Formation of charged particle tracks in glass-fiber microstructures

Glass-fiber disks intended for the image transfer in electrooptical transducers can be used as targets in microchannel Cerenkov track detectors. Calculated values of the coefficient of Cerenkov radiation trapping in the glass-fiber discs well agree with experiment, which confirms the hypothesis concerning a Cerenkov-type mechanism of the charged particle track formation in non-scintillating microfiber structures.     

Study of spin relaxation by a charged particle beam in a polarized 3He gas target

A model has been constructed for depolarization of a sample of polarized ³He by a charged particle beam. The predictions of this model have been tested experimentally for 0.25 to 1.0 μA of 3 MeV protons incident on a 0.5 to 5.0 Torr room-temperature target of polarized ³He. Good agreement has been found between the model and experiment.     

Cooling of energy spreads in charged particle beams using intratarget acceleration in gas cells

A device is described by which low cross section reactions using charged particle beams can be determined with very high energy resolution. Energy losses incurred by the projectiles during traversal of the target medium are compensated by intratarget acceleration, allowing the use of thick targets to obtain adequate reaction yields. Energy spreads originally present in the beam, as well as spreads introduced by straggling, are cooled through the interaction with crossed electric and magnetic fields. As an example the application of the technique to a search for parity mixing among nuclear levels in radiative alpha particle capture is discussed.     

An improvement to the space resolution of charged tracks

A simple tracking method is to look for the U, X and V triple coincidences in a wire chamber, but the space resolution is in general not satisfactory. In this paper, we consider the use of space correction for the inclined planes in a chamber. The resolution can be much improved for both the proportional chamber and the drift chamber. For proportional chambers, the combination of this method and the wire-spacing “drift distance” technique, further improved the resolution.     

A pulsed-periodic low-pressure volume discharge in a krypton-chlorine gas mixture

The initiation conditions and characteristics of a volume discharge in a krypton-chlorine mixture at low pressures (P≤1.0 kPa) were studied. It is shown that a constant voltage of U _ch 1.0 kV applied to a spherical anode-flat cathode system gives rise to a pulsed-periodic discharge with a pulse repetition rate of 1–50 kHz. The current-voltage characteristics of the discharge, the spectra of emission in a wavelength interval of Δ λ=130–350 nm, and oscillograms of the current and the total output emission intensity were studied as dependent on the partial composition and pressure of the krypton-chlorine mixture. It is shown that the discharge is a selective source of emission in the electronic-vibrational bands with λ=257 nm [Cl₂(D′-A′)], 222 nm [KrCl(B-X)], and 200 nm [C1₂**]. The volume discharge in the Kr-Cl₂ mixture can be used for the development of pulsed-periodic low-pressure excimer-halogen lamps.     

Critical behavior of a charged Bose gas

A fully self-consistent Hartre-Fock theory, using the Coulomb interaction screened by the polarization insertions calculated in the self-consistent random-phase approximation, is applied to thed-dimensional, dense, charged Bose gas at temperatures close to the transition temperatureT _c . The quasiparticle energy spectrum is calculated and shown to behave atT _c like ε(k)=Ak ^σ for smallk, and σ is calculated as a function of the dimensionalityd. The change in transition temperature from that of an ideal gas at the same density, and of the chemical potential are shown to be given by (T _c ?T _c0 )/T _c0 ≈Xr _s ^(d?2)/3 and μ _c ≈Yr _s ^2/3 , wherer _s is the ratio of the interparticle spacing to the Bohr radius. Approximate expressions are given for the coefficientsX andY. The critical exponents are calculated, and the system is shown to obey exact scaling.     

