Search Results (22 total)

A major expense and design challenge in carbon/proton cancer therapy machines are the isocentric gantries. The transport elements of the carbon/proton gantry are presently made of standard conducting dipoles. Because of their large weight, of the order of ∼100   tons, the total weight of the gantry with support structure is ∼600   tons. The novel gantry design that is described here is made of fixed field superconducting magnets, thus dramatically reducing magnet size and weight compared to conventional magnets. In addition, the magnetic field is constant throughout the whole energy region required for tumor treatment. Particles make very small orbit offsets, passing through the beam line. The beam line is built of combined-function dipoles such as a nonscaling fixed field alternating gradient (NS-FFAG) structure. The very large momentum acceptance NS-FFAG comes from very strong focusing and very small dispersion. The NS-FFAG small magnets almost completely filled the beam line. They first make a quarter (or close to a quarter) of an arc bending upward and an additional half of a circle beam line finishing so that the beam is pointed towards the patient. At the end of the gantry, additional magnets with a fast response are required to allow radial scanning and to provide the required position and spot size. The fixed field combined-function magnets for the carbon gantry could be made of superconducting magnets by using low temperature superconducting cable or by using high temperature superconductors.

This paper presents a method for compensating the vertical orbit change through the interaction region that arises when the beam enters the linear collider detector solenoid at a crossing angle. Such compensation is required because any deviation of the vertical orbit causes degradation of the beam size due to synchrotron radiation, and also because the nonzero total vertical angle causes rotation of the polarization vector of the bunch. Compensation is necessary to preserve the luminosity or to guarantee knowledge of the polarization at the interaction point. The most effective compensation is done locally with a special dipole coil arrangement incorporated into the detector (detector integrated dipole). The compensation is effective for both e⁺e^-and e^-e^-beams, and the technique is compatible with transverse-coupling compensation either by the standard method, using skew quadrupoles, or by a more effective method using weak antisolenoids.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

Differential cross sections for quasielastic electron scattering on ⁴⁰Ca have been measured at laboratory scattering angles of 45.5°, 90°, and 140° with bombarding energies ranging from 130 to 840 MeV. Transverse and longitudinal response functions have been extracted for momentum transfers from 300 to 500 MeV/c. Contrary to some previously reported results, the total observed longitudinal strength agrees with the relativistic Fermi gas prediction to within ±18%.

It is shown that the continuum missing-mass spectra for the (π^-,π⁺) and (π^-,p) reactions leading to extremely neutron-rich exotic nuclei can be explained in terms of phase-space distributions by invoking the presence of dineutrons as one of the products of the breakup. It is suggested that this indicates the presence of the dineutron as a cluster in these neutron-rich systems during their breakup. It is noted that these observations in weakly unbound systems may be analogs of the dineutron halos for which evidence has been found in weakly bound nuclei near the neutron drip line.

Inelastic electron scattering cross sections for ¹⁴C have been measured at a scattering angle of 180°, with incident beam energies ranging from 81.9 to 268.9 MeV. Transverse form factors were measured for transitions to low-lying natural-parity states, to unnatural-parity ‘‘stretched’’ J^π=4^- states, and to the J^π=2^- analog to the ¹⁴B ground state. Cross sections for 4^- states at 11.7 and 17.3 MeV are combined with pion scattering data to determine the isoscalar and isovector transition amplitudes. Form factors for other states are compared to shell-model calculations. From the excitation energy of the newly discovered J^πT=2^-2 state at 22.1 MeV, the ¹⁴-¹⁴B Coulomb energy difference is determined to be 2.25±0.10 MeV.

We have made a good-resolution, high-sensitivity search for a T=2 dibaryon in the missing-mass spectra for the reaction d(π^-, π⁺)π^-nn at 292 MeV. Our results are consistent with there being no resonance peak due to such a state in the mass region 2001-2070 MeV. 95%-confidence upper limits for the integrated cross sections for such a state are presented. It is found that a quasifree model calculation, without final-state interactions, considerably underpredicts the continuum yield in the vicinity of the threshold.

