Experimental investigation of multiple scattering of 662 keV gamma rays in zinc at 90°

Compton scattering investigations usually examine the case when photon has undergone only one Compton collision in the sample. The probability of a photon being scattered several times may be significant for a target of finite dimensions both in depth and lateral dimensions. The present experiment is undertaken to study the intensity and energy distributions of 662 keV gamma rays multiply scattered from a zinc target of various thicknesses at a scattering angle of 90° with the scattered photons being detected by an HPGe gamma detector. We observe that with an increase in target thickness, the number of multiply scattered photons also increases and saturates at a particular value of the target thickness (saturation depth). This supports the work of Paramesh, L., Venkataramaih, L., Gopala, K., Sanjeevaih, H. [1983. Z-dependence of saturation depth for multiple scattering of 662 keV photons from thick samples. Nucl. Instrum. Methods 206, 327–230]. The double Compton scattered peak is also observed in the experimental spectra, with a position in agreement with the predictions of Fernandez, J.E. [1991. Compton and Rayleigh double scattering of unpolarized radiation. Phys. Rev. A44, 4232–4248] and Barnea, G., Dick. C.E., Ginzburg. A.E., Seltzer. S.M. [1995. A study of multiple scattering background in Compton scatter imaging. NDT E Int. 28. 155–162].     

Non destructive evaluation of selected polymers by multiple scattering of 662 keV gamma rays

In this paper, multiple scattering of 662 keV gamma photons from targets of Carbon, Aluminium, Iron, Copper and polymers (Polypropylene, Polycarbonate, Polymethyl methacrylate, Polytetraflouroethylene and Polyvinyl chloride) is studied experimentally. Backscattered photons are detected by a NaI(Tl) detector placed at an angle of 90° to the incident beam. The single scattered events are reconstructed analytically to extract multiple scattered photons from the measured spectra. We observe that the number of backscattered photons increases with an increase in target thickness, and saturates at a particular value of the target thickness. This saturation thickness decreases with increasing atomic number of the target. The saturation thickness of the multiple scattering is used to assign effective atomic number of polymers. The experimental results are compared with the results obtained by Monte Carlo N-particle simulation code.     

Characterization of a material by probability of linear scattering using effect of target thickness

We report on an experimental test with 662 keV gamma photons scattered from a set of samples from ₆C, ₁₃Al, ₂₆Fe, ₂₉Cu, ₄₇Ag, ₈₂Pb and stainless steel for determination of probability of linear scattering, which can be used for characterization of a material. The results show that for the given target and scattering angle, the effect of target thickness in gamma photons scattering relates to single and multiple scattering and that the scattered events exponentially increase with an increase in target thickness and saturation at some values of thickness. The experimental results correlate with the typical function of energy transfer model.     

Depth distribution of multiple order X-ray scatter

Scatter can significantly affect quality of projectional X-ray radiographs and tomographic reconstructions. With this in mind, we examined some of the physical properties of multiple orders of scatter of X-ray photons traversing through a layer of scattering media such as water. Using Monte Carlo techniques, we investigated depth distributions of interactions between incident X-ray photons and water before the resulting scattered photons reach the detector plane. Effects of factors such as radiation field size, air gap, thickness of the layer of scattering medium and X-ray energy, on the scatter were included in the scope of this study. The following scatter characteristics were observed: (1) for a layer of scattering material corresponding to the typical subject thickness in medical imaging, frequency distribution of locations of the last scattering interaction increases approximately exponentially with depth, and the higher the order of scatter or the energy of the incident photon, the narrower is the distribution; (2) for the second order scatter, the distribution of locations of the first interaction is more uniform than that of the last interaction and is dependent on the energy of the primary photons. Theoretical proofs for some of these properties are given. These properties are important to better understanding of effects of scatter on the radiographic and tomographic imaging process and to developing effective methods for scatter correction.     

Measurement of effective atomic number and Rayleigh-to-Compton cross-section ratio for 145 keV gamma photons

The effective atomic numbers of composites and Rayleigh-to-Compton cross-section ratio of elements, in the range 6 ≤ Z ≤ 82 for 145 keV gamma photons, are determined experimentally. An HPGe (high purity germanium) semiconductor detector is placed, at scattering angle of 90°, to record the spectra originating from interactions of incident gamma photons with the target under investigations. The intensity ratio of Rayleigh-to-Compton scattered peaks, corrected for photo-peak efficiency of gamma detector and absorption of photons in the target and air column, is plotted as a function of atomic number and a best fit-curve is constituted. From this fit-curve, the respective effective atomic numbers of the scientific samples are determined. The measured values of cross-section ratio increases non-linearly with increase in atomic number and are found to agree with theoretical predictions based upon non-relativistic form factor, relativistic form factor, modified form factor and S-matrix theory.     

