Intermediate Beam Research Articles

Nuclear spectroscopy with fast exotic beams

Quadrupole collectivity in the proximity of the doubly-magic shell closure at N = Z = 28 has been studied using intermediate-energy Coulomb excitation of 54,56,58Ni and 52Fe. The results will be summarized and discussed in comparison to large-scale shell model calculations.A complementary experimental approach sensitive to the single-particle structure of exotic nuclei, one-neutron knockout at intermediate beam energies, has been applied to the proton-rich N = 16 isotones 34Ar, 33Cl and 32S as well as to 32Ar where the knockout residue 31Ar is the last particle-bound Z = 18 isotope. The reduction of single-particle strength (‘‘quenching’’) compared to shell-model calculations using the USD interaction is discussed in the framework of correlation effects beyond effective-interaction theory.

Dynamical Simulations of Supernovae Collapse and Nuclear Collisions via the Test Particle Method — Similarities and Differences

Test particle methods have been applied very successfully to the numerical simulation of heavy ion reactions at intermediate and high beam energies. Here we will show that the same techniques can be used successfully to simulate the dynamics of the collapse of type II supernovae precursors. We will focus special attention on the effects of collective angular momentum on the resulting supernova dynamics.

Effect of intermediate beam in track on train induced ground vibration

This study theoretically evaluates the effect of intermediate beam in track on train induced ground vibration. It notices the force acting from track to elevated structures and the input to the ground vibration. This paper considers models of track on elevated structure and of that directly supported on the ground. The following results are obtained; (1) the method to evaluate the effect of track rigidity is given; (2) the effect of rail rigidity is successfully compared with measures; (3) the effect of rigidity of the intermediate beam and its supporting spring is clearly given; and (4) the acceleration of deck slab in the elevated structure as band-pass level including human sensitivity is compared with regards to ladder and ballasted tracks.

The magnetized electron-acoustic instability driven by a warm, field-aligned electron beam

The electron-acoustic instability in a magnetized plasma having three electron components, one of which is a field-aligned beam of intermediate temperature, is investigated. When the plasma frequency of the cool electrons exceeds the electron gyrofrequency, the electron-acoustic instability “bifurcates” at sufficiently large propagation angles with respect to the magnetic field to yield an obliquely propagating, low-frequency electron-acoustic instability and a higher frequency cyclotron-sound instability. Each of these instabilities retains certain wave features of its progenitor, the quasiparallel electron-acoustic instability, but displays also new magnetic qualities through its dependence on the electron gyrofrequency. The obliquely propagating electron-acoustic instability requires a lower threshold beam speed for its excitation than does the cyclotron-sound instability, and for low to intermediate beam speeds has the higher maximum growth rate. When the plasma is sufficiently strongly magnetized that the plasma frequency of the cool electrons is less than the electron gyrofrequency, the only instability in the electron-acoustic frequency range is the strongly magnetized electron-acoustic instability. Its growth rate and real frequency exhibit a monotonic decrease with wave propagation angle and it grows at small to intermediate wave numbers where its parallel phase speed is approximately constant. The relevance of the results to the interpretation of cusp auroral hiss and auroral broadband electrostatic noise is briefly discussed.

In-beam ?-ray spectroscopy of fast beams at the NSCL

With the development of an array of highly-segmented germanium detectors, it now becomes possible to perform in-flight γ-ray spectroscopy experiments on intermediate energy beams with unprecedented γ-ray energy resolution. Presented in this report are examples of two techniques in which SeGA, the most highly-segmented operational germanium array for in-flight spectroscopy with fast beams, was used for the detection of γ rays. SeGA used in conjunction with a high-resolution magnetic spectrograph (S800) to detect the reaction residues in coincidence represents a powerful combination for in-beam γ-ray studies.

In-beam γ-ray spectroscopy of fast beams at the NSCL

With the development of an array of highly-segmented germanium detectors, it now becomes possible to perform in-flight γ-ray spectroscopy experiments on intermediate energy beams with unprecedented γ-ray energy resolution. Presented in this report are examples of two techniques in which SeGA, the most highly-segmented operational germanium array for in-flight spectroscopy with fast beams, was used for the detection of γ rays. SeGA used in conjunction with a high-resolution magnetic spectrograph (S800) to detect the reaction residues in coincidence represents a powerful combination for in-beam γ-ray studies.

Neural network evaluation of steel beam patch load capacity

This work presents a neural network modelling to forecast steel beam patch load resistance. In preceding studies, the results of a neural network system composed of four neural networks, have been compared and calibrated with experimental data and existing design formulae, showing a good agreement. Despite these results, the adopted system did not properly consider the differences in behaviour of slender, intermediate and compact beams. This paper introduces a new strategy based on a single neural network, which is trained with a different normalisation parameter. The neural network presented a maximum error value lower than 30%, while existing formulas presented errors greater than 40%.

