Unit Mass Of Air Research Articles

P117] Dose estimation of eye lens for pediatric inner ear X-ray diagnosis

Purpose Recently, digital X-ray tomosynthesis using flat panel detectors (FPD) has been used to diagnose the inner ears of pediatric patients. This imaging provides intermediate functionality between X-ray photographs and X-ray computer tomography (CT) scans. However, during inner ear diagnosis, digital X-ray tomosynthesis includes the eye lens in its field of view; an organ sensitive to X-ray doses. The purpose of this research is to evaluate the X-ray dosage upon the eye lens during inner ear diagnosis using digital tomosynthesis and to compare this dosage with X-ray CT exposure. Methods Small optically stimulated luminescence (OSL) dosimeters (nanodot: Nagase Landauer, Ltd.) were positioned on the eye lens of a phantom and on the bed of an X-ray TV device to measure the kinetic energy released per unit mass of air (air kerma). We performed tomosynthesis, assuming the conditions for an inner ear examination of an infant. The irradiant conditions were a tube voltage of 60–110 kV, an added filter of 0.1 mmCu, a swing angle θ of ± 20 °, and 76 photographs of a flame. The absorbed dose for the eye lens was calculated using the mass energy absorption coefficient ratio of the eye lens and air. In addition, the eye lens absorbed dose was compared with an X-ray CT scan. Results As the tube voltage increased, the absorbed dose increased. Moreover, when placed in a posterior-anterior (PA) position, as the phantom thickness increased, the absorbed dose decreased. On the contrary, when in an anterior-posterior (AP) position, as phantom thickness increased, the absorbed dose increased. Conclusions The eye lens absorbed dose in the PA position decreased by 90% compared to AP-positioning when using digital tomosynthesis for inner ear diagnosis of pediatric patients. Additionally, the eye lens absorbed dose in PA-positioned digital tomosynthesis decreased 93% compared to X-ray CT scans. Therefore, it is useful to reduce the exposure dose of the eye lens during inner ear diagnosis of pediatric patients via the use of digital tomosynthesis imaging.

2018 ACC/HRS/NASCI/SCAI/SCCT Expert Consensus Document on Optimal Use of Ionizing Radiation in Cardiovascular Imaging: Best Practices for Safety and Effectiveness.

2018 ACC/HRS/NASCI/SCAI/SCCT Expert Consensus Document on Optimal Use of Ionizing Radiation in Cardiovascular Imaging: Best Practices for Safety and Effectiveness.

The effect of air cavity size in cylindrical ionization chambers on the measurements in high-energy radiotherapy photon beams—an experimental study

The present investigation is a continuation of a previous study on the effect of the diameter of the air cavity in cylindrical ionization chambers on perturbation correction factors. Measurements were made using high-energy radiotherapy photon beams (4, 6 and 15 MV) in a water phantom. Two different pairs of cylindrical ionization chambers were used. The chambers in each pair had identical materials and construction but different air cavity diameters. The same methods were employed as in our previous investigation. The diameter of the air cavity in cylindrical ionization chambers influences the mass ionization (the measured ionization expressed per unit mass of air in the chamber air cavity) at the depth where the maximum ionization is observed and a normalization at this depth is therefore not correct. The corrections obtained at depths of 50 and 100 mm in the phantom showed that the air cavity diameter in cylindrical ionization chambers has a greater effect on the perturbation effects than the photon beam quality. The corrections found at depths of 50 and 100 mm are smaller than those currently used in dosimetry protocols.