Inelastic electron scattering cross sections for ⁴He have been measured at 180° for incident electron energies of 130 and 200 MeV. Spectra measured up to excitation energies of 54 MeV are relatively featureless and show no evidence for resolvable excitations. The data are compared with continuum shell-model calculations which include all one-body breakup channels.

The ground state and several excited states of ⁹He, the most neutron-rich nucleus to date, have been identified by means of the reaction ⁹Be(π^-, π⁺)⁹He. The mass excess of the ground state has been measured and it is found that the nucleus is unbound against single-neutron decay by 1.13±0.10 MeV only. It is found that the excited-state spectrum of this nucleus, which is very far from the valley of stability, is in good agreement with the predictions of "no-core" shell-model calculations whose parameters were optimized for the stable nuclei in the valley.

Transverse quasielastic electron scattering cross sections have been measured for the deuteron at 180° for incident electron energies of 220, 270, and 320 MeV. At the quasielastic peak the four-momentum transfers squared varied from 3.4 to 6.3 fm^-2. The measured spectra include the region from the elastic peak through the entire quasielastic peak. Results are compared with recent calculations incorporating meson-exchange currents and isobar configurations. At large neutron-proton separation energies, the data support the need for the inclusion of large isobar configuration components in the cross section.

Transverse inelastic electron scattering cross sections for ⁵⁶Fe have been measured at 180° in the quasielastic region for 12 incident electron energies. From these data transverse response functions have been extracted at constant three-momentum transfers of 250, 290, 330, 370, 410, 450, 490, and 530 MeV/c. The results in the quasielastic region have been compared with two relativistic Fermi gas models: one employing a momentum-transfer-dependent effective mass M^*, the other employing the free-nucleon mass. The region beyond the quasielastic peak has been compared with model calculations incorporating meson-exchange currents and nucleon-nucleon correlations. Transverse response function y scaling is also discussed.

The transverse ¹²C(e,e′) inelastic spectrum has been measured at 180° up to an excitation energy of 96 MeV for 150.6 MeV incident electrons. This spectrum is compared to a recent self-consistent random phase approximation calculation which includes multipolarities of J≤3. The calculated cross section is larger than the experimental cross section in the quasielastic peak region, and resonance states are predicted in the 20-35 MeV region which are not observed.

[NUCLEAR REACTIONS ¹²C(e,e′); E=150.6 MeV, θ=180°; measured σ(E,θ).]

Results are presented for the scattering of electrons through 180° from the ½^- ground state and the 3 / 2^- excited state at 6.32 MeV in ¹⁵N. The range of the momentum transfer q is from 0.70 to 3.25 fm^-1. Comparisons are made with the predictions of the 0_p-shell proton-hole model, a large basis 2ℏω shell model calculation, and core polarization models. In general, it was found that the theoretical description of the data improved markedly as the model space was expanded, but the predicted cross sections were consistently below the data for q>2.4 fm^-1. The present data rule out the low value of the Migdal parameter g^′ needed to describe the (e,e′) data for ¹²C and ¹³C, and do not support the previous suggestion that pion-condensation effects are important in finite nuclear systems.

NUCLEAR REACTIONS ¹⁵N(e,e′), E=70-327 MeV, θ=180°, measured σ(E, θ) for ground, 6.32 MeV levels. ¹³C deduced transverse form factors. Comparisons with models.

Inelastic cross sections for 180° electron scattering from ²⁰⁸Pb have been measured at incident energies of 40.5, 50.4, 60.3, and 75.2 MeV. Transverse electric form factors have been determined for the 3^- state at 2.614 MeV, the 5^- states at 3.198 and 3.708 MeV, the 2⁺ states at 4.085 and 6.21 MeV, the 4⁺ state at 4.323 MeV, and the 6⁺ state at 4.422 MeV. The results for these natural parity states are compared to the predictions of an incompressible, irrotational current model, and of a particle-hole model. All transverse electric form factors show strong contributions from intrinsic magnetization currents. Transverse form factors were obtained for the proposed 1⁺ state at 4.84 MeV, for the group of 1⁺ states at 7.48 MeV, and for several proposed 2^- states. A search for M1 transition strength was made up to excitation energies of 19 MeV. The future of electron scattering as a tool for probing M1 strength in ²⁰⁸Pb is discussed.

