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The experimental study of the 17O(n,α)14C reaction has been performed in the energy range 0-350 keV. This reaction could play an important role in explaining heavy elements (s-process) nucleosynthesis in various astrophysical scenario. To overcome the practical problems arising from the neutrons production, a new application of the Trojan Horse Method has been recently suggested. In more details, the 17O(n,α)14C reaction has been studied using the quasi-free 2H(17O,α14C)1H reaction, induced at an energy of 43.5 MeV. The measurement allows one to investigate the l=3, 75 keV resonance (E*=8.125 MeV, Jπ=5−), absent in the available direct measurements because of centrifugal suppression effects.

The acousto‐optic effect has been successfully used since the early 80’s in the design and construction of a variety of conventional optical fiber devices such as frequency shifters, couplers, filters and modulators. Acoustic waves can be employed to modulate the spectrum and switch the wavelength of conventional fiber Bragg gratings as well as for controlling the Q‐switching in distributed fiber lasers. Tunable devices induced by acoustic waves have also been demonstrated in photonic crystal fibers (PCF), whereas a resonance dip corresponding to an excited cladding mode can be tuned over the wavelength. In a similar work, but inducing an acoustic excitation over the longitudinal axis, long period gratings can be created in the transmission band of a solid core PCF. Recently, the availability of Bragg gratings in photonic crystal fibers enables several applications, particularly if their properties can be controlled in order to produce modulation or allow tunability. A way of achieving these effects is through the excitation of acoustic waves in the fibre, which allows a rapid method for shifting or modulating the Bragg wavelength. In this work the application of acoustic‐waves to microstructured fibers is reviewed and recent results on the modulation of fiber Bragg gratings in photonic crystal fibers are presented.

In this work the mechanical properties of a Photonic Crystal Fiber is achieved using concepts of the rules of mixture of composite materials in order to find the effective area, effective Young’s modulus and the effective density. Results achieved by analytical method are compared to results achieved through a commercial software. Simulation results of acoustic‐induced modulation of a Photonic Crystal Fiber Bragg grating obtained using adapted Finite Element and Transfer Matrix Methods is showed. The methodology applied to study the device consists of the achieving of Photonic Crystal Fiber mechanical properties; the strain field in the whole structure is obtained by using the Finite Element Method. Further, the calculated strain field is used on the Transfer Matrix algorithm to obtain the Fiber Bragg Gratings reflected spectrum. The results are compared with conventional Fiber Bragg Gratings Acousto‐Optic modulator. Numerical results show that, due to its smaller stiffness, compared to conventional Fiber Bragg Gratings the presence of Photonic Crystal Fiber Bragg Gratings causes an increasing on strain field along the grating when the modulator is excited by particular frequencies. This way, Photonic Crystal Fiber Bragg Gratings can be used in acousto‐optic modulators increasing the acousto‐optic efficiency and avoiding the need of tapers.

The object of this study was to evaluate the safety of large doses of microbubbles and ultrasound administered to the head of rabbits as if they were receiving acute stroke therapy of a similar nature. Materials and Methods: Female New Zealand White rabbits were used, N=24, in three groups 1] n=4 control (no treatment), 2] n=10 bubble control (ultrasound plus aspirin), and 3] n=10 target group (ultrasound plus aspirin plus MRX‐815 microbubbles). Group 3 was infused with IV bubbles over 1 hour at 0.16cc/kg. Ultrasound was delivered to the dehaired side of the head during bubble infusion and for 1 additional hour at 0.8 W/cm2 20% pulsed wave. Rabbits survived for 22 to 24 hours, were imaged with computerized tomography and 3 Tesla magnetic resonance imaging including contrast studies, and sacrificed. Tetrazolium (TTC) and Hematoxylin and Eosin (H&E) sections were made for pathological examination. Results: All 24 animals showed absence of bleeding, endothelial damage, EKG abnormalities, stroke, blood‐brain‐barrier breakdown, or other acute abnormalities. CT and MRI showed no bleeding or signs of stroke, but two animals had mild hydrocephalus. The EKGs showed normal variation in QTc. Rabbit behavior was normal in all. Minimal chronic inflammation unrelated to the study was seen in 5. Two animals were excluded because of protocol violations and replaced during the study. Conclusion: The administered dose of microbubbles and ultrasound demonstrated no detrimental effects on the healthy rabbit animal model.

