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The stoniness of topsoil can have a significant impact on the cost-effectiveness and quality of work in mechanized forest operations. The operations and their models should be selected on a stand-specific basis, while the physical properties of the soil, including stoniness, to achieve maximum efficiency and to minimize the damage caused by heavy forest machinery. The aim of this study was to examine whether the stoniness of the topsoil can be predicted using the gamma-ray values available from geophysical data collected at low altitude and using soil type information. Stoniness was measured at several sites with various soil types, which were then divided into stoniness index classes (SICs) for further analysis by ordinal regression analysis using gamma-ray and soil type data. The predictions associated with SIC classification were 52% accurate and 79% acceptable ([+ or -]1 class from the correct class), with kappa values of 0.55 and 0.72, respectively. The SIC prediction results were promising and showed the potential of gamma-ray and soil type data for estimating topsoil stoniness. Key words: forest trafficability, gamma-ray radiation, stoniness index, ordinal regression, kappa. La pierrosite de la couche superieure du sol peut avoir un impact important sur la rentabilite et la qualite du travail dans le cas des operations forestieres mecanisees. Les operations et leurs modeles devraient etre selectionnes en fonction des caracteristiques du peuplement tout en tenant compte des proprietes physiques du sol, y compris la pierrosite, afin d'atteindre une efficacite maximale et de minimiser les dommages causes par la machinerie forestiere de grande taille. La presente etude visait a determiner si la pierrosite de la couche superieure du sol peut etre estimee a partir des valeurs de rayons gamma provenant de donnees geophysiques recoltees a basse altitude et des renseignements sur le type de sol. La pierrosite a ete mesuree dans plusieurs stations couvrant differents types de sol qui ont ensuite ete divises en classes d'indice de pierrosite (CIP). Les donnees de rayons gamma et le type de sol ont ensuite ete integres dans une analyse de regression ordinale. Les previsions associees a la classification par CIP etaient precises a 52% et acceptables a 79% (erreur de [+ or -] 1 classe par rapport a la bonne classe), avec des valeurs kappa de respectivement 0,55 et 0,72. Ces resultats provenant de la classification par CIP sont prometteurs et mettent en evidence le potentiel des donnees de rayons gamma et du type de sol pour estimer la pierrosite de la couche superieure du sol. [Traduit par la Redaction] Mots-cles: traficabilite forestiere, rayonnement gamma, indice de pierrosite, regression ordinale, kappa., 1. Introduction The interest towards small-scale variations in soil characteristics and terrain topography has increased in recent times due to the challenges posed by varying weather conditions during rainy spring [...]

The double-gamma (γγ)-decay of a quantum system in an excited state is a fundamental second-order process of quantum electrodynamics. In contrast to the well-known single-gamma (γ)-decay, the γγ-decay is characterized by the simultaneous emission of two γ quanta, each with a continuous energy spectrum. In nuclear physics, this exotic decay mode has only been observed for transitions between states with spin-parity quantum numbers [J.sup.π] = [0.sup.+] (refs 1-3). Single-gamma decays--the main experimental obstacle to observing the γγ-decay--are strictly forbidden for these [0.sup.+] [right arrow] [0.sup.+] transitions. Here we report the observation of the γγ-decay of an excited nuclear state ([J.sup.π] = 11/2 2) that is directly competing with an allowed γ-decay (to ground state [J.sup.π] = 3/[2.sup.+]). The branching ratio of the competitive γγ-decay of the 11/[2.sup.-] isomer of [sup.137]Ba to the ground state relative to its single y-decay was determined to be (2.05 ± 0.37) X [10.sup.-6]. From the measured angular correlation and the shape of the energy spectra of the individual γ-rays, the contributing combinations of multipolarities of the γ radiation were determined. Transition matrix elements calculated using the quasiparticle-phonon model reproduce our measurements well. The γγ-decay rate gives access to so far unexplored important nuclear structure information, such as the generalized (off-diagonal) nuclear electric polarizabilities and magnetic susceptibilities (3)., Two-photon processes, that is, excitation and decay of a quantum state simultaneously involving two photons whose energy sum [E.sub.1] + [E.sub.2] matches the transition energy [E.sub.0], have been studied intensely [...]

Two-parameters formula based on the conventional collective rotational model is applied to describe superdeformed rotational bands (SDRB's) in nuclei in the A ~ 190 mass region, namely the five SDRB's [sup.192]Hg(SD1), [sup.194]Hg(SD1), [sup.194]Hg(SD2), [sup.194]Pb(SD1) and [sup.194]Pb(SD2). The bandhead spins of the observed levels have been extracted by first and second-hand estimation corresponding to pure rotator and our proposed formula respectively by plotting the E-Gamma Over Spin (EGOS) versus spin. A computer simulated search program is used to extract the model parameters in order to obtain a minimum root mean square (rms) deviation between the calculated and the experimental transition energies The values of spins resulting from second estimation method are excellent consistent with spin assignment of other models. The calculated transition energies, level spins, rotational frequencies, kinematic and dynamic moments of inertia are systematically examined. The difference in γ-ray transition energies Δ[E.sub.γ] between transitions in the two isotones [sup.192]Hg(SD1) and [sup.194]Pb(SD1) were small and constant up to rotational frequency [??]ω ~ 0.25 MeV. Therefore, these two bands have been considered as identical bands. The ΔI = 2 energy staggering observed in [sup.194]Hg(SD1) and [sup.194]Hg(SD2) of our selected SDRB's are also described from a smooth reference representing the finite difference approximation to the fourth order derivative of the transition energies at a given spin., 1 Introduction Superdeformed (SD) nuclei were observed in a wide range of nuclear chart, and a wealth of experimental data on the resulting superdeformed rotational bands (SDRR's) was accumulated in [...]

Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst (1-5). High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (5) (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times (6-8), when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets (9-11)., Magnetic fields play a crucial role in the physics of relativistic jets--for example, in their formation, acceleration and colliniation (1,12,13). On smaller spatial scales, there is a strong connection between [...]

