Backward Emission Research Articles

Proton-nucleus interactions at 640 MeV accompanied by backward emission of energetic protons

Spectra of protons of energies between 50 and 145 MeV emitted from carbon have been measured at angles from 105° to 160° with respect to the 640 MeV proton beam. The measurements have been carried out both inclusively and in coincidence with protons emitted at forward angles up to ±40° with energies from 255 MeV to 330 MeV. This energy interval has been chosen in accordance with the kinematics of quasifree scattering on two-nucleon groups. Inclusive differential cross sections at 140° and coincidence cross sections at the angle pair (− 12°, 122°) have also been measured with Be, Al, Cu and Pb targets. The data have been compared with the predictions of several models.

Raman generated synchronous short optical pulses for laser-matter interaction diagnostics

Forward and backward stimulated raman scattering (SRS) emitted under 532 nm, 75 ps pulse excitation is amplified by a travelling-wave dye amplifier. Temporal behaviour of the emissions is investigated with a streak camera. The backward raman-strokes emission of ethanol at 633 nm (linewidth 0.15 nm) produces pulses as short as 15 ps. With a rhodamine 640 amplifier, peak power reaches 10 MW under 50 MW excitation.

Observation of correlation between two fast protons in proton-nucleus interactions at 640 MeV

The differential cross section for the backward emission of fast protons of energies from 50 to 145 MeV has been measured in coincidence with forward outgoing protons (255 to 330 MeV) in proton - nucleus interactions by a scintillation counter method. The experimental conditions correspond to the kinematics of the quasi-free scattering of incident protons on two nucleons within the target nucleus. The results are compared with the predictions of several models describing backward fast proton emission.

Cooperative cascade emission

An experimental and theoretical study has been performed on the generating process of a cascade emission in a sample three-level system where the ground and the highest excited levels have been initially brought into a coherent superposition state by two-proton excitation. Experimentally the forward and the backward emissions of the upper and the lower transitions of the cascade were observed in Li, and each of the emission lines showed a characteristic growth. In the theoretical analysis it is found that a dephasing in the prepared superposition state is required for the cascade emission as a coupled three level superradiance to grow. Using the concepts of delay time, threshold, lifetime, etc. of the cooperative cascade emission, the general behavior of the experimental results is explained.

Energy dependence of backward particle emission from high-energy Hadron-nucleus collisions

Angularand kinetic-energy distributions of protons and pious emitted in laboratory backward direction from collisions of 28.5 GeV/c protons with tan ta lum nuclei, were previously reported (1). There, the increase of invariant cross-section of backward emission of protons and pions with incident energy was also reported, comparing with experimental data at lower energies by BAT.DI~ et al. (2) and BAYUKOV et al. (3). However in the case of proton spectrum, we were obliged to compare between results obtained by different nuclei in a wide range of mass number, because the experiments by BAYUKOV cta l . were carried out with carbon, cupper and xenon as target nuclei. Therefore, in the previous paper we discussed incident-energy dependence of proton spectrum (1), assuming the target nucleus mass number dependence of invar iant cross-section being A! obtained by BAYUKOV et aL (s). This assumption made incident-energy dependence of proton spect rum somewhat uncertain. In the case of pion spectrum, this uncertainty is small enough because the experiments with lead target were available to compare with our results. In this paper results obtained for K--Ta collisions are reported. Because the measurements were carried out for 12.6 GeV/c K.Ta interaction under the same experimental conditions as 28.5 GeV/c P-Ta collisions, incident-energy dependence of both pion and proton emission spectra is derived more definitely between 12.6 and 28.5 GeV/e. The difference of incident particles (Kand P) has only little effect for backward particle emission.

