摘要:

The optical properties of area detectors used in conjunction with Fabry–Pe´rot interferometers are analyzed. A system using a charge‐coupled device as a detector for Brillouin spectroscopy is described. With a 2 pass+2 pass tandem system the finesse ranges from 50 to 63. With a collection time of about 2.5 min, the intensity of the surface Rayleigh mode and the bulk acoustic modes of Si are comparable to those obtained by scanning for many hours. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147101

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate an optical method for the selective detection of Cu(II) ions in water using time‐resolved fluorescence resonance energy transfer from the dye rhodamine 800 encapsulated in a sensor. In comparison to copper, quenching by other metal ions such as cobalt, nickel, and chromium is shown to be negligible. The experimental arrangement incorporates picosecond diode laser excitation and time‐correlated single‐photon counting for detection. Down to 5 mM of copper deposited on the sensor can be measured and a linear response is obtained up to at least 50 mM. A lower limit of detection for the sensor in the region of 10 ppb is shown to be readily achievable with good resolution. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147090

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An apparatus for measuring absolute cross sections due to electron‐impact excitation out of the metastable levels of rare‐gas atoms via the optical method is described with the focus specifically on excitation out of the 2 3Smetastable helium level. The metastable helium target (He*) is prepared by charge exchange between 1.6 keV He+ions and cesium vapor. An electron beam crosses the fast metastable beam target at a right angle and the fluorescence is collected at right angles to both beams. The charge transfer reaction produces He atoms mainly in then=2 He levels. Because the target contains a negligible ground state He fraction, we can measure excitation cross sections from excitation threshold up to an arbitrarily high energy (keV regime) which represents a major improvement over previous metastable excitation cross sections measurements. The He* target density is extremely small (∼106atoms/cm3) yielding minuscule signal rates. We describe steps taken to maximize the signal‐to‐noise ratio. We discuss the implications of using a fast beam target including both the finite flight time of the excited atoms across the light gathering region and the reduction of the cascade contributions to the apparent cross sections. A discussion of the identification and elimination of various systematic effects is also given. To measure absolute cross sections, we explicitly determine the spatial distributions of both the electron and metastable beams, as well as the spatially dependent response of the fluorescence gathering region. We determine the absolute flux of fast metastable atoms using a thermal detector calibrated with a He+ion beam. As examples, we present absolute cross sections for excitation out of the 2 3Smetastable level into the 3 3Dand 4 3Dlevels. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147102

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A crossed‐beams experiment designed to study charge‐changing collisions between singly charged ions has been modified to extend its applicability to collisions between multiply charged ions in a broader range of collision energies. Computer simulations of the beam transport system and the new electrostatic analyzing units are presented. The ion‐optical predictions are tested experimentally. A data acquisition system that allows measurements of angular differential cross sections in ion–ion collisions is described. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147103

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have constructed ion optics which, when interfaced with a channel electron multiplier (CEM), make possible quantitative measurements of positive and negative ion fluxes. We describe the design and operation of a detection system using these optics and present a calibration of the CEM for low energy (0.2–8.7 keV) positive and negative oxygen ions. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147104

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

To develop a high‐current electron gun for an induction linac, a prototype of a Pierce‐type electron gun using planar 12‐mm‐diam lanthanum hexaboride (LaB6) is studied as a thermionic emitter at high current densities. The cathode is heated up to temperatures of 1750 °C by electron bombardment and thermal radiation from a tungsten heater. The heater that has the highest temperature in the gun is thermally isolated from the outer vacuum chamber with heat shields. The bombardment voltage of ∼1 kV is typically applied to a gap between the cathode and the heater. The gun has been operated up to voltages of 55 kV, obtaining a maximum current density of 20 A/cm2with a pulse width of 250 ns at a cathode temperature of 1600 °C. High‐voltage pulsing results show that the gun, with applied voltages of over 40 kV, is operated in space‐charge‐limited region at temperatures of over 1600 °C; also it is operated in a temperature‐limited region at temperatures of less than 1500 °C. An effective work function of 2.68 eV is obtained. The cathode, when heated up to 1600 °C, emits over 7 A of electrons with a ∼20% reduction after 850 h of continuous operation. These measurements were made between vacuum pressures of 10−6and 10−7Torr. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147105

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A very small Fermi‐type neutron chopper fashioned by cutting slots in a boron nitride cylinder was developed for use with a source of thermal and cold (subthermal velocity) neutrons. The original goal was to characterize spectra emerging from glass capillary fibers of less than 1 mm diameter, but other applications became apparent. For approximately 1 m flight paths, conventional nuclear electronics had to be adapted to the millisecond flight times. Both time‐to‐amplitude converter and multiscaling time‐data storage methods were used. Data corrections for the particular geometry are reviewed and applied to the present geometry. Among examples of its potential use, the spectrum of a newly installed cold source was measured. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147106

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A Nuclear particle scintillation imaging system, developed earlier by the authors, has been upgraded and tested for its radiographic performance using a low intensity Pu–Be (∼107n/s) source. The main objective of this work was to check the feasibility of a neutron radiography facility using a low intensity Pu–Be isotopic source and evaluate its performance. To accumulate the neutron exposure, an on‐line frame integration method was used for imaging static objects. Because integrated images from the system were mottled and poor in contrast, a video image processing system was employed to enhance the quality of the integrated images. Significant improvements in image quality are seen, when image processing techniques such as smoothing, contrast stretching, edge enhancement, and histogram equalization are employed. This article provides an overview of the improvement in the image quality consequent to implementation of image processing techniques. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147107

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The performance of a scintillating fiber (2 mm diameter) position sensitive detector (4.8×4.8 cm2active area) for the single bremsstrahlung luminosity monitor at the VEPP‐2M electron‐positron collider in Novosibirsk, Russia is described. Custom electronics is triggered by coincident hits in theYandYplanes of 24 fibers each, and reduces 64 photomultiplier signals to a 10‐bit (X,Y) address. Hits are accumulated (10 kHz) in memory and display (few Hz) the VEPP‐2M collision vertex. Fitting the strongly peaked distribution (∼3–4 mm at 1.6 m from the collision vertex of VEPP‐2M) to the expected QED angular distribution yields a background in agreement with an independent determination of the VEPP‐2M luminosity. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147108

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A computer‐controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio‐frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument’s capabilities. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147109

出版商:AIP    

年代:1996

数据来源: AIP