Understanding aquifer architecture is critical for managing groundwater resources in western Canada. Recent regulations have yielded abundant new gamma-ray well-log data from the principal aquifer in Alberta, the Paleocene Paskapoo Formation. A major obstacle to utilizing this data is the fact that gamma-ray measurements in the shallow subsurface are made through surface casing, which suppresses gamma-ray readings and effectively prohibits stratigraphic characterization. Here we describe and demonstrate a relatively simple and efficient method for normalizing gamma-ray data from stratigraphic horizons that are behind surface casing and apply this method to the Paskapoo Formation in west-central Alberta. The gamma-ray normalization procedure adjusts the cased gamma-ray values so that high and low percentile values of the resulting gamma-ray statistical distribution are equal to those of the non-cased values. The effectiveness of this procedure is demonstrated by comparing the normalized gamma-ray values from cased intervals with those from nearby wells without casing. Good matches between these wells, as well as the transition between normalized curves at the base of cased zones and the gamma-ray curves at the uppermost portion of uncased zones, suggest this methodology is effective for studying the Paskapoo Formation. The normalized curve allows cased and uncased intervals to be correlated, enabling improved stratigraphic characterization and mapping of fluvial sand bodies behind surface casing. This new data provides the framework for better characterization of aquifer dimensions and the derivation of stratigraphic parameters used to constrain hydrogeological models and enhance groundwater recovery. Pour gerer les ressources d'eau souterraine dans l'Ouest canadien, il est essentiel de comprendre l'architecture des aquiferes. De recentes reglementations ont permis d'obtenir de grandes quantites de donnees de diagraphie de puits par carottage au rayonnement gamma sur le principal aquifere de l'Alberta, la Formation de Paskapoo (Paleocene). Un des principaux obstacles a l'utilisation de ces donnees est le fait que les mesures par rayonnement gamma a de faibles profondeurs sous la surface sont effectuees a travers le tubage de surface, ce qui supprime les lectures de rayonnement gamma et empeche une caracterisation stratigraphique efficace. Dans le present article, nous decrivons et demontrons une methode relativement simple et efficace de normalisation des donnees de rayonnement gamma des horizons stratigraphiques qui se trouvent derriere le tubage de surface et nous appliquons cette methode a la Formation de Paskapoo dans le centre-ouest de l'Alberta. La procedure de normalisation du rayonnement gamma ajuste les valeurs 'encaissees'de rayonnement gamma afin que les valeurs percentiles, basses et elevees, de la distribution resultante de rayonnement gamma soient egales a celles des valeurs non'encaissees'. L'efficacite de cette procedure est demontree en comparant les valeurs de rayonnement gamma normalisees des intervalles encaisses a celles provenant de puits avoisinants sans tubage. En raison des bonnes concordances entre ces puits, et la transition entre les courbes normalisees a la base des zones encaissees et les courbes de rayonnement gamma a la partie superieure des zones non encaissees, cette methode serait efficace pour etudier la Formation de Paskapoo. La courbe normalisee permet la correlation des intervalles encaisses et des intervalles non encaisses, ce qui conduit a une amelioration de la caracterisation stratigraphique et de la cartographie des amas de sable fluvial a l'arriere du tubage de surface. Ces nouvelles donnees fournissent le cadre pour une meilleure caracterisation des dimensions des aquiferes et le calcul de parametres stratigraphiques utilises pour contraindre les modeles hydrogeologiques et rehausser la recuperation d'eau souterraine. [Traduit par la Redaction], Introduction The Western Canadian Sedimentary Basin (WCSB) of Alberta, Canada (Fig. 1), is one of the most intensely explored regions in North America, with thousands of new wells being drilled [...]

The gamma irradiation technique has been used to alter the dielectric and electro-optical properties of a liquid crystal material. The present paper reports a comparative study of dielectric and electro-optical properties of unirradiated EBHA nematic liquid crystal (NLC) with gamma-irradiated EBHA NLC. The dielectric measurement has been performed with variation in voltage and temperature within the frequency range 100 Hz-10 MHz. Variations in response time for both gamma- irradiated and unirradiated samples have also been measured and are well explained in the present paper. PACS Nos.: 77.84.Nh, 78.20.Ci, 77.22.Gm, 76.80.+y, 78.20.Jq. Nous soumettons un cristal liquide a une irradiation gamma, afin de modifier ses proprietes dielectriques et electrooptiques. Nous comparons ici les proprietes dielectriques et electro-optiques d'un cristal liquide nematique (NLC) EBHA non irradie avec celles d'un NLC EBHA irradie. Les mesures dielectriques sont faites avec variation de voltage et de temperature dans le domaine de 100 Hz a 10 MHz. Nous mesurons et expliquons egalement les variations dans le temps de reponse pour les deux echantillons, irradie et non irradie. [Traduit par la Redaction], 1. Introduction The modification in dielectric and electro-optical properties of liquid crystal (LC) caused by ion beam radiation is a new field of research. Ionizing particles like electrons, photons, and [...]

Transmission experiments were performed on wood in a narrow-beam geometry using a collimated gamma ray beam at 59.5 and 661.6 keV. The mass attenuation coefficients were determined from experiment, and effective atomic numbers were computed from theoretical equations. It was found that the mass attenuation coefficient decreases with increasing photon energy. Experimental values were compared with those from the XCOM database and with analytical results, and good agreement was achieved. This type of study gives some insight about photon interactions with wood materials. PACS Nos.: 29.30.kv, 31.70.-f, 32.80.-t. Nous etudions la dependance en Z des mesures d'interaction entre des photons et du materiel igne (bois). Nous determinons le coefficient d'attenuation massique du bois par des experiences de transmission d'un faisceau etroit focalise de rayons gamma de 59.5 et 661.6 keV. Nous observons que ce coefficient d'attenuation decroit lorsque croit l'energie des photons. Les resultats experimentaux pertinents sont compares avec des mesures d'appareils X commerciaux et des resultats obtenus analytiquement. Nous trouvons un bon accord entre ces resultats. Le nombre atomique effectif du bois est calcule a partir d'expressions theoriques. Ce type d'etude nous renseigne sur le bois en tant que materiel. [Traduit par la Redaction], 1. Introduction The Z dependence of photon interactions plays an important role in radiation studies. It is well known that a single number cannot represent the atomic number in composite [...]

