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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
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NASA NTRS1983

Comparison of Photon-photon and Photon-magnetic Field Pair Production Rates

Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense ( 10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field ( gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

Burns, M. L.↗
NASA NTRS1983

Comparison of photon-photon and photon-magnetic field pair production rates

Neutron stars were proposed as the site of gamma-ray burst activity and the copious supply of MeV photons admits the possibility of electron-positron pair production. If the neutron star magnetic field is sufficiently intense (10 to the 12th power G), both photon-photon (2 gamma) and photon-magnetic field (gamma) pair production should be important mechanisms. Rates for the two processes were calculated using a Maxwellian distribution for the photons. The ratio of 1 gamma to 2 gamma pair production rates was obtained as a function of photon temperature and magnetic field strength.

Burns, M. L.↗
NASA NTRS1984

Means and method for calibrating a photon detector utilizing electron-photon coincidence

An arrangement for calibrating a photon detector particularly applicable for the ultraviolet and vacuum ultraviolet regions is based on electron photon coincidence utilizing crossed electron beam atom beam collisions. Atoms are excited by electrons which lose a known amount of energy and scatter with a known remaining energy, while the excited atoms emit photons of known radiation. Electrons of the known remaining energy are separated from other electrons and are counted. Photons emitted in a direction related to the particular direction of scattered electrons are detected to serve as a standard. Each of the electrons is used to initiate the measurements of a time interval which terminates with the arrival of a photon exciting the photon detector. Only the number of time intervals related to the coincidence correlation and of electrons scattered in the particular direction with the known remaining energy and photons of a particular radiation level emitted due to the collisions of such scattered electrons are counted. The detector calibration is related to the number of counted electrons and photons.

Srivastava, S. K.↗
NASA NTRS1991

Magnetic two-photon scattering and two-photon emission - Cross sections and redistribution functions

The magnetic two-photon scattering cross section is discussed within the framework of QED, and the corresponding scattering redistribution function for this process and its inverse, as well as the scattering source function are calculated explicitly. In a similar way, the magnetic two-photon emission process which follows the radiative excitation of Landau levels above ground is calculated. The two-photon scattering and two-photon emission are of the same order as the single-photon magnetic scattering. All three of these processes, and in optically thick cases also their inverses, are included in radiative transport calculations modeling accreting pulsars and gamma-ray bursters. These processes play a prominent role in determining the relative strength of the first two cyclotron harmonics, and their effects extend also to the higher harmonics.

Alexander, S. G.↗
NASA NTRS1978

The effective penetration distance of ultrahigh-energy electrons and photons traversing a cosmic blackbody photon gas

The effective average energy loss for an energetic (at least about 10 to the 15th power eV) particle traversing the microwave background radiation is evaluated. Electron-photon transformations by Compton scattering and pair production (in photon-photon collisions) are computed, with the energy loss considered to be carried away by the least energetic of the outgoing particles. Considering the most energetic of the outgoing particles as the high-energy particle, the relative probability and mean time for the particle to be a photon or electron (or positron) is evaluated. The effects of synchrotron losses for electrons and positrons are emphasized and compared with Compton losses to determine a critical energy (for given magnetic field) above which synchrotron losses dominate. Magnetic deflections are also treated for the case where the magnetic field is disordered, having a characteristic 'cell' size.

Gould, R. J.↗
NASA NTRS1988

Electron-Photon Coincidence Calibration Of Photon Detectors

Absolute and relative detector efficiencies measured. Apparatus uses coincidence-counting techniques to measure efficiency of ultraviolet or vacuum ultraviolet detector at very low radiation intensity. Crossed electron and atomic beams generate photons used to calibrate photon detector. Pulses from electron counter and photon detector(s) processed by standard coincidence-counting techniques. Used to calibrate other detectors or make absolute measurements of incident photon fluxes.

Srivastava, Santosh K.↗
NASA NTRS1973

Optical coupling system for photon-photon coincidence experiments.