A novel and simple X ray optics ‘Owl’ capable of dark field imaging due to refraction contrast is under developement. That comprises a Bragg case asymmetric monochromator ‘M’ and an analyzer ‘A’ in a double crystal arrangement. ‘A’ has thickness of N × L, where N means integer and L the extinction distance in the Laue case or has a thickness that should provide reasonable transmittant X‐ray intensity in the Bragg case. The analyzer can only select the refracted light from object towards the forward diffraction direction, while completely suppresses the intensity toward the diffraction direction at the just Bragg position. Their angular width of diffraction was 0.3 μrad at X‐ray energy of 35keV. The spatial resolution available is at the order of 5μm or better. This method has a large potential of application to material science, biology and clinical medicine. Pictures shown as demonstration of dark field imaging is a ceramics with hexagonal outer size of 5 mm, containing 91 holes with diameter of 300μm an...

The safe storage of plutonium in the form of plutonium oxide (Pu02) is a major concern in countries with significant plutonium inventories . The goal is to stabilize and package oxide in such a way that the possibility of leaks and failures are unlikely. Currently in Russia, Pu02 is stored 1 at the Mining and Chemical Combine (MCC, Zheleznogorsk) and at the Siberian Chemical Combine (SCC, former Tomsk-7). (Plutonium metal is stored at PA 'Mayak' and is not addressed here) . Current storage containers for Russian Pu02 do not meet modern safety requirements . Further, every three years the gaskets have to be replaced . The containers can become over pressurized due to radiation processes and this results in possible container failures 1 . In the US, Pu02 is present at several Department of Energy (DOE) sites 2 . US reports of long time storage of Pu02 show a few cases of storage container failures 2 among thousand of intact cases. Major causes of malfunction are metal oxidation in non-airtight packages and gas pressurization from inadequately stabilized oxide . Because of these failures the US DOE adopted a standard 3 for stabilization, packaging and storage of plutonium-bearing material that addresses more » these vulnerabilities . « less

The coupled multiplier is a new approach to efficient generation of MeV d.c. power for accelerator applications. High voltage is produced by a series of modules, each of which consists of a high‐power alternator, step‐up transformer, and 3‐phase multiplier circuit. The alternators are connected mechanically along a rotating shaft, and connected by insulating flexible couplers. This approach differs from all previous d.c. technologies in that power is delivered to the various stages of the system mechanically, rather than through capacitive or inductive electrical coupling. For this reason the capital cost depends linearly on required voltage and power, rather than quadratically as with conventional technologies. The CM technology enables multiple electron beams to be driven within a common supply and insulating housing. MeV electron beam is extremely effective in decomposing organic contaminants in water. A 1 MeV, 100 kW industrial accelerator using the CM technology has been built and is being installed for treatment of wastewater at a petrochemical plant.

A formalism based on the Vlasov-Maxwell system has been developed that provides a fully kinetic description of a free-electron laser (FEL) operating in the high gain regime. The analysis allows for guiding of the optical beam through the gain process and guiding of the electron beam by the weak focusing provided by realistic wiggler gradients. Thus, betatron oscillations and emittance are naturally included. Additionally, intrinsic energy spread as well as energy spread due to space charge effects is included. The analysis predicts a novel electron beam equilibrium flow in which the effect of wiggler gradients tends to cancel that due to space charge, leading to a flow with reduced axial velocity spread. Since the FEL mechanism is sensitive to the axial velocity spread on the beam, this special flow appears to be useful in enhancing FEL gain. This and other issues related to FEL operation are discussed in this paper. It is shown that the scaled thermal velocity S=νth/(νb−νph) is a useful measure of beam q...