Polarized muonic beam with variable helicity

A special mode of muonic beam with an average momentum of 21 GeV/ c and opposite helicity from 40 GeV/ c π-meson decay (the soft part of muonic spectrum corresponding to backward emission of muons in the pion rest-frame; negative polarization of muonic beam) and from 28 GeV/ c μ-meson decay (the hard part of the muonic spectrum, positive polarization of muonic beam) has been realized at the IHEP muon beam channel with the view of search for parity-nonconservation effects in deep inelastic μN-interactions. The beam channel is automatically retuned from the operational mode with one helicity to that with the opposite one in each five accelerator cycles during the time intervals between the cycles. Muonic polarization was measured with the help of the energy spectrum of electrons from μ→eνν̃ decay in-flight. In the momentum range 19–23 GeV/ c the difference in polarization of two muonic beams was λ = 0.80±0.15.

Simple theory concerning the emission efficiency and energy deposition of electrons produced in a slab exposed to 1.25 MeV gamma rays

A simple theory concerning the photon induced electron emission and absorption is derived, based on the diffusion model proposed by Bethe, Rose and Smith. Analytical expressions are presented for emission efficiency and energy deposition of electrons produced in a slab exposed to 1.25 MeV gamma rays and compared to experimental measurements and Monte Carlo calculations. Although the agreement between them is generally good, in view of the simplified model, a considerable difference is shown for the forward emission efficiency in the case of a very thick slab compared to the electron range and for the backward emission efficiency in the case of a relatively thin slab or of very low atomic number material.

Secondary-electron emission in the backward and forward directions from thin carbon foils traversed by 25-250 keV proton beams

Kinetic secondary-electron emission from both surfaces, i.e. in the backward and forward directions, is measured and compared with a proton beam (20-250 keV) traverses thin carbon foils. It is found that total forward emission is larger than backward emission by a factor of up to 1.55. Electron energy distributions, measured using a retarding field suggest that an essential contribution to the production of secondary electrons, emitted with energies down to a few eV, originates from binary collisions of the protons with individual electrons in the target.

Backward Emission of Relativistic Particles in the Laboratory System in 200 GeV Proton-Nucleus Collisions

In proton-nucleus collisions at 200 GeV studied in nuclear emulsion, relativistic particles are found to be emitted in the laboratory backward hemisphere frequently. These backward particles consist of pions and protons of relatively high energy. Emission of backward particles increases rapidly with the mass number of the target nucleus. Backward emission of such high energy particles is difficult to explain by the simple superposition of proton-nucleon elementary interactions.

Die Sekundärelektronen-Ausbeute verschiedener Materialien bei Beschuß mit leichten Ionen hoher Energie / Secondary Electron Yield from Various Materials under the Impact of Light Ions at High Energies

Abstract The backward emission of secondary electrons from thick targets of graphite, aluminum, copper, molybdenum and tantalum under the impact of protons, deuterons, 3 He-ions and a-particles has been measured for incident energies in the MeV-range. The data are discussed within the scope of theoretical considerations based on low-energy studies taking into account the contribution due to ;< 5-rays.

X-ray-induced electron emission from metals

Energy and angular distributions of electrons (energies greater than 5 keV) emitted from metals irradiated by photons in the x-ray energy range were measured with a lithium-drifted silicon detector. The data presented here characterize electron emission distributions for normal photon incidence. They provide a systematic set of absolute distributions for quantitative comparisons to theoretical treatments of the combined photon and electron transport process. X-ray bremsstrahlung spectra with mean photon energies of 30 and 54 keV were used to induce electron emission from aluminum, copper, silver, and tantalum. Angular distributions for the higher-Z materials are found to be nearly cosine distributions in both the forward and backward emission directions, while the distributions for lower-Z materials deviate from a cosine distribution, tending to be more isotropic. Energy distributions are observed to change very little as a function of emission angle. Energy and angular distributions calculated by Monte Carlo and analytic techniques show good correlation with the measured distributions. Calculated forward and back (2π) emission efficiencies agree with experimental values within the uncertainties of these quantities (±15 to 20%). The generally good agreement between the experimental and theoretical results establishes the validity of the present techniques for calculating high-energy (greater than 5 keV) x-ray-induced electron emission from metals.

