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PubMed1980

Recent developments in instrumentation for emission computed tomography.

Equipment for emission tomography is currently undergoing a rapidly changing stage of development, both for single-gamma detection and for tomography using positron emitters. For single-gamma longitudinal tomography, the 7-pinhole collimator has won wide acceptance because of it simplicity and rapid reconstruction times. However, rotating slant-hole collimators overcome some of the disadvantages of the 7-pinhole method and may eventually be used more widely. For transverse single-gamma imaging, rotating gamma cameras are currently attracting the most interest and offer the best prospects for wise-spread application, since such instruments can be used also for routine studies. In the field of positron tomography, development of new positron cameras has moved from the research center to the commerical area, with at least four manufacturers now marketing tomographic units, all of the multiple-ring design. Small cyclotrons suitable for in-hospital use also are being offered by these companies. Most of the new positron tomographic units employ BGO crystals, which offer substantial advantages over Nal for this purpose. However, the recent introduction of cesium fluoride (CsF) as a detector for tomographic cameras offers the exciting possibility of using time-of-flight techniques for positron detection. This should substantially improve the attainable resolution, which presently is slightly less than 1 cm FWHM. The number of institutions involved in research using positron tomography has suddenly increased, in part because of the recent award of substantial research grants from NIH. Thus, a field which has grown very slowly over the past decade has taken a sudden spurt, and we can anticipate further growth during the coming decade as clinical utility improves.

Elementary Particles↗
PubMed1980

Special characteristics and potential of single photon emission computed tomography in the brain.

Single photon emission tomographic techniques for evaluation of the brain have as their major advantage the ability to employ readily available radionuclides, such as technetium-99m. With present radiopharmaceuticals, single photon emmision tomography of the brain primarily provides morphological information that may be complimentary to standard gamma camera images. Particular areas of assistance have included detection of basal lesions, delineation of multiplicity of lesions, definition of medial extent of abnormalities, clear separation of skull and intracranial abnormalities, and perhaps improved lesion characterization. Overall, however, the reported improvement in sensitivity has been relatively small. To optimally utilize the tomographic and quantiative capabilities of single emission tomography, new classes of radiopharmaceuticals must be developed that can penetrate the blood-brain barrier and provide information on CNS function and pathophysiology. If such radiopharmaceuticals can be labeled with single emission radionuclides, this technique has the potential to provide critically important information. The ultimate outcome of single emission tomographic techniques for the study of the brain may depend on radiopharmaceutical advances.

Blood-Brain Barrier↗
PubMed1980

Multiple photon coincidence tomography.

Coincidence scanning devices that measure the distribution of radioisotopes emitting multiple photons in nuclear cascade decays offer a possible supplementary approach to tomography in nuclear medicine. Design factors that serve to determine resolution, sensitivity, and statistical noise for the multiphoton coincidence linear scanner (MCLS), the total organ kinetic imaging monitor (TOKIM), and related systems have been well studied. Focused collimator coincidence scanner (FCCS) systems are capable of extremely high resolution--spherical cold lesions of less than 0.2 cu cm volume being easily detectable. Although FCCS scan speeds are too slow for imaging of large organs, scan times for small organs or for the rescanning of suspicious or ambigous regions appearing on conventional scans are well within practical clinical limits. In view of recent developments in the on-site cyclotron production of short-lived radioisotopes and the current interest in high resolution localization of neurologic receptors in vivo, FCCS systems may prove also to be of value in basic neurophysiologic studies.

Elementary Particles↗
PubMed1976

A possible two-photon effect in vitro using a focused laser beam.

A probable two-photon effect is described as a result of focusing an intense pulsed laser beam onto chromosomes of living cells. The effect was suggested after the derivation of a two-photon action spectrum and the demonstration of a lack of reciprocity.

Cell Line↗
PubMed1980

Macromolecular conformation in solution. Study of carbonic anhydrase by the positron annihilation technique.

