Energy Spectrum Of Radiation Research Articles

Passive Detection of Concealed Strontium-90 Radioisotope Thermoelectric Generators in Transport

Many radioisotope thermoelectric generators (RTGs) used in civilian and military applications employ 90Sr, a high-energy beta emitter. The possibility of indirect or deliberate contamination of the environment with this isotope is not negligible. Detection and identification of a concealed 90Sr RTG is possible by monitoring the continuous-energy spectrum of the bremsstrahlung radiation emitted as the source's betaparticles interact with the active material inside the source and with the surrounding container and shielding material. This detection concept is verified by measuring the energy spectrum of the bremsstrahlung radiation emitted from a small-activity shielded 90Sr source, using two modest energy-resolution detectors: a NaI(Tl) crystal and a BC-408 plastic scintillator. These measurements were in turn utilised to verify the results obtained from Monte Carlo simulations, to determine the detector response for a realistic RTG source. The minimum detection time was then estimated as a function of the activity of the source and thickness and type of surrounding shielding.

Depth profile of free volume in a mixture and copolymers of poly(N-vinyl-pyrrolidone) and poly(ethylene glycol) studied by positron annihilation spectroscopy.

Effect of hydrogen bonding on the depth profile of the free-volume in a mixture (weight ratio of 65:35) of poly(N-vinyl-pyrrolidone) (PVP) and poly(ethylene glycol) (PEG) and the copolymers of vinyl pyrrolidone with poly(ethylene glycol) diacrylate (PVP-PEGDA) and monomethacrylate (PVP-PEGMMA) was studied using positron annihilation spectroscopy. Doppler broadening energy spectra of annihilation radiation and positron annihilation lifetime were measured as a function of positron incident energy (0-30 keV). Significant variations of the free-volume depth profile in terms of the S parameter, ortho-positronium lifetime, intensity, and lifetime distribution are observed as a result of the hydrogen-bonding replacement of covalent bonds. The polymer mixture with hydrogen bonding through two sides of PEG short chains has a larger free volume and a wider distribution than the comb-structured PVP-PEGMMA and the network structured PVP-PEGDA. A longer ortho-positronium lifetime is observed near the surface than in the bulk. This is interpreted in terms of surface effect, free volume, and hydrogen bonding for drug delivery applications of polymeric materials.

The Stress–Strain State of Thin-Walled Structures Exposed to Radiation

Mathematical models of radiation-induced physical processes in materials are analyzed. An approximate method is proposed to determine thermal and radiation strains depending on the energy spectrum and components of radiation. The stress–strain state of thin plates is studied with allowance for radiation effects

The modern conception of the INCA project

Abstract The goals and status of the INCA Project are presented. New technique based on the ionization-neutron calorimeter (INCA) and designed to study the energy spectrum and composition of the primary cosmic radiation in the “knee” region as well as the spectrum of primary electrons in the range 0.1–10 TeV is discussed.

The cosmic ray energy spectrum around the knee measured with the GAMMA array at Mt. Aragats

Experimental data on EAS characteristics with Ne > 105 are used to calculate the so-called αe-parameter which is directly connected with the energy of the primary cosmic ray radiation. It is shown that the distribution of showers selected by a constant value of this parameter is isotropic, and the measurement of the αe-spectrum is a direct way to obtain the primary energy spectrum. Using the αe-parameter, the primary all-particle energy spectrum of the cosmic radiation in the knee region is obtained. The energy spectrum is compared with the corresponding data of other experiments.

BIOLOGICAL EFFECTS OF COSMIC RADIATION IN LOW-EARTH ORBIT

Space exploration poses health hazards to the crews of manned missions. Exposure to cosmic radiation and loss of bone density are considered the two most important risk factors for long-term missions. Stochastic risk deriving from cosmic radiation exposure can be estimated by physical dosimeters, using appropriate conversion factors. Recent measurements of space radiation fluence and energy spectra will improve current estimates. Biological dosimetry can be used as a tool to determine the risk directly from biological damage. Chromosomal aberrations in astronauts' peripheral blood lymphocytes have been used as a biomarker of cancer risk. In this paper we will also discuss countermeasures to radiation damage, focusing on the problem of shielding in space.