Monte Carlo analyses of multiple backscattering of gamma rays

We have written a Monte Carlo code to simulate the experimental results of a previously reported study. We were able to analyse the energy distributions of photons that reached the detector system after suffering several successive Compton scatterings in the target. We have also investigated how the number of multiply backscattered events depends on the target thickness and the energy of the primary photons.     

Determination of the sticking coefficient and scattering dynamics of water on ice using molecular beam techniques

The sticking coefficient for D(2)O impinging on crystalline D(2)O ice was determined for incident translational energies between 0.3 and 0.7 eV and for H(2)O on crystalline H(2)O ice at 0.3 eV. These experiments were done using directed molecular beams, allowing for precise control of the incident angle and energy. Experiments were also performed to measure the intensity and energy of the scattered molecules as a function of scattering angle. These results show that the sticking coefficient was near unity, slightly increasing with decreasing incident energy. However, even at the lowest incident energy, some D(2)O did not stick and was scattered from the ice surface. We observe under these conditions that the sticking probability asymptotically approaches but does not reach unity for water sticking on water ice. We also present evidence that the scattered fraction is consistent with a binary collision; the molecules are scattered promptly. These results are especially relevant for condensation processes occurring under nonequilibrium conditions, such as those found in astrophysical systems.     

基于瞬发伽马谱学的元素重建算法

质子治疗中的瞬发伽马射线是质子和靶标之间核反应的产物,瞬发伽马射线的特征能量和强度可以用来确定靶中元素的种类和数量,在之前的实验中已经证明,无论反应截面多么复杂,一旦确定了被照射元素和入射质子的能量,元素浓度与伽马射线光子数之间就存在一定的线性关系。然而,这种线性关系很难应用于医学成像,而且氢的非线性行为迄今尚未研究。本文将这种线性关系推广到包括氢等非线性情况的混合元素材料,并提出了一种通用的数学形式,即基于瞬发伽马谱学的重建算法 (PGSRA)。PGSRA的基本假设是样品材料的PGS与元素的每摩尔伽马射线有某种关系。对于碳和氧,这种关系是线性的,而对于氢,这种关系是非线性的。由于2.23 MeV的伽马线来源于中子吸收辐射,我们仔细研究了氢非线性行为。利用蒙特卡罗模拟验证了碳、氧和氢的不同组合,如PMMA、戊二醇和乙醇二醇的线性和非线性关系。在这项工作中开发的PGSRA可能是PGS和医学成像之间的第一座桥梁。     

On the creation of high energy bremsstrahlung and intensity by a multitarget and repeated focusing of the scattered electrons by small-angle backscatter at the wall of a cone and magnetic fields—A possible way to improve linear accelerators in radiotherapy and to verify Heisenberg-Euler scatter

The yield of bremsstrahlung from collisions of fast electrons (energy at least 6 MeV) with a Tungsten target can be significantly improved by exploitation of Tungsten wall scatter in a multi-layered target. The Tungsten wall can serve to refocuse small angle scattered electrons. It is necessary that the thickness of one Tungsten layer does not exceed 0.02 mm. Further repeated focusing of electrons results from suitable magnetic fields with field strength between 0.5 T and 6 T (if the cone with multi-layered targets is rather narrow). Linear accelerators in radiation therapy only need repeated focusing by wall scatter without further magnetic fields (standard case: ca. 100-000 plates with 0.01 mm thickness and 1 mm distance between the plates). The construction of a very narrow bremsstrahlung beam with extremely high photon intensity requires an additional strong magnetic field (order 1-6 T), which provides the possibility to check Heisenberg-Euler scatter of high energy photons.     

Z dependence of mass attenuation coefficient at 59.54 keV photon energy: experimental assessment of binding energy effects

Mass attenuation coefficients of 59.54 keV photons were measured in elements with atomic number ranging from low to high, and including lanthanides whose K-shell binding energies were close to those of incident photons. Comparison with the most reliable data from tabulations in current use reveals some disagreement in the interval of binding energy values close to 59.54 keV. The significant disagreement reported by other authors for certain elements was not confirmed by the present investigation.     