The structural features of carbonic anhydrase (carbonate hydro-lyase; EC 4.2.1.1) in aqueous solution were probed by the positron annihilation technique. The data obtained under varying conditions of temperature, pH, and enzyme concentration were interpreted in terms of the free volume model. The change of enzymic activity with temperature is accompanied by a change in free volume of the protein. Upon thermal denaturation an irreversible change in free volume of the molecule occurred. At low temperatures the protein-water interactions were investigated. These results are discussed in terms of current concepts of structure-function relationships in proteins. This study shows the sensitivity of the positron annihilation method toward the structure of proteins related to their overall conformation and to the nature of bound water.

Animals↗
PubMed1983

Photon and fluorescence correlation spectroscopy and light scattering of eye-lens proteins at moderate concentrations.

The bovine eye-lens protein, alpha L-crystallin, has been studied with photon correlation spectroscopy to obtain the mutual diffusion coefficient, Dm, with fluorescence correlation spectroscopy to determine the tracer diffusion coefficient, DT, and with light scattering to get the isothermal osmotic compressibility (delta pi/delta c) P,T. The concentration dependence of Dm, DT, and (delta pi/delta c) P,T up to a volume fraction phi of the protein of 2.5 x 10(-2) has been interpreted on the basis of four different interaction potentials: (a) an extended hard-sphere potential; (b) a shielded Coulomb potential; (c) a shielded Coulomb interaction where the effect of counterions is included; (d) a simple mixed potential. The three parameters Dm, DT, and (delta pi/delta c) P,T have also been combined in the generalized Stokes-Einstein equation, Dm = [(delta pi/delta c)P,T . (1--phi) . (DT)]/(kappa B . T). Our results indicate that, in the case that photon correlation spectroscopy gives the mutual diffusion coefficient Dm, the applicability of the Stokes-Einstein equation can be questioned; or that, when one assumes the Stokes-Einstein equation to be valid, there is significant discrepancy between the result of photon correlation spectroscopy and Dm.

Animals↗
PubMed1978

Dental x-ray spectrometry with an Si(Li) semiconductor.

Spectra from a dental x-ray apparatus with varying tube potentials and various added filters were measured with the use of an Si(Li) semiconductor. The mean energies of the spectra were calculated to estimate radiation qualities under various conditions. A phantom lip made of Arcylite was used to compare the attenuated quantities of radiation incident on the lip, according to the radiation quality, resulting from various tube potentials and added filtration.

Elementary Particles↗
PubMed2000

Biological desulfurization in an optical-fiber photobioreactor using an automatic sunlight collection system.

Biological desulfurization using C. thiosulfatophilum has many more advantages over conventional physico-chemical methods due to low operational cost and no production of secondary pollutants. However, it requires effective and economical supply of light energy, which is a key factor in determining the success of commercialization. In this study, optical-fiber photobioreactor with internal illumination system was applied to increase the light availability. Furthermore, sunlight was used as the main light energy in the daytime and metal-halide lamp was applied as an additional light energy at night. Most UV light was eliminated by the chromatic aberration of the aspherical lenses in the solar light collector and 60% of infrared light intensity was eliminated. Physical scratching optical fibers enhanced the light availability about five times as much as that with unscratched ones in the previous study, but it resulted in the adsorption problem of elementary sulfur particles deteriorating light diffusivity considerably in a long operation. In order to solve this problem, scratched optical fibers were inserted into pyrex-glass tubes, which made light diffusivity nearly the same as that without glass tubes. Removal rate per unit cell concentration, using sunlight in the daytime and a metal-halide lamp at night, was 0.41 <0.73 micromol H(2)S min(-1)/(mg protein l(-1)) using a 400 W metal-halide lamp day and night, since the automatic sunlight collection system can transmit the light intensity as only 10% of that with a metal-halide lamp.

Adsorption↗
PubMed1987

A semiempirical nuclear fragmentation model.

An abrasion/ablation model of heavy ion fragmentation is derived which includes a second order correction for the surface energy term and provides a reasonable representation of the present elemental fragmentation cross sections. The full development of the model must await the resolution of disagreement among different experiments and an expansion of the experimental data base to a broader set of projectile-target combinations.

Carbon↗
PubMed1997

Accurate universal parameterization of absorption cross sections II--neutron absorption cross sections.

