Spectrum Of Ionizing Radiation Research Articles

Potential Role of Natural Products to Combat Radiotherapy and Their Future Perspectives.

Cancer is the second leading cause of death in the world. Chemotherapy and radiotherapy (RT) are the common cancer treatments. In addition to these limitations, the development of adverse effects from chemotherapy and RT reduces the quality of life for cancer patients. Cellular radiosensitivity, or the ability to resist and overcome cell damage caused by ionizing radiation (IR), is directly related to cancer cells’ response to RT. Therefore, radiobiological research is emphasizing chemical compounds ’radiosensitization of cancer cells so that they are more reactive in the IR spectrum. Recent years researchers have seen an increase in interest in natural products that have antitumor effects with minimal side effects. Natural products, on the other hand, are easy to recover and therefore less expensive. There have been several scientific studies done based on these compounds that have tested their ability in vitro and in vivo to induce tumor radiosensitization. The role of natural products in RT, as well as their usefulness and potential applications, is the goal of this current review.

COLEGRAM, a flexible user-friendly software for processing of ionizing radiation spectra

COLEGRAM is a freely available spectrometry software dedicated to the study of ionizing radiation spectra. It can handle alpha, beta, gamma and X-ray spectra, proposing twenty-eight specific peak shapes in order to fit complex spectra using the non-linear least-squares fitting method. Different optimization cost functions can be used to perform the mathematical adjustment, which is guided by a user-friendly interface. COLEGRAM is also able to perform batch processing on a large number of spectra copying fitted peak information, based on a predefined model. General characteristics of the code and typical application examples are given to illustrate its potential.

Ions of heavy elements at the epoch of reionization of helium

The thermal and ionization evolution of the circumgalactic and intergalactic gas at the epoch of reionization of helium (HeII), is considered in a non-equilibrium(time-dependent) approach. The influence of line and continuum absorption by HeII ions on the ion states of metals and the ratios of their column densities in diffuse (with a temperature T ≲ 105 K) circumgalactic and intergalactic gas irradiated by ionizing radiation with a power-law spectrum, characteristic of quasars and distorted by HeII absorption, and the extragalactic background radiation. The ion states of nitrogen, oxygen, and neon can be used to study the possible distortion of the spectrum at ∼40–150 eV. The column-density ratios CIII/CIV and SiIII/SiIV are good indicators of absorption in resonance lines of helium (∼40–54 eV). The SiIV/CIV ratio depends only weakly on spectral variations in this energy range. The OIII/OIV ratio is most promising as an indicator of HeII continuum absorption (∼54–150 eV). Consequently, joint analyses of the OIII/OIV and CIII/CIV (or SiIII/SiIV) ratios aimed at studying the reionization of helium can be used to place better constraints on the shape of the ionizing radiation spectrum, both in the region of absorption resonance lines and in the continuum.

Metal-enriched, subkiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy★

We report the serendipitous detection of a 0.2 L$^*$, Lyman-$\alpha$ emitting galaxy at redshift 2.5 at an impact parameter of 50 kpc from a bright background QSO sightline. A high-resolution spectrum of the QSO reveals a partial Lyman-limit absorption system ($N_\mathrm{HI}=10^{16.94\pm0.10}$ cm$^{-2}$) with many associated metal absorption lines at the same redshift as the foreground galaxy. Using photoionization models that carefully treat measurement errors and marginalise over uncertainties in the shape and normalisation of the ionizing radiation spectrum, we derive the total hydrogen column density $N_\mathrm{H}=10^{19.4\pm0.3}$ cm$^{-2}$, and show that all the absorbing clouds are metal enriched, with $Z=0.1$-$0.6 Z_\odot$. These metallicities and the system's large velocity width ($436$ km$\,$s$^{-1}$) suggest the gas is produced by an outflowing wind. Using an expanding shell model we estimate a mass outflow rate of $\sim5 M_\odot\,$yr$^{-1}$. Our photoionization model yields extremely small sizes ($<$100-500 pc) for the absorbing clouds, which we argue are typical of high column density absorbers in the circumgalactic medium (CGM). Given these small sizes and extreme kinematics, it is unclear how the clumps survive in the CGM without being destroyed by hydrodynamic instabilities. The small cloud sizes imply that even state-of-the-art cosmological simulations require more than a $1000$-fold improvement in mass resolution to resolve the hydrodynamics relevant for cool gas in the CGM.

