Photoelectric energy spectrometer Patent
Spectrometer using photoelectric effect to obtain spectral data
Becker, R. A.↗
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Laser extensometer
Drift-compensated and intensity-averaged laser-based system uses optical and photoelectric effects for precise measurement of small thermally-induced size changes. Final output signal is directly proportional to size of sample shadow and independent of laser intensity, detector dark current, and lateral motion of sample.
Stocker, P. L.↗
Gamma-ray astronomy: Nuclear transition region
This monograph reviews the major theoretical and experimental efforts made during the past 12 years in gamma-ray astronomy over the energy range from 10 keV to about 100 MeV, where nuclear-transition lines are expected. Early attempts to detect celestial gamma rays are recounted, mechanisms of gamma-ray line and continuum production are examined, and formulas giving the various possible differential gamma-ray spectral shapes are provided. Predicted fluxes are discussed for solar gamma rays as well as for gamma emission from supernova remnants, supernovae, neutron stars, flare stars, the galactic core and disk, black holes, and diffuse sources. Gamma-ray interactions with matter are analyzed, particularly the photoelectric effect, Compton scattering from free electrons, and pair production in nuclear fields. Significant results are summarized for observations of gamma rays from the sun as well as from point and extended sources within and beyond the Galaxy, including diffuse fluxes and transient gamma-ray bursts. Factors pertaining to the design of gamma-ray astronomy experiments are considered, especially detector background limitations, gamma-ray production within instruments, and present-day detection methods.
Chupp, E. L.↗
The electric potential of particles in interstellar space released from a nuclear waste payload
Mechanisms for charging a grain in the interplanetary medium include: (1) capture of solar wind electrons; (2) capture of solar wind protons; (3) ejection of electrons through the photoelectric effect due to the solar radiation; (4) escape of beta particles from beta emitters in the grain; and (5) escape of alpha particles from alpha emitters in the grain. The potentials on both nonradioactive and radioactive grains are considered with relation to particle size and time, and the distance from the Sun. Numerical results are presented where the waste mix is assumed to be PW-4b.
Williams, A. C.↗
Performance characteristics of CCDs for the ACIS experiment
The search for the optimum CCD to be used at the focal surface of the Advanced X-ray Astrophysics Facility (AXAF) is described. The physics of the interaction of X-rays in silicon through the photoelectric effect is reviewed. CCD technology at the beginning of the AXAF definition phase is summarized, and the results of the CCD enhancement program are discussed. Other sources of optimum CCDs are examined, and CCD enhancements made at MIT Lincoln Laboratory are addressed.
Garmire, Gordon P.↗
The Gamma-Ray Observatory
The scientific goals and the design of the NASA Gamma-Ray Observatory (GRO), planned for launch in mid-1990, are described together with the experiments to be performed on the GRO mission and the instruments to be flown on the Observatory. GRO contains a complement of four instruments to span the spectrum from 0.03 to 20,000 MeV in energy, three of which are optimized to make gamma-ray observations using either the photoelectric effect, the Compton scatter, or the pair production processes; the fourth instrument is optimized for high-sensitivity observations of transient events and time-variable sources. The instruments are the Oriented Scintillation Spectrometer Experiment, the Compton Telescope, the Energetic Gamma-Ray Experiment Telescope, and the Burst and Transient Source Experiment.
Kniffen, Donald A.↗
PAHs molecules and heating of the interstellar gas
Until now it has remained difficult to account for the rather high temperatures seen in many diffuse interstellar clouds. Various heating mechanisms have been considered: photoionization of minor species, ionization of H by cosmic rays, and photoelectric effect on small grains. Yet all these processes are either too weak or efficient under too restricting conditions to balance the observed cooling rates. A major heat source is thus still missing in the thermal balance of the diffuse gas. Using photoionization cross sections measured in the lab, it was shown that in order to balance the observed cooling rates in cold diffuse clouds (T approx. 80 K) the PAHs would have to contain 15 percent of the cosmic abundance of carbon. This value does not contradict the former estimation of 6 percent deduced from the IR emission bands since this latter is to be taken as a lower limit. Further, it was estimated that the contribution to the heating rate due to PAH's in a warm HI cloud, assuming the same PAH abundance as for a cold HI cloud, would represent a significant fraction of the value required to keep the medium in thermal balance. Thus, photoionization of PAHs might well be a major heat source for the cold and warm HI media.