Evidence for Enhanced Land–Atmosphere Feedback in a Warming Climate

Abstract Global simulations have been conducted with the European Centre for Medium-Range Weather Forecasts operational model run at T1279 resolution for multiple decades representing climate from the late twentieth and late twenty-first centuries. Changes in key components of the water cycle are examined, focusing on variations at short time scales. Metrics of coupling and feedbacks between soil moisture and surface fluxes and between surface fluxes and properties of the planetary boundary layer (PBL) are inspected. Features of precipitation and other water cycle trends from coupled climate model consensus projections are well simulated. Extreme 6-hourly rainfall totals become more intense over much of the globe, suggesting an increased risk for flash floods. Seasonal-scale droughts are projected to escalate over much of the subtropics and midlatitudes during summer, while tropical and winter droughts become less likely. These changes are accompanied by an increase in the responsiveness of surface evapotranspiration to soil moisture variations. Even though daytime PBL depths increase over most locations in the next century, greater latent heat fluxes also occur over most land areas, contributing a larger energy effect per unit mass of air, except over some semiarid regions. This general increase in land–atmosphere coupling is represented in a combined metric as a “land coupling index” that incorporates the terrestrial and atmospheric effects together. The enhanced feedbacks are consistent with the precipitation changes, but a causal connection cannot be made without further sensitivity studies. Nevertheless, this approach could be applied to the output of traditional climate change simulations to assess changes in land–atmosphere feedbacks.

Experimental investigation of the effect of air cavity size in cylindrical ionization chambers on the measurements in 60Co radiotherapy beams

In the late 1970s, Johansson et al (1978 Int. Symp. National and International Standardization of Radiation Dosimetry (Atlanta 1977) vol 2 (Vienna: IAEA) pp 243–70) reported experimentally determined displacement correction factors (pdis) for cylindrical ionization chamber dosimetry in 60Co and high-energy photon beams. These pdis factors have been implemented and are currently in use in a number of dosimetry protocols. However, the accuracy of these factors has recently been questioned by Wang and Rogers (2009a Phys. Med. Biol. 54 1609–20), who performed Monte Carlo simulations of the experiments performed by Johansson et al. They reported that the inaccuracy of the pdis factors originated from the normalization procedure used by Johansson et al. In their experiments, Johansson et al normalized the measured depth–ionization curves at the depth of maximum ionization for each of the different ionization chambers. In this study, we experimentally investigated the effect of air cavity size of cylindrical ionization chambers in a PMMA phantom and 60Co γ-beam. Two different pairs of air-filled cylindrical ionization chambers were used. The chambers in each pair had identical construction and materials but different air cavity volume (diameter). A 20 MeV electron beam was utilized to determine the ratio of the mass of air in the cavity of the two chambers in each pair. This ratio of the mass of air in each pair was then used to compare the ratios of the ionizations obtained at different depths in the PMMA phantom and 60Co γ-beam using the two pairs of chambers. The diameter of the air cavity of cylindrical ionization chambers influences both the depth at which the maximum ionization is observed and the ionization per unit mass of air at this depth. The correction determined at depths of 50 mm and 100 mm is smaller than the correction currently used in many dosimetry protocols. The results presented here agree with the findings of Wang and Rogers’ Monte Carlo simulations and show that the normalization procedure employed by Johansson et al is not correct.

Accuracy of EGSnrc calculations at energies for the response of ion chambers configured with various wall materials and cavity dimensions

In this investigation, five experimental data sets are used to evaluate the ability of the EGSnrc Monte Carlo code to calculate the change in chamber response associated with changes in wall material and cavity dimension at 60Co energies. Calculations of the ratios of response per unit mass of air as a function of cavity volume for walls ranging from polystyrene to lead are generally within 1%-3% of experiments. A few exceptions, which are discussed, include 20%-30% discrepancies with experiments involving lead-walled chambers used by Attix et al. [J. Res. Natl. Bur. Stand. 60, 235-243 (1958)] and Cormack and Johns [Radiat. Res. 1, 133-157 (1954)], and 5% discrepancies for the graphite chamber of Attix et al. (relative to data for other wall materials). Simulations of the experiment by Whyte [Radiat. Res. 6, 371-379 (1957)], which varied cavity air pressure in a large cylindrical chamber, are generally within 0.5% (wall/electrode materials ranging from beryllium to copper). In all cases, the agreement between measurements and EGSnrc calculations is much better when the response as a function of cavity height or air pressure is considered for each wall material individually. High-precision measurements [Burns et al., Phys. Med. Biol. 52, 7125-7135 (2007)] of the response per unit mass as a function of cavity height for a graphite chamber are also accurately reproduced, and validate previous tests of the transport mechanics of EGSnrc. Based on the general agreement found in this work between corresponding experimental results and EGSnrc calculations it can be concluded that EGSnrc can reliably be used to calculate changes in response with changes in various wall materials and cavity dimensions at 60Co energies within a accuracy of a few percent or less.