We report the activity measured in rainwater samples collected in the Greater Sudbury area of eastern Canada on 3, 16, 20, and 26 April 2011. The samples were γ-ray counted in a germanium detector and the isotopes [sup.131]I and [sup.137]Cs, produced by the fission of [sup.235]U, and [sup.134]Cs, produced by neutron capture on [sup.133]Cs, were observed at elevated levels compared to a reference sample of ice water. These elevated activities are ascribed to the accident at the Fukushima Dai-ichi nuclear reactor complex in Japan that followed the 11 March 2011, earthquake and tsunami. The activity levels observed at no time presented health concerns. PACS Nos: 28.41.Bm, 23.90.+w Nous avons mesure la radioactivite d'echantillons d'eau de pluie recueillis dans la region de Sudbury, dans l'est canadien, les 3, 16, 20 et 26 avril 2011. Nous avons utilise un compteur γ au germanium et avons observe que les rayonnements provenant des isotopes [sup.131]I et [sup.137]Cs, produits de la fission de [sup.235]U et du [sup.134]Cs, produit de la capture de neutron par [sup.133]Cs, sont plus intenses que ceux provenant d'un echantillon d'eau de fonte servant de reference. Ces niveaux eleves de radioactivite sont attribues a l' accident du complexe de reacteurs Dai-ichi de Fukushima au Japon, suivant le tsunami du 11 mars 2011. Les niveaux observes de radioactivite ne presentent aucun danger pour la sante. [Traduit par la Redaction], 1. Introduction The nuclear accident in the Fukushima area in Japan released radioisotopes into the atmosphere, which have been measured in several locations in Asia [1-3], North America [4-8], and [...]

Problem statement: Gamma irradiation has been successfully used to prepare a spherical cadmium sulfide CdS/Poly Vinylpyrolidone (PVP) quantum dots nanoparticles with enhancement of their optical band gap energy and thermal properties at room temperature and under ambient pressure. Sodium thiosulfate was used as a sulfur source in an aqueous solution. The formation of lower band gap energy of CdS/PVP nanoparticles and thermal stability can be controlled by using different irradiation doses. TEM images showed that the CdS/PVP particle size tends to be smaller and with better distribution as irradiation dose increases. Approach: Gamma ([gamma]) irradiation offered many advantages for the preparation of metal nanoparticles by producing large number of hydrated electrons during [gamma]-ray irradiation, which can reduce the metal ions to zero valiant metal particles. Results: CdS/PVP nanoparticles were successfully prepared in one-step by [gamma]-irradiation technique in an aqueous system at room temperature and under ambient pressure. The particle size was found to be less than 10 nm based on the Transmission Electron Microscopy (TEM) that depended on the irradiation doses value, which showed a well distribution with a controlled size as doses change. The presence of PVP polymer was considered an important reason that influenced the shape and the distribution of those nanoparticles. The optical band gap energy of those nanoparticles was calculated by using the UV-VIS absorption spectra. Thermal analysis TGA showed that the composite had a higher degradation temperature than the PVP alone. A possible mechanism of the formation of cadmium sulfide by irradiation system was proposed. Conclusion: This result indicated that [CdSO.sub.4] can effectively dope PVP and enhance the optical and thermal properties. In addition, [gamma]-irradiation is an effective technique for preparing inorganic/organic nanocomposites. Key words: CdS/PVP, band gap energy, TEM, thermal properties, gamma irradiation, INTRODUCTION Nanotechnologies are now poised to revolutionize the electronic, chemical and biotechnology industries and biomedical fields. There are many interesting areas in nanotechnology. One of the most important aspects of [...]

Rotation-vibration coupling parameter b at different spins is calculated on fitting the experimental energy for each nucleus in the framework of the General Asymmetric Rotor Model (Zhi. Phys. Rev. C, 51, 141 (1995)). Taking the even and odd spin energy sequences of the gamma band as separate bands besides the yrast band at large asymmetry (γ ≥ 20°), three values of the moment of inertia parameters a ([a.sub.r], [a.sub.e], and [a.sub.0]) are calculated from the band head energies. A striking correlation in a and b versus the product of the number of valance protons and neutrons ([N.sub.p][N.sub.n]) is obtained. These trajectories and the γ versus [N.sub.p][N.sub.n] correlation (Yan et al. Phys. Rev. C, 48, 1046 (1993)) are capable of predicting the unknown energies of the ground and gamma bands of even xenon and barium nuclei, knowing only an external parameter NpNn. This introduces the possibility of a simpler description of the structural evolution of these transitional nuclei. PACS Nos: 21.10.Re, 21.60.Ev, 27.60.+j Nous calculons le parametre b de couplage rotation-vibration en ajustant l'energie expeerimentale Eln pour chaque noyau dans le modele du Rotateur Asymetrique Generalise (GARM) (Zhi. Phys. Rev. C, 51, 141 (1995)). En prenant les sequences de spin pair et impair de la bande gamma comme deux bandes diffeerentes a grande symeetrie (γ [mayor que o igual a] 20[grados]), nous calculons deux valeurs pour le parametre a ([a.sub.c] et [a.sub.0]) et une autre valeur [a.sub.r] pour la bande du fondamental a partir des energies des tetes de bande. Nous obtenons une correlation etonnante dans a et b versus [N.sub.p][N.sub.n], le produit du nombre de protons et de neutrons de valence. Ces trajectoires, avec la correlation γ--[N.sub.p][N.sub.n], (Yan et al. Phys. Rev. C, 48, 1046 (1993)), permettent de predire les energies inconnues des bandes du fondamental et γ meeme du Xe et du Ba, sous la seule connaissance du parametre exteerieur et [N.sub.p][N.sub.n], ce qui indique la possibilite d'une description plus simple de revolution structurelle de ces elements de transition. [Traduit par la Redaction], 1. Introduction In the past few decades, extremely rich experimental data have been accumulated in low-lying nuclear spectroscopy. The observed levels are interwoven in a rich and complicated manner and [...]