Verstraete, Laurent↗
A rare gas optics-free absolute EUV photon spectrometer for solar system studies
We have developed a prototype spectrometer for space applications which require long term absolute EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer operating at a few eV, and followed by an electron multiplying detector, pulses due to individual electrons are counted. The overall efficiency of this process is essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided.
Daybell, M. D.↗
A rare gas optics-free absolute photon flux and energy analyzer to provide absolute photoionization rates of inflowing interstellar neutrals
A prototype spectrometer has been developed for space applications requiring long term absolute EUV photon flux measurements. The energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer, followed by an electron multiplier detector, pulses due to individual electrons are counted. The overall efficiency of this process can be made essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided. A very important feature of this approach is its freedom from the problem of overlapping spectral orders that plagues grating EUV spectrometers. An instrument with these features has not been flown before, but is essential to further advances in our understanding of solar EUV flux dynamics, and the coupled dynamics of terrestrial and planetary atmospheres. The detailed characteristics of this optics-free spectrometer are presented in the publications section.
Judge, Darrell L.↗
A rare gas optics-free absolute photon flux and energy analyzer for solar and planetary observations
We have developed a prototype spectrometer for space applications requiring long term absolute EUV photon flux measurements. In this recently developed spectrometer, the energy spectrum of the incoming photons is transformed directly into an electron energy spectrum by taking advantage of the photoelectric effect in one of several rare gases at low pressures. Using an electron energy spectrometer, followed by an electron multiplier detector, pulses due to individual electrons are counted. The overall efficiency of this process can be made essentially independent of gain drifts in the signal path, and the secular degradation of optical components which is often a problem in other techniques is avoided. A very important feature of this approach is its freedom from the problem of overlapping spectral orders that plagues grating EUV spectrometers. An instrument with these features has not been flown before, but is essential to further advances in our understanding of solar EUV flux dynamics, and the coupled dynamics of terrestrial and planetary atmospheres. The detailed characteristics of this optics-free spectrometer are presented in the publications section.
Judge, Darrell L.↗
Anatomy of the Photodissociation Region in the Orion Bar
Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photo-dissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(l) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.
Tielens, A. G. G. M.↗
Charging of Single Micron Sized Dust Grains by Secondary Electron Emission: A Laboratory Study
We present the details of a new laboratory study whose objective is to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. Specifically, to investigate under what conditions and to what extent do particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and ultraviolet radiation environment The emphasis is the study of the two charging mechanisms, secondary emission of electrons and photoelectric effect. The experiment uses a technique known as electrodynamic suspension of particles. With this technique, a single charged particle is electrodynamically levitated and then exposed to a controlled environment. Its charge to mass ratio is directly measured. Viscous drag measurements and the light scattering measurements characterize its size and optical characteristics. The environment to which the particle is expose may consist of room temperature and pressure or a rarefied atmosphere where only one major gaseous constituent is present, or, as in this case, a vacuum environment under electron bombardment or UV radiation . In addition, the environment can be cycled as part of the experiment. Therefore, using this technique, a single particle can be repeatedly exposed to a controlled environment and its response measured, or a single particle can be exposed to similar environments with minor differences and its response measured as a function of only the changed environmental conditions.
Spann, James F., Jr.↗
Preliminary Results from a Laboratory Study of Charging Mechanisms in a Dusty Plasma
A laboratory investigation has been developed to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. The intent is to investigate under what conditions particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and ultraviolet radiation. Primary emphasis is on two charging mechanisms: secondary emission of electrons and the photoelectric effect. Preliminary results are presented.
Venturini, Catherine C.↗
Preliminary Results from a Laboratory Study of the Charging Mechanisms of Particles in a Dusty Plasma
A laboratory study has been developed to experimentally study the interaction of micron sized particles with plasmas and electromagnetic radiation. The intent is to investigate under what conditions particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and ultraviolet radiation. Primary emphasis is on two charging mechanisms: secondary emission of electrons and the photoelectric effect. Preliminary results are presented.
