Analysis of dose-LET distribution in the human body irradiated by high energy hadrons

For the purposes of radiological protection, it is important to analyse profiles of the particle field inside a human body irradiated by high energy hadrons, since they can produce a variety of secondary particles which play an important role in the energy deposition process, and characterise their radiation qualities. Therefore Monte Carlo calculations were performed to evaluate dose distributions in terms of the linear energy transfer of ionising particles (dose-LET distribution) using a newly developed particle transport code (Particle and Heavy Ion Transport code System, PHITS) for incidences of neutrons, protons and pions with energies from 100 MeV to 200 GeV. Based on these calculations, it was found that more than 80% and 90% of the total deposition energies are attributed to ionisation by particles with LET below 10 keV microm(-1) for the irradiations of neutrons and the charged particles, respectively.     

A high vacuum portable exsiccator

It is often necessary to transport from one laboratory to another thin films under vacuum, made of materials which are chemically very reactive. One example is the use of nuclear targets, very often expensive, which are produced in certain locations and employed somewhere else, sometimes overseas. Thus it is indispensable to use containers which are able to maintain a vacuum inside which is better than 10⁻³ mbar and for relatively long periods. At our laboratory a stainless steel container has been constructed of about 11 capacity which is able to keep a vacuum better than 2 × 10⁻⁵ mbar for more than 3 weeks.     

保护气氛铝箔真空退火炉的研制

铝箔作为一种在工业及民用广泛应用的产品,其在制造过程中软化退火工序是保障产品质量的重要一环.本文就铝箔的结构特点及制作工艺,分析了铝箔用外热式真空炉退火的特点,指出了在保护气氛下真空退火比其他热处理方法具有明显的优势.同时,描述了设备各组成部分,主要技术参数及结构特点等.并通过设备测试及厂家多年实际应用,证明设备的可靠性,为以后同类设备的研制积累了宝贵的经验.     

Sputter deposition of dielectric films using a magnetic field for protection from high energy electrons

Thin films of SiO₂ and Al₂O₃ were prepared by r.f. sputtering. For protection from energetic electrons in the plasma, deposition was carried out in an area protected by a magnetic field of appropriate strength.The deposited films are free of pinholes, show sound insulation characteristics and have good adhesion to the substrate.     

A large area substrate heater for ultra high vacuum

The experimental difficulties of heating a relatively large area of a highly reactive material like silicon in ultra high vacuum to temperatures near its melting point have been considered. Various methods of heating are investigated and a design with multiple substrate heating facility is described. The substrates are heated by flat resistively heated tungsten radiator inside a water-cooled enclosure. The performance of the substrate heater, its calibration, and the relationship between the substrate temperature and the radiator temperature are discussed.     

The influence of cylindrical air cavities on fluence distributions of high energy electrons

The perturbation of dose distribution caused by air cavities in electron-irradiated media can be appreciable. A Monte Carlo program is developed to determine the effect of a cylindrical air cavity embedded in a homogeneous medium on the fluence distribution. The axis of the cylindrical cavity is assumed normal to the incident electron beam. The case of 10 MeV electrons and carbon as a homogeneous medium is considered.A study of the fluence and current distributions showed that close to and behind the cavity there is a focusing effect on the particles along the central axis of the beam. The characteristic hot spots in the fluence and current profiles beneath the cavity at its shadow edges are not observed.     

A small analytical quadrupole mass spectrometer designed for operation in high and ultra high vacuum systems

The characteristics of a small quadrupole mass spectrometer are described in detail. These show that the requirements of an analytical instrument for use in high and ultra high vacuum systems have been met. The performance is adequate for the measurement of partial pressures down to and below 10^?11 torr. This is achieved with constant sensitivity over the range 0–200 amu with a resolution adequate to separate completely individual peaks up to 50 amu. The instrument does not have an electron multiplier. The consequent disadvantages of a relatively slow response and a limitation to the minimum detectable pressure are compensated by a higher stability and a smaller, simpler, and reliable instrument. Observations with a number of units over a period of many months indicate a maximum change in sensitivity of any one and a difference between individual instruments to be of the order of ±20%. This is therefore a gauge head of approximately the same size as a modulated BA gauge with the same sensitivity, stability and baking characteristics.     

