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Results are presented for the absolute bremsstrahlung yields at a backward angle of 135°from 53 keV electrons on gold targets of thickness ranging from 66 to 28 976 g / cm 2 . The target thicknesses range from thin enough for single collision conditions to apply to thick enough for the yield to be dominated by multiple interactions. The results for all thicknesses are found to be in very good agreement with the predictions of PENELOPE, a Monte Carlo program which is based on ordinary bremsstrahlung and does not include any contribution from polarization bremsstrahlung. Absolute doubly differential cross sections are computed for the thinnest targets. The results are compared with two theoretical free atom cross section models, one for ordinary bremsstrahlung only and the second, the stripping approximation, for total bremsstrahlung including a contribution from polarization bremsstrahlung. The results agree with the predictions of ordinary bremsstrahlung for radiated photon energies from 5 to 53 keV and do not agree with the predictions of the stripping approximation. The conclusion, in contrast with recent free gas atom results, is that the absolute yields from solid films are well described by ordinary bremsstrahlung and do not require any additional polarizational bremsstrahlung contribution.

Zinc dialkyldithiophosphates (ZDDPs) are one of the most common anti-wear additives present in commercially-available motor oils. The ZDDP concentrations of motor oils are most commonly determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). As part of an undergraduate research project, we have determined the Zn concentrations of eight commercially-available motor oils and one oil additive using neutron activation analysis (NAA), which has potential for greater accuracy and less sensitivity to matrix effects as compared to ICP-AES. The 31 P nuclear magnetic resonance ( 31 P-NMR) spectra were also obtained for several oil additive samples which have been heated to various temperatures in order to study the thermal decomposition of ZDDPs.

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Experimental results are presented comparing the intensity of the bremsstrahlung produced by electrons with initial energies ranging from 10 to 20-keV incident on a thick Ag target, measured at forward angles in the range 0˚ to 55˚. When the data are corrected for attenuation due to photon absorption within the target, the results indicate that the detected radiation is distributed anisotropically only at photon energies, k, that are approximately equal to the initial energy of the incident electrons, E o . The results of our experiments suggest that as k /E o → 0, the detected radiation becomes essentially isotropic due primarily to the scattering of electrons within the target. A comparison to the theoretical work of Kissel et al. [6] suggests that the angular distribution of bremsstrahlung emitted by electrons incident on thick targets is similar to the angular distribution of bremsstrahlung emitted by electrons incident on free-atom targets only when k /E o ≈1. The experimental data are also in approximate agreement with the angular distribution predictions of the Monte Carlo program, PENELOPE.

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We performed experiments in which both open-ended and closed carbon nanotubes were exposed to 2.46 GHz microwaves over the course of several irradiation and cooling cycles at a pressure of ~ 10-6 torr. The spectra of the radiation emitted from the nanotubes indicate that the intensity of the emitted radiation with wavelengths of 650–1000 nm increased during the irradiation cycles. However, the intensity of the radiation emitted from untreated nanotubes increased substantially more than the intensity of the radiation emitted from nanotubes that had been chemically treated in order to open nanotube ends. As open-ended nanotubes have a lower work function than closed nanotubes, and as nanotube ends are known to open as they are heated, our results suggest that the mechanism responsible for the emission of infrared, visible and ultraviolet radiation from carbon nanotubes exposed to microwaves is field emission-induced luminescence.