We are evaluating the use of polyatomic and cluster primary ion beams for characterization of semiconductor materials by secondary ion mass spectrometry using both magnetic sector and time-of-flight SIMS instruments. Primary ion beams of SF5+, C8− and CsC6− have been used to analyze low energy arsenic implants in silicon, boron delta-doped structures, thin gate oxides, metal multilayers, organic surface contamination and photoresist thin films. Compared to monoatomic bombardment under the same conditions, cluster ion beams offer improved depth resolution for silicon depth profiling and a reduction in sputter-induced topography for metals. For organic materials, the use of a cluster ion beam can give large improvements in yield for characteristic secondary ions and can minimize beam-induced degradation in some materials.

The TRIPLE Collaboration has performed measurements of the helicity dependence of the neutron resonance cross section for many nuclides. More than 70 statistically significant parity violations have been observed. Generic enhancements amplify the signal for symmetry breaking and the stochastic properties of the compound nucleus permit the strength of the symmetry-breaking interaction to be determined without knowledge of the wave functions of individual states. The measurements are concentrated in the regions of the 3p and 4p maxima of the neutron strength function-near A=110 and A=230. The results to date are summarized.

In order to extend our knowledge of the weak spreading width to the nuclear mass 30 region, parity-violation measurements have begun at the Triangle Universities Nuclear Laboratory using the 31P(p,α0)28Si reaction. Longitudinally polarized protons are scattered from 31P nuclei at several MeV, and a large solid angle silicon-strip detector detects the alpha particles at backward angles. By rapidly reversing the spin direction of the protons, we measure the helicity dependence of the alpha yield. A discussion of the working system and preliminary results are given.

X- and gamma-ray imaging techniques in nondestructive evaluation (NDE) and assay (NDA) have been increasing use in an array of industrial, environmental, military, and medical applications. Much of this growth in recent years is attributed to the rapid development of computed tomography (CT) and the use of NDE throughout the life-cycle of a product. Two diverse examples of CT are discussed. (1) The computational approach to normal joint kinematics and prosthetic joint analysis offers an opportunity to evaluate and improve prosthetic human joint replacements before they are manufactured or surgically implanted. Computed tomography data from scanned joints are segmented, resulting in the identification of bone and other tissues of interest, with emphasis on the articular surfaces. (2) They are developing NDE and NDE techniques to analyze closed waste drums accurately and quantitatively. Active and passive computed tomography (A and PCT) is a comprehensive and accurate gamma-ray NDA method that can identify all detectable radioisotopes present in a container and measure their radioactivity.

Molybdenum nitride has a potential application in multi layer capacitors. Since this material is not readily available in bulk form, molybdenum nitride powder, consisting of a mixture of the nitrides Mo2N and MoN has been compacted to 12 mm circular, 1–2 mm thick discs utilizing shock-compression technique. Powders were packed to 55–67 percent of the crystal density and shock compacted using a plate impact shock recovery system at 1.35 to 1.81 km/s impact velocity. The recovered compacts were characterized by scanning electron microscope, x-ray diffraction and cyclic voltammetry to evaluate its electrochemical stability in sulphuric acid. This paper presents the optimization technique used for compaction and the characteristics of the recovered compacts.

Recent parity non-conservation (PNC) measurements in nuclei use the compound nucleus as a laboratory for the study of symmetry breaking, with the symmetry breaking matrix elements treated as random variables. We plan to measure parity-violating longitudinal analyzing powers Az in (p,α) scattering on resonances in A∼30 nuclei. Since the resonances are often narrow, the proton beam energy must be carefully controlled. In addition, since the effects are expected to be small (Az

The average size and shape of magnetic domains in a material can be determined from the precession of polarized neutrons traversing the material. Epithermal neutrons (0.5 eV

A new measurement of the parity‐conserving, time reversal noninvariant (PC TRNI) fivefold correlation has been performed at TUNL, using 6.7 MeV polarized neutrons and a cryogenically aligned holmium target. The PC TRNI spin correlation coefficient A5 is measured to be (1.1±2.3)×10−5, consistent with time reversal invariance.

Measurements have been performed on the helicity dependence of the neutron resonance cross section for many nuclei by our TRIPLE Collaboration. A large number of parity violations are observed. Generic enhancements amplify the signal for symmetry breaking and the stochastic properties of the compound nucleus permit the strength of the symmetry-breaking interaction to be determined without knowledge of the wave functions of individual states. A total of 15 nuclei have been analyzed with this statistical approach. The results are summarized.