SU-FF-T-237: Exposure Rate Calculation: Effect Of Photon Divergence Near A Radioactive Source

The objective is to show that near a radioactive source the commonly used exposure rate equation has to be modified in order to take photon divergence into consideration. This is accomplished by showing the derivation of the standard equation in detail and then illustrating where photon divergence needs special consideration. The commonly used equation for calculating the exposure rate is Eq.1 and the modified equation Eq.2. The reason for the modification is that the irradiated volume per unit entrance area is larger at close proximities. This means that charge produced per unit volume per photon penetrating the entrance area is smaller at close proximities than at a distance. Since the exposure is defined as charge liberated per unit volume or unit mass of air this results in Eq.1 overestimating the exposure rate. This is of relevance (a deviation of 10% or more between expected and measured value) at distance smaller than 5 cm. At larger distances the difference between both equations becomes negligible. An experiment using a Tc‐99m point source and a calibrated exposure rate meter is performed to compare theoretical and experimental values and to show the difference between the predictions of the two equations. This comparison showed very good agreement of the measured values and the predicted values based on Eq.2 and an overestimation of the exposure rate calculated using Eq.1. This has also implications for the tabulation of Gamma factors ( ) and their units: (mR⋅cm∧2)/(mCi⋅hr) vs. (mR⋅cm∧3)/(mCi⋅hr). Eq. 1 : Ẋ [ mR hr ] = Γ Activity dis tan ce 2 Eq. 2 : Ẋ [ mR hr ] = Γ 3 Activity (dis tan ce + 1) 3 − dis tan ce 3 .

Pathways Relating Soil Moisture Conditions to Future Summer Rainfall within a Model of the Land–Atmosphere System

In this paper, the key pathways and mechanisms through which soil moisture conditions affect future rainfall over the U.S. Midwest are investigated using a regional climate model. A series of numerical experiments are performed to identify these pathways using the drought of 1988 and flood of 1993 as representative events. The results suggest that the soil moisture–rainfall feedback is an important mechanism for hydrologic persistence during the late spring and summer over the midwestern United States. They indicate that the feedback between soil moisture and subsequent rainfall played a significant role in enhancing the persistence of the drought of 1988 and the flood of 1993. It is found that there is a pronounced asymmetry in the sensitivity of simulated rainfall to specified initial soil moisture. The asymmetry acts to favor a stronger soil moisture–rainfall feedback during drought conditions as opposed to flood conditions. Detailed analyses of the simulations indicate that the impact of soil moisture on both the energy and water budgets is crucial in determining the strength of the soil moisture–rainfall feedback. Anomalously high soil moisture tends to 1) increase the flux of high moist static energy air into the planetary boundary layer from the surface via an increase in net surface radiation, 2) reduce the planetary boundary layer height thus increasing the moist static energy per unit mass of air, and 3) reduce the amount of entrained air of low moist static energy from above the planetary boundary layer. Each of these effects are additive and combine to increase the moist static energy per unit mass of air in the planetary boundary layer. This increase results in an increase in the frequency and magnitude of convective rainfall events and a positive feedback between soil moisture and subsequent rainfall.

Entrainment in cumulus clouds, II: Drop size variability

AbstractA new analysis method for examining the effects of entrained subsaturated air on cloud drop sizes is described. This, independently, gives information about height changes following dilution with subsaturated air, and hence about whether the cloud parcels received the subsaturated air when higher or lower than their present level. The physical details of the entrainment mechanisms are first discussed to provide a basis for interpreting the data.Drop‐size distributions, measured by a Forward Scattering Spectrometer Probe and obtained from aircraft cloud samples at constant altitude in convective clouds in Montana, are used to analyse these cloud processes. The volume averaged drop radii for each parcel (i.e. each measured spectrum), in several clouds for several horizontal traverses in each, are plotted against concentration, given here in the form of drop numbers per unit mass of air. This concentration from parcel to parcel depends on the fraction of subsaturated air which has been entrained. The entity‐type entrainment mixing mechanism provides a satisfactory explanation for all the examples found in this study, where the average drop radius changes very little with drop‐number concentration from parcel to parcel. Alternative mechanisms are discussed and found to be insufficient.

