Engineering topics

Aprile, Elena

Publications and source records attributed to Aprile, Elena.

12 records

NASA NTRS1995

Vacuum ultraviolet light source utilizing rare gas scintillation amplification sustained by photon positive feedback

A source of light in the vacuum ultraviolet (VUV) spectral region includes a reflective UV-sensitive photocathode supported in spaced parallel relationship with a mesh electrode within a rare gas at low pressure. A high positive potential applied to the mesh electrode creates an electric field which causes drifting of free electrons occurring between the electrodes and producing continuous VUV light output by electric field-driven scintillation amplification sustained by positive photon feedback mediated by photoemission from the photocathode. In one embodiment the lamp emits a narrow-band continuum peaked at 175 nm.

Aprile, Elena↗

NASA NTRS1994

A high resolution liquid xenon imaging telescope for 0.3-10 MeV gamma-ray astrophysics: Construction and initial balloon flights

An instrument is described which will provide a direct image of gamma-ray line or continuum sources in the energy range 300 keV to 10 MeV. The use of this instrument to study the celestial distribution of the (exp 26)Al isotope by observing the 1.809 MeV deexcitation gamma-ray line is illustrated. The source location accuracy is 2' or better. The imaging telescope is a liquid xenon time projection chamber coupled with a coded aperture mask (LXe-CAT). This instrument will confirm and extend the COMPTEL observations from the Compton Gamma-Ray Observatory (CGRO) with an improved capability for identifying the actual Galactic source or sources of (exp 26)Al, which are currently not known with certainty. sources currently under consideration include red giants on the asymptotic giant branch (AGB), novae, Type 1b or Type 2 supernovae, Wolf-Rayet stars and cosmic-rays interacting in molecular clouds. The instrument could also identify a local source of the celestial 1.809 MeV gamma-ray line, such as a recent nearby supernova.

Aprile, Elena↗

NASA NTRS1993

A High Resolution Liquid Xenon Imaging Telescope for 0.3-10 MeV Gamma Ray Astrophysics: Construction and Initial Balloon Flights

The results achieved with a 3.5 liter liquid xenon time projection chamber (LXe-TPC) prototype during the first year include: the efficiency of detecting the primary scintillation light for event triggering has been measured to be higher than 85%; the charge response has been measured to be stable to within 0.1% for a period of time of about 30 hours; the electron lifetime has been measured to be in excess of 1.3 ms; the energy resolution has been measured to be consistent with previous results obtained with small volume chambers; X-Y gamma ray imaging has been demonstrated with a nondestructive orthogonal wires readout; Monte Carlo simulation results on detection efficiency, expected background count rate at balloon altitude, background reduction algorithms, telescope response to point-like and diffuse sources, and polarization sensitivity calculations; and work on a 10 liter LXe-TPC prototype and gas purification/recovery system.

Aprile, Elena↗

NASA NTRS1993

The polarization sensitivity of the liquid xenon imaging telescope

The properties and the expected performance of a liquid xenon (LXe) gamma ray imaging telescope, optimized for the MeV energy region, are presented. The unique potential of this telescope as a Compton polarimeter is particularly emphasized. Based on Monte Carlo simulations we show that the modulation factor is as high as 40 percent at 1 MeV with a detection efficiency close to 20 percent. These figures of merit combined with the excellent background suppression capability of the three dimensional position sensitive LXe detector yield sensitivity at the three sigma level to polarization fractions as small as a few percent for strong sources, even in a balloon flight.

Aprile, Elena↗

NASA NTRS1992

Development of a High Resolution Liquid Xenon Imaging Telescope for Medium Energy Gamma Ray Astrophysics

In the third year of the research project, we have (1) tested a 3.5 liter prototype of the Liquid Xenon Time Projection Chamber, (2) used a prototype having a 4.4 cm drift gap to study the charge and energy resolution response of the 3.5 liter chamber, (3) obtained an energy resolution as good as that previously measured by us using chambers with drift gaps of the order of millimeters, (4) observed the induction signals produced by MeV gamma rays, (4) used the 20 hybrid charge sensitive preamplifiers for a nondestructive readout of the electron image on the induction wires, (5) performed extensive Monte Carlo simulations to obtain results on efficiency, background rejection capability, and source flux sensitivity, and (6) developed a reconstruction algorithm for events with multiple interaction points.