Search for a ΔΔ(1236) component of the deuteron

The dp → nnp π +, dp → ppn π 0 and dp → ppp π - reactions at 3.33 GeV/ c deuteron momentum on the proton target were studied in order to search for a ΔΔ configuration in the deuteron. The frequent backward emission of the (p π +), (n π o ) and (p π −) systems in the deuteron rest frame was observed. The origin of the effect was analysed from the point of view of a possible ΔΔ admixture in the deuteron wave function. Some other sources which may contribute to the signal are indicated.

Use of electron and proton beams for production of very low frequency and hydromagnetic emissions

The feasibility of using helical partical beams (∼10 kev, 1 A) fired from orbiting satellites to produce backward Doppler-shifted cyclotron emission (very low frequency from electrons, hydromagnetic or micropulsations from protons) is considered. It is found that the frequency and position of emission can be controlled by choice of particle energy and by gyrophase modulation (or ‘rotation’) of the beams at the desired frequency. Phase spread of the prephased beams through both natural processes and limitations of accelerators, as well as through radiative instability of the beams, should not be serious. Emitted powers of tens of watts are expected.

Relative Positions of Fundamental and Second Harmonic Type III Bursts

Observations of the relative positions of fundamental and second harmonic bursts can be used to study refraction and scattering effects in the corona. Smerd, Wild and Sheridan have pointed out that the observed positions of type II bursts can be interpreted as favouring the backward emission of the second harmonic in a smooth corona. In this case the harmonic is seen after reflection from near the fundamental plasma level. Several other examples of type II and type III bursts have been reported which show this effect. We wish to present further evidence from a recent study of a large number of type III bursts observed with the 80 MHz heliograph and 158 MHz interferometer.

The Computation of Photon Radiation Induced Electron Emission

In recent years a variety of models have been developed for the computation of the photon radiation-induced electron emission from matter, ranging from pure Monte Carlo models, which while rigorous are quite costly for application as an engineering tool, to pure analytical models, which while convenient and inexpensive have strictly limited ranges of validity. The limitations of analytical models due to the neglect of Auger and secondary contributions to the emission current and due to the neglect of electron multiple scattering in the emission calculation are examined in this paper. A one-dimensional model is developed for predicting the relative magnitudes of the photoelectron, Compton, Auger, and secondary electron contributions to the emission current, and the model predictions are correlated with experimental data. It is concluded that a generally applicable emission model should include treatment of the Auger and secondary electrons as well as the photoelectrons and Compton electrons. The significance of electron multiple scattering in the calculation of the emission is examined through comparisons of analytical, Monte Carlo, and experimental data. It is concluded that while multiple scattering may be neglected in the calculation of forward emission efficiency, it must not be neglected in the calculation of backward emission effeciency or angular distribution of emission. An alternative emission computational model is introduced which utilizes a synthesis of analytical and Monte Carlo techniques. Comparisons of the model predictions to experimental data for forward and backward emission efficiency, energy spectrum, and angular distribution are included.

Collapsing objects and the backward emission of light

A general and comprehensive analysis is presented of the characteristics of light emitted from a collapsing, non-rotating gas within the framework of general relativity. The results are contrasted with the analogous special relativistic situation. It is found that there exist restrictions on the range and frequency shift of escaping light that are purely general relativistic. One particularly interesting result is that, unlike the special relativistic analog, light emitted from an optically thick collapsing gas will never be received blue-shifted by an observer.

Backward emission of neutrons from a shield irradiated with 660 MeV protons

Backward emission of neutrons from a shield irradiated with 660 MeV protons

Distributions angulaires par niveaux dans la réaction 28Si(n, α) 25Mg à 14.8 MeV

The 28Si(n, α) 25Mg reaction induced by 14.8 MeV neutrons has been studied with the help of the nuclear emulsion method. The angular distributions of the groups of alpha particles leaving the residual nucleus in its ground state and in its two first excited levels (0.584 and 0.976 MeV) have been obtained; they show a predominance of backward emission.