The Improved Landmine Detector System, a militarily fielded, teleoperated vehicle-mounted multi-sensor landmine detector, uses a thermal neutron analysis (TNA) detector to confirm the presence of a mine by detecting the bulk nitrogen in its explosives. To improve the nitrogen sensitivity or measurement times of the TNA detector, higher gamma ray rates will be required. The chief bottleneck to achieving the maximum possible performance from the present TNA or future versions is the relatively slow fluorescent decay time of the NaI(TI) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(TI) with respect to parameters relevant to TNA landmine detection, including efficiency, energy resolution, linearity, available size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in such a TNA application. Large (7.62 cm x 7.62 cm) La[Br.sub.3]:Ce scintillators, and to a lesser degree La[Cl.sub.3]:Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron analysis and associated particle imaging bulk explosives detectors. Index Terms--Gamma ray detection, gamma ray spectroscopy, inorganic scintillators, security applications, scintillation detectors, thermal neutron capture gamma ray analysis.

Compton imaging is a gamma ray imaging technique that has many possible applications including homeland security and medical imaging. Using the Compton scattering formula the origin of a scattered [lambda]-ray can be localized to a point on the surface of a cone using a minimum of two position and energy measurements. List-mode Maximum likelihood expectation maximization (MLEM) is an iterative statistical algorithm that makes successive approximations to the most probable source distribution that would have led to the observed data. Conventional MLEM is often performed in two dimensions, which still requires knowledge of the source-to-detector distance. We propose iteration over all three spatial dimensions in order to maximize the probability in three-dimensional space. This paper reports on the development of a three-dimensional MLEM (3DMLEM) algorithm to reconstruct images from a Compton imager in three dimensions for single, multiple and line sources. Several techniques for reducing convergence times are also discussed. Index Terms--Algorithms, compton scattering, nuclear imaging.

The Nuclear Compton Telescope (NCT) is a balloon-borne telescope designed to study astrophysical sources of nuclear line emission and polarization at soft gamma-ray (0.2-10 MeV) energies. NCT uses high-purity germanium strip detectors for 3D tracking of photon interactions. Compton imaging enables effective background rejection, resulting in a compact but highly efficient instrument. The NCT prototype completed a successful flight from Fort Sumner, New Mexico in 2005. We have since integrated additional detectors, updated the readout electronics, and improved other flight systems. Two flights of the full instrument are upcoming: a conventional flight in New Mexico and a long duration flight from Australia. We give an overview of the instrument and its status prior to the planned balloon flights. Index Terms--Compton imaging, gamma-ray astronomy detectors, gamma-ray imaging, germanium radiation detectors.

This study compares the light yield as a function of gamma-ray energy for several Lu-and Y-based silicate and aluminate scintillators. These comparisons illustrate the effects of crystal matrix, growth atmosphere, activator concentration, and co-doping on proportionality. The radioisotopic sources used in this study produce gamma-rays and X-rays from 22 keV to 1.3 MeV. The samples investigated are 10 x 10 x 10 mm in size and have the following single-phase compositions: LSO:Ce; LSO:Ce, Ca; LPS:Ce; LuAG:Pr; YSO:Ce; and YSO:Ce, Ca. The light yield vs. gamma-ray energy response is similar for scintillators with similar crystal structures, despite significant variations in growth atmosphere and activator concentration. Additionally, sample-to-sample variation is significantly reduced in the Ce-doped oxyorthosilicates when calcium is added as a co-dopant. Overall, the silicates measured in this study exhibit similar non-proportional responses, and in general are less proportional in the lower energy range compared to LuAG and other aluminates. Index Terms--Non-proportionality, scintillation, scintillators.

Thallium bromide (TlBr) is a high atomic number (81, 35), dense (7.56 g/[cm.sup.3]) wide band gap (2.68 eV) semiconductor. In addition, TlBr has a cubic crystal structure and melts congruently at a relatively low temperature (~460 C). Recently, mobility-lifetime product of electrons in TlBr has been reported to be greater than 0.001 [cm.sup.2]/V [5]. These properties make TlBr a promising material for room temperature gamma radiation detection. Employing device designs such as small pixel arrays that depend primarily on the motion of a single carrier type allows fabrication of thicker devices with better energy resolution than planar devices of the same thickness. We report on our recent progress in developing larger TlBr detectors. Over the past several months we have increased the electron mobility-lifetime product of our TlBr by more than one order of magnitude. Electron mobility-lifetime values as high as 3.0 x [10.sup.-3] [cm.sup.2]/V have been measured. Devices with small pixel design have been built with 3, 5, and 10 nun thickness and pixel pitch of 1 mm, 1.5, and 2.0 mm respectively. Pulse height spectra have been recorded over a range of energies from 60 keV to 662 keV. Energy resolution (FWHM) as high as approximately 5% at 122 keV and 1.7% at 662 keV has been obtained without any 3-D corrections. Such arrays are well suited for 3-D correction techniques similar to those applied to CZT devices, indicating that further improvement in energy resolution should be achievable. These latest results demonstrate promise for TlBr as a room temperature semiconductor gamma ray detector. Index Terms--Detector arrays, energy resolution, gamma-ray spectroscopy, semiconductor detectors.

Over 25 1-[cm.sup.3] CdZnTe crystals produced using the Traveling Heater Method at Redlen Technologies have been characterized. The charge carrier mobility and lifetime, and charge carrier transport uniformity of each crystal were measured using alpha particles. Some of the crystals were made into coplanar-grid detectors and their performance characterized using 662 keV gamma rays. The average electron mobility-lifetime product for these crystals was found to be a factor of about five times greater than that measured from crystals obtained over the last decade from two other commercial crystal growers. The coplanar-grid detectors produced from the material typically achieved an energy resolution at 662 keV near 2% FWHM when operated at room temperature. This is comparable to the best coplanar-grid detectors commercially produced today. Index Terms--CdZnTe detectors, gamma-ray spectroscopy detectors, charge carrier lifetime, charge carrier mobility.