A new energy-efficient approach to high vacuum pumping

Recent experiments have shown that an efficienty trapped mechanical rotary pump operating with completely degassed oil is capable of pressures in the 10^?7 mbar range. By greatly enlarging the zeolite trap and mounting it immediately adjacent to the work chamber it can be made to funtion simultaneously as a high speed sorption pump for vapours. Outgassed vapours from the work chamber and vapours originating from the pump oil are both pumped by the zeolite. The zeolite is operated at room temperature except during bakeout and is maintained at very low surface coverages to obtain corresponding low equilibrium pressures of water and hydrocarbons. Gases which are not sorbed by the zeolite are pumped by the mechanical pump. Vapour pumping continues for periods of months even when all power to the system is shut down. High vacuum is attainable within a few minutes after reapplying power. If desired, the zeolite can be cooled to raise the pumping speeds for all gases to approximately those for vapours, and to reduce ultimate pressures to the 10^?8 mbar range. This principle can be used as the basis for practical pumping systems which provide clean high vacua with low power consumption. Two pumping stations with speeds for vapours in the 12/s^?1 and 400ls^?1 range, respectively, are discussed.     

Influence of multiple scattering on energy loss stragglings for electrons

Elastic multiple scattering for electrons transmitted through carbon foils was studied. The probability distribution for single-nuclear scattering was evaluated using the Born approximation and the electron densities were calculated using the Hartree-Fock approach with the Wigner-Seitz boundary condition. An estimate of the average increase in path length over the depth of penetration was made. Energy loss stragglings for electrons transmitted through carbon foils were calculated and compared with experimental data.     

A low-voltage Penning cell for vacuum measurement and vacuum technology

This paper presents new results on the performance of a special cold-cathode gauge. The use of an AC and DC voltage simultaneously as the power source makes it possible to ignite and sustain a discharge at a significantly lower voltage than normal over a wide pressure range (from 5 to 3×10⁻⁶ Pa). The Penning discharge voltage can be as low as 20 V at a pressure of 0.3 Pa and 300 V in high vacuum. For low values of pressure, the discharge current has a monotonously increasing dependence on the gas pressure. If a low RF voltage is applied to a high-voltage DC discharge, the discharge current increases in many times. These discharge properties can be used to improve the performance of devices that use the Penning and other magnetic discharges (total and partial pressure gauges, leak detectors, ion pumps, ion sources and hot plasma sources). A vacuum gauge of this type combines the best features of magnetic discharge and hot cathode ionization gauges.     

Apparatus for low-temperature fatigue tests in high vacuum

The construction of an apparatus for low-temperature fatigue tests in vacuum is described. The electromagnetic system used for generating dynamic loads makes it possible to test flat specimens in alternating symmetrical bending at a 50 cps frequency. A vacuum of the order of 5 · 10^–9 mm Hg can be produced by the evacuating system which includes a hydrogen condensation pump. The specimens are cooled with liquid nitrogen. Some tentative data on the influence of vacuum and low temperatures on the fatigue strength of stainless steel are reported.     

A thermocouple vacuum gauge for low vacuum measurement

The construction of a thermocouple vacuum gauge for the range of pressures from 200 to 800 mbar is reported. The gauge differs from similar ones that cover the medium vacuum region. The main difference is that the thermocouple is not fixed to the filament, as usual, but is placed at some distance from the filament.     

A clocked,fast electronics trigger for high energy physics

For a Fermilab experiment we have designed and built gated-pulse-stretcher modules which allow us to clock all of the fast electronics with the accelerator rf, thus simplifying the trigger design.