摘要:

A laboratory spectrometer designed for routine extended x‐ray absorption fine structure (EXAFS) measurements in dispersive mode is described. Factors determining energy range and resolution are detailed. An empirical energy calibration procedure is proposed. EXAFS spectra obtained for copper and zirconium metal foil and molecular complex ZrOCl2compare favorably with data obtained using a conventional synchrotron facility.

ISSN:0034-6748    

DOI:10.1063/1.1144909

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The fundamental studies of a repetitive soft flash x‐ray generator having a high‐durability diode for high‐speed radiography in biomedical and technological fields are described. This generator consisted of the following essential components: a constant negative high‐voltage power supply, a line‐type high‐voltage pulser with two 10 m coaxial‐cable condensers, each with a capacity of 1.0 nF, a thyratron pulser as a trigger device, an oil‐diffusion pump, and a flash x‐ray tube. The x‐ray tube was of a diode type which was evacuated by an oil‐diffusion pump with a pressure of approximately 6.7×10−3Pa and was composed of a planar tungsten anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The space between the anode and cathode electrodes (AC space) could be regulated from the outside of the tube. The two cable condensers were charged from −40 to −60 kV by a power supply, and the output voltage was about −1.5 times the charged voltage. Both the first peak voltage and current increased according to increases in the charged voltage, and the maximum values of the voltage and current were about 90 kV and 0.72 kA, respectively. The pulse widths had values of less than 100 ns, and the maximum x‐ray intensity was approximately 1.1 &mgr;C/kg at 0.5 m per pulse. The repetition rate was less than 54 Hz, and the maximum focal spot size was about 2.0×2.5 mm.

ISSN:0034-6748    

DOI:10.1063/1.1144910

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present experimental results about a position‐sensitive &ggr; detector with a diameter of 75 mm, a position resolution of 3.5 mm, and a good linearity for 662 keV &ggr; rays using a NaI or plastic scintillator. The detector is designed to solve some of the Anger camera’s readout problems and to be as close as possible to the sample in a 90° perturbed angular correlation experiment. It might substitute up to 100 smaller detectors with the same angular resolution or could cover 70% of the 4&pgr; geometry in crystal ball experiments. The setup allows easy and fast signal processing in angular correlation experiments due to the use of point symmetry in the experiment as well as in data analysis.  

ISSN:0034-6748    

DOI:10.1063/1.1144911

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method for using inexpensivePINphotodiodes for applications involving gamma radiation detection over several orders of magnitude in intensity is discussed. A description of the response characteristics of thePINdiode and its associated electronics is presented. Application of the detector to a radioactivity transporter, radioisotope delivery system, radiochemical processor, and radio‐high pressure liquid chromatograph is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144912

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The thermally induced change of the birefringence of a high‐birefringence fused‐silica optical fiber, when exposed to a proton beam (2 MeV, 0.5–44 nA, 5‐mm spot diameter), was measured with a fiber‐optic polarimetric sensor. A short length (5 cm) of 125‐&mgr;‐diam, single‐mode, polarization‐maintaining optical fiber was put orthogonally to the beaminvacuoand the linear polarization of a HeNe laser beam launched into the fiber was analyzed by a polarizer and recorded by a photodetector. The response of the sensor both to a continuous and to a modulated proton beam was studied. The photodetector output, which varies with the cosine of the induced relative phase retardance between the fiber eigenmodes, provides a dc or an ac (10 Hz test modulation frequency) measurement of the beam current. This device acts as a proton beam intensity monitor, with minimum beam perturbation and a sensitivity of 0.1 nA. Its possible use also as a beam position monitor or as a wire‐scanner beam profiler is suggested.

ISSN:0034-6748    

DOI:10.1063/1.1144913

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this article a novel design for signal anodes for ultrafast microchannel plate detectors is introduced. A detector assembly was designed and built with an impedance‐matched transition line (50 &OHgr; line resistance) from anode to cable connector which is considerably smaller than other, commercially available, solutions and at the same time has about four times the active area with no limitations for up scaling to even larger active areas. Theoretical proof is given that the impedance matching can be achieved over the entire transition line. The design makes use of a bipolar geometry and is flexible to accommodate differing experimental needs. The design was chosen to optimize for small overall size with good temporal response at the same time. The detector was tested with an alpha particle source and an excellent time response was obtained. Although the design was driven by special needs for space application the detector can be applied wherever short timing pulses are needed.  

ISSN:0034-6748    

DOI:10.1063/1.1144914

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A modified crossed‐beam apparatus to measure charge‐transfer cross sections of metallic elements in wide impact‐energy range (10–1000 eV) has been developed. The ion optics to extract charge‐transferred ions from the primary neutral atomic beam was improved, and the background noise due to the collisions on residual gas and the charged particles produced by scattered laser light was reduced, and as the result, the S/N ratio of the charge‐transferred ion signal was significantly improved to be ≳100 at 10 eV impact energy. The reduction of primary ions extracted from the ion source in the atomic beam at low impact energy was compensated for by the improvement of the S/N ratio, and the impact energy for which the cross section can be measured was extended to a lower energy (∼10 eV).

ISSN:0034-6748    

DOI:10.1063/1.1144915

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new high‐pressure NMR probehead designed for a 400 MHz widebore NMR spectrometer is described. For the first time, the electrical leads of the rf circuit, the tubes for the thermostating liquid and the high‐pressure fluid, as well as the wires of the Pt‐100 resistor for temperature control, are all fitted at the bottom of the high‐pressure vessel. The sample can easily be removed through a top plug, which allows a relatively fast exchange of the sample. A rather simple design leads to a low‐cost construction. The high‐pressure vessel and the rf circuit are placed inside a standard probehead jacket, such that the high‐pressure probehead can be fitted into the superconducting magnet in the same way as a commercial probehead.

ISSN:0034-6748    

DOI:10.1063/1.1144916

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Methods for increasing the bandwidth of time‐domain‐reflectometry (TDR) dielectric spectroscopy using variable‐time‐scale sampling are presented. Consecutive segments of the TDR transient are sampled with increasing time increments and the entire transient transformed into the frequency domain using a running Laplace transform. Instrumentation artifacts are identified and controlled by examining reflected transients for stray artifacts prior to transformation, either on individual time scales or on a composite log time scale. Transform algorithms are verified usingspicesimulation in both time and frequency domains. Results are presented for a conducting salt solution, showing continuous dielectric spectra from 100 kHz to 5 GHz in the frequency domain, and requiring acquisition over six decades of time in the time domain to capture the entire response.

ISSN:0034-6748    

DOI:10.1063/1.1144917

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A second‐generation constant force profiler is described combining a capacitance based stylus force probe with interferometric optical metrology to monitor position of the specimen carriage. The probe has a vertical range of 15 &mgr;m with a resolution of 0.23 nm and a flat bandwidth response with a −3 dB cutoff at 228 Hz. Passing the output signal through a single pole 200 Hz low‐pass filter, an overall system peak‐to‐peak broadband noise of less than 5 nm is observed. Manufactured primarily from inexpensive materials, the instrument demonstrates a stability of around 1 nm min−1under controlled laboratory conditions. Using an inexpensive motor/gearbox/micrometer open‐loop drive with velocity variations of up to 20%, profiles showing nanometer repeatability over 15 mm traces are demonstrated. Also shown is a profile of a soft contact lens in the hydrated state. The effect of the contact stiffness on the stylus probe/specimen interaction is illustrated by examining the dynamics of the force probe system while operating in the repulsive mode.

ISSN:0034-6748    

DOI:10.1063/1.1144918

出版商:AIP    

年代:1994

数据来源: AIP