The new NACP- and ICRU-dosimetry protocols for dosimetry of high-energy photon and electron radiation

In 1980 the NACP (Nordic Association of Clinical Physics) published new recommendations for the absorbed dose determination in electron and photon beams having maximum energies between 1 and 50 MeV and in addition a supplement in 1981 specially devoted to problems in dosimetry using low-energy electrons, with /7o < 15 MeV [8,9]. These protocols as well as the ionization chamber calibration procedure based on the very recent ICRU electron dosimetry Report 35 [4] will be discussed. Also, some background, not appearing in these reports, will be given. tors, and define the conditions (i.e. irradiation geometry and beam qualities) for which they are valid. It is often not understood that it is necessary to use a consistent set of numerical data both for the application of cavity theory at the Standards Laboratory to determine exposure or kerma and at the hospital for the conversion factors (cf. page 4 in ICRU Report 35). In order to stress this point the complete calibration chain must be analysed. The exposure for 6~ gamma rays, Xc, is determined at the Standards Laboratory from absolute measurements of J , ir, the electric charge (of one sign) per unit mass of air by using the relationship (see e.g. ref. 5).

A non-linear surface layer model

A model has been developed to investigate surface layer regime on the basis of a relation between mixing length and the total (kinetic and potential) energy per unit mass of air. Important features of the model include non-linear profiles of turbulent characteristics. The provided asymptotic behaviour indicates considerable consistency with the classical turbulent models.

An elementary parcel model with explicit condensation and supersaturation

Abstract The development of droplet size, supersaturation, and temperature in an ascending, unmixed parcel of cloudy air was investigated using a numerical model in which condensation and supersaturation are explicitly calculated. Of particular interest was the steady‐state value which the super‐saturation attains, and the time required to reach this value. The results were found to be in reasonable agreement with an approximate analytical solution of the equations that predicts a steady‐state supersaturation equal to G(p, T)U/vr, where G(p, T) is a known thermodynamic function of temperature and pressure, U is the updraft speed (assumed constant), v is the number of droplets per unit mass of air (assumed constant), and r is the droplet radius. The approach to this limiting value is very nearly exponential, with a time constant equal to G(p, T)/Q 1 vr, where Q 1 is a function of temperature. Without giving up the possibility of approximate analytical solutions, the equations can be elaborated to allow an ...

The Effects of Scattering and Ground Reflection on the Solar Energy Absorbed by Ozone in a Rayleigh Atmosphere

Abstract The effects of Rayleigh scattering and Lambert ground reflection on the solar energy absorbed by ozone in the earth's molecular atmosphere are evaluated on the basis of a complete solution of the transfer equation. The results show that these processes increase the following over that for a purely-absorbing atmosphere: 1) the total solar energy absorbed by ozone in a unit atmospheric column, 2) the energy absorbed per unit mass of air at all levels (except below 100 mb at low sun), and 3) the heating rates due to the absorption of solar energy by ozone. In each case, the magnitude of the increase can vary considerably depending on the solar zenith angle and the reflectivity of the underlying surface.

Some Radar Measurements of Turbulence in Snow

The Doppler spectrum of snow contains information about the turbulent wind field in which the snow is embedded. The average spread of the spectrum is proportional to the kinetic energy per unit mass of air in turbulent eddies that are generally smaller than the radar-sampled volume. The time variations in the mean value of velocity in the Doppler spectrum can be analyzed to determine the kinetic energy in eddies that are larger than the sampled volume. Thus from the time behavior of Doppler signals from snow can be estimated the total turbulent energy and the partitioning of this energy between large and small scales. Root-mean-square turbulent velocities computed on the basis of this technique were found to range between 0.4 and 2 m sec−1, with most of the values less than 1 m sec−1. Approximately three-quarters of the energy is usually in wavelengths shorter than 100 m. The data on the partitioning of eddy energy show considerable scatter, but there is some resemblance to the relationship expected from a Kolmogorov spectral law.

