The potential of particle therapy due to focused dose deposition in the Bragg peak has not yet been fully realized due to inaccuracies in range verification. The purpose of this work was to correlate the Bragg peak location with target structure, by overlaying the location of the Bragg peak onto a standard ultrasound image. Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the cyclotron inflector. The chopper limited the train of bunches so that 2 Gy were delivered in [Formula: see text]. The ion pulse generated thermoacoustic pulses that were detected by a cardiac ultrasound array, which also produced a grayscale ultrasound image. A filtered backprojection algorithm focused the received signal to the Bragg peak location with perfect co-registration to the ultrasound images. Data was collected in a room temperature water bath and gelatin phantom with a cavity designed to mimic the intestine, in which gas pockets can displace the Bragg peak. Phantom experiments performed with the cavity both empty and filled with olive oil confirmed that displacement of the Bragg peak due to anatomical change could be detected. Thermoacoustic range measurements in the waterbath agreed with Monte Carlo simulation within 1.2 mm. In the phantom, thermoacoustic range estimates and first-order range estimates from CT images agreed to within 1.5 mm.

Gas desorption and electron emission coefficients were measured for 1 MeV potassium ions incident on stainless steel at grazing angles (between 80 and 88 from normal incidence) using a new gaselectron source diagnostic (GESD). Issues addressed in design and commissioning of the GESD include effects from backscattering of ions at the surface, space-charge limited emission current, and reproducibility of desorption measurements. We find that electron emission coefficients e scale as 1= cos up to angles of 86 , where e 90. Nearer grazing incidence, e is reduced below the 1= cos scaling by nuclear scattering of ions through large angles, reaching e 135 at 88. Electrons were emitted with a measured temperature of 30 eV. Gas desorption coefficients 0 were much larger, of order 0 10 4. They also varied with angle, but much more slowly than 1= cos. From this we conclude that the desorption was not entirely from adsorbed layers of gas on the surface. Two mitigation techniques were investigated: rough surfaces reduced electron emission by a factor of 10 and gas desorption by a factor of 2; a mild bake to 220 had no effect on electron emission, but decreased gas desorption by 15% near grazing incidence. We propose that gas desorption is due to electronic sputtering.

Contaminating clouds of electrons are a concern for most accelerators of postive-charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly-, wealdy-, and un-magnetized. We describe o w approach to such self-consistency, and in particular a scheme for interpolating between full-orbit (Boris) and dr&kinetic particle pushes that enables electron time steps long compared to the typical gyro period in the magnets. We present tests and applications: simulation of electron clouds produced by t h e e Werent lcinds of sowces indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the High-Current Experiment (HCX)

An experiment was performed at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two α-decay chains, produced via the 243 Am(48 Ca,xn) 291-x Mc reaction, that were separated by mass-tocharge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to 284 Nh (Z=113), the α-decay daughter of 288 Mc (Z=115), while the second occurred at A/q=288 and was assigned to 288 Mc. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) massnumber assignments. Atoms of superheavy elements (SHE) have been produced at the Joint Institute for Nuclear Research (JINR) in compound-nucleus reactions between 48 Ca projectiles and actinide targets (hot fusion reactions) for nearly 20 years [1-3]. During the last several years, SHE production in such hot fusion reactions has been reported from laboratories in the USA [4-6], Germany [7-11], and Japan [12], both

During heavy-ion operation in several particle accelerators worldwide, dynamic pressure rises of orders of magnitude were triggered by lost beam ions that bombarded the vacuum chamber walls. This ioninduced molecular desorption, observed at CERN, GSI, and BNL, can seriously limit the ion beam lifetime and intensity of the accelerator. From dedicated test stand experiments we have discovered that heavy-ion-induced gas desorption scales with the electronic energy loss (dE e =dx) of the ions slowing down in matter; but it varies only little with the ion impact angle, unlike electronic sputtering. DOI: 10.1103/PhysRevLett.98.064801 PACS numbers: 41.75.Ak, 34.50.Dy, 79.20.Rf Energetic ions incident on matter sputter target material and also desorb gas from the target surface. The sputter and desorption yields (number of sputtered or desorbed particles per ion impact) are known to be linked to the energy loss of the projectile inside the target. Two energy loss regimes, nuclear and electronic, have been known for decades. An example for potassium ions impacting onto stainless steel, calculated with the SRIM code [1], is shown in Fig. 1. Here for low projectile energies the nuclear energy loss dominates and for higher energies the electronic energy loss dominates the total energy loss. Sputter and desorption yield measurements from 1 m thick targets in the regime of electronic energy loss have shown that both scale with the electronic energy loss dE e =dx n to the power of n 1-3. This was observed for targets of frozen gases [2 -5], for sputtering from micron-thick coatings of protein [6,7], and for desorption of nitrogen from a conductor (carbon) by 6-13 MeV=u ions (u is the nucleon mass) [8,9]. Electronic sputtering and desorption from 1 m thick targets is found to vary with the ion impact angle from normal, , as 1=cos m to the first or higher power of m [5,10].Our research was motivated by the copious gas desorption that results from lost heavy ions striking particle accelerator vacuum chambers leading to dynamic pressure rises which limit the beam intensity in a number of heavyion accelerators [11]. Related work dates back more than 30 years, when a vacuum instability in the Intersecting Storage Rings (ISR) at CERN was identified above a critical beam current [12]. Recent requirements for orders of magnitude increase in beam intensity have motivated our search for further understanding and mitigation mechanisms. In preparation for the heavy-ion program of the Large Hadron Collider at CERN, beam-loss induced molecular desorption was intensively studied in ultra-highvacuum chambers at CERN's Heavy-Ion Accelerator (LINAC 3) [13] and the Super Proton Synchrotron (SPS) [14]. Large effective desorption yields of up to 2 10 4 molecules=Pb 53 ion (4:2 MeV=u) and 3:7 10 4 molecules=In 49 ion (158 GeV=u) were measured for ions impacting under various angles [ 0 (perpendicular), 84.8 , 89.2 at LINAC 3, and 88.3 at the SPS] onto stainless steel samples which were chemically cleaned, 950 C vacuum fired, and in situ baked at...