Application of Focused Ion Beam Miller in Fracture Characterization

Abstract: Focused ion beam (FIB) miller is a new tool used for the examination of micro-fracture in ceramics. In this work, a FIB miller was employed to investigate fracture events involved in indentation and scratch tests of two differentα-sialon microstructures of the same chemical composition. The subsurface cross-sections were prepared via FIB milling and crack characteristics in both the surface and subsurface were identified. Crack interactions and the effect of microstructure on cracking were revealed. Keywords: Focused ion beam (FIB) miller, microstructure, fracture, indentation Introduction FIB millers are commonly found in the semiconductor industry, where they are used to deposit, etch, mill and image specimens during circuit modification and defect analysis. However, the FIB is becoming increasingly popular in studying fracture behaviour of ceramics, particularly for analysing subsurface damage following surface contact [1, 2]. The FIB uses a liquid metal ion source to emit gallium ions in a high vacuum environment. These particles are accelerated by an energy of between, typically, 5 and 50 keV, forming a fine (~10 nm diameter) energetic beam of gallium ions, which is then focusedonto the specimen surface by electrostatic lenses. When the ions impact and/or implant into the specimen, secondary electrons, secondary ions and atoms are sputtered from the surface. If the beam current is large (~ 10nA), through the insertion of a large beam-limiting aperture, the sputtering rate is very high and sections can be milled rapidly into the surface of the specimen. This is achieved by using the system software to draw a “mill-box” on the area of interest, so that milling occurs locally around specific microstructural features. After milling the beam current can then be reduced to a lower level (~ 10pA), by the insertion of a smaller aperture, and either the positive secondary ions or secondary electrons can be detected and used to form images similar to those acquired by a SEM. By using this method, subsurface features can be rapidly and precisely imaged. However, the FIB can be used in other ways, for example rastering the ion beam over the surface of specimen, at intermediate beam currents (~350 pA) will lead to localised surface etching and the generation of high contrast from multiphase materials. In this way, the relationship between surface features, such as cracks, and microstructure, can be readily assessed [2]. These features of the FIB can be utilized for the characterization of cracks in ceramics. In the past, cracks induced in ceramics by either indentation [3] or scratching [4] were identified typically from direct observation on the sample surface using either optical microscopy or SEM. When asubsurface cracks became critical, either ceramographic polishing [5] or a bonded-interface technique [6] was used for the preparation of subsurface cross-sections. It is noted that both techniques may introduce damage into the original cracks and consequently affect the reliability of identification. Furthermore, the two techniques could not reveal the interaction of microstructure and cracks, which is vital to fracture analysis and design of tougher ceramics. However, using the FIB, the subsurface cross-sections of ceramics can be prepared rapidly with minimal damage. Further, the area of interest can be etched to reveal the effect of microstructure on cracking. In this study,Ca α-sialon ceramic was used as a model material. he FIB was first sed toT u characterize the indentation-induced cracks in the samples, and underscore the effect of

Research into the advanced experimental methods for precision ion stopping range measurements in matter

The article presents the results of the experimental research on precision measurement of total stopping range and energy deposition function of intermediate and heavy ion beams in cold solid matter. The “thick target” method proves to be appropriate for this purpose. Two types of detectors were developed which provide an error of the total stopping range measurement of less than 3% and of the beam energy deposition function of about 7%. The experiments with 58Ni+26, 197Au+65, and 238U+72 ion beams in the energy range 100–300 MeV/u were performed on SIS-18 (Gesellschaft für Schwerionenforschung, Darmstadt) in 1999–2001. The measured data on the total stopping ranges for the above ion species in bulk and foiled Al and Cu targets are presented. The investigation showed that there is a noticeable discrepancy between the measured stopping ranges and the theoretically predicted ones. Also, it was shown that realistic ion energy deposition depends on the type of target (bulk or foiled). Further investigation is necessary to clarify the latter.

Calculation of depth-dose distribution of intermediate energy heavy-ion beams

A complex straggling algorithm is presented to calculate depth-dose distribution of intermediate energy heavy-ion beam. Relative dose Bragg curves of carbon and oxygen ion beams with intermediate energies were computed according to the algorithm above. Comparisons between the relative doses predicted and measured were taken up. The Bragg curves predicted by the complex straggling algorithm show a good agreement with the experimental data. So the reasonableness of this algorithm and its reliability for calculating depth doses were verified. Hence the principle and method to deduce the depth-dose distribution of therapeutic beam was integrated after this algorithm was developed.

