Dead-time Losses Research Articles

Details of dead time losses in scaling and multiscaling

An electrometer is employed to investigate dead time effects in scaling and multiscaling. The electrometer method as presented gives accurate values for the dead time over a wide range of counting rates. An expression is also developed for the ``between channel'' dead time of a multiscaler, and a simple method of determining this time is also given. The technique as outlined allows the exact determination of the nonlinearity caused by dead time losses.

Automatic corrections for deadtime effects and lineshape changes due to source decay in positron-annihilation experiments

Correction systems are described for minimizing the changes in deadtime losses and in lineshape produced by the variation in count rate from intense, short-halflife sources. Application to the counting of 64Cu annihilation radiation in positron experiments employing angular-correlation and Doppler techniques is described. Both techniques have been improved by decreasing, by an order of magnitude, their sensitivities to change of counting rate.

Correction for counting losses in multichannel time analyzers

The formulae expressing corrections for dead-time losses, for measurements performed with multichannel analyzers operating in time mode are derived. The reasoning concerns analyzers in which the dead time is variable, from the moment of the pulse arrival till the moment when the memory cycle is finished. A series of measurements has been carried out to check if the formulae are correct.

Ein neutronenzählkanal mit hoher zeitlicher auflösung

For reactor-kinetic studies a high-resolution neutron counting channel equipped with a fission counter detector was developed. It processes pulse-rates up to 10 7 cps, whereby dead-time losses at that counting rate are 12%. The designed pulse amplifier has a rise-time of 2 ns with a current gain of 2.4 × 10 3.

Dead time, decay and background effects in counting

The combined effects of background, decay and dead time losses in counting are considered, particularly as they relate to the variance of the measure of the true counting rate. Expressions are given for the variances attached to the several components in coincidence counting.

Dead-Time Losses of Multichannelized Delayed Coincidence Spectrometer

Counting losses of multichannelized delay lines are calculated and a delayed coincidence spectrometer is designed. As the results of the calculation, 10 delay lines are prepared as a multichannelized delay line in the spectrometer. In order to set the delay times of 10 delay lines exactly the same, a digitally controlled system is employed. The experimental results of counting losses and delayed coincidence rates show good agreements with the calculated results. According to the investigation of the counting loss of the multichannelized spectrometer, it is noted that the counting efficiency of the 10 channelized spectrometer is about 400 times better than that of a single channel spectrometer.

Quantitative Nondispersive X-Ray Fluorescence Analysis of Highly Radioactive Samples for Uranium and Plutonium Concentration *

AbstractFluorescent x-ray energy spectra were successfully acquired from uranium and plutonium in 400:1 ratios in samples containing 2 Ci/gram of mixed fission products. The analytical system consists of a silver transmission anode x-ray tube, a low-Z scattering chamber, a magnetic ß-ray trap, a beam monitor probe, a commercial Si(Li) detector, a set of modified electronics to handle the large γ-ray overload rate, and a Computer analyzer using a higher-level language to handle data reduction.The Computer programs used to obtain peak areas from the closely spaced uranium and plutonium (Lα 1+2) peaks were constructed to make use of knowledge of upper-edge tailing gained in this experiment. Programs are being developed to properly remove background under the uranium and plutonium peaks. Absorption effects in the larger samples have been measured using the ratio of uranium (Lℓ) to uranium (Lα) peak area and are incorporated in the data-analysis schemes. A titanium monitor probe, consisting of a fixed titanium plate near the sample, introduces a constant-area titanium K x-ray line into the spectrum. The program uses the area of this peak to correct for effects of total exciting flux, geometry, and system dead-time losses. Standard samples of various types are used to generate calibration curves from which quantitative results are obtained.Samples are taken from dissolved high-burnup power-reactor fuel rods. The liquid sample is acidic and has a radiation level at one foot of approximately 2 R/hr ß and 300 mR/hr γ. Sample preparation involves only the evaporation of the liquid sample on a 1/2-mil polycarbonate substrate and subsequent sealing with another layer of polycarbonate film. The samples are then mounted in standard 35-mm slide-holders.Preliminary testing on a limited number of prepared uranium and plutonium samples indicates a precision of about 1% and an accuracy of about 2%, over a range of 1 to 58 μg total mass. The samples have not yet been verified by independent chemical analysis. The system has been installed at the AEC Savannah River facility for extensive testing.

A method of correcting for count rate losses in dynamic gamma camera studies

The losses occurring within the gamma camera may be subdivided between dead time losses which can be corrected for if the dead time is known and the variable paralysable dead time losses for which a correction cannot easily be made. A paralysable dead time, unlike a conventional dead time, is one when the duration of the insensitive periods is not fixed, but may be renewed by any scintillation event occurring during the insensitive period. This latter type of dead time occurs in the preamplifiers and mixers of a gamma camera. By far the major effect is in the mixers. The fraction of input pulses lost depends on the total number of scintillation events detected, which includes events causing pulses outside the gamma camera analyser window. A method of obtaining a correction factor for paralysable dead time losses is described. This technique permits quantitative dynamic studies to be performed at count rates in excess of 105 per second.