An efficient optical coupling system is presented that promises to be useful in experiments where it is necessary to collect a large fraction of emitted photons, as in photon-photon coincidence experiments. Narrow bandpass interference filters are an integral part of the proposed system.

Masterson, K. D.↗
NASA NTRS1984

Photon-photon absorption and the uniqueness of the spectra of active galactic nuclei

The effects of the feedback of e(+)-e(-) pair reinjection in a plasma due to photon-photon absorption of its own radiation was examined. Under the assumption of continuous electron injection with a power law spectrum E to the minus gamma power and Compton losses only, it is shown that for gamma 2 the steady state electron distribution function has a unique form independent of the primary injection spectrum. This electron distribution function can, by synchrotron emission, reproduce the general characteristics of the observed radio to optical active galactic nuclei spectra. Inverse Compton scattering of the synchrotron photons by the same electron distribution can account for their X-ray spectra, and also implies gamma ray emission from these objects. This result is invoked to account for the similarity of these spectra, and it is consistent with observations of the diffuse gamma ray background.

Kazanas, D.↗
NASA NTRS1984

Photon-photon absorption and the uniqueness of the spectra of active galactic nuclei

The effects of the feedback of e(+)-e(-) pair reinjection in a plasma due to photon-photon absorption of its own radiation was examined. Under the assumption of continuous electron injection with a power law spectrum E to the minus gamma power and Compton losses only, it is shown that for gamma 2 the steady state electron distribution function has a unique form independent of the primary injection spectrum. This electron distribution function can, by synchrotron emission, reproduce the general characteristics of the observed radio to optical active galactic nuclei spectra. Inverse Compton scattering of the synchrotron photons by the same electron distribution can account for their X-ray spectra, and also implies gamma ray emission from these objects. This result is invoked to account for the similarity of these spectra, and it is consistent with observations of the diffuse gamma ray background.

Kazanas, D.↗
NASA NTRS1982

Photon bunching and the photon-noise-limited performance of infrared detectors

The photon-noise-limited performance of a radiation detector exposed to a thermal background of temperature T is analyzed by calculating the resulting specific detectivity. Both ideal photon detectors of arbitrary quantum efficiency eta and ideal thermal detectors of arbitrary emissivity eta are considered; and the effects of both shot noise and excess noise are taken into account. The relative contributions of these two sources depend on the quantum efficiency or emissivity of the system. For frequencies nu such that hnu/kT is much less than eta, excess noise can make an appreciable contribution to the total system noise. For the case of the detection of the narrow-band radiation, the specific detectivity is independent of eta in the limit hnu/kT is much less than eta.

Boyd, R. W.↗
NASA NTRS1989

Born-approximation and radiative corrections to pair production in photon-photon collisions

Aspects of pair production in photon-photon collisions, which can be of great importance in a variety of astrophysical settings, are examined. In particular, the correction associated with the use of Coulomb rather than plane-wave functions to describe the outgoing e(+) e(-) is evaluated. This is important only in the energy domain near threshold where e(+) e(-) are nonrelativistic, and the effect is evaluated. Because of the extreme simplicity of the nonrelativistic Born limit, the corresponding derivation is briefly outlined using noncovariant perturbation theory. The relative magnitude of the Born correction is comparable to radiative-correction effects. These effects can be evaluated easily in the nonrelativistic limit, and an approximate calculation is outlined.

Gould, Robert J.↗
NASA NTRS1992

EPR experiment and 2-photon interferometry: Report of a 2-photon interference experiment

After a very brief review of the historical Einstein, Podolsky, and Rosen (EPR) experiments, a new two-photon interference type EPR experiment is reported. A two-photon state was generated by optical parametric down conversion. Pairs of light quanta with degenerate frequency but divergent directions of propagation were sent to two independent Michelson interferometers. First and second order interference effectors were studied. Different than other reports, we observed that the second order interference visibility vanished when the optical path difference of the interferometers were much less than the coherence length of the pumping laser beam. However, we also observed that the second order interference behaved differently depending on whether the interferometers were set at equal or different optical path differences.

