J. O. Kephart

Comparison of channeling radiation from diamonds with and without platelets

Channeling‐radiation spectra produced by planar‐channeled relativistic positrons and electrons in Type‐Ia and Type‐IIa diamonds have been measured. Because of the presence of platelets in the Type‐Ia diamond, some of the spectra measured for this crystal differ markedly from their counterparts for the Type‐IIa diamond. These striking differences illustrate the potential applications of channeling radiation as a diagnostic tool for studies of impurities or defects in crystals.

Electron and positron channeling radiation from type-Ia and type-IIa diamonds☆

Abstract Planar channeling radiation spectra have been obtained from type-IIa and type-Ia diamonds with 54.5 and 30.5 MeV electrons and with 54.4 MeV positrons. Type-IIa diamonds are relatively free of impurities while Type-Ia diamonds contain “platelet defects” [N atoms bonded in the (100) plane]. For platelet free (type-IIa) diamond, theoretical calculations are found to fit experimental results quite well for electron channeling radiation. However, significant discrepancies (~ 5%) exist between the theoretical predictions and the positron data. Measurements on a type-Ia diamond show large differences in the planar channeling radiation spectra which are anisotropic and which depend upon whether electrons or positrons are used as a probe.

On the dependence of electron planar channeling radiation upon lattice vibration amplitude

Abstract The energies of photons arising from transitions between low-lying bound states of channeled electrons are sensitive to the lattice vibration amplitude. It is shown that calculations incorporating accepted values of Debye temperatures for C (diamond), Si, Ge, and GaAs lead to excellent agreement with experiment for all cases, save Si. Channeling radiation data from Si are then used to derive a Debye temperature which is shown to be consistent with temperature dependent measurements in both planar and axial channeling.

Electron channeling radiation from diamonds with and without platelets

Channeling‐radiation spectra produced by planar‐channeled, 30.5‐MeV electrons in Type‐Ia and Type‐IIa natural diamonds have been measured and are compared with previous results for 54.5‐MeV electrons. Because of the presence of platelets precipitated along the (100) planes in the Type‐Ia diamond, the energies of the (100) spectral peaks are shifted downward relative to those for the Type‐IIa diamond. We have developed a model to explain this effect.

Positron and electron channeling radiation from germanium

Abstract Channeling-radiation spectra have been obtained from a germanium crystal with ≈54.3 MeV positrons and electrons and with 16.9 MeV electrons. Theoretical calculations were performed and are found to agree reasonably well with the experimental results. When the emission spectra for (110) planar channeling in diamond, silicon, and germanium are compared, the corresponding lines for both positrons and electrons are found to be lowest in energy for silicon.

Electron and positron planar channeling radiation from diamond

Abstract Channeling-radiation spectra have been obtained from a diamond with ≈ 54.5 MeV electrons and positrons. Theoretical calculations are found to fit the experimental results well for electrons, but significant discrepancies exist between theoretical predictions and the positron data.

Channeling-radiation measurements at Lawrence Livermore National Laboratory

In the last few years, the amount and quality of channeling-radiation data have increased enormously, owing largely to much improved experimental capabilities. Current results included improved interplanar potentials for diamond, the description of the effect of platelets in diamond as an average thermal vibration, an improved determination of the Debye temperature of silicon, an improved determination of the thermal-vibration amplitude of LiD, and the demonstration that LiF crystal structures can survive intense electron bombardment. 40 references, 8 figures.

Planar channeling radiation from relativistic positrons and electrons in LiF

Abstract Channeling radiation has been measured for planar-channeled 54- and 83-MeV positrons and 17-, 31-, and 54-MeV electrons in the ionic crystal LiF. The results are shown to be in reasonable, but not perfect, agreement with the results of many-beam calculations based upon a model of the crystal as an array of isolated Li+ and F− ions.

Characteristics and Applications of Radiation from Channeled Particles

Charged particles channeled in crystals traverse nearly periodic trajectories, which produce radiation that has spectral peaks at photon energies determined by the particle energy and the periodicity of the motion. This effect is analogous to the radiation enhancement that occurs when a magnetic undulator is placed in a storage ring. For ¿=10 to 100, the period of the motion is several hundred to several thousand lattice sites in the crystal, so that the forward. directed emission is in the soft-to-hard x-ray portion of the spectrum. Channeling radiation can be used to study the channeling phenomenon, to investigate the properties of crystals in which channeling occurs, and as a source of x-rays.

The Study of Material Properties Using Channeling Radiation

A possible application for channeling radiation is for the investigation of properties of crystals in which the channeling occurs. In this paper we present some general considerations concerning channeling radiation as a measurement technique and describe several specific exakples.