Aprile, Elena↗

NASA NTRS1991

Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy

The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results were obtained on the following topics: (1) long distance drift of free electrons in LXe (purity); (2) scintillation light yield for electrons and alphas in LXe (triggering); and (3) ionization yield for electrons and gamma rays in LXe (energy resolution). The major results from the investigations are summarized.

Aprile, Elena↗

NASA NTRS1991

Particle astrophysics

The following scientific areas are reviewed: (1) cosmology and particle physics (particle physics and the early universe, dark matter, and other relics); (2) stellar physics and particles (solar neutrinos, supernovae, and unconventional particle physics); (3) high energy gamma ray and neutrino astronomy; (4) cosmic rays (space and ground observations). Highest scientific priorities for the next decade include implementation of the current program, new initiatives, and longer-term programs. Essential technological developments, such as cryogenic detectors of particles, new solar neutrino techniques, and new extensive air shower detectors, are discussed. Also a certain number of institutional issues (the funding of particle astrophysics, recommended funding mechanisms, recommended facilities, international collaborations, and education and technology) which will become critical in the coming decade are presented.

Sadoulet, Bernard↗

NASA NTRS1990

A study of the scintillation light induced in liquid xenon by electrons and alpha particles

The time dependence and the intensity of the primary scintillation light in liquid Xe excited by Am-241 alpha particles and Bi-207 internal-conversion electrons were measured at different electric-field strengths. High-purity liquid Xe was used to fill a parallel-plate ionization chamber equipped with a CaF2 window coupled to a UV-sensitive photomultiplier tube. The effect of the specific ionization density on the scintillation light and the time correlation between the light signal and the charge signal is reported. It is demonstrated that the fast scintillation signal produced in liquid Xe by an ionizing particle provides an ideal trigger in a detector aiming at a complete three-dimensional event reconstruction with an excellent background rejection capability.

Aprile, Elena↗

NASA NTRS1990

A gamma-ray imaging telescope based on liquid xenon

A liquid-xenon time projection chamber (TPC) is discussed in terms of its utility as an imaging telescope for high energy astrophysics. The concept exploits the efficiency of xenon as an ionization and scintillation medium for imaging astrophysical gamma-ray sources. The design fundamentally follows the approach of an ionization calorimeter functioning as a TPC dedicated to 3D tracking. A schematic diagram of the instrument is presented, and the device measures the ionization signals - resulting from gamma-ray interactions with xenon - on collection electrodes. The liquid xenon instrument permits the identification of the direction of the Compton electron and thereby determines the location of the source. The energy region of 1-30 MeV is covered by the instrument, and source localization is possible for the entire range.

Aprile, Elena↗

NASA NTRS1989

A liquid xenon imaging telescope for 1-30 MeV gamma-ray astrophysics

A study of the primary scintillation light in liquid xenon excited by 241 Am alpha particles and 207 Bi internal conversion electrons are discussed. The time dependence and the intensity of the light at different field strengths have been measured with a specifically designed chamber, equipped with a CaF sub 2 light transmitting window coupled to a UV sensitive PMT. The time correlation between the fast light signal and the charge signal shows that the scintillation signals produced in liquid xenon by ionizing particles provides an ideal trigger in a Time Projection type LXe detector aiming at full imaging of complex gamma-ray events. Researchers also started Monte Carlo calculations to establish the performance of a LXe imaging telescope for high energy gamma-rays.

Aprile, Elena↗

NASA NTRS1989

Development of liquid xenon detectors for gamma ray astronomy

The application of liquid xenon in high-resolution detectors for gamma-ray astronomy is being investigated. Initial results from a pulse-shape analysis of ionization signals in a liquid-xenon gridded chamber indicate that it is possible to achieve the necessary liquid purity for the transport of free electrons with simple techniques. The energy resolution has been measured as a function of applied electric field, using electrons and gamma-rays from a 207Bi source. At a field of 12 kV/cm the noise-substracted energy resolution of the dominant 569-keV gamma-ray line is 34 keV FWHM (full width at half maximum). This value is mostly determined by recombination of electron-ion pairs on delta-electron tracks.

Aprile, Elena↗

NASA NTRS1989

A liquid xenon imaging telescope for 1-30 MeV gamma-ray astrophysics

Aprile, Elena↗