Nuclear fragmentation and the number of particle tracks in tissue

For high energy nuclei, the number of particle tracks per cell is modified by local nuclear reactions that occur, with large fluctuations expected for heavy ion tracks. Cells near the interaction site of a reaction will experience a much higher number of tracks than estimated by the average fluence. Two types of reaction products are possible and occur in coincidence; projectile fragments, which generally have smaller charge and similar velocity to that of the projectile, and target fragments, which are produced from the fragmentation of the nuclei of water atoms or other cellular constituents with low velocity. In order to understand the role of fragmentation in biological damage a new model of human tissue irradiated by heavy ions was developed. A box of the tissue is modelled with periodic boundary conditions imposed, which extrapolates the technique to macroscopic volumes of tissue. The cross sections for projectile and target fragmentation products are taken from the quantum multiple scattering fragmentation code previously developed at NASA Johnson Space Center. Statistics of fragmentation pathways occurring in a cell monolayer, as well as in a small volume of 10 x 10 x 10 cells are given. A discussion on approaches to extend the model to describe spatial distributions of inactivated or other cell damage types, as well as highly organised tissues of multiple cell types, is presented.     

Two dogmas of charged particle optics

Designs of charged particle optical systems are invariably based on two assumptions: (1) The existence of a reference trajectory and (2) midplane symmetry. The reference trajectory is taken to be the path of a charged particle with certain specified initial conditions. Conditions which break the continuity of the reference trajectory are misalignments of magnets, excess horizontal field in a bending magnet, and vertically bending field in a horizontally bending magnet.Even if midplane symmetry is violated in a magnetic system it is usually respected in each magnetic element. Violation of midplane symmetry in a bending magnet occur if the field is not symmetric about the magnetic midplane.Equations of motion have been worked out for the case where both the above mentioned conditions are violated. Solutions have been produced and incorporated into the first- and second-order formalism of charged particle optics.     

Forces acting on a charged particle in an alternating electric field

The well-known expression for a force acting on a charged particle in a high-frequency electric field is generalized to the case of a particle moving in a medium with a friction proportional to the velocity. The high- and low-frequency limits of validity of this generalization are considered. Possible applications of the results are considered.

     

Reduction of byproduct particle size using low-pressure plasmas generated by a cylindrical-shaped electrode

In the case of a plasma-enhanced chemical vapor deposition, large amounts of byproduct particles arrive at a vacuum pump in spite of the use of cleaning process. As these particles are accumulated on internal components of a vacuum pump, its performance is reduced. A plasma reactor located right before a vacuum pump is proposed with an aim to reduce the size and quantity of byproduct particles, thereby to improve the durability of a vacuum pump. The plasma reactor and electrode all have a concentric cylindrical shape, which allows the device to be easily connected to pre-existing vacuum pipelines without any disturbance to the exhaust stream. The sizes of byproduct particles before the vacuum pump are quite diverse in the range of tens of nanometers to tens of micrometers. The plasma reactor makes the size and quantity of byproduct particles much smaller, and the particles larger than 1 μm are not observed anymore. This result indicates that the vacuum pump durability can be significantly improved by using plasmas.     

Measurements of alpha particle energy using nuclear tracks in solids methodology

In this paper we present a method for the measurement of alpha particle energy using polycarbonate materials as nuclear track detectors (NTDs). This method is based on the interaction of the radiation with the solid-state materials, using the relationship between the energy deposited in the material by the ionising particle and the track developed after an established chemical process. The determination of the geometrical parameters of the formed track, such as major axis, minor axis and overall track length, permit determination of the energy of the alpha particle. The track analysis is performed automatically using a digital image system, and the data are processed in a PC with commercial software. In this experiment 148Gd, 238U, 230Th, 239Pu and 244Cm alpha particle emitters were used. The values for alpha particle energy resolution, the linear response to energy, the confidence in the results and the automatisation of the procedure make this method a promising analysis system.     

Investigation of epitaxial GaAs charged particle detectors

The performance of a GaAs detector based on epitaxial material was studied. Results for the electrical characteristics and alpha spectra measurements are presented.     