The measurement of resolving time of scintillation cameras

A scintillation camera used for rapid quantitative dynamic function studies must cope with a bolus containing several mCi of activity. At such rapid counting rates dead-time losses are significant and require correction. The author has evaluated dead-time losses in two versions of the Anger camera, as determined from camera scalar data, and also following acquisition into two models of small computer data processing systems. Measurements included the sequential addition of several identical aiquots of activity under the camera detector, and the familiar two-source method.

Dead-time losses in a buffered data recording system

Expressions are derived for the average fraction of events that will be stored (i.e. not lost) when completely random events (i.e. with exponentially distributed interarrival times) are fed through a buffer with capacity n events into a data store with constant dead-time (service time). The data store can be synchronized with a clock of any cycle time. Transfer times are neglected, except between the buffer and the data store.

A Dead Time Correction for Gamma-Ray Spectroscopy

In a discussion of the interpretation of the data obtained by a multichannel analyzer from a sample containing mixed gamma-ray emitting isotopes, it is concluded that dead time losses influence both the magnitude and shape of the composite spectrum. A relation including appropriate corrections is presented.

Normal and random pulse generators for the correction of dead-time losses in nuclear spectrometry

Severe systematic errors can be encountered when using a normal pulse generator for the correction of dead-time losses in nuclear spectrometry. These errors can be avoided if the ratio between the theoretical dead-time produced by the pulser and that produced by the detector signals is kept below 0.1, and a correction factor can be applied if this ratio is increased in order to improve the precision of the measurements. The use of a so called “random” pulse generator, which does not cause these systematic errors, is recommended.

Comparison of several methods proposed for correction of dead-time losses in the gamma-ray spectrometry of very short-lived nuclides

Methods proposed by several authors for correction of dead-time losses in the gamma-ray spectrometry of very short-lived nuclides are reviewed and discussed. Experimental results obtained using four of the simplest ones are presented. The choice of the proper method for each dead-time range is discussed.

Digital Pulses Delayed with Substantially Reduced Deadtime

A delay module, NIM compatible, which can retard digital pulses through the entire range of 0.1 μsec–10 msec has been developed. The novel feature of the unit is an internal distribution system for six delay monostables that substantially reduces the deadtime which otherwise would be imposed for at least the duration of the delay. For example, if the product of count rate times deadtime is 0.9, the added deadtime loss due to this delay module can be about 0.1% (a 500‐fold improvement over a single delay monostable). There are two modes of operation which depend upon the method of deadtime avoidance: scaling or cyclic distribution. Both methods yield similar results. There is also a test mode for calibration of the unit as well as for accurate determination of the delay interval. By the inclusion of appropriate gating arrangements, rapid and accurate delay calibrations can be performed by a random‐pulse averaging method used in conjunction with a precision oscillator. The design of the circuit, operating experience, method of calibration, and results of calibration are included in the report.

The reduction of dead time losses in multichannel scaling experiments

The finite dead time of multichannel scalers introduces distortion at high counting rates. This distortion is reduced by use of a system which delays any pulse that arrives during the dead time until the scaler is capable of accepting it. When used with an instrument with a dead time of typically 5 mu 8 the delay generator described reduces signal losses from up to 40% to a few tenths of a percent, the residual loss being that associated with a dead time of typically 25 ns. At high count rates the dead time rises above 25 ns but may be calibrated as a function of count rate.

Corrections for Dead-Time Losses in the Measurement of Gamma-Ray Spectra of Short-Lived Radionuclides

Multichannel analyzers are necessary tools in activation analysis. The reliability of the analytical results depends on the correction for dead time. When measuring long-lived radionuclides, this c...

Processing of pulse trains using rate multipliers in nuclear instrumentation

This note calls attention to some of the properties of binary rate multipliers in the generation of digital functions. The binary rate multiplier, which comprises an assembly of flip-flops and gates is now much used in regular rate processing. Here attention is called to the fact that under certain conditions, it may also be employed for random rate processing, such as arise in nuclear instrumentation. As an example, a circuit is given for the automatic correction of deadtime losses.

Convertisseur temps-amplitude de haute resolution

A time-to-pulse height converter of the Start-Stop variety is described. The circuit can accept high counting rates at both inputs and the dead time losses are limited only by the number of conversions per second. The intrinsic resolution is 2.8 × 10 −12 sec.

Reduction of processing losses in on-line or off-line acquisition of random counts at high rates

Experiments in which random events are counted at rapidly varying event rates are subject to deadtime errors which cannot be readily corrected for. Such losses can be minimized, however, through the use of a fast prescaler or distributor. The deadtime loss for prescalers and distributors is calculated here, under very general assumptions, and a practical prescaler is described.

The asymptotic method of dead-time correction in poissonian distribution

The problem of correcting for dead-time losses an experimental counting distribution measured with a nonparalyzable device exposed to a poissonian source of particles is here discussed. An approximate analytical method for estimating the mean frequency of the source and the dead-time of the system is given. The involved statistical and systematic errors are detailed and graphs allowing their rapid determination or the proper design of an experiment are reported. The correctness of the proposed method has been successfully tested against stochastic simulations and experiments.