Incident Charged Particles Research Articles

Output Pulse Amplitude from Lithium-Drifted Detector-Amplifier Combination under Conditions of Carrier Diffusion and Bulk and Surface Recombination

A calculation has been made of the output pulse amplitude obtained from an idealized lithium-drifted detector-amplifier combination under conditions where an incident charged particle generates a charge distribution in the field-free region of the detector which is a general function of position. An expression is derived for the probability P that a hole initially generated at a given position diffuses out of the field-free region as a function of position, bulk lifetime, and surface recombination velocity. For an amplifier with a ``long'' time constant, one obtains directly from P and the initial charge distribution the maximum amplitude of the output pulse. The output pulse amplitude is evaluated for actual charge distributions generated in the detector by incident charged particles. In principle, from measurements with charged particles and the results presented, the depth of the lithium-diffused region and the magnitude of the surface recombination velocity may be determined.

The transport of neutrons produced by 3-GeV proton-lead nucleus collisions through a labyrinth and comparison with experiment

Calculated values of the thermal-neutron flux and the neutron flux above the cadmium cutoff as a function of position in a labyrinth of rectangular concrete ducts are compared with experimental values. In the calculations the approximation of neglecting all incident neutrons with energy greater than 10 MeV and all incident charged particles was made. The results do not give an unambiguous answer concerning the validity of this approximation because the calculated and experimental values are in good agreement in only one of the three cases considered.

Initial-state m quantization in binary-encounter theory

A detailed comparison has been made between the binary-encounter and Bethe theories for ionization of the (2p, 0) hydrogen atom by a fast incident charged particle. For this purpose we have mathematically reformulated the binary-encounter theory to treat the non-isotropic velocity distribution in the initial state of the atom considered. The pronounced dip found before in the Bethe theory is reproduced in the binary-encounter theory and is shown to be caused solely by the angular part of the initial-state wave function. Good agreement between the theories is found for energy transfers > 1 ryd. Applications to other initial states and other atoms are discussed.

On the measurement of momentum transfer in nuclear interactions

It is shown that a lower limit for the momentum transferred to the target nucleus by an incident fast charged particle may be obtained by measuring the directions of the emitted particles, without need to measure individual momenta. In cases with no unseen neutral particles, and negligible energy transfer, a value of the longitudinal momentum transfer may be obtained also. A technique is developed which is useful in distinguishing processes involving small momentum transfer, such as Coulomb and diffraction dissociation.

Optical Emission from Irradiated Foils. I

The present work is concerned with the emission of optical radiation from foils irradiated with charged particles. A generalization of the Ginsburg-Frank treatment is presented in which the wave properties of normally incident charged particles are accounted for in the Born approximation. The foil is assumed to be of finite thickness and to possess a dielectric constant of the form $\ensuremath{\epsilon}(\ensuremath{\omega})={\ensuremath{\epsilon}}_{1}(\ensuremath{\omega})+i{\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$. Detailed prediction of the energy and angle distribution of emitted photons is made. The present result is shown to reduce to that obtained by Ferrell if $\ensuremath{\epsilon}(\ensuremath{\omega})$ appropriate to a free electron gas is assumed and if one takes $\frac{{v}_{i}}{c}\ensuremath{\ll}1$, where ${v}_{i}$ is the speed of the incident particle. Numerical results have been obtained for foils of Ag and Al.

The origin of nitrogen ionization in the upper atmosphere

Although the N 2 + First Negative bands in twilight are probably the result of resonance scattering by N 2 + ions, the symmetry of morning and evening observations make it unlikely that the ionization is produced by sunlight in the E-region. If the flux in the He II λ304 line is as high as 15 erg cm −2 sec −1, the observed First Negative system intensities can be accounted for, and the nitrogen ionization is localized in the F-region. If the flux in the λ304 line is much smaller, the ionization must be produced by incident charged particles in the E-region.