Broadband emission from a relativistic electron bunch in a semi-infinite waveguide

A study is made of the excitation of a transition radiation pulse during the injection of a charged particle bunch through the end metal wall into a semi-infinite cylindrical waveguide. Exact analytic expressions for the fields of a thin ring-shaped bunch are obtained in terms of the Lommel functions of two variables. The energy efficiency, power, and spectrum of radiation emitted from a finite-size charged bunch in a vacuum waveguide are calculated numerically with allowance for the multimode nature of the excited field. It is shown that, under certain conditions, the bunch can generate a short, high-intensity electromagnetic pulse with a broad frequency spectrum. The effect of various parameters of the charged bunch-waveguide system (such as the bunch current, bunch duration, and waveguide radius) on the generation efficiency of a transition radiation pulse is investigated.

Characterization of the surface layer of LB-films using a slow positron beam

Abstract Langmuir–Blodgett films were studied using a variable energy slow-positron beam. We measured the energy spectra of positron annihilation radiation for Cd and Mg eicosanoid films and obtained the V- and S-parameters as a function of the incident positron energy, E. In the V-E curves of Cd eicosanoid films, there were dips at the positron energy whose mean implantation depth corresponding to the first and second Cd 2+ layers from the surface. These dips are interpreted as the result of inhibition of Ps formation by the Cd 2+ ions. The S-parameter was found to be sensitive to chemical composition of the film and also to possible structural change due to heat treatment. Our results suggest that positron beams provide valuable information about the microstructure of the Langmuir-Blodgett films.

Measurements of the power and energy spectrum of radiation of the plasma liners

A diagnostic complex based on bolometers and X-ray diodes is developed and tested. The complex is designed for measurements of the power and the energy spectrum of the pulses of soft X-rays in a quanta energy range of 70–1500 eV. Both thin films and filters formed by pulsed gas-puff in the tube of the diagnostic channel were used as X-ray filters. Experiments were carried out on a high current generator under a load current up to 2 MA. Soft X-ray pulses with a power of about 1 TW and a duration of about 40 ns were formed by the implosion of krypton liners.

Direct evidence of positron trapping at polar groups in a polymer-blend system

Energy spectra of positron annihilation radiation were measured in polymer blends of polyethylene and ethylene vinyl acetate copolymer (E/VA) by means of the coincidence Doppler broadening technique. Positron annihilation with the core electrons of oxygen was appreciably increased by the addition of small amounts of E/VA to polyethylene and was detected with a sensitivity one order of magnitude higher than would be expected from the number density of the oxygen atoms in the polymer blends. This clearly shows that the positron is sensitively trapped by the polar acetate group of E/VA and demonstrates the usefulness of positrons as a sensitive chemical probe for polar structures in a nonpolar polymer matrix with high positron mobility. [S0163-1829(99)00941-8].

Generation of quasimonochromatic transition radiation X-rays using a K-shell photoabsorption edge

Abstract We propose a simple method to produce quasimonochromatic X-rays by means of photoabsorption-edge transition radiation tuned by tilting a foil stack. We have calculated and measured energy spectra of transition radiation for two types of radiators. One is a titanium-foil stack, and the other is composed of a Kapton-foil stack and a titanium filter. For the first type, the spectra can be easily tuned by tilting the foil stack to the electron beam, and the energy width of X-rays is reduced to one-third of that for the normal incidence of electrons. The easy tunability and narrow width was also obtained for the second type. The two types of radiator show almost the same performance if an adequate condition is satisfied. However, the second type radiator is applicable in wider energy range of X-rays than the first type radiator.