Energy absorption build-up factors in teeth

Geometric progression fitting method has been used to compute energy absorption build-up factor of teeth [enamel outer surface, enamel middle, enamel dentin junction towards enamel, enamel dentin junction towards dentin, dentin middle and dentin inner surface] for wide energy range (0.015?C15?MeV) up to the penetration depth of 40 mean free path. The dependence of energy absorption build-up factor on incident photon energy, penetration depth, electron density and effective atomic number has also been studied. The energy absorption build-up factors increases with the penetration depth and electron density of teeth. So that the degree of violation of Lambert?CBeer (I?=?I ₀e^???t ) law is less for least penetration depth and electron density. The energy absorption build-up factors for different regions of teeth are not same hence the energy absorbed by the different regions of teeth is not uniform which depends on the composition of the medium. The relative dose of gamma in different regions of teeth is also estimated. Dosimetric implication of energy absorption build-up factor in teeth has also been discussed. The estimated absorption build up factors in different regions of teeth may be useful in the electron spin resonance dosimetry.     

Tables of nuclear constants for gamma activation analysis

Tables of nuclear data were compiled for the purpose of routine gamma (photon) activation analysis. The tables are arranged in two parts. The first one lists the readionuclides in order of their atomic number. In the second one, the emitted gamma-ray photons are tabulated in order of increasing energy. Tables contain the gamma emitters produced by the following photonuclear reactions: (γ, γ), (γ, n), (γ, p), (γ, p+n), (γ, 2n), (γ, 3n), (γ, 4n), (γ, 2p), (γ, α), (γ, α+n), (γ, α+p). This set corresponds to the maximum energy of the bremsstrahlung of roughly 45 MeV. The program for output of the tabulated data is made such that it is possible to reduce the data as required for specific irradiation and measuring conditions (reaction thresholds, energy and intensity of gamma-rays, half-lives and target elements).     

New method for processing gamma backscattering spectra to estimate saturation depth and to determine thickness of aluminum and steel materials

In this study, we present a new gamma spectrum processing method is applied to analyze experimental scattering spectra on aluminum and steel for determining the intensity of the single scattering component. Based on these results, the saturation depth of aluminum and steel materials are 78.8 and 22.5 mm, respectively. The thickness of both materials is determined with a maximum relative deviation of about 7% in comparison with real thickness. Besides, the result also shows that we can use the new spectrum processing method, which is a simple, and useful solution to determine the material thickness, for NaI(Tl) detector and a low activity source.     

Influence of ultrasonic, microwave, and thermal effects on photoinduced charge transfer in poly(3-hexylthiophene)-Methanofullerene composites: EPR study

Radical pairs, polarons, and anion radicals of fullerenes that are induced in bulk heterojunctions of two composites, poly(3-hexylthiophene) with 6,6-phenyl-C₆₁-butanoic acid methyl ester and with 6,6-phenyl-C₆₂-butanoic acid bis(methyl ester), by photons with an energy of 1.98–2.73 eV at 77 K are studied via the method of photoinduced electron paramagnetic resonance. It is found that a part of the polarons and anion radicals of fullerenes are entrapped by energy traps of the polymer matrix, the quantity and depth of which are determined by ordering in the composites and the energy of exciting photons. A comparative study of the influence of composite treatment with ultrasonic, microwave, and thermal annealing on the formation and main resonance parameters of spin charge carriers in these bulk heterojunctions demonstrates a sharp gain in the number of charge carriers during illumination of the polymer-methanofullerene system, and the maximum effect is observed for photons with energies of 1.98 and 2.1 eV. This treatment procedure leads to the development of crystalline domains in the polymer matrix and increases the efficiency of light-energy conversion.     