Modeling the emission of an H II region containing a bubble-like structure

The influence of a bubble-like structure around a starburst within the H II regions on the shape of the ionizing spectrum and the generation of the observed emission lines was studied using multicomponent photoionization modeling. The distributions of density and other physical parameters in such bubble-like structures were determined by Weaver et al. in 1977. The first two components represent the region of the stellar wind from the central starburst region. The gas density and electron temperature distributions in these components were described by the solution of the system of equations of continuity and energy transfer with account for the heat conductivity. The third component represents a thin layer of gas with a high density that emerges due to the passage of a normal shock wave of the stellar wind. The fourth component represents a “typical” H II region. The ionizing radiation spectra were set from the calculated evolutionary models whose free parameters determine the physical conditions within the “bubble.” The influence of the stellar wind bubble on the shape of the ionizing radiation spectrum and the generation of fluxes in important emission lines was analyzed.

Non-equilibrium ionization states and cooling rates of photoionized enriched gas

Non-equilibrium (time-dependent) cooling rates and ionization state calculations are presented for low-density gas enriched with heavy elements (metals) and photoionized by external ultraviolet/X-ray radiation. We consider a wide range of gas densities and metallicities and also two types of external radiation field: a power-law and an extragalactic background spectra. We have found that both cooling efficiencies and ionic composition of enriched photoionized gas depend significantly on the gas metallicity and density, the flux amplitude and the shape of ionizing radiation spectrum. The cooling rates and ionic composition of the gas in non-equilibrium photoionization models differ strongly (by a factor of several) from those in photoequilibrium due to overionization of the ionic states in the non-equilibrium case. The difference is maximal at low values of the ionization parameter and similar in magnitude to that between the equilibrium and non-equilibrium cooling rates in the collisionally controlled gas. In general, the non-equilibrium effects are notable at T≲ 106 K. In this temperature range, the extent of mismatch between the two ionic states and their ratios between the photoequilibrium and the photo-non-equilibrium models reach a factor of several. The net result is that the time-dependent energy losses due to each chemical element (i.e. the contributions to the total cooling rate) differ significantly from the photoequilibrium ones. We advocate the use of non-equilibrium cooling rates and ionic states for gas with near-solar (and above) metallicity exposed to an arbitrary ionizing radiation flux. We provide a parameter space (in terms of temperature, density, metallicity and ionizing radiation flux), where the non-equilibrium cooling rates are to be used. More quantitatively, the non-equilibrium collisional cooling rates and ionization states are a better choice for the ionization parameter log U≲−5. The difference between the photoequilibrium and the photo-non-equilibrium decreases with the ionization parameter growth, and the photoequilibrium can be used for ionization parameter as high as log U≳−2 for Z≲ 10−2 Z⊙ and log U≳ 0 for Z∼ Z⊙. Thus, the non-equilibrium calculations should be used for the ionization parameter range between the above-mentioned values. In general, where the physical conditions favour collisional ionization, the non-equilibrium (photo)ionization calculations should be conducted.

Determination of energy distribution in ionizing radiation spectrum of Orion nebula

Determination of energy distribution in ionizing radiation spectrum of Orion nebula

Space Solar Patrol data and changes in weather and climate, including global warming**This article was originally submitted for inclusion with the papers from the 9th International Symposium on Measurement Science and Intelligent Instruments (ISMTII-2009), published in the May 2010 issue.

In this paper, the results obtained during the execution of several ISTC projects are presented. The general aim of these projects has been the study of global changes in the environment, connected with solar activity. A brief description of the optical apparatus of the Space Solar Patrol (SSP) developed and built in the framework of the ISTC projects 385, 385.2, 1523 and 2500 is given. The SSP is intended for permanent monitoring of spectra and absolute fluxes of soft x-ray and extreme ultraviolet (x-ray/EUV) radiation from the full disk of the Sun which ionizes the upper atmosphere of the Earth. Permanent solar monitoring in the main part of the ionizing radiation spectra 0.8–115 (119) nm does not exist. The apparatus of the SSP was developed in the years 1996–2005 with multiyear experience of developing such apparatus in S I Vavilov State Optical Institute. The basis of this apparatus is the use of unique detectors of ionizing radiation—open secondary electron multipliers, which are ‘solar blind’ to near UV, visible and IR radiation from the Sun, and new methodology of these solar spectroradiometric absolute measurements. The prospects are discussed of using the SSP data for the investigation and forecast of the influence of solar variability on the weather and climate including global warming and also on the biosphere including human beings (proposal 3878).