A semiconductor Compton camera that combines silicon (Si) and Cadmium Telluride (CdTe) detectors was developed, and its imaging capability was examined with various kinds of gamma-ray targets such as a point source, arranged point sources and an extended source. The camera consists of one double-sided Si strip detector and four layers of CdTe pad detectors, and was designed to minimize the distance between a scatterer and the target. This is because the spatial resolution with Compton imaging improves as the target approaches the scatterer. This new camera realizes a minimum distance of 25 mm. By placing the target at a distance of 30 mm from the detector, resolving power better than 3 mm was demonstrated experimentally for a 364 keV ([sup.131]I) gamma-ray. Positional determination with accuracy of 1 mm was also demonstrated. As a deconvolution method, we selected the iteration algorithm (called List-Mode Expectation-Maximizing Maximum Likelihood), and applied it to several kinds of experimental data. The Compton back projection images of the arranged point sources and an extended object were successfully deconvolved. Index Terms--CdTe detector, Compton camera, gamma-ray imaging, silicon strip detector.

In any gamma-ray detector, each event produces electrical signals on one or more circuit elements. From these signals, we may wish to determine the presence of an interaction; whether multiple interactions occurred; the spatial coordinates in two or three dimensions of at least the primary interaction; or the total energy deposited in that interaction. We may also want to compute listmode probabilities for tomographic reconstruction. Maximum-likelihood methods provide a rigorous and in some senses optimal approach to extracting this information, and the associated Fisher information matrix provides a way of quantifying and optimizing the information conveyed by the detector. This paper will review the principles of likelihood methods as applied to gamma-ray detectors and illustrate their power with recent results from the Center for Gamma-ray Imaging. Index Terms--Depth of interaction, gamma-ray detectors, maximum-likelihood estimation, scintillation cameras, semiconductor arrays.

Analytic formulas and Monte Carlo simulation are used to calculate and compare the sensitivity of circular and polygonal orbits at different points in the Field of View (FoV) for both pinhole and slit-slat collimation. Results show that for a given slit-slat collimator an N-sided polygonal orbit tangent to the FoV generally provides average sensitivity lower than the tightest circular orbit consistent with the same aperture angle, but with better spatial resolution that can be traded for sensitivity for a constant-resolution comparison. This generally results in a slight advantage for the polygonal orbit. However, this advantage depends on the clearance that must be allowed between the orbit and the FoV and decreases quickly, vanishing when even a few millimeters of space are left, which in practice is necessary to accommodate mechanical constraints. For a pinhole collimator the advantage for the tangent polygonal orbit is more consistent, but similar conclusions are reached again when clearance is considered. A direct comparison at constant resolution between slit-slat and pinhole collimation in a single transverse plane is shown to be possible with parameters typical of small-animal imaging applications only for detectors with excellent intrinsic resolution; in this case, pinhole collimation is shown to be more sensitive in magnifying geometries, but reduced axial FoV and increased axial blurring should also be considered for a more complete comparison. Index Terms--Gamma-ray cameras, medical imaging, SPECT.

Polymer insulating materials installed in electrical and electronic devices are widely used in spacecraft and nuclear power stations where the polymers are exposed to energetic radioactive rays. The chemical structure can be changed by radiation induced reactions that possibly gives rise to the alteration of characteristics of surface charge, which can enhance the local electrical field and cause surface discharge that damages the insulation. For the safe use of the material, it's necessary to gain a good understanding of radiation effect on surface charge accumulation. In this paper, polyethylene was employed as test sample which was previously irradiated in air up to 100 kGy and then up to 1000 kGy with dose rate of 10 kGy / h by using a [sup.60]Co gamma-source. The sample surface was corona charged by applying a series of dc stresses on needle electrode that was set 6 mm above the surface. An electrostatic probe was designed to measure the surface charge density immediately after the charging process. Obtained results show the dependence of surface charge distribution upon the radiation dose varying as a function of the polarity of charging particles. It is suggested that surface charge accumulation depends upon the behavior of localized surface states, which is altered by radiation-induced degradation and cross-linking reactions of the chemical structure. Index Terms--polyethylene, gamma-ray irradiation, surface charge, localized surface states, cross-linking, degradation.

We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ray sources distributed in the environment. Unlike standard 3D tomographic methods, this technique does not require the radioactive sources to be bounded within a predefined physical space. In the present implementation, the gamma-ray imaging system is based on two large planar HPGe double sided segmented detectors, which are used in a Compton camera configuration. A LIDAR system is used in conjunction with the gamma-ray imaging system to confine the gamma-ray image space to the interior of physical objects situated within the detection range of the gamma-ray imager. This approach results in superior image contrast and efficient image reconstruction. Results demonstrating the operating principle are reported. Index Terms--Compton scatter imaging, gamma-radiation, radiation imaging, semiconductor detectors.

This paper measures the sample to sample variation in the fight yield proportionality of NaI(TI), and so explores whether this is an invariant characteristic of the material or whether it depends on the chemical and physical properties of the tested samples. We report on the electron response of nine crystals of NaI(TI), differing in shape, volume, age, manufacturer and quality. The proportionality has been measured at the SLYNCI facility in the energy range between 3.5 to 460 keV. We observe that while samples produced by the same manufacturer at approximately the same time have virtually identical electron response curves, there are significant sample to sample variations among crystals produced by different manufacturers or at different times. In an effort to correlate changes in the electron response with details of the scintillation mechanism, we characterized other scintillation properties, including the gamma response and the x-ray excited emission spectra and decay times, for the nine crystals. While sample to sample differences in these crystals were observed, we have been unable to identify the underlying fundamental mechanisms that are responsible for these differences. Index Terms--Nonproportionality, radiation detector, scintillator.

In this paper we present the studies performed on a set of [Lu.sub.3] [Al.sub.5][O.sub.12] :Pr (LuAG:Pr) crystals with praseodymium concentration between 1.5 and 10%, grown by the micro-pulling-down ([micro]PD) technique. The research comprises the measurements of X-ray excited emission spectra and [sup.137]Cs gamma-ray pulse height spectra in a range from 78 to 600 K, and thermoluminescence glow curves. Based on experimental data we discuss the dependence of scintillation properties of [Lu.sub.3][Al.sub.5][O.sub.12]:Pr on praseodymium content and temperature. The main attention is focused on a distinct increase of scintillation yield with temperature, which we attribute to existence of shallow electron traps and their temperature-dependent contribution to scintillation of LuAG:Pr. An active role of traps is demonstrated by a novel experiment combining X-ray and laser excitation. Index Terms--LuAG:Pr, light yield, scintillation mechanism, trap.

