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The significance and novelty of the present work are the preparation of the non-lead ceramic by the general formula of (1-x) K0.5Na0.5NbO3-xLa Mn0.5Ni0.5O3 (KNN-LMN) with different x (0 . . . > (HVL)(x=0.25) is reported for half-value layer values against gamma photon. From the attained results, it can be concluded that increaisng the rate of x results in the better shielding proficiency in terms of neutron and gamma photon for chosen KNN-LMN-based lead-free ceramics.

In this article, the full energy peak efficiency of NaI detector using non-axial cylindrical sources is calculated by using a new efficient theoretical approach. This approach depends on using the efficiency transfer method and analytical calculations of the average path length of a gamma photon inside the source to the detector system. Measured efficiencies made by using 152Eu aqueous radioactive cylindrical sources with volumes 25 ml and 400 ml. Comparing calculated efficiencies to the measured one showed good agreement enabling the validation of this approach.

We have identified a mechanism of collective nuclear de-excitation in a Bose-Einstein condensate of $^{135}$Cs atoms in their isomeric states, $^{135m}$Cs, suitable for the generation of coherent gamma photons. The process described here does not correspond to single-pass amplification, which cannot occur in atomic systems due to the large shift between absorption and emission lines, nor does it require the large densities associated to standard Dicke super-radiance. It thus overcome the limitations that have been hindering the generation of coherent gamma rays in many systems. Therefore, we propose an approach for generation of coherent gamma rays, which relies on a combination of well established techniques of nuclear and atomic physics, and can be realized with currently available technology., published in Physics Letters B

In this paper, the average energy of the $\gamma$ -photon ( $E_{\mathrm {a},\mathrm{ph}}$ ) is calculated and the correlation between $\log E_{\mathrm{a},\mathrm{ph}}$ and the logarithm of the synchrotron peak frequency ( $\log\nu_{\mathrm{p}}$ ) is discussed for a sample of 620 BL Lac objects. The results show that there exists a positive correlation between the $\gamma$ -photon energy and the synchrotron peak frequency for BL Lac objects, which implies that the $\gamma$ -ray emissions are related to the low-energy emissions of radio to X-ray bands, and the high energetic $\gamma$ -ray emissions are only partially from the synchrotron self-Compton process (SSC) for BL Lac objects.

The present studies aimed to investigate the effects of energy dependence of parameters characterizing multiply backscattering of gamma photons. The numbers of multiply backscattered events are found to be increasing with thickness of copper target, and saturate for a particular thickness known as saturation thickness. The saturation thickness is found to be decreasing with increase in incident gamma photon energy, and also is not altered by the variation in collimator opening. The number, energy and dose albedos, characterizing the reflection probability of a material, are also evaluated. For each of the incident gamma photon energy, the number and energy albedos show an increase with increasing target thickness, and finally saturate. Monte Carlo calculations support the results of present experimental work.

The backscattered peak and albedos are important for the estimation of exposure distribution and for better understanding the phenomenon of the backscattering of gamma photons. To characterize the backscattering probability of gamma photons interacting with different atomic numbers (Z), number (A N), energy (A E) and dose (A D) albedos are experimentally evaluated. The response function converts the observed pulse-height distribution of a NaI(Tl) scintillation detector to a true photon spectrum. For each of the incident gamma photon energies, the number and energy albedos show an increase with the increasing target thickness, and finally saturate. The energy albedos are found to be decreasing with the increase in the atomic number of the target material and incident gamma photon energy. The dose albedos do not differ significantly from the energy albedos for the chosen incident gamma photon energies.

The gamma photons continue to soften in energy as the number of scatterings increases in the target having finite dimensions both in depth and lateral dimensions. The number of multiply scattered photons increases with an increase in target thickness, and saturates at a particular value of the target thickness known as saturation thickness (depth). The present measurements are carried out to study the energy dependence of saturation thickness of multiply scattered gamma photons from targets of various thicknesses. The scattered photons are detected by a properly shielded NaI(Tl) gamma ray detector placed at 90° to the incident beam. We observe that the saturation thickness increases with increasing incident gamma photon energy. Monte Carlo calculations based upon the package developed by Bauer and Pattison [Compton scattering experiments at the HMI (1981), HMI-B 364, pp. 1–106] support the present experimental results.

A new approach to the observation of electromagnetic-induced transparency in gamma optics is proposed. For this purpose, the propagation of a resonant gamma photon in a 57Fe magnetic medium affected by an external radiofrequency (RF) field is considered. It is demonstrated that, in the case of crossing-anticrossing, a resonant RF field significantly transforms gamma-optical properties of the medium that become dependent on its parameters. This allows coherent control of the group velocity of gamma photons and controlled filtering of unpolarized gamma radiation in the sample to be realized.