Venturini, Catherine C.↗
Infrared Emission and Thermal Processes in Spiral Galaxies
In this research we constructed theoretical models of the infrared and submillimeter line and continuum emission from the neutral interstellar medium in the Milky Way and external galaxies. The model line intensities were compared to observations of the Galactic disk and several galaxies to determine the average physical properties of the neutral gas including the density, temperature, and ultraviolet radiation field which illuminates the gas. In addition we investigated the heating mechanisms in the Galactic disk and estimated the emission rate of the [C 11] 158 micrometer line as a function of position in the Galaxy. We conclude that the neutral gas is heated mainly by the grain photoelectric effect and that a two phase (CNM+WNM) is possible between Galactic radii R = 3 kpc and R = 18 kpc. Listings of meeting presentations and publications are included.
Mundy, Lee↗
The Electrostatic Levitation Facility at NASA's Marshall Space Flight Center
Containerless processing is an important area of research in materials science. Electrostatic levitation (ESL) represents an emerging technology which permits containerless processing in a vacuum environment. NASA's Marshall Space Flight Center (MSFC) established a levitation facility to provide a critical resource to the microgravity materials science research community to continue and enhance ground-based research in the support of the development of flight experiments during the transition to Space Station. During ESL processing, charged specimens are levitated in the electrostatic field produced by the system's electrodes. Three sets of positioning electrodes represent the heart of the MSFC system. Two dual-axis position sensitive detectors provide input for the PID control-loop computer. Sample position is maintained by adjusting the control voltages for the power supplies of the positioning electrodes. A UV source refreshes the charge on specimens during processing via the photoelectric effect. Lasers permit sample heating independent of positioning. The processing chamber typically operates under vacuum condition approximately = 10(exp -7) Torr. Electrostatic levitation provides a materials science research tool for investigations of refractory solids and melts. Topics of investigation include thermophysical properties, phase equilibria, metastable phase formation, undercooling and nucleation, time-temperature-transformation diagrams and other aspects of materials processing. Current capabilities and recent results of processing studies for metals, alloys and oxides will be reviewed.
Rogers, Jan R.↗
Heating And Cooling of the Interstellar Medium
This talk will review the various heating and cooling processes in the interstellar medium. The most important heating processes include the photoelectric effect on dust grains and PAH molecules. Cooling of the gas in the interstellar medium is dominated by emission in the far infrared fine structure lines of OI, CII, SiII, and CI, and the rotational transitions of CO. Many of these lines have been observed from air borne platform, in particular the Kuiper Airborne Observatory. Which of these heating and cooling processes dominates in a given region depends on its physical and especially chemical conditions, which in turn depend themselves on the interstellar UV radiation field. As a result of the interplay of these processes, the interstellar medium is organized in various structures with distinctly different physical conditions (ie., temperature, density, and degree of ionization). Over the last decade, the dominant cooling lines of the neutral interstellar medium have been studied using the Kuiper Airborne Observatory. Because of sensitivity, these observations have concentrated on dense regions illuminated by strong UV fields from nearby stars, so-called Photo Dissociation Regions (PDRs). These observations allow us to study in detail the interaction of UV photons and the interstellar gas and dust. Detailed theoretical models have been developed for PDRs. These will be reviewed and compared to the observations. Finally, anticipated crucial results of future space-based missions (SIRTF, ISO) will be pointed out.
Tielens, Alexander G. G.↗
Cooling of the Interstellar Medium
This talk will review the various heating and cooling processes in the interstellar medium. The most important heating processes include the photoelectric effect on dust grains and PAH molecules. Cooling of the gas in the interstellar medium is dominated by emission in the far infrared fine-structure lines of OI, CII, SiII, and CI, and the rotational transitions of CO. Which of these heating and cooling processes dominates in a given region depends on its physical and especially chemical conditions, which in turn depend themselves on the interstellar UV radiation field. As a result of the interplay of these processes, the interstellar medium is organized in various structures with distinctly different physical conditions (i.e., temperature, density, and degree of ionization). The dominant cooling lines of the neutral interstellar medium have been studied using the Kuiper Airborne Observatory, balloon-borne instruments, and recently space-based missions (IRTS, ISO). These observations have concentrated on dense regions illuminated by strong UV fields from nearby stars, so-called PhotoDissociation Regions (PDRs). These observations allow us to study in detail the interaction of UV photons observations allow us to study in detail the interaction of UV photons and the interstellar gas and dust. Detailed theoretical models have been developed for PDRs. These will be reviewed and compared to the observations. Recent space based missions have measured the dominant cooling line of the galaxy, the [CII] 158 micron line. These observations and their implications will be reviewed.
Tielens, A. G. G. M.↗