An accurate knowledge of the X-ray source spectrum is required in order to optimize X-ray Computed Tomography systems. A simulation model based on the Monte Carlo code GEANT4 was developed to determine the X-ray spectrum generated by a 450kV tube. The X-ray spectra were measured using a Cadmium Telluride stack detector. The measured spectra were corrected for spurious detector effects and detector efficiency. The X-ray spectra simulated by GEANT4 were validated by comparison with X-ray spectra measured at 350, 400 and 450kV. We observed a good agreement between the simulated and the measured X-ray spectra. In addition, we simulated and measured attenuation curves using aluminium and copper filtration. The comparison of the attenuation curves shows an excellent agreement.
Physical mechanisms involved in insulators submitted to electron irradiation inside a scanning electron microscope (SEM) are investigated by combining some simple considerations of electron trapping mechanisms with basic equation of electrostatics. To understand such mechanisms, only widely irradiated samples having a uniform trapping sites distribution are considered. This hypothesis leads to develop simple models for the trapped charge distributions and subsequently for the distribution of the electric field build-up in ground coated specimens as investigated in electron probe microanalysis (EPMA). This enables us to study the distortion of the Φ(ρz) function (the depth distribution of characteristic X-ray production) as well as the modification of the specimen’s local composition. In this paper, an experimental method, using a series of quartz samples, is described for evaluating the magnitude of the electric field build-up within specimens; thus allowing to establish clearly the electric field influence on the measured Φ(ρz) function.
The cosmic ray experiment KASCADE, set up in Forschungszentrum Karlsruhe, Germany as a multi-detector installation, studying the electromagnetic, the muonic and the hadronic extensive air showers (EAS) component for each observed shower event, has explored the primary energy spectrum and the mass composition of cosmic rays in the energy range of the so called ,,knee" (around 3 PeV). The multidimensional analyses reveal a distinct knee (change of the spectral index of a power-law description) in the energy spectra of the light primary cosmic rays and the dominance of heavy particles with increasing energy. This result provides some important implications, discriminating various conjectures and astrophysical models of the origin of the knee. The KASCADE-Grande experiment is an upgrade of the KASCADE experiment extending the detection area by a factor of 10. It is motivated by studies of a higher primary energy range, looking for the knee-like features of the heavy components, which are expected to appear in the range of 100 PeV. The lecture describes details of motivation, of experimental lay-out and of first studies with KASCADE-Grande.
We have performed Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE) analyses with an external proton millibeam on archaeological bones in order to determine possible alteration processes in their burial environment (dissolution, uptake and diffusion of foreign ions). The PIXE method enables us to quantify the post-mortem alteration by determining the concentration profile of several trace elements like Al, Si, S, Mn, Fe, Cu, Zn and Sr in transverse bone sections, while that of fluorine is inferred from PIGE analysis. Examples of concentration profiles of archaeological bone cross sections from the Seine river site in Paris, Bercy (4000 B.C.), are shown.
The use of parallel-plate spark chambers for obtaining tracks of particles throughout the entire plane normal to - the magnetic field is discussed. For example, a 50-gap spark chamber in a 13-kgauss field observed the tracks of particles at all angles with the plates. The chamber operates in a combined track-sampling and track-delineating mode; a series of streamers delineates the path of a particle moving parallel to the plates, or nearly so. Illustrations are given showing slow electrons and delta rays produced in soft showers. An efficiency per gap of about 95% (if only a single track is present) is obtained by flowing through the chambers a gas mixture of 30% helium and 70% argon by volume, where about 1% of the mixture is bubbled through ethyl alcohol. (N.W.R.)
Semiconductor junction detectors have many advantages for applications in low-energy nuclear physics, and no experiment with charged particles should in future be designed without full consideration of the possibilities of the new detectors. The design of amplifiers has already been influenced by the requirements of semiconductor counters, but there are still many problems in handling and storing the wealth of data that can be obtained with a number of detectors operated simultaneously. Conduction counters are at present at an earlier stage of development, but in many ways are simpler to understand than junction counters. This chapter discusses the applications of semiconductor counters in nuclear physics. The study of semiconductor detectors and their response to nuclear radiation provides a valuable new method of investigating the solid-state physics of semiconductors. There are many possible experiments in this field if only those who practise these two branches of physics can be brought together. Advances in the physics of semiconductors and in the technology of their preparation will make new developments in radiation detectors possible.
A single-gap spark detector is described, through which ionizing particles may pass only at certain locations. A piezoelectric transducer and time delay circuit are used to determine the location at which the spark occurs, by measuring the time required for the sound from the spark to reach the transducer. The locating system has only a single transducer, and can therefore measure only onedimensional distances. (T. F.H.)
A new method has been developed to measure the spectra of gamma radiation emitted in cascade disintegrations. Use is made of a two-crystal scintillation spectrometer and a gated multi-channel analysing device. The pulses produced by summing the outputs of the two crystal-photomultiplier combinations are selected by a single-channel differential discriminator. The output of this differential discriminator gates the multi-channel analyser whenever the sum pulse corresponds to the release in the crystals of the full energy available in the cascade. The spectrum displayed is that of either of the two detectors. The most important features of the technique are:1.(a) only “full-energy” peaks are detected;2.(b) improved resolution is obtained especially at higher gamma-ray energies;3.(c) one γ-γ or p-γ-γ angular correlation experiment determines the angular correlation of the gamma rays of all double cascades deexciting a given level.
The response of a 134″ × 2″ NaI(T1) cylinder to neutrons in the pulse height region between 2.5 and 7 MeV gamma energy equivalent was studied as a function of incident neutron energy for a range of neutron energies between room scattered neutrons and 1.162 MeV. The Li7(p, n) Be7 reaction was used as a source of neutrons since it is relatively free from high energy gamma ray background. Monoergic neutron response curves were obtained for neutron energies of 166 keV, 341 keV, and 469 keV. All other distributions were for proton energies giving rise to two neutron groups. The pulse height distributions were measured for a fixed number of counts of a shielded long counter at each neutron energy. The long counter was calibrated against Ilford C2 emulsions for the case of 1.162 and 0.698 MeV neutrons in order to obtain the neutron flux from the long counter counts. The pulse height distributions are nearly linear between 4 and 6.6 MeV. The extrapolations of these distributions intersect the gamma equivalent axis at approximately the binding energy of the last neutron in I128.
Thin films of carbon were prepared in a vacuum chamber by passing a current of 100 amps through carbon electrodes and allowing the carbon to evaporate on microscope slides coated with NaCl. (W.D.M.)
A general formula is given for the calculation of the inscattering correction which is to be applied to the total cross section for fast neutrons, as measured by transmission experiments. It is shown that inelastic scattering and (n, 2n) reactions are negligible for this evaluation: only elastic scattering is to be taken into account. This influence can be estimated by comparison with some experimental results or by application of the diffraction theory of neutron scattering using, as nuclear radius, R = r0A13 where r0 = 1.25 × 10−13 cm; the maximum error involved in this evaluation is ± 20%.
A read-out system is described which by a substraction method gives recorded number of pulses in the different channels on a scaler. The arrangement is specially made for binary coded analyzers.