Performance of gamma camera collimators used for single photon emission computed tomography imaging with 123I-isopropyl iodoamphetamine

123I Produced by 124Te(p, 2n)123I reaction is contaminated with 124I (less than 5%) and 126I (less than 0.3%). High energy photons from these mixed radioiodine compromise seriously image quality due to scattered photons and to septal penetration in the collimator. Four collimators of LEAP (for low energy all purpose), LEHR (for low energy high resolution), MESI (for medium energy made by Siemens) and MENU (for medium energy made by nuclear technology) mounted on a rotating gamma camera (Siemens, ZLC-7500), were examined in order to select a suitable collimator for 123I SPECT (single photon emission computed tomography) imaging. Sensitivities were measured with a plane source (5 X 5 X 0.5 cm) at the collimator face and distances from 2 to 30 cm in air. And, spatial resolutions in FWHM (full width at half maximum) and FWTM (full width at tenth maximum) were determined from line spread functions with planar and SPECT imaging. From the comparison of collimator performances with 99mTc and 123I, both collimators for low energy were not useful for 123I imaging. In other two collimators for medium energy, however, apparently the effect of septal penetration by the higher energy photons were also recognized, MENU with high geometrical resolution was more suitable for 123I SPECT imaging compared with MESI. And, it is important to perform the SPECT imaging with radius as short as possible.     

Reflection of electrons and photons from solids bombarded by 0.1 - to 100-MeV electrons

Electron and photon reflection ratios (in number and energy) for absorbers bombarded by electrons have been computed with the ITS Monte Carlo system version 3. Electrons of energies from 0.1 to 100 MeV have been assumed normally incident on an effectively semi-infinite absorber. The absorbers considered are elemental solids of atomic numbers from 4 to 92. The data on the electron reflection ratios agree rather well with the experimental data collected from literature except some discrepancies when the number-reflection ratio is small. For photons, the number-reflection ratio increases with increasing energy, but the energy-reflection ratio shows a maximum around 10 MeV. Empirical equations for the electron reflection ratios and the photon energy-reflection ratio are given (for electrons, graphs only).     

Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphite surface. II. H-physisorbed case

Following previous investigation of collision induced (CI) processes involving hydrogen atoms chemisorbed on graphite [R. Martinazzo and G. F. Tantardini, J. Chem. Phys. 124, 124702 (2006)], the case in which the target hydrogen atom is initially physisorbed on the surface is considered here. Several adsorbate-substrate initial states of the target H atom in the physisorption well are considered, and CI processes are studied for projectile energies up to 1 eV. Results show that (i) Eley-Rideal cross sections at low collision energies may be larger than those found in the H-chemisorbed case but they rapidly decrease as the collision energy increases; (ii) product hydrogen molecules are vibrationally very excited; (iii) collision induced desorption cross sections rapidly increase, reaching saturation values greater than 10 A2; (iv) trapping of the incident atoms is found to be as efficient as the Eley-Rideal reaction at low energies and remains sizable (3-4 A2) at high energies. The latter adsorbate-induced trapping results mainly in formation of metastable hot hydrogen atoms, i.e., atoms with an excess energy channeled in the motion parallel to the surface. These atoms might contribute in explaining hydrogen formation on graphite.     

CMOS image sensor for detection of interferon gamma protein interaction as a point-of-care approach

Complementary metal oxide semiconductor (CMOS)-based image sensors have received increased attention owing to the possibility of incorporating them into portable diagnostic devices. The present research examined the efficiency and sensitivity of a CMOS image sensor for the detection of antigen–antibody interactions involving interferon gamma protein without the aid of expensive instruments. The highest detection sensitivity of about 1 fg/ml primary antibody was achieved simply by a transmission mechanism. When photons are prevented from hitting the sensor surface, a reduction in digital output occurs in which the number of photons hitting the sensor surface is approximately proportional to the digital number. Nanoscale variation in substrate thickness after protein binding can be detected with high sensitivity by the CMOS image sensor. Therefore, this technique can be easily applied to smartphones or any clinical diagnostic devices for the detection of several biological entities, with high impact on the development of point-of-care applications.     

In-situ spectrometry of137Cs in the soil by an unfolding method

The approach is based on in-situ measurements performed with a portable high-resolution germanium -spectrometer and on calculations of the depth distribution by an unfolding method. To unfold the depht distribution of¹³⁷Cs concentration in soil four detector responses and the iterative procedure SAND II were used. The detector responses consist of the responses to primary 662 keV photons and to photons scattered in soil with the rest energies of 620–655 keV. The detector is used with and without collimator. The method is sufficiently sensitive for measurements of¹³⁷Cs concentration in soil 10 years after the Chernobyl accident. The results are compared to laboratory analyses of collected soil samples and with a standard method of in-situ spectrometry.