Detection of neutron clusters

A new approach to the production and detection of bound neutron clusters is presented. The technique is based on the breakup of beams of very neutron-rich nuclei and the subsequent detection of the recoiling proton in a liquid scintillator. The method has been tested in the breakup of intermediate energy (30–50 MeV/nucleon) 11Li, 14Be, and 15B beams. Some six events were observed that exhibit the characteristics of a multineutron cluster liberated in the breakup of 14Be, most probably in the channel 10Be+4n. The various backgrounds that may mimic such a signal are discussed in detail.Received 27 November 2001DOI:https://doi.org/10.1103/PhysRevC.65.044006©2002 American Physical Society

Versatile focusing using a combination of toroidal and Kirkpatrick–Baez mirrors

Toroidal mirrors can be used to efficiently focus synchrotron radiation for magnifications near 1. At the Pacific Northwest Consortium-Collaborative Access Team (PNC-CAT) insertion device beamline, a toroidal mirror is used to focus the entire undulator beam to a spot size of 400(H)×100(V) μm2. For large demagnifications, Kirkpatrick–Baez (KB) mirrors are a good choice. Spot sizes down to 1 μm have been achieved at PNC-CAT. However, these mirrors only collect a fraction of the undulator beam, and result in a highly divergent beam with a short working distance. To achieve an intermediate beam size with less divergence, the toroidal and KB mirrors can be combined. The toroidal mirror reduces the beam to match the entrance aperture of the KB mirrors. This combination can provide beam sizes below 100 μm while collecting the entire undulator beam and providing a convenient working distance. Thus, the beam size, working distance, and divergence can be tailored to the needs of the experiment.

The BIE100 ECR ion source

BIE100, an all-permanent-magnet-based electron cyclotron resonance (ECR) ion source, has been under development at Berkeley Ion Equipment (BIE). With a relatively small but optimized source magnet volume, the maximum peak magnetic field strengths of the BIE100 reach 13 kG on axis and 11 kG at the plasma chamber walls, respectively. Microwaves of frequencies of 12.75 and 14 GHz are to simultaneously heat the plasma electrons. The development goal of this ECR ion source is to further explore the capabilities of ECR ion source in the efficient production of the intermediate and high charge state rare ion beams needed for the generation of rare ion beams and industrial applications. This article will present the design features of the BIE100 ion source and its current status.

Calculation of depth-dose distribution of intermediate energy heavy-ion beams

Calculation of depth-dose distribution of intermediate energy heavy-ion beams

In-beam gamma-ray spectroscopy with exotic beams at the NSCL

Projectile fragmentation provides radioactive beams at intermediate velocities (v/c = 0.3-0.5) by physical means of fragment separation. With the development of position-sensitive photon detectors it has become possible to measure the energies and directions of photons emitted in-flight from such fast-moving exotic beams. This allows the reconstruction of the photons' energies emitted from an exotic projectile with high accuracy. It can be advantageous to employ photon detection in experiments with exotic beams since photons can traverse matter easily and their attenuation can be calculated. Experiments with standard luminosities can be carried out at intermediate beam energies with thick secondary targets (order of g/cm2) and very low incident beam rates (order of particle/s or less). Experimental success in this field is strongly correlated with the development of photon detectors such as position-sensitive scintillation detectors or segmented germanium detectors. In-beam gamma-ray spectroscopy of fast exotic beams has been successfully used at all projectile fragmentation facilities in intermediate-energy heavy-ion inelastic scattering experiments, knockout reactions and fragmentation reactions. Here, we focus on experimental results for neutron-rich exotic nuclei in the π(sd )-shell. Measurements and detector developments carried out at the NSCL at Michigan State University during the last four years are discussed.

PARMELA_B: a new version of PARMELA with coherent synchrotron radiation effects and a finite difference space charge routine

Recent interest in advanced laser light sources has stimulated development of accelerator systems of intermediate beam energy, 100–200 MeV, and high charge, 1–10 nC, for high power FEL applications and high energy, 1–2 GeV, high charge, SASE-FEL applications. The current generation of beam transport codes which were developed for high-energy, low-charge beams with low self-fields are inadequate to address this energy and charge regime, and better computational tools are required to accurately calculate self-fields. To that end, we have developed a new version of PARMELA, named PARMELA_B and written in Fortran 95, which includes a coherent synchrotron radiation (CSR) routine and an improved, generalized space charge (SC) routine. An electron bunch is simulated by a collection of macro-particles, which traverses a series of beam line elements. At each time step through the calculation, the momentum of each particle is updated due to the presence of external and self-fields. The self-fields are due to CSR and SC. For the CSR calculations, the macro-particles are further combined into macro-particle-bins that follow the central trajectory of the bend. The energy change through the time step is calculated from expressions derived from the Liénard–Wiechart formulae, and from this energy change the particle's momentum is updated. For the SC calculations, we maintain the same rest-frame-electrostatic approach of the original PARMELA; however, we employ a finite difference Poisson equation solver instead of the symmetrical ring algorithm of the original code. In this way, we relax the symmetry assumptions in the original code. This method is based upon standard numerical procedures and conserves momentum to first order. The SC computational grid is adaptive and conforms to the size of the pulse as it evolves through the calculation. We provide descriptions of these two algorithms, validation comparisons with other CSR and SC methods, and a limited comparison with experimental results.