Lead Glass Čerenkov Radiation Photon Spectrometer

A spectrometer for analyzing photons of energies extending up to several Bev has been constructed and used successfully. This instrument essentially consists of a cylinder of glass, 12-in. diam and 14-in. long containing 52% of PbO, viewed by four 5-in. diam photomultipliers. High-energy photons incident along the spectrometer axis produce electron showers in the transparent high-Z glass. The total Čerenkov radiation emitted by these electrons and detected by the phototubes is nearly proportional to the energy of the incident photon, from 50 Mev to at least 1.4 Bev. The spectrometer has been calibrated over this range of photon energies by the pulses produced by electrons of the same energies. Above 200 Mev the measured energy resolution of the spectrometer is 30% and is approximately independent of energy. For elimination of incident charged particles during the analysis of γ rays the spectrometer is operated in coincidence with a preceding photon-identifying counter system.

On the Foundation and the Applicability of Williams-Weizsäcker Method

The energy spectrum of the virtual photon field accompanied by a high energy charged particle which has been derived classically by Williams and W eizsiiclcer independently is derived here by the Feynman-Dyson method, and the equivalence between the Williams-Weizsiicker and the Feynman­ Dyson methods is verified in a general way when the El).ergy transferred from an incident charged particle is small. It is also qualitatively shown that the cross section derived by the Williams-Weizsiidcer method gives a correct order of magnitude. Let us consider a fast charged particle moving with velocity almost equal to light velocity. The field of this particle is almost identical with that of a set of photons with various frequencies. The electromagnetic action of this particle on another charged particle, say at rest, is equivalent to that of these virtual photons. This simplified method (W-W method) is often of great help and yields the same results as the Feynman-Dyson method (F-D method) in several cases, for example Bremsstrahlung3>, the pair production by a charged particle4> and the 1C production by p.-meson5>, etc. This agreement is based on the fact that the longitudinal and scalar photon fields accompanied by the incident charged particle is neglected as compared with the transverse one as was shown classically by Williams and also implicitly on the fact that the energy spectrum of the virtual trans­ verse photon derived by him is essentially the same as the one to be derived &om the F-D method. In our previous. paper6l on the electron pair creation by charged particles, we showed that the contribution to the cross section arises mainly from the process that the spin of the incident particle does not flip and the direction of polarization of the virtual photon is transverse, and the energy spectrum of the virtual transverse photon becomes the same as the classical one when the energy transferred &om the incident particle to the created pair is very small. This conclusion was derived essentially by separating .. the contributions to the cross section according to the directions of the polariza­ tion of the virtual photon. Therefore this separation procedure suggests the possibility of extending the above conclusion to more general cases. To generalize this conclusion &om the quantum electrodynamical point of view is the content of this paper.

The beta-ray sensitivity of autoradiographic stripping film.

In many investigations in which autoradiography is involved it is useful to know the sensitivity of the film. This sensitivity may be expressed as the average number of photographic grains in the film rendered developable by each incident charged particle. For example, in experiments in which radioactive iron (59Fe) is detected in individual red blood cells by means of an autoradiograph, it is of interest to know the actual 59Fe content of each cell. Knowing the sensitivity of the film, one may determine the quantity of 59Fe present from the number of developed grains above each cell. The purpose of the present investigation was to measure the sensitivity of a particular autoradiographic stripping film for three spectra of β-ray energies. The film tested was the widely used Kodak Autoradiographic Stripping Film (NT2a). Recently published work by Lamerton and Harriss (1954) indicates that in this film the number of grains per incident β particle is independent of exposure for grain densities below 30 grain...