Shih, Y. H.↗
NASA NTRS1985

Study of photon emission by electron capture during solar nuclei acceleration. 3: Photon production evaluations

Lower limits of photon fluxes were evaluated from electron capture during acceleration in solar flares, because the arbitrary q sub c asterisk assumed in this work evolves very slow with velocity, probably much more slowly than the physical actual situation: in fact, more emission is expected toward the IR region. Nevertheless the authors claim to show that the factibility of sounding acceleration processes, charge evolution processes and physical parameters of the source itself, by the observational analysis of this kind of emissions. For instance, it would be interesting to search observationally, for the predicted flux and energy drift of F sub e ions interacting with the atomic 0 and F sub e of the source matter, or, even more feasible for the X-ray lines at 4.2 keV and 2.624 + 0.003 KeV from Fe and S ions in ionized Fe at T = 10 to the 7th power K respectively, the 418 + or - 2 eV and 20 + or - 4 eV lines of Fe and S in ionized Fe at 5 x 10 to the 6th power K, which are predicted from Fermi acceleration.

Perez-Peraza, J.↗
NASA NTRS1992

Magnetic photon splitting and gamma ray burst spectra

The splitting of photons into two photons becomes both possible and significant in magnetic fields in excess of 10(exp 12) Gauss. Below the threshold energy, 2m sub e c(exp 2) for single photon pair production, splitting can be an astronomically observable phenomenon evident in gamma ray burst spectra. In such circumstances, it was found that magnetic photon splitting reprocesses the gamma ray burst continuum by degrading the photon energy, with a net effect that is quite similar to pair cascade reprocessing of the spectrum. Results are presented for the spectral modifications due to splitting, taking into account the different probabilities for splitting for different polarization modes. Unpolarized and polarized pair cascade photon spectra form the input spectra for the model, which calculates the resulting splitting reprocessed spectra numerically by solving the photon kinetic equations for each polarization mode. This inclusion of photon polarizations is found to not alter previous predictions that splitting produce a significant flattening of the hard X ray continuum and a bump at MeV energies below a pair production turnover. The spectrum near the bump is always strongly polarized.

Baring, Matthew G.↗
NASA NTRS1991

Avalanche photodiode photon counting receivers for space-borne lidars

Avalanche photodiodes (APD) are studied for uses as photon counting detectors in spaceborne lidars. Non-breakdown APD photon counters, in which the APD's are biased below the breakdown point, are shown to outperform: (1) conventional APD photon counters biased above the breakdown point; (2) conventional APD photon counters biased above the breakdown point; and (3) APD's in analog mode when the received optical signal is extremely weak. Non-breakdown APD photon counters were shown experimentally to achieve an effective photon counting quantum efficiency of 5.0 percent at lambda = 820 nm with a dead time of 15 ns and a dark count rate of 7000/s which agreed with the theoretically predicted values. The interarrival times of the counts followed an exponential distribution and the counting statistics appeared to follow a Poisson distribution with no after pulsing. It is predicted that the effective photon counting quantum efficiency can be improved to 18.7 percent at lambda = 820 nm and 1.46 percent at lambda = 1060 nm with a dead time of a few nanoseconds by using more advanced commercially available electronic components.

Sun, Xiaoli↗
NASA NTRS1972

Calculation of the lunar photon albedo from galactic and solar proton bombardment.

The lunar photon albedo due to cosmogenic and primordial photon sources has been calculated. The individual photon leakage spectra from prompt photons produced by galactic cosmic ray (GCR) and solar cosmic ray (SCR) induced nuclear interactions, from the decay of GCR- and SCR-induced radionuclides, and from the decay of naturally occurring radionuclides are given. An approximate estimate of the leakage from the photon-electron cascade initiated by the decay of neutral pions is also given. Monte Carlo methods have been used to determine the nucleon-meson cascade, and discrete-ordinates methods were used for the photon and low-energy neutron transport.

Armstrong, T. W.↗