Excitation of a rectangular waveguide by pulsed electric and magnetic currents

We consider the problem of excitation of electromagnetic fields by electric and magnetic currents that are present in a rectangular waveguide. The space-time Green’s functions are obtained for a waveguide with ideally conducting walls. The primary attention is given to analysis of the energy spectrum of radiation and the influence of the finite duration of the current pulse and the finite dimensions of the conductor with the current on the above spectrum. It is shown that the influence of the above properties on the spectrum is weak at low frequencies and increases with frequency.

Study of mass composition and energy spectrum of primary cosmic radiation by the imaging atmospheric Cherenkov technique

Imaging atmospheric Cherenkov telescopes (IACT) have proven to be, up to now, the most effective instruments for the observation of primary TeV -radiation from astrophysical objects. The high detection rate as well as the capability of accurate reconstruction of air-shower parameters by the IACT technique also allow the use of the imaging technique for the study of the energy spectrum and mass composition of cosmic rays. In this paper we discuss the potential of this technique for the separation of different components of cosmic rays in the energy region 1-. We show that the imaging technique allows adequate separation of showers produced by protons from the contributions of all other nuclei, including -particles, and thus allows a measurement of the energy spectrum of the proton component at TeV energies. Such measurements can currently be performed by operating single IACTs designed originally for -ray astronomical purposes. The effective separation of different nucleus groups of the cosmic radiation is a more difficult problem. It benefits from the stereoscopic reconstruction of the shower development in the Earth's atmosphere. Our calculations show that simultaneous detection of air showers by two IACTs located at a distance of about 100 m from each other allows an effective separation of the proton, -particle, medium (O), heavy (Si), and very heavy (Fe) groups of cosmic-ray nuclei.

Proposal for a new calibration experiment at Chacaltaya for a primary mass estimation in the “knee” region

A new EAS experiment at the observation level 550 g/cm 2 and a new shower selection devoted to unbiased estimations of the mass composition and energy spectrum of the primary cosmic radiation at energies 10 4 – 10 5 GeV is proposed and analyzed in an attempt to carry calibration between the direct and indirect methods for primary cosmic flux studies. For this purpose, the existing Chacaltaya EAS array has to be designed with 4 new triggering systems and a powerful (1600 m 2 ) muon detector with E μ ≥ 0.6 GeV.

Characteristics of the absorbed dose to water standard at ENEA

The primary standard of absorbed dose to water established at ENEA for the Co-60 gamma-ray quality is based on a graphite calorimeter and an ionometric transfer system. This standard was recently improved after a more accurate assessment of some perturbation effects in the calorimeter and a modification of the water phantom shape and size. The conversion procedure requires two corresponding depths, one in graphite and one in water, where the radiation energy spectra must be the same. The energy spectra at the corresponding points were determined by a Monte Carlo simulation in water and graphite scaled phantoms. A thorough study of the calorimeter gap effect corrections was also made with regard to their dependence on depth and field size. A comparison between the ionization chamber calibration procedures based on the standards of absorbed dose to water and of air kerma was also made, confirming the consistency of the two methods.

X-Ray Microdiffraction for VLSI

AbstractWe describe how x-ray microbeam diffraction is being used to measure strain with micronscale spatial resolution. Micron-scale x-ray beams can be obtained using tapered glass capillaries. With the high brightness and broad energy spectrum of synchrotron radiation and the energy dispersive capabilities of commercially available, liquid nitrogen cooled x-ray detectors, spatially resolved strains in a sample can be determined along different directions without having to rotate the sample, in contrast with more conventional methods using monochromatic x-ray diffraction. This is a major advantage in achieving micron-scale spatial resolution. Strain sensitivities on the order of 2×10−4 have been achieved in such measurements. White beam x-ray microdiffraction has been applied for the first time in real-time studies of thermal and electromigration related strain distributions in passivated Al-on-Si conductor lines. Results of measurements on a single 10μm-wide line are described.