Passage of Charged Particles through Plasma

The plasma has been treated phenomenologically as a homogeneous dispersive medium characterized by a dielectric constant which is a function not only of the frequency of the applied field (as in conventional dispersive media) but also on its wave number. The representation of plasma as a dispersive medium is subject to certain validity criteria which are satisfied for such typical cases as the ionosphere and electrical discharge through gases but is not satisfied for electrons in the conduction band of a metal. The passage of charged particles through plasma is investigated by means of straightforward application of Maxwell's equations for a dispersive medium. The Debye screening, which is applicable to the potential of an incident particle having velocity $V\ensuremath{\ll}{〈{v}^{2}〉}^{\frac{1}{2}}$ (where ${〈{v}^{2}〉}^{\frac{1}{2}}$ is the root mean square velocity of plasma electrons), loses its significance when $V\ensuremath{\gg}{〈{v}^{2}〉}^{\frac{1}{2}}$; and in the latter case, the potential decreases with the distance in accordance with an inverse cube law. The stopping power has been calculated for slow incident charged particles having $V\ensuremath{\ll}{〈{v}^{2}〉}^{\frac{1}{2}}$ and for fast particles having $V\ensuremath{\gg}{〈{v}^{2}〉}^{\frac{1}{2}}$ in a plasma comprising electrons distributed in accordance with Maxwell-Bolzmann and Fermi-Dirac statistics. For slow particles the results represent an extension of the formula of Fermi and Teller. An expression has been derived for the distribution of the polarization density in the space surrounding a moving particle.

The Čerenkov Effect and the Dielectric Constant

A quantum-mechanical theory of the \ifmmode \check{C}\else \v{C}\fi{}erenkov radiation is developed wherein the refractive medium is treated not as a continuum but as an aggregation of atoms. The atoms and the electromagnetic field are considered as forming a single system which interacts with an incident charged particle. The \ifmmode \check{C}\else \v{C}\fi{}erenkov radiation arises in first-order transitions induced by this interaction. The nature of this process suggests a quantum-mechanical definition of the dielectric constant with the aid of which the theory yields the well-known properties of the \ifmmode \check{C}\else \v{C}\fi{}erenkov radiation. The definition of the dielectric constant is shown to lead to the same expression for this quantity as is given by the Kramers-Heisenberg dispersion formula.

The emission of the negative system of nitrogen from the upper atmosphere and the significance of the twilight flash in the theory of the ionosphere

The cause of the emission of the negative band system of nitrogen from the upper atmosphere during twilight is investigated. A study is made of the two possible excitation mechanisms, N 2 ( X 1 Ʃ g + ) + hv →N 2 + ( B 2 Ʃ u + ) + e and N 2 + ( X 2 Ʃ g + ) + hv →N 2 + ( B 2 Ʃ u + ). It is shown that the latter is far more effective than the former, irrespective of the assumptions adopted regarding the solar flux in the unobservable spectral region. From the transition probability associated with it (which is evaluated in the appendix) combined with various intensity estimates, an upper limit is obtained for the number of N 2 + ions normally present in the E and F layers during twilight. It appears that N 2 + ions form but a minute fraction of the total ion content. The significance of this in the theory of the formation of the ionized layers is discussed. The simplest interpretation is that ionization of molecular nitrogen is unimportant; and a reasonable scheme that invokes only the ionization of oxygen atoms and molecules is available. However, by introducing certain arbitrary assumptions a more elaborate interpretation is conceivable so that the view that the E layer arises from the action of high-energy coronal photons, which ionize all atmospheric constituents, cannot be finally rejected. Various aspects of the layers are discussed, and observational and experimental work, which might yield evidence on the ionization mechanisms operative, is suggested. It is pointed out that the remarkable rarity of N 2 + ions proves conclusively that recombination between the charged particles present in the ionosphere cannot be the origin of the nocturnal radiation of the nitrogen band systems. On some occasions the resonance emission at twilight is of unusually high intensity. It is presumed that this is due to incident charged particles increasing the concentration of N 2 + ions. The possible contribution that these charged particles may make to the night-sky light by direct excitation collisions is briefly examined. Sunlit aurorae (which are essentially similar to the twilight flash) are also discussed.

THE ORIGIN OF THE NIGHT SKY LIGHT

Theories of the origin of the night sky light are discussed. It is pointed out that evidence from the absolute intensity, the altitude, the space and time variations, the correlations with magnetic activity, and the particular lines and bands appearing in the spectrum, indicates that the emission is not solely connected with the potential energy associated with the region of dissociated oxygen or with the ionized layers but partly arises from incident charged particles (such as produce aurorae). The suggestion is made that it is the action of the Störmer current that allows these particles to approach sufficiently close to the Earth at low latitudes.