 < λ < 420 nm. CTS is a measure of the wavelength dependence of actinic flux attenuation by clouds and shows an approximately linear dependence with solar zenith angle. When the solar zenith angle is high, the CTS is largest because of the enhanced path length of radiation through the scattering medium. The dependence of measured CTS under a range of atmospheric conditions is explored; the slopes of the CT being rationalized in terms of the cloud optical depth and single scattering albedo of the cloud. The appearance of a short‐wave enhancement in CT in a multiple scattering environment is noted in agreement with theory. The photolysis frequency coefficients j(O1D) and j(NO2), calculated from the measured actinic fluxes, are compared to observe the effect of wavelength‐dependent attenuation of actinic flux on photochemical reactions. After the subtraction of the effect of changing overhead ozone column, the effect of cloud was quite variable in that j(NO2) was found to be reduced to a greater extent than j(O1D) by some clouds or vice versa depending on the individual case. The results clearly demonstrate that photolysis frequencies in the UVB and UVA do not vary linearly under different atmospheric conditions in a cloudy field.

The HERA-B ring imaging Cherenkov counter

The HERA-B RICH uses a radiation path length of 2.8 m in C 4F 10 gas and a large 24 m 2 spherical mirror for imaging Cherenkov rings. The photon detector consists of 2240 Hamamatsu multi-anode photomultipliers with about 27 000 channels. A 2:1 reducing two-lens telescope in front of each photomultiplier tube increases the sensitive area at the expense of increased pixel size, resulting in a contribution to the resolution which roughly matches that of dispersion. The counter was completed in January of 1999, and its performance has been steady and reliable over the years it has been in operation. The design performance of the Ring Imaging Cherenkov counter was fully reached: the average number of detected photons in the RICH for a β=1 particle was found to be 33 with a single-hit resolution of 0.7 and 1 mrad in the fine and coarse granularity regions, respectively.

MODELING RADIATION TRANSMISSION, INTERCEPTION AND REFLECTION IN A HEDGEROW APPLE ORCHARD IN THE NORTHEASTERN PORTUGAL

MODELING RADIATION TRANSMISSION, INTERCEPTION AND REFLECTION IN A HEDGEROW APPLE ORCHARD IN THE NORTHEASTERN PORTUGAL

Uncertainties in CT-based radiation therapy treatment planning associated with patient breathing

Purpose : To evaluate uncertainties associated with treatment-planning computed tomography (CT) data obtained with the patient breathing freely. Methods and Materials : Patients with thoracic or abdominal tumors underwent a standard treatment-planning CT study while breathing quitely and freely, followedy CT scans while holding their breath at normal inhalation and normal exhalation. Identifical treatment plans on all three CT data sets for each patient pointed out differences in: (a) radiation path lengths; (b) positions of the organs; (c) physical volumes of the lung, liver, and kidneys; (d) the interpretation of plan evaluation tools such as dose-volume histograms and normal tissue complication probability (NTCP) models; and (e) how well the planning CT data set represented the average of the inhalation and exhalation studies. Results : Inhalation and exhalation data differ in terms of radiation path length (nearly one quarter of the cases had path-length differences >1 cm), although the free breathing and average path lengths do not exhibit large differences (0–9 mm). Liver and kidney movements averaged 2 cm, whereas differences between the free breathing and average positions averaged 0.6 cm. The physical volume of the liver between the free breathing and static studies varied by as much as 12%. The NTCP calculations on exhale and inhale studies varied from 3 to 43% for doses that resulted in a 15% NTCP on the free-breathing studies. Conclusion : Free-breathing CT studies may improperly estimate the position and volume of critical structures, and thus may mislead evaluation of plans based on such volume dependent criteria such as dose-volume histograms and NTCP calculations.

Average photon path-length of radiation emerging from finite atmospheres

The determination of the average path-length of photons emerging from a finite planeparallel atmosphere with molecular scattering is discussed. We examine the effects of polarisation on the average path-length of the emergent radiation by comparing the results with those obtained for the atmosphere where the scattering obeys the scalar Rayleigh function. Only the axial radiation field is considered for both cases.

