Incident Particle Type Research Articles

Molecular-Dynamics Simulations of Low-Energy Ion/Surface Interactions During Ion-Beam-Assisted Thin Film Deposition.

ABSTRACTMolecular dynamics simulations are performed of low-energy ion irradiation of two-dimensional Cu islands on a Cu(111) surface. The irradiation of the surface with low-energy particles influences the mobility of the atoms in the surface region and therefore may alter the thin film growth Mode. The effect of 100 eV Ar+ ions incident at grazing angles is limited to situations in which the ions hit the edges of the islands. In Most cases the islands lose one or two atoms. Changing the angle-of-incidence or changing the type of the incident particle has a strong influence on the size distribution of the two-dimensional islands.

Order-of-magnitude method for estimating the fluence that optimizes the critical current in particle-irradiated cuprate superconductors

The particle fluence that maximizes the critical current enhancement in cuprate superconductors is shown to be closely related to the nonionizing energy loss (displacement damage) of a given particle. In many cases, only the incident particle type and energy need to be known in order to allow an order-of-magnitude prediction of the optimal fluence for enhancing the critical current.

Excitation of gases with positive ions

The aurora borealis presents problems the solutions to which depend partly on knowing the cross sections for the excitation of states in atmospheric gases by the impact of energetic protons and electrons. We have begun a study of the excitation processes induced in N 2 and O 2 by energetic incident positive ions (H +, H 2 +, H 3 +). The particles, accelerated with a 2 MV Van de Graa accelerator, enter a differentially pumped gas cell in which the pressure can be varied up to 80 mTorr and held constant to 0.1 mTorr at each setting. Light generated in the cell is observed at 90 ° to the particle beam. The light is reflected by a mirror system so as to enter the input slit of a 1-m, air, Czerny-Turner spectrometer. The 1200 1/mm grating is blazed at 500 nm. A cooled 9659B photomultiplier tube detects the light which appears at the exit slit, and transmits intensity information to a 4000-channel multiscaler. The incident beam is received on an insulated plate, and the collected charge provides a signal which advances both the grating angle and the channel in the multiscaler. Using a line width of 0.03 to 0.1 nm, we have obtained spectra from 360 to 750 nm. Many transitions have been identified, most from N 2 + O 2 −, but some from neutral molecules and monatomic emitters. Data have been taken as a function of pressure and type of incident particle for a particle velocity corresponding to 500 keV protons. There is no discernible difference in relative yield for the different bombarding species. The line intensities all appear to be linear with pressure over the range we used. We will describe our results and discuss our approach to making cross-section measurements. Possible extensions of the experiments into different directions will also be mentioned.

A search for glueballs and a study of doouble pomeron exchange at the CERN intersecting storage rings

We present results from a study of centrally produced mesons in 3 × 10 6 events with two small-angle protons at the CERN Intersecting Storage Rings. A high-statistics sample of exclusive pp → pp π + π − events at √ s = 63 GeV has been obtained, where the reaction mechanism is dominated by double pomeron exchange. Scalar or tensor glueballs may be produced by this process. The π + π − mass spectrum has a distinctive structure, and analysis shows that the data are dominantly S-wave up to 1600 MeV. The behaviour of the D-wave provides evidence for a 2 ++ resonance ( M = 1480 ± 50 MeV, Γ = 150 ± 50 MeV) in addition to the f(1270). We also show data on exclusive K + K −, p p, and π +π −π +π − production, and on the analogous reaction αα → ααπ + π − at √ s = 126 GeV. Flavour independence is suggested by the observation of approximately equal numbers of K +K − and π + π − pairs for mass above 1 GeV. The mass spectra are also apparently independent of √ s (45, 63, 126 GeV) and incident particle type (p, α).

Bose-Einstein correlations in αα, pp and [formula omitted] interactions

Bose-Einstein correlations between pions produced in the central region of rapidity in αα, pp and p p interactions have been studied at the ISR. The parameters r and τ c -often interpreted as the radius and depth of the π-emitting region - are found to be independent of incident particle type but to depend on the mean charged multiplicity. In high multiplicity events, the pions appear to originate from a larger space-time region.

