Scan pattern optimization for uniform proton beam scanning.

Magnetic beam scanning allows one to spread proton beam over the desired radiation field area, improving beam utilization and conformity to the target area. This article discusses generic scan forms for generating uniform circular and rectangular fields and establishes criteria that can be applied to optimize selected scan patterns. During construction of the Midwest Proton Radiotherapy Institute (MPRI), Indiana University developed a magnetically scanned beam spreading system for the 3 m long gantry nozzle.

Structural evolution of the dihydrate to anhydrate crystalline transition of trehalose as measured by wide-angle X-ray scattering.

Wide-angle X-ray scattering measurements were performed to record structural changes during the transition from trehalose dihydrate to crystalline anhydrous alpha-trehalose. The results show that large dihydrate crystals rearrange into smaller sized alpha crystals; from the peak widths we calculate a crystallite size of typically approximately 40 trehalose molecules. We find that the dehydration probably takes place in a two-step process with different time scales for both the water removal step and the molecule rearrangement step.

Monolayer sorption of neon in mesoporous silica glass as monitored by wide-angle x-ray scattering.

We report measurements of the x-ray scattering intensity as mesoporous silica glasses are filled with neon. The intensity of the first peak in the liquidlike diffraction pattern increases nonlinearly with mass adsorbed. We outline a simple model assuming that the major coherent contribution to the first peak in the scattering function S(Q) is due to interference from nearest-neighbor scatterers.

Tidal effects and the proximity decay of nuclei.

We examine the decay of the 3.03 MeV state of (8)Be evaporated from an excited projectilelike fragment following a peripheral heavy-ion collision. The relative energy of the daughter alpha particles exhibits a dependence on the decay angle of the (8)Be(*), indicative of a tidal effect.

Multichannel detectors for profile measurements in clinical proton fields.

Two beam profile measurement detectors have been developed at Indiana University Cyclotron Facility to address the need for a tool to efficiently verify dose distributions created with active methods of clinical proton beam delivery. The multipad ionization chamber (MPIC) has 128 ionization chambers arranged in one plane and is designed to measure lateral profiles in fields up to 38 cm in diameter. The MPIC pads have a 5 mm pitch for fields up to 20 cm in diameter and a 7 mm pitch for larger fields, providing the accuracy of field size determination about 0.

Combined X-Y scanning magnet for conformal proton radiation therapy.

Light-ion beams have several features that make them very effective in radiation therapy applications. These include favorable depth dose distribution, finite penetration range, and high radiobiological efficiency. Moreover, magnetic scanning methods allow one to spread an ion beam to an exact image of a complex tumor shape.

Measurement of the absolute n p scattering differential cross section at 194 MeV.

We describe a double-scattering experiment with a novel tagged neutron beam to measure differential cross sections for np backscattering to better than +/-2% absolute precision. The measurement focuses on angles and energies where the cross section magnitude and angle dependence constrain the charged pion-nucleon coupling constant, but existing data show serious discrepancies among themselves and with energy-dependent partial-wave analyses. The present results are in good accord with the partial-wave analyses, but deviate systematically from other recent measurements.

Proposed Measurement of the Beta-Neutrino Correlation in Neutron Decay.

Currently, the beta-neutrino asymmetry has the largest uncertainty (4 %) of the neutron decay angular correlations. Without requiring polarimetry this decay parameter can be used to measure λ (ga/gv ), test Cabibbo-Kobayashi-Maskawa (CKM) unitarity limit scalar and tensor currents, and search for Charged Vector Current (CVC) violation. We propose to measure the beta-neutrino asymmetry coeffcient, a, using time-of-flight for the recoil protons.

Measurement of Parity Violation in np Capture: the NPDGamma Experiment.

The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry A γ in the reaction [Formula: see text]. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, providing a theoretically clean determination of the weak pion-nucleon coupling. A new beam-line at the Los Alamos Neutron Science Center (LANSCE) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized (3)He spin filter and captured in a liquid para-hydrogen target.

Neutron Measurements and the Weak Nucleon-Nucleon Interaction.

The weak interaction between nucleons remains one of the most poorly-understood sectors of the Standard Model. A quantitative description of this interaction is needed to understand weak interaction phenomena in atomic, nuclear, and hadronic systems. This paper summarizes briefly what is known about the weak nucleon-nucleon interaction, tries to place this phenomenon in the context of other studies of the weak and strong interactions, and outlines a set of measurements involving low energy neutrons which can lead to significant experimental progress.

LENS: A New Pulsed Neutron Source for Research and Education.

A new pulsed neutron source is under construction at the Indiana University Cyclotron Facility (IUCF). Neutrons are produced via (p,n) reactions by a low-energy proton beam incident on a thin beryllium target. The source is tightly coupled to a cold methane moderator held at a temperature of 20 K or below.

Axial observables in d-->p--> breakup and the three-nucleon force.

We have measured three axial polarization observables in d-->p--> breakup with a polarized 270 MeV deuteron beam on a polarized proton target. Axial observables are zero by parity conservation in elastic scattering but can be easily observed in the breakup channel at the present energy. Based on a symmetry argument, the sensitivity of these observables to the three-nucleon force might be enhanced.

Vector and tensor polarization lifetimes for a stored deuteron beam.

The time dependence of the vector and tensor polarization of a 270 MeV stored deuteron beam was measured near a depolarizing resonance, which was induced by an oscillating, longitudinal magnetic field. The distance to the resonance was varied by changing the oscillation frequency. The measured ratio of the polarization lifetimes is tau(vector)/tau(tensor)=1.

Observation of the charge symmetry breaking d+d-->4He+pi(0) reaction near threshold.

We report the first observation of the charge symmetry breaking d+d-->4He+pi(0) reaction near threshold. Measurements using a magnetic channel (gated by two photons) of the 4He scattering angle and momentum (from time of flight) permitted reconstruction of the pi(0) "missing mass," the quantity used to separate 4He+pi(0) events from the continuum of double radiative capture 4He+gamma+gamma events. We measured total cross sections for neutral pion production of 12.

Measurement of gamow-teller strength for 176Yb --> 176Lu and the efficiency of a solar neutrino detector.

We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem.