Constant Fraction Timing Research Articles

A digital signal processing module for gamma-ray tracking detectors

We have designed and constructed an 8-channel digital signal processing board for the GRETINA spectrometer. The digitizer samples each of 8 inputs at 100 MHz with 12-bit resolution. Employing a large on-board FPGA, the board derives an energy, leading-edge time, and constant-fraction time from the input signal providing the functionality of a conventional analog electronics system. Readout and control of the digitizer is done over a VME bus. The digitizer's performance met all requirements for processing signals from the GRETINA spectrometer.

A DSP equipped digitizer for online analysis of nuclear detector signals

In the framework of the NUCL-EX collaboration, a DSP equipped fast digitizer has been implemented and it has now reached the production stage. Each sampling channel is implemented on a separate daughter-board to be plugged on a VME mother-board. Each channel features a 12-bit, 125 MSamples/s ADC and a Digital Signal Processor (DSP) for online analysis of detector signals. A few algorithms have been written and successfully tested on detectors of different types (scintillators, solid-state, gas-filled), implementing pulse shape discrimination, constant fraction timing, semi-Gaussian shaping, gated integration.

CsI:X(X=Li+,K+,Rb+단결정의 섬광특성

CsI에 활성제로 Li, K, Rb를 첨가하여 CsI(Li), CsI(K) 및 CsI(Rb) 단결정을 Czochralski방법으로 육성하였다. <TEX>$^{137}CS$</TEX>(0.662 MeV)에 대한 CsI(Li:0.2 mole%) 섬광체의 에너지 분해능은 14.5%이었고 CsI(K:0.5 mole%) 섬광체는 15.9%이었으며 CsI(Rb:1.5 mole%) 섬광체는 17.0%이였다. 이들 CsI(Li), CsI(K) 및 CsI(Rb) 섬광체의 <TEX>$\gamma$</TEX>선 에너지에 대한 에너지 교정곡선은 선형적 이였다. 일정비율 시간분석법(CFT :constant-fraction timing method)으로 측정한 CsI(Li:0.2 mole%), CsI(K:0.5 mole%) 및 CsI(Rb:1.5 mole%) 성광체의 시간 분해능은 각각 9.0 ns, 14.7 ns 및 9.7 ns이였다. CsI(Li:0.2 mole%), CsI(K:0.5 mole%) 및 CsI(Rb:1.5 mole%) 섬광체의 형광감쇠시간은 각각 <TEX>${\tau}_1=41.2\;ns$</TEX>, <TEX>${\tau}_2=483\;ns$</TEX>, <TEX>${\tau}_1=47.2\;ns$</TEX>, <TEX>${\tau}_2=417\;ns$</TEX> 및 <TEX>${\tau}_1=41.3\;ns$</TEX> 및 <TEX>${\tau}_2=553\;ns$</TEX>이였다. 그리고 CsI(Li:0.2 mole%), CsI(K:0.5 mole%) 및 CsI(Rb:1.5 mole%) 단결정의 인광감쇠시간은 각각 0.51 s, 0.57 s 및 0.56 s이였다. CsI single crystals doped with lithium, potassium or rubidium were grown by using Czochralski method at Ar gas atmosphere. The energy resolutions of CsI(Li:0.2 mole%), CsI(K:0.5 mole%) and CsI(Rb:1.5 mole%) scintillators were 14.5%, 15.9% and 17.0% for <TEX>$^{137}Cs$</TEX>(0.662 MeV), respectively. The energy calibration curves of CsI(Li), CsI(K) and CsI(Rb) scintillators were linear for <TEX>$\gamma$</TEX>-ray energy. The time resolutions of CsI(Li:0.2 mole%), CsI(K:0.5 mole%) and CsI(Rb:1.5 mole%) scintillators measured by CFT(constant-fraction timing method) were 9.0 ns, 14.7 ns and 9.7 ns, respectively. The fluorescence decay times of CsI(Li:0.2 mole%) scintillator had a fast component and slow one of <TEX>${\tau}_1=41.2\;ns$</TEX> and <TEX>${\tau}_2=483\;ns$</TEX>, respectively. The fluorescence decay times of CsI(K:0.5 mole%) scintillator were <TEX>${\tau}_1=47.2\;ns$</TEX> and <TEX>${\tau}_2=417\;ns$</TEX>. And the fluorescence decay times of CsI(Rb:1.5 mole%) scintillator were <TEX>${\tau}_1=41.3\;ns$</TEX> and <TEX>${\tau}_2=553\;ns$</TEX>. The phosphorescence decay times of CsI(Li:0.2 mole%), CsI(K:0.5 mole%) and CsI(Rb:1.5 mole%) scintillators were 0.51 s, 0.57 s and 0.56 s, respectively.

A NaI-NaI Coincidence Low Background Counting System for Low-level Gamma-ray Measurements.

A NaI-NaI coincidence low background counting system has been constructed to be used in radioenvironmental measurements. The slow timing technique, using the constant fraction timing single channel analyzer and coincidence unit, was used in the present system. The coincidence efficiencies of systems employing two and four NaI (Tl) detectors have been evaluated. A scintillation preamplifier with multiple inputs was constructed for summing the outputs of PM tubes. The performance of the system was tested using radioactive point sources and environmental samples. The detection efficiency of the NaI-NaI coincidence system employing four NaI (Tl) detectors was found to be high enough to measure low-level γ-ray activity of desired isotope in environmental samples with neither high background contribution nor interferences from other isotopes.

Improvements through Pulse Shape Analysis in X-Ray Spectrometry Using Si(Li) Detectors

Peak pile-up and other pulse distortion effects in an Si(Li) detector for x-ray spectroscopy were studied using pulse shape analysis. The pile-up interval, τ, was reduced to about 100 ns by using a combination of selection criteria on leading edge, constant fraction and zero-crossing time signals as functions of pulse height on pulses from an Si(Li) detector used for x-ray detection. Distortions in charge collection, giving rise to tailing effects, were also studied. Such effects were observed and pulses were isolated, but no major reduction in the background could be achieved. The pile-up reduction technique was successfully applied to the analysis of geological specimens resulting in improved detection limits.

Improvements through Pulse Shape Analysis in XRay Spectrometry Using SiLi Detectors

Peak pile-up and other pulse distortion effects in an Si(Li) detector for x-ray spectroscopy were studied using pulse shape analysis. The pile-up interval, τ, was reduced to about 100 ns by using a combination of selection criteria on leading edge, constant fraction and zero-crossing time signals as functions of pulse height on pulses from an Si(Li) detector used for x-ray detection. Distortions in charge collection, giving rise to tailing effects, were also studied. Such effects were observed and pulses were isolated, but no major reduction in the background could be achieved. The pile-up reduction technique was successfully applied to the analysis of geological specimens resulting in improved detection limits.

An integrated, CMOS, constant-fraction timing discriminator for multichannel detector systems

An integrated, CMOS, constant-fraction timing discriminator (CFD) designed to accommodate the special requirements of large, multichannel detector systems is described. This CFD features on-chip, zero-crossing shaping and an automatic walk setting to limit the number of user adjustments. The circuit is realized in the Orbit 1.2 micron, N-well, CMOS process and operates with a 5 V power supply. The time walk in a 100:1 dynamic range (-15 mV to -1.5 V) is less than /spl plusmn/250 ps for a 10 ns rise time/10 ns fall time signal, yet the power dissipation is about 2 mW/channel. The discriminator has a 170 micron pitch, is 800 microns long, and is structured for arraying multiple channels on a single die. >

Performance of a simple drift tube with a large square cross section

Abstract A spatial resolution and an incident angle dependence were measured in a cosmic ray test of a simple drift tube with a square cross section of 8×8 cm2. By optimizing the anode diameter (100 μm) and cell size, and by choosing P10 gas (Ar90%+CH410%), the incident angle dependence can be made negligibly small. The spatial resolution is dependent largely upon the threshold level of the discriminator; the best value of 310 μm (rms) was obtained by using a handmade constant fraction timing discriminator.

Simulation Study of Time-Walk Issues for Drift Tubes

Time walk is evaluated for a drift tube of 2.9 cm in diameter filled with P10 gas, with an anode wire of 70 µm in diameter. Its magnitude, if the shaping is of Poisson type and a leading-edge discriminator is used, is found to be 2-10 ns when 50% gain variation is allowed in the gas multiplication. On the other hand, the use of a constant fraction timing discriminator is expected to reduce this to the order of 0.1 ns.

Constant fraction timing with scintillation detectors

A model is presented for constant-fraction pick-off timing with scintillator-photomultiplier detectors based on a statistical method for leading-edge timing. Many of the essential features of this technique are obtained including prompt response, the dependence of full width at half maximum (FWHM) on the dynamic range of pulse heights and on the maximum energy deposited in the scintillator, and the effect of delay time on the optimum resolution in CFPHT (constant fraction of pulse height trigger) and ARC (amplitude-risetime compensation) timing. The 'walk' component in this technique is also satisfactorily reproduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A time-to-amplitude converter with constant fraction timing discriminators for short time interval measurements

The construction and the performance of a time-to-amplitude converter equipped with constant fraction discriminators is described. The TAC consists of digital and analog parts which are constructed on two printed circuit boards, both of which are located in a single width NIM module. The dead time of the TAC for a start pulse which is not followed by a stop pulse within the time range of the device (∼ 100 ns) is only ∼ 100 ns, which enables one to avoid counting rate saturation even with a high random input signal rate. The differential and integral nonlinearities of the TAC are better than ± 1.5% and 0.0.5%, respectively. The resolution for input timing pulses of constant shape is 20 ps (fwhm), and less than 10 ps (fwhm) with a modification in the digital part. The walk error of the constant fraction timing discriminators is presented and various parameters affecting it are discussed. The effect of the various disturbances in linearity caused by the fast ECL logic and their minimization are also discussed. The time-to-amplitude converter has been used in positron lifetime studies and for laser range finding.

Timing Electronics and Fast Timing Methods with Scintillation Detectors

Time spectroscopy involves the measurement of the time relationship between two events. This paper reviews time pick-off techniques, practival time-pickoff circuits, and timing with scintillation detectors. A detailed comparison is made between leading-edge timing and constant-fraction timing. Typical timing resolution results are given for 60Co.

Search forμ+→e+γ

This paper describes a kinematically complete search for the muon decay ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$. The experiment used a magnetic spectrometer outfitted with proportional chambers to measure the positron momentum vector and a large segmented NaI(T1) array to determine the $\ensuremath{\gamma}$-ray energy and impact point. The positrons were mostly from normal muon decay while the $\ensuremath{\gamma}$ rays were mostly from internal and external bremsstrahlung. Approximately 3\ifmmode\times\else\texttimes\fi{}${10}^{2}$ muons were stopped in a 50-mg/${\mathrm{cm}}^{2}$ polyethylene target. The relative timing between the positron and the $\ensuremath{\gamma}$ ray was measured with a resolution of 1.9 ns full width at half maximum (FWHM) by the use of a plastic-scintillator hodoscope for the positron and by NaI(T1) constant-fraction timing for the $\ensuremath{\gamma}$ ray. The positron energy resolution averaged over all data was 8.8% FWHM, and the $\ensuremath{\gamma}$-ray energy resolution was 8% FWHM, both at 52.8 MeV. When the $\ensuremath{\gamma}$ ray is assumed to originate at the same place in the target as the positron, the rms error in the measurement of the angle between the positron and $\ensuremath{\gamma}$-ray momentum vectors was 37 mrad. The acceptance of the apparatus for ${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma}$ events was (1.75\ifmmode\pm\else\textpm\fi{}0.04)%. A maximum-likelihood analysis established a 90%-confidence upper limit for the branching ratio $\frac{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\gamma})}{\ensuremath{\Gamma}({\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}})}$ of 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$.

The influence of charge collection characteristics on HPGe detector timing performance

The expected response of a constant fraction timing discriminator to pulse shapes from a coaxial HPGe detector has been calculated for several choices of charge drift length and impurity concentration over a range of calculated detector bias, and also for both possible electron and hole drift directions. Optimum timing performance is obtained with impurity concentrations of the order of 10 10 cm −3 and when electrons drift towards the detector centre.

Zero Cross-Over Timing with Coaxial Ge(Li) Detectors

The performance of zero cross-over timing systems of the constant fraction or amplitude rise time compensated type using coaxial Ge(Li) detectors is analyzed with special attention to conditions that compromise their energy-independence advantage. The outcome is verified against existing experimental results, and the parameters that lead to minimum dispersion, as well as the value of the dispersion to be expected, are given by a series of charts.

The Time-of-Flight System on the Goddard Medium Energy Gamma-Ray Telescope

A scintillation counter time-of-flight system has been incorporated into the Goddard 50 cm by 50 cm spark chamber gamma-ray telescope. This system, utilizing constant fraction timing and particle position compensation, digitizes up to 10 ns time differences to six bit accuracy in less than 500 ns. Event selection decisions, discriminating against upward-moving particles, are made prior to spark chamber triggering. The performance of this system during a November 1978 balloon flight is discussed.

A zero crossing discrimination technique for constant fraction timing

A zero crossing discrimination technique is given for constant fraction timing. A very simple method makes a walkingless timing possible, independently of delay and fraction settings.

Timing properties of coaxial HPGe detectors

The dependence of the timing characteristics of a true coaxial HPGe detector on bias has been determined. Optimum performance of 2.0 ns fwhm and 4.25 ns fwtm was obtained at a bias just above the depletion voltage. The general variation of timing characteristics is compared with the results of a model of the pulse generation process in the HPGe detector and the response of the constant fraction timing discriminator.

A modern positron lifetime spectrometer

The construction of a positron lifetime spectrometer is described and the test results presented. A constant fraction timing discriminator and a special construction for the time-to-amplitude converter form the advanced and vital parts of the system, which is assembled using ECL components (MECL-III). Improved properties are achieved in terms of time resolution, counting rate, system simplicity and stability. The system provides a 60Co fwhm time resolution of 145 ps, maximum coincidence rate ∼5×10 4 s −1, single rate ∼5×10 6 s −1, and stability of time zero <0.5 ps over a month. It allows the measurement of an asymmetrical lifetime spectrum in a few minutes and of a symmetrical spectrum in a few seconds with adequate statistical accuracy.

The influence of Ge(Li) detector pulse shape variations on constant fraction and snap-off timing discriminators

The influence of the systematic variations inherent in the pulse shapes from Ge(Li) detectors on the timing characteristics of the snap-off and constant fraction discriminators is calculated. The results are compared with experimental measurements. The expected and observed performance of the two timing discriminators is discussed.