Needs in medical diagnosis, especially for early and reliable breast cancer detection, lead us to consider developments in scintillation crystals and position sensitive photomultiplier tubes (PSPMT) in order to develop a high-resolution medium field γ -ray imaging device. However the ideal detector for γ -rays represents a compromise between many conflicting requirements. In order to optimize different parameters involved in the detection process, we have developed a Monte Carlo simulation software. Its aim was to study the light distribution produced by a gamma photon interacting with a pixellated scintillation crystal coupled to a PSPMT array. Several crystal properties were taken into account as well as the intrinsic response of PSPMTs. Images obtained by simulations are compared with experimental results. Agreement between simulation and experimental results validate our simulation model.

The collision integral cross sections are obtained and computed for several experimentally realizable cases to understand the various features of the higher-order process known as double photon Compton scattering. The computational work carried out using the Mathematica software package generally corresponds to three different incident gamma photon energies of {sup 137}Cs (661.65 keV), {sup 65}Zn (1.12 MeV), and that from the radiative capture of {sup 19}F (6.14 MeV). The characteristic features revealed a need to be investigated experimentally to check for their support to the currently acceptable theory of this quantum electrodynamics process. An experimental technique has been suggested for the measurement of these collision integral cross sections.

It is argued that the dominant subleading shape-function contributions to the endpoint region of the charged-lepton energy spectrum in B -> X_u l nu decays can be related in a model-independent way to an integral over the B -> X_s gamma photon spectrum. The square root of the fraction of B -> X_u l nu events with charged-lepton energy above E_0=2.2 GeV can be calculated with a residual theoretical uncertainty from subleading shape-function effects that it safely below the 10% level. These effects have therefore a minor impact on the determination of |V_{ub}|., 8 pages, 1 figure. Final version to appear in Physics Letters B. By a smarter choice of weight function, m_b and lambda_1 have been eliminated from the final results. A paragraph has been added mentioning the potentially sizeable uncertainty due to duality violations and spectator-dependent effects. The discussion of the results obtained in refs. [7,8] has been made more accurate

A compact mono-energetic positron beam system has been constructed at The University of Hong Kong in order to perform positron re-emission measurements, after fast positrons from a radioactive 22Na source moderated by a variety of samples. The positron re-emission measurements are performed at a vacuum of 10−8 Torr. Re-emitted slow positrons are guided by longitudinal magnetic fields provided by three field coils located outside the vacuum tank and are detected by a gamma photon insensitive channel electron multiplier (CEM). The radioactive source, the sample, the focusing grid, the retarding-field energy analyzer (RFA) and the CEM detector were put into a compact assembly having a length of 33 cm and a diameter of 6 cm. Positron re-emission from W(1 1 1), GaN/SiC, Ga/GaN/SiC, 4H and 6H–SiC surfaces have been studied. The moderator conversion efficiencies of these samples are reported.

124I has a half-life of 4.2 days, which makes it suitable for imaging over several days along uptake and washout phases. However, it has a low positron branching ratio (23%), because high-energy gamma photons (602 to 1,691 keV), which degrade image quality, are emitted in cascade with positrons. In this study, we measured the single gamma photon fraction of 124I on Inveon PET scanner. Methods: to measure the single gamma photon fraction (SGF) of 124I, we measured the sensitivities of 124I and 18F from energy windows. The spill over ratios (SORs) of 124I were measured to assess the effect of single gamma photons fractions. Results: the SGF were 31%, 24%, and 3% in 0350 ~ 75, 0350 ~ 65, and 0350~ 55 keV, respectively. After single gamma corrections the SOR was decreased by 13% point. Conclusion: the proposed method for measuring the single gamma photons fraction of 124I will be useful to correct the single gamma photons from 124I PET. This information would also be useful to quantify the 124I PET.

I report results from the CLEO collaboration on semileptonic B decays, highlighting measurements of the Cabibbo-Kobayashi-Maskawa matrix elements |Vub| and |Vcb|. I describe the techniques used to obtain the recent improvements in precision for these measurements, notably the use of the b -> s gamma photon spectrum to constrain non-perturbative hadronic effects in semileptonic B decays., 13 pages, 5 figures, presented at Beauty 2002