Some developments in neutron and charged particle dosimetry

There is an increasing need for dosimetry of neutrons and charged particles. Increasing exposure levels are reported in the nuclear industry, deriving from more frequent in-service entries at commercial nuclear power plants, and from increased plant decommissioning and refurbishment activities. Another need stems from the compliance with requirements of the regulations and standards. The European Council directive 96/29 requires dosimetric precautions if the effective dose exceeds 1 mSv a(-1). On average, aircrew members exceed this value. Further, there is a trend of increasing use of charged particles in radiotherapy. The present situation is that we have reasonably good photon dosemeters, but neutron and charged particle dosemeters are still in need of improvements. This work highlights some of the developments in this field. It is mainly concentrated on some developments in passive dosimetry, in particular thermally and optically stimulated luminescent detectors, indicating the direction of ongoing research. It shows that passive dosemeters are still a very active field. Active dosemeters will not be discussed with the exception of new developments in microdosimetric measurements [new types of tissue equivalent proportional counters (TEPCs)]. The TEPC is unique in its ability to provide a simultaneous determination of neutron / charged particle / gamma ray doses, or dose equivalents using a single detector.     

Fine structure of carbon films deposited from a microwave low-pressure gas discharge

We have studied the conditions of synthesis and the fine structure of carbon films of various structural modifications possessing preset electrical properties. The phase diagram of polymorphous transformations is constructed for carbon films grown from the plasma of microwave discharge in low-pressure ethanol vapor. Technological factors influencing the efficiency of extracting diamondlike microcrystals from a hydrocarbon matrix have been studied. Depending on the extraction regime and initial layer thickness, the size of extracted microcrystals can vary from 10–12 to 100–120 nm, while their surface concentration may reach 1.4×10⁷ cm⁻².     

Establishment and verification of a primary low-pressure gas flow standard at NIMT

This paper presents the establishment and verification of a primary low-pressure gas flow standard with the capacity of 0.005 L/min to 24 L/min (at 23 °C and 101.325 kPa), newly established at National Institute of Metrology of Thailand (NIMT). This facility is a mercury-sealed piston prover consisting of three precision-machined glass cylinders. Flow measurement can be carried out manually or semi-automatically. The electronics were installed in a separate console to minimize their thermal impact on the gas temperature. Special care was taken in designing the facility to ensure sound and representative gas pressure and temperature measurement. The relative expanded uncertainty of mass flow measurement was evaluated to be less than 0.13%. To verify the measurement capability and performance of the new facility, a bilateral comparison with the piston prover at Center for Measurement Standards (CMS), Taiwan was conducted. The transfer standard used was a set of three critical flow venturis with dedicated thermometers. Eight flow rates of dry air ranging from 42 mL/min to 14.5 L/ min at 0 °C and 101.325 kPa (0.055 g/min to 18.87 g/min) were tested. Comparison results showed that the E _n values for the flow measurements at NIMT with reference to CMS were all well less than unity, demonstrating good agreement between the two participants.     

QUADOS intercomparison: a summary of photon and charged particle problems

QUADOS, a Concerted Action of the European Commission, has promoted an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of radiation transport codes. Eight problems were selected for their relevance to the radiation dosimetry community, five of which involved photon and proton transport. This paper focuses on the analysis of the photon and charged particle problems. The neutron problems were presented in a paper at the NEUDOS9 conference.     

Rotational moment in thermal vibrations of a bound charged particle in a constant magnetic field

The effect of a constant magnetic field on thermal vibrations of a charged particle in a condensed medium was theoretically studied. It is shown that the particle and its surroundings in the constant magnetic field are subjected to a constant rotational moment, the direction of which is determined by the sign of the particle charge and the direction of the magnetic induction. The magnitude of mechanical stresses induced by this moment in the medium is found to change in a stepwise manner upon a “phase transition” of the particle from the bound to the free state.     

First operation with a crystal septum to replace a magnet in a charged particle beam

Particle channeling in a bent crystal at Fermilab has been used to replace a magnet in a secondary charged particle beam. The maximum momentum of particles that could be transmitted to an experimental location was raised from the magnetic septum limit of 225 GeV/c to the full primary beam momentum of 400 GeV/c.