Stratospheric ice nucleus measurements from balloons

The ice nucleus content of stratospheric air was measured at one height in the range 13 to 27 km, on each of 13 experiments, by means of a vacuum pump and filters carried on large balloons. The concentrations were in close agreement with those found by Telford (1960) using an expansion cold chamber in an aeroplane and, per unit mass of air, were comparable with the extreme maxima recorded at the ground in long sequences of measurements in Australia. It is suggested that localised rapid transfer of air from stratosphere to lower troposphere is a probable cause of some ice nucleus storms at the ground. The source of the stratospheric ice nuclei is uncertain but reasons are given for supposing the nuclei to be of extra-terrestrial origin. DOI: 10.1111/j.2153-3490.1963.tb01375.x

Stratospheric ice nucleus measurements from balloons

The ice nucleus content of stratospheric air was measured at one height in the range 13 to 27 km, on each of 13 experiments, by means of a vacuum pump and filters carried on large balloons.&#x0D; The concentrations were in close agreement with those found by TELFORD (1960) using an expansion cold chamber in an aeroplane and, per unit mass of air, were comparable with the extreme maxima recorded at the ground in long sequences of measurements in Australia. It is suggested that localised rapid transfer of air from stratosphere to lower troposphere is a probable cause of some ice nucleus storms at the ground. The source of the stratospheric ice nuclei is uncertain but reasons are given for supposing the nuclei to be of extra-terrestrial origin.

Measurement of the ratio Em/Jm for betatron radiation.

Earlier measurements of the ratio Em/Jm for Co60 radiation have been made at the Saskatoon Cancer Clinic by J. P. Bernier and the present writers. A detailed report of this work is being published in Radiation Research. The method employed in the measurement of the ratio for betatron radiation is essentially the same, with minor modifications to facilitate integration of the dose. A small sample of carbon (20 gm.) was thermally isolated and supported in the path of the beam from the University of Saskatchewan 22-MEV betatron. The value of Em, the energy absorbed per unit mass by the sample on exposure to a given amount of this radiation, was measured. An ionization chamber having physical dimensions identical to those of the absorption sample was supported in the same position in the radiation beam. A measurement was made of Jm, the ionization produced per unit mass of air in the sensitive volume of the chamber by the same given amount of radiation. If we apply the Bragg-Gray relation, the ratio of these two quantities gives an experimental determination of the product Wρm, where W is the average energy required to produce an ion pair in air and ρm is the ratio of the mass-stopping power of carbon to that of air. If, then, a value for ρm is calculated from theoretical considerations, we may determine W. A tabulation of results appears above. It is interesting from a clinical point of view to compare the values of Em∕Jm> for Co60 and betatron radiation. It can be seen from the values in the table that 6 per cent less energy is absorbed per gram for betatron radiation than for Co60 radiation for the same ionization dose. This difference is due to the change in the stopping-power ratio, pm. ρm decreases with increasing photon energy because of the increasing importance of the polarization or density effect in carbon. The values of W for Co60 and betatron radiation differ by a negligible amount. After completion of the betatron experiments, the apparatus, in its modified form, was used to remeasure Em∕Jm for Co60 radiation. The results obtained checked very well with the original measurements made by Bernier et at. and are an indication of the reproducibility of these measurements.