The Gamma Ray Energy Tracking In-Beam Nuclear Array (GRETINA), capable of determining the energy and position (within 2 mm) of each gamma-ray interaction point and tracking multiple gamma-ray interactions, has been designed. GRETINA will be composed of seven detector modules, each with four highly pure germanium crystals. Each crystal has 36 segments and one central contact instrumented by charge sensitive amplifiers. Two custom designed modules, the Digitizer/Digital Signal Processing (DSP) and the Trigger Timing and Control, compose the electronics of this system. The Digitizer/DSP converts the analog information with 14-bit analog to digital converters (operating at 100 MS/s, and digitally processes the data to determine the energy and timing information of the gamma interactions with the crystal. Each Digitizer/DSP is controlled by and sends trigger information to the Trigger Timing & Control system through a bidirectional Gbit link. Presently four different trigger algorithms are planned for the trigger system and can be selected for trigger decision. In this paper the details of the electronics and algorithms of the GRETINA data acquisition and trigger system are presented and the performance is reviewed. Index Terms--Data acquisition systems, digital signal processing, gamma-ray spectrometer, trigger systems.

High-energy (> 100 keV) photon detectors are often made thick relative to their lateral resolution in order to improve their photon-detection efficiency. To avoid issues of parallax and increased signal variance that result from random interaction depth, we must determine the 3D interaction position in the imaging detector. With this goal in mind, we examine a method of calibrating response statistics of a thick-detector gamma camera to produce a maximum-likelihood estimate of 3D interaction position. We parameterize the mean detector response as a function of 3D position, and we estimate these parameters by maximizing their likelihood given prior knowledge of the pathlength distribution and a complete list of camera signals for an ensemble of gamma-ray interactions. Furthermore, we describe an iterative method for removing multiple-interaction events from our calibration data and for refining our calibration of the mean detector response to single interactions. We demonstrate this calibration method with simulated gamma-camera data. We then show that the resulting calibration is accurate and can be used to produce unbiased estimates of 3D interaction position. Index Terms--3D interaction position, depth of interaction, gamma-ray imaging, mean detector response calibration, maximum likelihood estimation, multiple-hit event filtering.

A computed tomography (CT) system using high-energy monochromatic photons is one of the best choices for non-destructive tests, to detect flaws or defects in manufactured items for the purpose of improving quality control, and quality assurance. We have developed such a CT system based on laser-Compton X-rays, which were generated with an electron accelerator and a laser beam. Using 10 MeV laser-Compton X-rays, an experimental study for non-destructive tests of concrete specimens with computed tomography were performed. We successfully obtained CT images. Index Terms--Computed tomography, electron accelerator, gamma-ray, laser-Compton, non-destructive test.

We have constructed a unique instrument for use in the search for orphan sources. The system uses gamma-ray imaging to 'see through' the natural background variations that effectively limit the sensitivity of current devices. The imager is mounted in a 4.9-m-long trailer and can be towed by a large personal vehicle. Source locations are determined both in range and along the direction of travel as the vehicle moves. A fully inertial platform coupled to a global positioning system receiver is used to map the gamma-ray images onto overhead geospatial imagery. The resulting images provide precise source locations, allowing rapid follow-up work. The instrument simultaneously searches both sides of the street to a distance of 50 m (100-m swath) for millicurie-class sources with excellent performance as determined using source injection studies and Receiver-Operator-Characteristic techniques. Index Terms--Coded-aperture imager, gamma-ray detectors, gamma-ray imagers, nuclear imaging, orphan source search.

Experiments using dose rates of 40 and 1270 rads/min from Co-60 and dual optical wavelengths, 850 and 1310 nm, are conducted to estimate fiber optic attenuation at other dose rates using low order kinetics models. The irradiation-induced attenuation is fit to power and saturating exponential models. The 1310 nm data exhibit a linearly increasing term with the saturating exponential whereas the 850 nm results do not. Representation of the long-term low-dose-rate induced attenuation is an impetus for developing a difference equation fitting routine that better characterizes the signal loss and has the capability of predicting the attenuation at saturation. Index Terms--Gamma-ray effects, optical fiber cables, optical fiber radiation effects, photon radiation effects.

Frisch-ring CdZnTe detectors have demonstrated both good energy resolution, < 1% FWHM at 662 keV, and good efficiency in detecting gamma rays, highlighting the strong potential of CdZnTe materials for such applications. We are designing a hand-held gamma-ray spectrometer based on Frisch-ring detectors at Brookhaven National Laboratory. It employs an 8 x 8 CdZnTe detector array to achieve a high volume of 19.2 [cm.sup.3], so greatly improving detection efficiency. By using the front-end application-specific integrated circuits (ASICs) developed at BNL, this spectrometer has a small profile and high energy-resolution. It includes a signal processing circuit, digitization and storage circuits, a high-voltage module, and a universal serial bus (USB) interface. In this paper, we detail the system's structure and report the results of our tests with it. Index Terms--CdZnTe, CZT detector array, Frisch-ring detector, gamma-ray spectrometer.

In this work, we present results of measurements of spectra of [alpha]-particles carried out on semi-insulating (SI) InP detectors. The detectors were fabricated from Ti and Zn co-doped SI InP crystals grown by Czochralski technique. Tests of detectors performance with s-particles emitted from [sup.241]Am (5.48 MeV) radioactive source are reported. Excellent detectors performance has been evaluated by values of charge collection efficiency 99% and energy resolution ~ 1% obtained from the spectra measured at 230 K. Such high performance can be explained by InP doping with suitable Ti atoms and co-doping with low concentration of Zn acceptors sufficient for the full compensation of shallow donors, to reach SI properties. The electron mobility of reported SI InP detectors co-doped with Ti and Zn has been found to be equal to 2510 [cm.sup.2][V.sup.-1][s.sup.-1] at room temperature. This value is much higher than that obtained previously with our SI InP co-doped with Ti and Mn or with InP crystals converted to SI state by temperature annealing. Excellent detector performance and high electron mobility makes the reported InP material promising to be used for the of X-rays and [gamma]-radiation. Index Terms--Gamma ray, InP, particle detector, radiation detector, semi-insulating.

