Michiyuki Nakamura

A digital gain stabilizer for a multiparameter pulse-height-recording system☆

Abstract A digital gain stabilizer is developed for use with a multiparameter pulse-height-recording system. Corrections are made for gain drifts of any origin in the spectrometer system. Stability of peak channel numbers to 0.1% or better is obtained over extended periods of time without significant loss in resolution. A method for stabilizing on a peak at any location in the spectrum is described. This method requires only four decimal switches as compared to the many switches normally used. Three decimal switches select the channel location of the stabilizing peak and another switch selects the number of channels adjacent to the peak to be included for stabilization. Gain corrections are introduced into the system by means of a variable-gain amplifier. This provides an inexpensive method for controlling the gain without requiring any alterations to the existing equipment.

Germanium Fet--A Novel Low-Noise Active Device

A novel device for low-noise amplification-the germanium junction field-effect transistor (JFET)--is introduced. The properties of germanium and silicon at cryogenic temperatures are summarized. Based on the conclusions of this summary, a theoretical comparison between germanium and silicon JFETs is made, followed by a comparison of commercially available JFETs from both materials. A low-noise preamplifier featuring liquid-helium-cooled germanium JFETs was built and operated with semiconductor radiation detectors. Pulse generator resolution of the preamplifier for zero external capacitance is 0.28 keV FWHM (Ge) with a slope of 0.018 keV/pF. Actual resolution obtained with the silicon detector for low-energy x rays is 0.37 keV.

Forty‐Megacycle Scaler

A fast scaler is described that employs a fast flip‐flop circuit of unique design. With techniques applied to fast trigger circuits, this flip‐flop circuit has been triggered at a rate higher than 50 megacycles per second and has a double‐pulse resolution of 20 millimicroseconds. A 40‐megacycle scaler, with a scale of eight and employing this fast flip‐flop as a basic element, has been built at this Laboratory.

Germanium FET-A3- a novel element for low-noise preamplifiers

Abstract A preamplifier based on germanium FETs and having 0.3 keV resolution is described. assistance of W.LL. Crowder.

Multichannel detector for use in particle spectrometers

A 15-channel scintillation counter has been constructed for use in magnetic spectrometers with extended focal line. It utilizes 15 organic scintillators placed along the focal line. The scintillators are optically coupled in binary code to four photomultiplier tubes. The output pulses from these tubes are electronically converted into standard current pulses (weighted 1, 2, 4, 8) in a common resistor. The resulting voltage pulse is proportional to the position of the scintillator giving the light pulse, and can be displayed on a “kicksorter”. The results of an experimental test of the multichannel electron detector are described. Further improvements are expected with use of a fifth multiplier tube in coincidence with the above mentioned tubes.

High-Resolution Beta- and Gamma-Ray Spectrometer

A high-resolution semiconductor beta- and gamma-ray spectrometer is described. The spectrometer consists of a silicon or germanium detector, low-noise field-effect transistor preamplifier, and a linear amplifier. The requirements for the different sections for high-resolution performance are outlined. The detectors used are low-capacitance, low-leakage devices cooled to low temperatures. The preamplifier utilizes the low-noise characteristics of a cooled junction-field-effect transistor. These characteristics are described and several types of FETs are compared. A single FET, incorporated in a voltage-sensitive input stage, provides an optimum signal-to-noise ratio. Pulse generator resolution of the preamplifier for zero external capacitance is 0.4 keV FWHM (Ge) with a slope of 0.038 keV/pF. Typical resolution obtained in the spectrometer in the low-energy region is 0.7 keV. Recent measurements show that the cooling system is one of the main noise sources of the spectrometer. More than 20% improvement in resolution was observed in preliminary experiments when this noise source was suppressed.

Beam Position Monitor System for Storage Rings

Beam position monitors (BPM) for synchrotron light storage rings usually consist of beam pickup electrodes, coaxial relays and a narrowband receiver. While accurate, these systems are slow and of limited use in the commissioning of an accelerator. A beam position monitor is described which is intended to be a principal diagnostic during debug and routine running of a storage ring. It is capable of measuring the position of a single bunch on the first or nth orbit to an accuracy of a few percent. Stored beam position is more accurately measured with averaging techniques. Beam position changes can be studied in a bandwidth from DC to a few MHz. The beam monitor electronics consist of a separate amplification, detection, and sampling channel for each beam pickup electrode. Fast switches in each channel permit selection of the nth turn for measurement (single bunch mode). A calibration pulse is injected into each channel after beam measurement to permit gain offsets to be measured and removed from the final data. While initially more costly than the usual beam position monitor system, this system will pay for itself in reduced storage ring debug and trouble shooting time.

Non-linear clock for digitizers

Abstract A digital method for generating pulses whose frequency varies with time is described. The variation of frequency obtained is stable, controllable and predictable. These pulses used in conjunction with time or charge digitizers allow measurements over a wider range of time or energy in a digitizer having memory or buffer store of a limited number of bits or channels. A mathematical relationship between a non-linear clock and an equivalent linear clock is given which makes this method extremely flexible and useful.

Hypercryogenic Detector-Fet Unit--Core of High-Resolution Spectrometer

A hypercryogenic high-resolution x-ray and ?-ray spectrometer is described. The spectrometer consists of a lithium-drifted germanium detector and a germanium-junction field-effect transistor (JFET) preamplifier. The detector is operated at its optimum temperature, which is in the range of 10-30° K. The JFETs are operated at liquid helium temperature. This results in 0.28 keV FWHM preamplifier resolution with a slope of 0.018 keV/pF. Resolutions of the order of 0.4 keV are obtained with low capacitance detectors for low-energy x rays. The ? rays of 57Co are measured with 0.68 keV FWHM. The described spectrometer was used to study some aspects of the trapping effects in germanium detectors.

Fast Signal Calibration Systems for Large Detector System Front Ends

The fast risetime of the calibration signal in a 10 ns front end of a large detector system presents problems not generally encountered in a slower system. The distribution of these signals also presents its own unique set of problems. We have arrived at solutions which are applicable to large systems requiring fast risetime calibration signals in a small volume of space.