Galactic cosmic radiation model and its applications

A model for the differential energy spectra of galactic cosmic radiation as a function of solar activity is described. It is based on the standard diffusion-convection theory of solar modulation. Estimates of the modulation potential based on fitting this theory to observed spectral measurements from 1954 to 1989 are correlated to the Climax neutron counting rates and to the sunspot numbers at earlier times taking into account the polarity of the interplanetary magnetic field at the time of observations. These regression lines then provide a method for predicting the modulation at later times. The results of this model are quantitatively compared to a similar Moscow State University (MSU) model. These model cosmic ray spectra are used to predict the linear energy transfer spectra, differential energy spectra of light (charge < or = 2) ions, and single event upset rates in memory devices. These calculations are compared to observations made aboard the Space Shuttle.

The Quest for the Laws Governing Radiations and the Search for Beneficial Innovations

The last few years of the 19th Century saw the initial discoveries of ionizing radiation. These seminal discoveries were followed by an era of intensive studies of the physics related to radiation and clinical applications. The quantum theory revolutionized the ideas about nuclear structure and had a major impact on the physics of radiation. The discoveries of artificial radioactivity and of the neutron and the associated nuclear research have led to the availability of a variety of labeled compounds important to the study of human metabolism. Radioimmunoassay is an example, while other labeled compounds have therapeutic significance. New concepts in the acceleration of electrons and positive ions have contributed to the ability to concentrate radiation energy. New concepts in physics have led to the development of significant and versatile forms of diagnostic imaging. An example is computed tomography. Magnetic resonance is another example of an important physical concept which, decades after its discovery, made possible important applications in imaging and spectroscopy. Unlike ionizing radiation, the less energetic radiofrequency photons can convey information about molecular bonds but do not have sufficient energy to break them. Photon and positron emission scanning and tomography provide external images of internal concentrations of radionuclides, permitting the noninvasive determination of function. Dosimetry is fundamentally important to the diagnostic and therapeutic uses of radiation at both microscopic and macroscopic levels. A variety of radiation measuring instruments have been designed and studied for different purposes, including those based on radiation chemical response. Mammography is just one of the diagnostic applications where dosimetry, detector sensitivity characteristics, the radiation energy spectrum and image resolution are all vital parameters. In radiation treatment, physical and mathematical developments and quantitative radiation biology have increasingly led to optimum conformal radiation treatment, with dosimetry as a guiding parameter.

Investigation of the Magnetic Properties of the Ni77/Fe14.4/Cu4.5/Mo0.5/Cr2.2/Si0.2 Alloy

The positron annihilation and Μossbauer effect measurements in permalby Νi77/Fe14.4/Cu4.5/Mo0.5/Cr2.2/Si0.2 for different cooling rates have been performed. The results have been discussed in view of the magnetic properties of the alloy. Based on the energy spectra of positron annihilation radiation and 57 Fe Mossbauer spectra, the positron polarization coefficient and the hyperfine field distributions have been calculated, respectively. We demonstrate that the results of both, positron annihilation and Mossbauer effect measurements, are in very close relation to the initial permeability μ0.4 (at H = 0.4 A/m) and resistivity measurements.

Further development of the «gamma» array for investigation of primary particles and gamma-quanta with energies 105–107 GeV at Mt. Aragats

Specific simulations of EAS registrated in Aragats experiment and initiated by primary hadrons and gamma-quanta are performed. It is shown that, increasing the area of the 5 GeV muon detector in the «Gamma» array to 500 m2, taking into account the large effective area of the central calorimeter 1600 m2 and using the proposed selection criteria, in the selection of γ-showers a background discrimination could be realized at 95% level for energies ∼106 GeV. A new method for EAS registration with constant efficiency independent of the nature of the initiating primary particles could be realized essentially increasing the sensitive area of the electron flux detectors placed at a distance of ∼120m from the centre of the «Gamma» array. By this method, unbiased information about the energy spectrum and mass composition of the primary cosmic radiation at energies 105–108 GeV would be obtained.