In this paper, a new pulse shape discrimination algorithm for a triple-layer phoswich detector is implemented and tested. The three-layer detector which was used in this experiment was originally designed for simultaneous detection of beta particles and gamma rays in a mixed radiation field. The first two layers are specifically designed for beta particles and the third layer is designed for gamma-ray interaction. The pulse output of the photomultiplier is digitized and sent to the host computer for further processing. A de-noising algorithm based on the Wavelet Transform (WT) is implemented to reduce the effect of noise introduced by the noisy analog channel and by the photomultiplier tube. Three new timing features were extracted and given as input to a fuzzy interface system (FIS). The FIS output indicates to which scenario the input signal belongs. Compared to the non-fuzzy method which was initially implemented for this detector, the fuzzy algorithm shows a better performance in separating beta and gamma spectra, especially at high energies. Also, fewer pulses are rejected, due to classification as unknown pulses, and interaction in multiple layers is detected more efficiently. Index Terms--Digital pulse shape discrimination, fuzzy logic, nuclear spectroscopy, phoswich detectors, wavelet de-noising.

Image quality in nuclear medicine is a trade-off between image contrast and resolution, since there are conflicting requirements of crystal thickness and collimator-hole dimensions. The sensitivity, or efficiency, which determines the contrast-to-noise ratio, however, is constrained primarily by pulse-mode operation, in which gamma ray interactions are recorded once every deadtime period. Nuclear images also suffer from image blurring due to gamma rays penetrating the collimator septa and due to misplaced pileup events arising from the coincidence detection of Compton-scattered gamma rays. Multi-zone detector architecture (MZDA) and the use of pileup prevention circuitry (PPC) lead to reduction of the detector's effective deadtime, and hence to significant extension of the count-rate range of the camera. This in turn allows the source activity to be increased to make up for sensitivity that will be lost on changing the detector and collimator-hole dimensions to improve spatial resolution. Misplaced pileup suppression (MPS) circuitry, also described in this paper, enables image blurring from Compton-scattered radiation to be reduced to 1/P of its level in a single zone detector, P being the PMT array size. The paper first develops the theoretical relationships relating to the trade-offs between efficiency and resolution, the distribution of scintillation light from interaction points in the crystal, the share of the light exposure of individual PMTs and of clusters of PMTs, and the cross-talk between clusters of PMTs. The paper then presents an outline of the implementation of an S-zone camera with PPC of order 1, based on hexagonal and rectangular arrays of PMTs. A hexagonal array of 331 1.27-cm PMTs, which will have S [approximately equal to] 35 detector-zones on average, can, for instance, use a 1.7-mm thick and 29-cm diameter NaI(TI) crystal to design a camera with twice the sensitivity of a single-zone camera of the same array size, which will also provide a spatial resolution of 2.1 mm at the collimator face and 3.4 mm at 10 cm from the collimator face. Index Terms--Contrast-to-noise ratio, depth of interaction (DOI), geometric efficiency, intrinsic spatial resolution, misplaced pileup suppression (MPS), multi-zone detector architecture (MZDA), pileup prevention circuitry (PPC).

98 SPEAR sensors from eV Products have been evaluated for their use in a portable Compton camera. The sensors have a 5 mm x 5 mm x 5 mm CdZnTe crystal and are provided together with a preamplifier. The energy resolution was studied in detail for all sensors and was found to be 6% on average at 59.5 keV and 3% on average at 662 keV. The standard deviations of the corresponding energy resolution distributions are remarkably small (0.6% at 59.5 keV, 0.7% at 662 keV) and reflect the uniformity of the sensor characteristics. For a possible outside use the temperature dependence of the sensor performances was investigated for temperatures between 15 and 45 deg Celsius. A linear shift in calibration with temperature was observed. The energy resolution at low energies (81 keV) was found to deteriorate exponentially with temperature, while it stayed constant at higher energies (356 keV). A Compton camera built of these sensors was simulated. To obtain realistic energy spectra a suitable detector response function was implemented. To investigate the angular resolution of the camera a [sup.137]Cs point source was simulated. Reconstructed images of the point source were compared for perfect and realistic energy and position resolutions. The angular resolution of the camera was found to be better than 10 deg. Index Terms--CdZnTe, Compton camera, CZT, energy resolution, gamma-ray, imaging, simulation.

Gamma ray tomography has been used to visualize fluid distributions in a rotating fluid coupling in different operation points at a pump speed of 780 rpm and lower turbine speeds. The gamma ray computed tomography system comprises a Cs-137 isotopic source and a high resolution gamma ray detector. An angle synchronized tomographic data acquisition technique was applied to produce sharp slice images from different positions along the coupling axis. The data have been used to assess the hydraulic behavior of the fluid coupling and to help improve our understanding of the flow structure development and its implications on torque transfer in such a device. [DOI: 10.1115/1.2953295] Keywords: gamma ray tomography, fluid coupling, two-phase flow measurement

We expand upon the idea of using [gamma]-rays for nuclear photofission of [sup.238]U at the giant dipole resonance to generate rare neutron-reach nuclei. The SPIRAL II project proposes the employment of 10-20-MeV Bremsstrahlung [gamma]-rays generated by a 45-MeV electron beam/http://ganinfo.in2p3.fr/research/ developments/spira12/index.html/. In this paper, we explore the possibility of using a Compton [gamma]-ray source for such a process. The Collider Accelerator Department at Brookhaven National Laboratory is developing high-current (up to 1 A), high-brightness (down to l-mm x mrad normalized emittance), and high-energy energy-recovery linacs (up to 20-GeV electron beam energy for eRHIC). These electron beams are perfectly suited for generating photon beams with tremendous average power, approaching the megawatt level. The range of photon's energy extends from subelectronvolts from free-electron lasers to 10 GeV from the Compton process. In this paper, we focus on a [gamma]-ray source for producing rare isotopes. Index Terms--Energy recovery linac, free electron laser, gamma rays, isotopes far away from the island of stability, laser Compton backscattering, laser-generated [gamma]-ray beam, nuclear resonance, nucleosynthesis in supernova explosions, photodisintegration, photofission, polarization, polarized positron source, rare isotopes, transmutation of used nuclear fuel.