Dominant Lethal Mutations in the Honeybee: A Perspective 50 Years Later

Dominant Lethal Mutations in the Honeybee: A Perspective 50 Years Later

Slit observations and empirical calculations for H ii regions

When analysing H ii regions, a possible source of systematic error on empirically derived quantities, such as the gas temperature and the chemical composition, is the limited size of the slit used for the observations. In order to evaluate this type of systematic error, we use the photoionization code aangaba to create a virtual photoionized region and mimic the effect of a slit observation. A grid of models was built varying the ionizing radiation spectrum emitted by a central stellar cluster, as well as the gas abundance. The calculated line surface brightness was then used to simulate slit observations and to derive empirical parameters using the usual methods described in the literature. Depending on the fraction of the object covered by the slit, the empirically derived physical parameters and chemical composition can be different from those obtained from observations of the whole object. This effect is mainly dependent on the age of the ionizing stellar cluster. The low-ionization lines, which originate in the outer layers of the ionized gas, are more sensitive to the size of the area covered by the slit than the high-ionization forbidden lines or recombination lines, because these lines are mainly produced closer to the inner radius of the nebula. For a slit covering 50 per cent or less of the total area, the measured [O iii], [O ii] and [O i] line intensities are less than 78, 62 and 58 per cent of the total intensity for a young H ii region (t < 3 Myr); for older objects the effect due to the slit is less significant. Regarding the temperature indicator T[O iii], the slit effects are small (usually less than 5 per cent) because this temperature is derived from [O iii] high-ionization lines. On the other hand, for the abundance (and temperature) indicator R23, which depends also on the [O ii] line, the slit effect is slightly higher. Therefore, the systematic error due to slit observations on the O abundance is low, being usually less than 10 per cent, except for H ii regions powered by stellar clusters with a relative low number of ionizing photons between 13.6 and 54.4 eV, which create a smaller O++ emitting volume. In this case, the systematic error on the empirical O abundance deduced from slit observations is more than 10 per cent when the covered area is less than 50 per cent.

Ultraviolet Continuum, Physical Conditions, and Filling Factor in Active Galactic Nuclei

The narrow-line region of active galaxies is formed by gas clouds surrounded by a diluted gas. Standard one-dimensional photoionization models are usually used to model this region in order to reproduce the observed emission lines. Since the narrow-line region is not homogeneous, two major types of models are used: (1) those assuming a homogeneous gas distribution and a filling factor less than unity to mimic the presence of the emitting clouds and (2) those based on a composition of single-cloud models combined in order to obtain the observed spectra. The first method is largely used but may induce misleading conclusions, as shown in this paper. The second one is more appropriate but requires a large number of observed lines in order to limit the number of single models used. After discussing the case of an extragalactic H II region, for which the ionizing radiation spectrum is better known, we show that one-dimensional models for the narrow-line region with a filling factor less than unity do not properly mimic the clumpiness but just simulate an overall lower density. Multicloud models lead to more reliable results. Both models are tested in this paper, using the emission-line spectra of two well-known Seyfert galaxies, NGC 4151 and NGC 1068. It is shown that ionizing radiation spectra with a blue bump cannot be excluded by multicloud models, although excluded by Alexander et al. using homogeneous models with a filling factor less than unity.

Are the narrow-line regions of active galactic nuclei optically thick?

The possibility of the narrow-line region (NLR) of AGN being optically thin to the hydrogen Lyman continuum is discussed. It is shown that, for a large sample of AGN, as the He II/H-beta ratio increases the low-excitation line ratios decrease, also indicating that the NLRs have different optical depths to the hydrogen Lyman continuum. Some NLRs are radiation-bounded, others are matter-bounded. This implies that attempts to fit an average emission-line spectrum by lumping together observations of several objects are not realistic, and that any claim concerning the shape of the ionizing radiation spectrum obtained using optically thick models for the NLR should be reconsidered. 25 references.