A Calorimetric Determination of the Energy Required to Produce an Ion Pair in Air for Cobalt-60 Gamma-Rays

When Xor y-rays are absorbed in a material, their energy is imparted to electrons which then lose energy through ionization and excitation of the atoms of the material. In 1953 the International Commission on Radiological Units defined the rad as the unit of absorbed dose; 1 rad is 100 ergs of energy absorbed per gram of irradiated material (1). A calorimetric determination of the absorbed dose is very attractive in principle because of its directness. It is necessary to assume that all the absorbed energy is ultimately degraded into the form of heat. In the past, calorimetric methods have not been very practicable because of the difficulty in measuring the small temperature changes involved. For this reason, absorbed dose has usually been determined indirectly from measurement of the ionization of the gas in an ionization chamber. In calculating absorbed dose in absolute units, such as the rad, from ionization measurements one must know the value of W, the average energy expended in producing one ion pair in the gas.) In the experiments reported here, the value of W for air has been determined by a comparison of the energy absorbed in the wall of an ionization chamber and the ionization produced in the air volume of the chamber. The energy absorbed per unit mass of the wall, Em , and the ionization per unit mass of air, Jm , are related by the Bragg-Gray formula (2, 3),

Adiabatic Air Flow

IN most aerodynamical problems it is convenient to consider the aircraft to be stationary and the air to be flowing with a speed equal to the flight speed in a direction opposite to the direction of the flight. This practice simplifies the investigation of the motion of the aircraft and is perfectly legitimate from the mathematical point of view. Thus, if the flight speed is v, the kinetic energy or the dynamic head, q, of unit mass of air is ½ρv2. It the air is allowed to flow through a restriction, for example, a radiator or an air intake duct, the velocity of flow is reduced, and the dynamic energy thus lost is converted into the pressure energy. In most problems it is sufficiently accurate to assume that air is an incompressible fluid so that the density remains constant, and the flow changes can be investigated by applying the well‐known Bernoulli's Equation, viz., p+½ρv2=constant. This assumption is not strictly true, as the flow changes are usually brought about very quickly and there is little chance for the heat generated to be dissipated. However, the error made by this simplified assumption is not very large if the flight speed is fairly low. But in the case of high‐speed aircraft, e.g. a fighter aircraft, the above assumption involves a considerable error. To make a due allowance for the suddenness of the change, it would be necessary to discard the notion of the incompressibility of air and to use the adiabatic law between the pressure and the density of air. Thus, a better and a truer picture of the actual state of affairs would be obtained by assuming the air to be compressible and to investigate its effect on the pressure, density, and the temperature of the air. It is proposed to make a theoretical investigation of this problem on these lines and to present the results in the form of tables, graphs, and nomograms which could be easily applied in the solution of any practical problem on the flow changes.

The atmospheric height distribution of band-absorbed solar radiation

The band absorption of radiation incident on the atmosphere at any zenith angle χ is considered, when the relation between the absorption coefficient α and the wave-length λ has the form of the error function, so that αλ = α0exp[-(λ-λ0)2/λw2] ≡ α0exp(-l2), where l = (λ - λ0)/λw, and the intensity of the incident radiation is either constant across the absorption band or varies linearly across it. The height distribution of absorbed-energy density, the height of maximum volume absorption, the spectral composition of the energy absorbed at any level, and the proportionate daily variation of absorption density, are first discussed without any special assumption as to the height distribution of the absorbing constituent in the atmosphere. The height distribution of absorbed energy per unit mass of air is shown to depend only on a single function of a single parameter μ, which itself depends on the level, the angle of incidence χ, and the total absorption coefficient A0 of the atmosphere in the centre of the absorption band. The general results are afterwards discussed in relation to the special case of an exponential height distribution of the absorbing constituent, with scale-height H. It is shown that in this case, whatever the angle χ, (i) the height of maximum absorption per unit volume is at a distance 0.616H below the level of maximum monochromatic absorption at the centre λ0 of the band; (ii) the maximum volume density of absorbed energy at angle χ is cos χ times that for vertical incidence, as in the case of monochromatic absorption; (iii) above the level of maximum band absorption the height distribution of absorption differs only slightly from that in the case of monochromatic absorption, but below the maximum level the band-absorption layer extends further down than the monochromatic-absorption layer. If the absorption in the band-fringes where |l| ≥ 2 be neglected, the band-absorption layer is thicker than the monochromatic-absorption layer by approximately 2H, the excess thickness being in the part of the layer below the level of maximum absorption.