On the conversion of charge-exchange cross sections to “GT” strength: Anomalies in odd- A nuclei

Gamow–Teller (GT) transitions are the most common weak interaction processes of spin–isospin (στ) type in atomic nuclei. They are of interest not only in nuclear physics but also in astrophysics; they play an important role in supernovae explosions and nucleosynthesis. The direct study of weak decay processes, however, gives relatively limited information about GT transitions and the states excited via GT transitions (GT states); β decay can only access states at excitation energies lower than the decay Q-value, and neutrino-induced reactions have very small cross-sections. However, one should note that β decay has a direct access to the absolute GT transition strengths B(GT) from a study of half-lives, Qβ-values and branching ratios. They also provide information on GT transitions in nuclei far-from-stability. Studies of M1γ transitions provide similar information. In contrast, the complementary charge-exchange (CE) reactions, such as the (p,n) or (3He, t) reactions at intermediate beam energies and 0°, can selectively excite GT states up to high excitation energies in the final nucleus. It has been found empirically that there is a close proportionality between the cross-sections at 0° and the transition strengths B(GT) in these CE reactions. Therefore, CE reactions are useful tools to study the relative values of B(GT) strengths up to high excitation energies. In recent (3He, t) measurements, one order-of-magnitude improvement in the energy resolution has been achieved. This has made it possible to make one-to-one comparisons of GT transitions studied in CE reactions and β decays. Thus GT strengths in (3He, t) reactions can be normalised by the β-decay values. In addition, comparisons with closely related M1 transitions studied in γ decay or electron inelastic scattering [(e,e′)], and furthermore with “spin” M1 transitions that can be studied by proton inelastic scattering [(p,p′)] have now been made possible. In these comparisons, the isospin quantum number T and associated symmetry structure in the same mass A nuclei (isobars) play a key role. Isospin symmetry can extend our scope even to the structures of unstable nuclei that are far from reach at present unstable beam factories.

Implementation of pencil kernel and depth penetration algorithms for treatment planning of proton beams

The implementation of two algorithms for calculating dose distributions for radiation therapy treatment planning of intermediate energy proton beams is described. A pencil kernel algorithm and a depth penetration algorithm have been incorporated into a commercial three-dimensional treatment planning system (Helax-TMS, Helax AB, Sweden) to allow conformal planning techniques using irregularly shaped fields, proton range modulation, range modification and dose calculation for non-coplanar beams. The pencil kernel algorithm is developed from the Fermi-Eyges formalism and Molière multiple-scattering theory with range straggling corrections applied. The depth penetration algorithm is based on the energy loss in the continuous slowing down approximation with simple correction factors applied to the beam penumbra region and has been implemented for fast, interactive treatment planning. Modelling of the effects of air gaps and range modifying device thickness and position are implicit to both algorithms. Measured and calculated dose values are compared for a therapeutic proton beam in both homogeneous and heterogeneous phantoms of varying complexity. Both algorithms model the beam penumbra as a function of depth in a homogeneous phantom with acceptable accuracy. Results show that the pencil kernel algorithm is required for modelling the dose perturbation effects from scattering in heterogeneous media.

Two-stage systems with intermediate beam retarding for energy and spatial analysis of photoelectrons

Abstract New promising electron-optical schemes of analyzers for high-resolution energy and angular analysis of photoelectrons are proposed. The analyzers use an electron beam deceleration between two energy-dispersive stages, and are based on polar-toroidal and spherical deflectors or toroidal mirrors. The application of these schemes is advantageous for structural surface studies with the photoemission excited by a synchrotron radiation.

A position sensitive high-efficiency NaI(Tl) photon-detection system for use with intermediate energy radioactive ion beams

We have built an array of position-sensitive NaI(Tl) photon detectors for use in radioactive beam experiments at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The array consists of 38 cylindrical NaI(Tl) detectors oriented co-axially in three concentric rings around the particle-beam axis. Each crystal has a diameter of 5 cm, is 17 cm long and is read out by two photomultiplier tubes, one at each end of the crystal. Because of the position-dependent attenuation of the scintillation light in the crystal it is possible to determine both the photon energy and the interaction point of the photon in the detector. This photon detection system is very well suited for the investigation of exotic nuclei which, at the NSCL, are produced in fragmentation reactions. Exotic beams produced by this method have high velocities and potentially low particle rates. Both of these properties are addressed in the described setup. The Doppler shift due to the large beam velocities is corrected on an event-by-event basis using the known interaction positions of the photons in the detector. Low particle rates can be accommodated with particle–γ coincidence measurements and the high efficiency of the array.