A recent parameterization (here after referred as paper I, Ref. [4]) of absorption cross sections for any system of charged ions collisions including proton -nucleus collisions, is extended for neutron-nucleus collisions valid from approximately 1 MeV to a few GeV, thus providing a comprehensive picture of absorption cross sections for any system of collision pair (charged and/or uncharged). The parameters are associated with the physics of the problem. At lower energies, the optical potential at the surface is important and the Pauli operator plays an increasingly important role at intermediate energies. The agreement between the calculated and experimental data is better than earlier published results.

Elementary Particle Interactions↗
PubMed1998

Nuclear absorption cross sections using medium modified nucleon-nucleon amplitudes.

We extract the in-medium nucleon-nucleon amplitudes from the available proton-nucleus total reaction cross sections data. The retrieval of the information from the experiment makes these estimates very reliable. Simple expressions are then given for the in-medium nucleon-nucleon amplitudes for any system of colliding nuclei as a function of energy. Excellent agreement is demonstrated in ion-nucleus absorption cross sections.

Aluminum↗
PubMed1998

Sources of inner radiation zone energetic helium ions: cross-field transport versus in-situ nuclear reactions.

Radial transport theory for inner radiation zone MeV He ions has been extended by combining radial diffusive transport, losses due to Coulomb friction and charge exchange reaction with local generation of 3He and 4He ions due to nuclear reactions taking place on the inner edge of the inner radiation zone. From interactions between high energy trapped protons and upper atmospheric constituents we have included a nuclear reaction yield helium flux source that was numerically derived from a nuclear reaction model originally developed at the Institute of Nuclear Researches of Moscow, Russia and implemented in the computer system at the University of Campinas, Brazil. Magnetospheric transport computations have been made covering the L-shell range L=1.0 to 1.6 and the resulting MeV He ion flux distributions show a strong influence of the local nuclear source mechanism on the inner zone energetic He ion content.

Cosmic Radiation↗
PubMed1998

Transport of light ions in matter.

A recent set of light ion experiments are analyzed using the Green's function method of solving the Boltzmann equation for ions of high charge and energy (the GRNTRN transport code) and the NUCFRG2 fragmentation database generator code. Although the NUCFRG2 code reasonably represents the fragmentation of heavy ions, the effects of light ion fragmentation requires a more detailed nuclear model including shell structure and short range correlations appearing as tightly bound clusters in the light ion nucleus. The most recent NUCFRG2 code is augmented with a quasielastic alpha knockout model and semiempirical adjustments (up to 30 percent in charge removal) in the fragmentation process allowing reasonable agreement with the experiments to be obtained. A final resolution of the appropriate cross sections must await the full development of a coupled channel reaction model in which shell structure and clustering can be accurately evaluated.

Carbon↗
PubMed1998

Microscopic fragmentation model for galactic cosmic ray studies.

We describe theoretical considerations for developing models of heavy ion fragmentation appropriate for galactic cosmic ray studies. Previous models have been based on parametric fits to limited experimental data or models that ignored some aspects of the reaction dynamics, including nuclear cluster effects. The abrasion-ablation description of the fragmentation process is re-formulated to describe the excitation spectrum of pre-fragment nuclei. The resulting spectrum is shown to be related to the many-body response of the nuclear ground-state and excited states, and an approach to simplify this function is discussed. An analytic solution to the nuclear de-excitation process is described which includes a realistic level spectrum of the GCR nuclei (A < 60). Comparisons are made to experiments for fragmentation of 24Mg, 32S, and 56Fe beams on several targets and results are discussed.

Cosmic Radiation↗
PubMed1997

Abrasion-ablation model for neutron production in heavy ion collisions.

In intermediate energy nucleus-nucleus collisions, neutron production at forward angles is observed to occur with a Gaussian shape that is centered near the beam energy and extends to energies well above that of the beam. This paper presents an abrasion-ablation model for making quantitative predictions of the neutron spectrum. To describe neutrons produced from the abrasion step of the reaction where the projectile and target overlap, we use the Glauber model and include effects of final-state interactions. We then use the prefragment mass distribution from abrasion with a statistical evaporation model to estimate the neutron spectrum resulting from ablation. Measurements of neutron production from Ne and Nb beams are compared with calculations, and good agreement is found.

Cosmic Radiation↗