Prompt [gamma] activation analysis (PGAA) has been further developed to analyze reacting components inside a chemical reactor. The new method, in situ PGAA, was used to determine the hydrogen-to-palladium molar ratio under various conditions of palladium-catalyzed alkyne hydrogenation. The H/Pd molar ratio was successfully measured in the range of 0.1-1.0 in an ~2-g catalytic reactor containing a few milligrams of palladium catalyst. The amount of hydrogen was only a few tens of micrograms, and the detection limit was ~5 [micro]g, i.e., at ppm level compared to the whole reactor. The description of the device, methodological developments, a feasibility study, and results of a series of catalytic measurements are presented.

Pixellated thallium bromide (TlBr) gamma-ray spectrometers were fabricated and evaluated with the depth sensitive single polarity charge sensing technique. The detectors exhibited energy resolutions of 2.22%, 1.22% and 1.11% for 356 keV, 662 keV and 1.33 MeV, respectively, at room temperature. Direct measurements of electron mobility-lifetime products in TlBr detectors were performed. An electron mobility-lifetime product of 4.1 x [10.sup.-3] [cm.sup.2]/V was obtained from a TlBr detector. Index Terms--Position-sensitive detector, semiconductor detector, thallium bromide.

The present work describes the procedure developed for the standardization of [sup.18]F by means of a coincidence system using a plastic scintillator detector in 4[pi] geometry, named 4[pi](PS)[beta]--[gamma] which was developed at the Nuclear Metrology Laboratory in IPEN, Sao Paulo, Brazil. The main advantage of this detector system is the ability to perform primary standardizations without the need for a coating of a metal layer on the radioactive source film for rendering it conductive, as usually necessary for proportional counter measurements. The measurements were also performed with a conventional 4[pi](PC)[beta]--[gamma] coincidence system, which makes use of a 4[pi] proportional counter for charged particles or X-ray detection coupled to a pair of NaI(T1) scintillation counters. The gamma-ray window was set to measure the 511 keV gamma-rays produced by positron annihilation. The detector efficiency was changed by moving the electronic discriminator threshold. The observed activity values were extrapolated to 100 % efficiency and the results showed good agreement between the two detector systems. Index Terms--Coincidence, fluorine-18, plastic scintillator, standardization.

The spectral response of several crystals grown by the Traveling Heater Method (THM) were investigated. An energy resolution of 0.98% for a Pseudo Frisch-Grid of 4 x 4 x 9 [mm.sup.3] and 2.1% FWHM for a coplanar-grid of size 11 x 11 x 5 [mm.sup.3] were measured using [sup.137]Cs-662 keV. In addition a 4% FWHM at 122 keV has also been measured on 20 x 20 x 5 [mm.sup.3] monolithic pixellated devices. The material shows great potential toward producing large-volume detectors with spectral performance that meets the requirement for high-resolution gamma-ray spectroscopy. Index Terms--Coplanar-grid, CZT, depth correction, gamma-ray, THM.

Lanthanum halide (LA[X.sub.3] : Ce) scintillators are currently being assessed by ESA for use as remote sensing gamma-ray spectrometers on future planetary missions. Such missions place a raft of constraints and requirements on sensor technology, which invariably stem from environmental and resource issues. In the past, NaI(T1) and CsI(T1) based spectrometers offered great advantages in term of device simplicity, reliability and detection efficiency but with poor energy resolution. Lanthanum halides combine these attributes with much higher energy resolution and their extensive deployment in future missions seems assured. In fact, La[Br.sub.3] spectrometers are currently baselined for most missions in planning. In this paper, we describe the needs of remote gamma-ray sensing and efforts by the European Space Agency to develop and qualify the next generation of spectrometers based on La[Br.sub.3] for interplanetary space missions. We contrast their performance to large volume Ge detectors and show that in the context of minimally resourced spacecraft, they represent a more attractive solution. Index Terms--Extraterrestrial measurements, Gamma-ray spectroscopy detectors, remote sensing, scintillation detectors.

Ce[Br.sub.3] crystals have been studied to assess their utility as potential gamma ray spectrometers for future ESA planetary missions. Pulse height spectra, scintillation time profiles, X-ray excited emission spectra, and photoinminescence spectra have been recorded as a function of temperature between 78 and 600 K. In addition, the influence of exposing Ce[Br.sub.3] to various doses of gamma rays from a strong [sup.60]Co source on its scintillation performance has been investigated. Index Terms--Ce[Br.sub.3], energy resolution, La[Br.sub.3]:Ce, radiation damage, scintillation yield, scintillator, self-absorption.

Options for optimizing the energy and spatial resolution of gamma-ray imaging detectors based on thick, monolithic crystals shaped like fiat-topped pyramids were studied. Monte Carlo simulations were made of the scintillation light transport for evaluating the effect of four parameters on the energy resolution, the spatial resolutions, and the depth of interaction (DOI) resolution of the gamma-ray imaging detector. These four parameters are: the reflectivity of the surface coating; the scatter mean free path; the absorption mean free path of the scintillation light; and the angle that defines the inclination of the sides of the pyramidal frustum. In real detectors, the values for the mean free paths for optical photons are normally not known. We estimated these by comparing MC simulations of detector resolutions to measurements for three gamma-ray imaging detectors with LYSO and LSO from different suppliers and with different surface coatings and geometries. The gamma-ray imaging detector measures the energy, centroids, and depth of interaction of the gamma-ray. DOI enhanced charge dividing readouts were used to measure the depth of interaction. Index Terms--Crystal geometry, gamma ray imaging, interaction depth, monolithic scintillator, surface coating.