I report results from the CLEO collaboration on semileptonic B decays, highlighting measurements of the Cabibbo-Kobayashi-Maskawa matrix elements Vcb and Vub. I describe the techniques used to obtain the recent improvements in precision for these measurements, including the use of the b -> s gamma photon spectrum to reduce hadronic uncertainties in semileptonic B decays. I also report new measurements of Vcb using the inclusive semileptonic branching fraction BF(B -> X e nu) and of Vub through study of the q^2 dependence of B -> pi l nu and B -> rho l nu., 3 pages, 3 figures, uses svjour.cls, submitted to Proceedings of EPS 2003

The energy and intensity distributions of multiple backscattering of 279, 320, 511 and 662 keV gamma photons emerging from targets of different elements are observed as a function of the target thickness. To characterize the backscattering, probabilities of gamma photons of different energies interacting with different atomic number (Z), energy (AE), number (An) and dose (AD) albedos are experimentally evaluated. The number and energy albedos are plotted as a function of incident gamma photon energy and atomic number (Z) of the target. The numbers of these multiple backscattered events show an increase with increasing target thickness and then saturate for a particular thickness of the target (the saturation thickness (depth)). The energy albedo is found to decrease with increasing incident gamma photon energy. The response function converts the observed pulse-height distribution of a NaI(Tl) detector to a true photon spectrum. Monte Carlo calculations support the present experimental results. The present measurements are carried out to study how the entities the gamma photon number albedo and the energy albedo vary as a function of the incident energy of the gamma photons, and the atomic number and thickness of an irradiated target.

A simple and economical passive graded shielding which is combination of low and high Z materials for HPGe detector for background radiation minimisation is developed for better identification of the peaks in acquired spectrum by reducing Compton continuum. The present paper discusses the design and advantages of the passive graded shielding (lead + copper + aluminium) which encloses the HPGe detector. The passive graded shielding improved sensitivity of the detector and reduced Minimum Detectable Activity (MDA) for planchet source from 19.6% to 11.7% for gamma photon energies in the range of 81–1408 keV and brought down the MDA, 35.25 GBq d –1 and 35.26 GBq d –1 for 133 Xe and 135 Xe respectively which was 72.31 GBq d –1 and 78.27 GBq d –1 for noble gases in gaseous effluents before shielding of the detector. The passive graded shielding as integral part is considerably very useful for radiological protection at nuclear power/research reactors by minimising background radiation.

In this paper we investigate anharmonic lattices that support the formation and propagation of Toda solitons along their chains. The main objective is to examine the influence of Toda solitons (TS) on the Mossbauer emission of gamma photons. Furthermore we conclude that it can be expected that the emission of hard gamma rays may be instrumental in producing narrow Toda solitons even at low temperatures. A manifestation of this phenomenon could be through an anomalous increase of the coefficient of thermal conductivity.

The response matrix of a 7.6 cm × 7.6 cm NaI(Tl) scintillation detector has been formed by calibration at 15 gamma ray energies in the range 0.095 MeV to 7.5 MeV. The detector response functions at the matrix mid-bin energies were produced by linear interpolations of the experimental calibrations. The response matrix was tested by unfolding the detector pulse height distributions from sources 88 Y and 24 Na using the code RADAK and comparing with established data. Experimental energy build up factors are presented for the penetration of 16 N gamma rays through steel and compared with calculations using the code PIPE.

The unfolding codes FERDOR and RADAK were selected to compare gamma photon spectra from experimental measurements. The input data were obtained from penetration measurements of 6 MeV gamma photons from a 0.86 m diameter uniform isotropic disc source through 10 cm of steel and 5 cm and 10 cm of lead. Both codes produced similar spectra but RADAK allows adjustment to the response matrix elements within real constraints and has a realistic approach to error analysis. RADAK is recommended as a standard unfolding code to provide experimental benchmark data.

Experimental data which demonstrate the potential of obtaining bearing information on gamma ray photon sources at ranges out to 1200 feet are presented. Collimation of multislit collimators was achieved with beamwidths of approximately 0.5° and 17°. Energy levels of 0.661 MeV from 137Cs and 1.17 and 1.33 MeV from 60Co sources were used with effective strengths up to 20 curie. The dependence of the parameters affecting angular accuracy was evaluated as a function of range, base energies and containments in the ray path.

The performance characteristics presented in this paper are: (1) the characteristics of gamma photon imaging with the Digital Autofluoroscope, (2) the resolution and efficiency of multihole and pinhole collimators, (3) a quantitative discussion of the image distortion inherent in pinhole collimators and of the penetration of the pinhole edges. In this discussion, it is pointed out that the various correction modes available, such as normalization of stored data and background suppression, are a means of removing the image distortion evident with pinhole collimators and of restoring image quality loss due to penetration of septa and pinhole edges. Also discussed is the use of the pinhole collimator as a means of magnifying small organs and minifying large ones.