Production of low mass dimuons at high transverse momentum: Study of ϱ, ω, π resonances

We use low mass dimuons (0.35 < M μμ ⩽ 2 GeV/ c 2) to analyse the production at high transverse momentum ( P T ⩾ 2 GeV/ c) of the resonances ϱ, ω, π. We have studied the variation of the cross section with the type of incident particle (π, K, p) at 150, 200, 280 GeV/ c and the nuclear effects by comparison of platinum and hydrogen targets. There is no significant difference between the slopes of the transverse momentum distributions with those observed at lower P T (0 < P T < 2 GeV/ c), meanwhile x F-distributions show a leading effect in the production of gf by kaons at these relatively high transverse momenta.

A study of high transverse energy interactions of 150 and 300 GeV pions and protons on a hydrogen target using a large acceptance calorimeter

Interactions of 150 GeV pions and 300 GeV pions and protons on hydrogen which result in final states with large transverse energy in the central rapidity region −0.88 < y < 0.67 were studied with a calorimeter trigger. The dependence of the cross section on the azimuthal acceptance of the trigger, on the beam energy and on the incident particle type and the jet properties of the events were investigated. No dominant two-jet structure was found. Nevertheless, the parton spectrum in the colliding hadrons appears to be relevant for large transverse energy reactions.

Production of Muon Pairs by 225-GeV/cπ±,K+,p±Beams on Nuclear Targets

Results are presented from a large-acceptance experiment in which muon-pair production was observed in the mass range 2 to 11 GeV/${\mathit{c}}^{2}$. Data were taken with ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{+}$, and ${p}^{\ifmmode\pm\else\textpm\fi{}}$ beams at 225 GeV/c on carbon, copper, and tungsten targets. Differential cross sections and the production dependence on pair mass, ${x}_{\mathrm{F}}$, ${p}_{T}$, incident-particle type, and target nucleus are discussed.

Hadronic Production of Massive Muon Pairs: Dependence on Incident-Particle Type and on Target Nucleus

Data from a study of muon pairs produced in hadron-nucleus collisions are compared with the Drell-Yan model. Comparison of dimuon production by ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons on an isoscalar target shows evidence for a charge asymmetry characteristic of an isospin-nonconserving electromagnetic process. The average transverse momentum of the pairs increases smoothly with pair mass. Data taken on carbon and tin targets are used to extract the dependence on target atomic weight.

Calculations Related to the Possible Use of Photons, Neutrons, Negatively Charged Pions, Protons, and Alpha Particles in Radiotherapy

Calculated results are presented for absorbed dose, LET spectrum, and cell-survival probability as a function of position when photons, neutrons, negatively charged pions, protons, and alpha particles are incident on a tissue phantom. The beam parameters for each type of incident particle were chosen to be approximately those appropriate to the single-port irradiation of a small cylindrical volume (1 cm in radius and 2 cm in height) centered about a depth of 15 cm in the 30-cm-thick tissue slab. Both monoenergetic (15 MeV) neutrons and neutrons produced by $35\text{-}{\rm MeV} {}^{2}{\rm H}$ on Be are considered. The cell-survival-probability calculations are carried out using the model developed by R. Katz et al., and results are presented for both aerobic and anoxic T-1 kidney cells. Spatially dependent OER's and RBE's for each type of particle considered are also given.

The calculation of proportional counter-energy deposition spectra from experimental data

A convolution technique developed by Kellerer which can be used to generate energy deposition spectra from experimental data has been applied to 45 MeV protons. The data presented here were produced by 600 MeV protons passing through a tissue-equivalent gas. The technique is utilized by means of a computer program. It requires an experimental energy deposition spectrum measured with a proportional counter of pathlength s (here s approximately 1*10-4 g cm-2), input. Additional energy deposition spectra can be generated for pathlengths, si, in the range 0.3s<or=si<or=2s, for the same type and energy of incident particle. This technique facilitates experimental work needed to produce microdosimetric patterns of energy deposition for biological sites of arbitrary shape and size.

The dispersion energy relation for ultra-high energy nuclear reactions in emulsion

When a large volume of data from cosmic ray emulsion reactions is analysed it is found that the variation of the mean dispersion s in the log tan theta plot of the charged secondaries, at each energy, follows a linear characteristic when plotted against the log energy of the incident particle. The slope of the characteristic is peculiar to the type of incident particle, and is higher for nucleon-nucleon collisions than for pion-nucleon events.

A fast computing circuit for particle identification using signals from a ΔE, E counter telescope

A circuit is described which uses the natural characteristics of a field-effect transistor to form from the combined pulses of a solid state counter telescope, an analogue signal characteristic of the incident particle type. The response is ideal in the sense that the device operates without adjustment over a wide energy range, and with ΔE counters of arbitrary thickness.