We describe the construction and operation of a large (0.4 mole) solid 3He target polarized to 37% by the ‘‘brute force’’ technique at 12 mK in a 7 Tesla magnetic field. The target has been employed at the Triangle Universities Nuclear Laboratory to study by neutron transmission measurements the excited states of the 4He nucleus. Such a target has particular advantages for experiments using neutrons or other beams which produce little target heating.

A new measurement of the parity‐conserving, time reversal noninvariant (PC TRNI) fivefold correlation has been performed at Triangle Universities Nuclear Laboratory, using 6.57 MeV polarized neutrons and a cryogenically aligned holmium target. The PC TRNI spin correlation coefficient A5 is measured to be (1.1±2.3)×10−5, consistent with time reversal invariance. A bound of 3.8×10−3 (99% confidence) is extracted for the ratio of PC TRNI to TRI nuclear matrix elements.

The parity and time‐reversal symmetries can be studied in neutron‐nucleus interactions. Parity non‐conserving asymmetries have been observed for many p‐wave resonances in a compound nucleus and measurements were performed on several nuclei in the mass region of A∼100 and A∼230. The statistical model of the compound nucleus provides a theoretical basis for extracting mean‐squared matrix elements from the experimental asymmetry data, and for interpreting the mean‐squared matrix elements. The constraints on the weak meson‐exchange couplings calculated from the compound‐nucleus asymmetry data agree qualitatively with the results from few‐body and light‐nuclei experiments. The tests of time‐reversal invariance in various experiments using thermal, epithermal, and MeV neutrons are being developed.

A retrospective look at the evolution of some of the ideas on the role of electron beam quality in the operation of a free‐electron laser is presented. New results that include the effect of optical guiding are discussed and applied to the scaling of compact free‐electron lasers.

We discuss the effect of beam emittance and energy spread in a free‐electron laser operating in the gain‐focusing regime. The variation of growth rate, radius of curvature of wavefronts, filling factor and efficiency with emittance and energy spread is derived. The analysis is based on the Vlasov‐Maxwell system of equations and results are obtained by minimizing a variational functional. When plotted as a function of emittance, the efficiency at maximum growth rate peaks at a nonzero value of emittance. For small values of energy spread, the efficiency at maximum growth rate increases with energy spread, in contrast to intuitive expectations.

In this talk I describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C. S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized {sup 60}Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the strong interaction can contribute, we expect much smaller asymmetries, of order 10{sup {minus}7}. In the work I will describe here we study the effects of the weak interaction through the signal of the parity violation associated with that interaction. There are two basic classes of experiment used to detect parity violation. The first relies on the measurement of a cross section or width that would vanish if parity were conserved. One example of this type of experiment in nuclear physics is the decay of an unnatural parity state to a 0+ nucleus and an {alpha}-particle. Such measurements have been made for two nuclei: {sup 16}O(2{sup {minus}}) {implies} {sup 12} C(g.s)more » + {alpha} and {sup 20}N{var epsilon}(1{sup +}) {implies} {sup 16} O(g.s) + {alpha}. Parity-violating widths as small as of 10{sup {minus}10} eV have been measured in these experiments. The second class of experiments involves a measurement of pseudo-scalar observables which are odd under parity inversion. These involve correlations between spin and linear angular momenta, for example circular polarization of {gamma}-rays ({sigma}{sub {gamma}} {center dot} {kappa}{sub {gamma}}) or longitudinal analyzing power ({sigma}{sub p} {center dot} {kappa}{sub p}). 20 refs., 6 figs.« less

The TRIPLE collaboration has begun a multi year program of study of symmetry violation using the intense pulsed polarized epithermal neutron beam available at LANSCE (Los Alamos Neutron Scattering Center). The parity violation experiments consist of measurement of the helicity dependence of neutron transmission at p‐wave resonances in compound nuclei. A recent success has been the first determination of the spreading width of the weak interaction in 239U.