NUCLEAR REACTIONS ²⁰⁸Pb(e, e^′), E=40.5, 50.4, 60.3, and 75.2 MeV, measured σ(180°). ²⁰⁸Pb deduced levels and transverse form factors. Enriched target, magnetic spectrometer.

The form factor for elastic magnetic scattering of electrons from ¹³C has been measured to a maximum momentum transfer of 3.29 fm^-1. No reasonable p-shell model, with or without one-pion exchange currents, could be found to explain the relative enhancement observed in the M1 form factor above q≃2 fm^-1.

NUCLEAR REACTIONS ¹³C(e, e), E=80-338 MeV; measured σ(E, θ). ¹³C deduced M1 form factor. Comparison with shell model.

A simple Lane model is used to parametrize the energy systematics of the isospin splitting of high-spin magnetic states in non-self-conjugate nuclei. A strength parameter V₁=106±10 MeV is found.

The Einstein-Kurşunoǧlu and the Einstein-Bonnor unified-field-theory equations for the time-independent, spherically symmetric electric and magnetic fields are reduced to an ordinary integrodifferential equation of the type previously solved by numerical methods. It is found that specifying the mass and charge of the electric monopole along with using Dirac's value for the magnetic charge is sufficient to determine the mass of the magnetic monopole in the Einstein-Kurşunoğlu and the Einstein-Bonnor theories. The observed mass of the electron and the large (unobserved) mass of the magnetic monopole do not disagree with these unified field theories.

Inelastic electron scattering is used to identify M8 transitions and assign J^π=8^- to states at E_x=8.314, 8.949, 9.974, 10.677, and 13.263 MeV excitations. Shell-model calculations within the model space [g_{9 / 2}⊗(f_{7 / 2}^-3)]_8^- suggest that the four lowest states are T=1 and the strongest excitation, to the state at 13.263 MeV, is T=2.

The Einstein-Kurşunoǧlu nonsymmetric field theory has a distributed particle solution for the spherically symmetric time-independent case where g₂₃≠0. The mass of the particle is derived from the field energy when the integration constants are chosen to avoid singularities. Linearization of the equations yields the Klein-Gordon equation for the charge density. The field functions are similar to a solution previously found for Bonnor's modification of the nonsymmetric theory.

A numerical solution is obtained for the electric spherically symmetric field in Bonnor's unified field theory. This solution can be interpreted as a distributed particle with a finite self-energy. Important constants of the theory k and p are evaluated by assuming the particle carries the electron's charge and mass.

The transverse electromagnetic form factors squared of the ¹²C 2⁺ levels at 4.439 MeV (T=0) and at 16.107 MeV (T=1) have been measured by means of 180° electron scattering over a momentum-transfer range from q=0.51 to 2.05 fm^-1. Evidence is presented for appreciable contributions of nuclear convection currents to the transverse 4.439-MeV form factor at low q, and spin magnetization contributions to the transverse 16.107-MeV form factor at higher q.

We report calculations of the structures and energies of monovalent ions (mainly Li⁺ and F^-) dissolved in a number of alkali-halide hosts. Our results are used to discuss the observation of such ions in certain crystals at positions diplaced from the regular lattice sites. The calculations use the HADES program together with recently derived interionic potentials. In contrast to previous theoretical studies in this field, we obtain good agreement with experiment in a substantial majority of cases, without making any arbitrary alterations to the potentials. Moreover, our results agree with recent experimental investigations of the effect of pressure on Li⁺-doped KCl; calculations with a contracted lattice show that the Li⁺ ion goes on center, in agreement with the experimental findings at higher pressures. Such calculations therefore provide a highly critical test of our potentials and the generally good agreement between theory and experiment reported in our study therefore confirms the accuracy of our lattice models. Our results are also used to discuss in general terms those factors that determine whether off-center displacements occur in specific alkali halides. We show how the observed trends are determined by a balance between short-range repulsion and polarization terms.