Average photon path-length of radiation emerging from finite atmospheres

Average photon path-length of radiation emerging from finite atmospheres

A time-dependent climatic feedback system involving sea-ice extent, ocean temperature, and CO<sub>2</sub>

An idealized, time and latitude dependent, nonlinear, basically thermodynamic model is developed for an equinoctial, all-ocean planet to illustrate the possible roles of a number of positive and negative feedbacks that are present in the earth's climatic system. The mean atmospheric properties (e.g., temperature and cloud cover) and the sea-surface temperature are treated as fast response parts of the total system that are coherent with the sea ice extent measured by the sine of the ice edge latitude, ?. The mean depth- and latitude-average ocean temperature, ?, is the other prognostic variable that can vary along with ? over long time periods. The model is based on a set of parameterizations for all the modes of heat transfer across the top of the sea water, some of which represent considerable improvements over those incorporated in previous statistical dynamical climate models. In particular, the sensible heat flux now includes the “rectifier” effects associated with synoptic air mass exchanges that arise as a consequence of the baroclinicity of the atmosphere. This introduces a strong positive feedback leading to instability of the system, that can be viewed as the physical manifestation of the more familiar “ice-albedo” feedback. Another positive feedback included is due to longwave emissivity changes associated with CO 2 changes that, in turn, are postulated to arise in response to the variations of mean ocean temperature ?. Among the negative feedbacks is one due to the insulating effect of sea ice on ? (which, in turn, influences the ice edge extent through an upward subsurface heat flux at the ice edge), and another due to the changes of the amount and path length of solar radiation at the ice edge. The model is expressed mathematically as a coupled autonomous polynomial system of 6th degree governing the two state variables ? and ?. Analyses are made of the equilibria, sensitivity of the equilibria to changes in all the parameters, linear stability and structural stability of the equilibrium paths for changes in selected parameters of special interest (e.g., the solar constant and CO 2 level) constituting climatic prediction of the “second kind”. Finally, some phase plane portraits for specified values of parameters are presented showing the evolution of the system from arbitrary initial conditions (prediction of the “first kind”) and illustrating the time dependent properties of the system. For one reasonable set of parameters, damped oscillations of a period on the order of a thousand years are obtained, while for other possible parameter values unstable behavior is manifest. Because of the instabilities for large departures from equilibrium, this system cannot exhibit stable limit cycles (i.e., auto-oscillatory behavior), but realistic modifications are suggested that offer the possibilities of such behavior. DOI: 10.1111/j.2153-3490.1980.tb00938.x

A New Approach to Spatially Resolved Flame Temperature Measurements

Spatially resolved flame temperatures are spectroscopically measured using the slope method, over small (≃0.7 μl), relatively homogenous volumes of flame gases. The spatial resolution is uniquely obtained by introducing Co as a thermometric species into isolated volumes via the use of a droplet injection technique. By this method the emission of light is restricted to a limited volume, whose position in the flame can be accurately determined and controlled. Vertical resolution is determined by the width of the entrance slit of the monochromator employed (100 μm in this study), and horizontal resolution is limited by the width of the emission cloud formed by the injected droplets (1 to 3 mm). The possibility of self-absorption effects are greatly reduced because of the short radiation path length involved. The performance of the method is illustrated by its application to the spatial temperature mapping of the secondary reaction zone of a cylindrical air-acetylene flame. The effects of N2 as a sheathing gas and flame stoichiometry on the radial and vertical temperature distribution of the flame are also investigated. It is determined that a large, virtually isothermal, central zone exists in the flame.

A surface effect in the photodissociation of CO 2 and its significance for the theory of the Martian atmosphere

The pressure and radiation path length dependence of CO 2 photodissociation by 1849 Å, show that it occurs in adsorbed layers, rather than in the gas phase. Previous estimates of dissociation rates in the Martian atmosphere may therefore be much too large.