Height Converter Research Articles

First studies of electron transport along small gas gaps of novelfoil radiation converters for fast-neutron detectors

Novel high-efficiency fast-neutron detectors weresuggested for fan-beam tomography applications. They combine multi-layerpolymer converters in gas medium, coupled to thick gaseous electronmultipliers (THGEM). Neutron-induced scattering on the converter's hydrogennuclei results in gas ionization by the escaping recoil-protons between twosuccessive converters. The electrons drift under the action of a homogeneouselectric field, parallel to the converter-foil surfaces, towards aposition-sensitive THGEM multiplying element.In this work we discuss the results of a systematic study of the electrontransport inside a narrow gap between successive converter foils, whichaffects the performance of the detector, both in terms of detectionefficiency and localization properties. The efficiency of transportingionization electrons was measured along a 0.6 mm wide gas gap in 6 and 10 mmwide polymer converters. Computer simulations provided conceptualunderstanding of the observations. For drift lengths of 6 mm, electrons wereefficiently transported along the narrow gas gap with minimaldiffusion-induced losses; an average collection efficiency of 95% wasachieved for ionization electrons induced by few keV photoelectrons. The 10mm height converter yielded considerably lower efficiency due to electricaland mechanical flaws of the converter foils. The results indicate thatdetection efficiencies of ∼ 7% can be expected for 2.5 MeV neutronswith 300-foils converters, of 6 mm height, 0.4 mm thick foils and 0.6 mm gasgap.

Jitter debugging two laser experiments

A method to overcome the problem of timing jitter in two laser experiments is described. The technique involves the use of a time-to-pulse height converter to measure the interpulse separation and a data acquisition system capable of recording this and other experimental parameters on a shot-to-shot basis. The method is estimated to be useful in measurement systems with resolution down to 10 ps.

A correction formula for the counting loss in using a time to pulse height converter and experimental verification of the formula

A correction formula for the counting loss in a TPHC-PHA time analyzer is verified experimentally, after deriving the formula by several methods and obtaining a more refined correction formula. The experiment is made by the application of a gate circuit, which inhibits irrelevant signals, to conventional electronic equipment for measuring the neutron time-of-flight spectra. Lastly we propose the application of the method used in our experiments to general spectra measurement.

A multi-angle detector system for fast neutron time-of-flight spectroscopy

A multi-angle fast neutron time-of-flight spectrometer operating in the nanosecond range is described. The system consists of eight detectors at angles between 20° and 160°. For all the detectors only one time-to-pulse height converter is used. The pulsed 10 MeV tandem accelerator, the detectors and electronic circuitry, the computer coupling and a neutron producing gas target are discussed. Examples of experimental application are given.

Precision 1 ghz time calibrator for time to amplitude converters

A simple circuit in a single-width NIM module is described which allows precise calibration of a time-to-pulse height converter by screening a 1 GHz calibration frequency as a periodic oscillation on a multi-channel analyzer.

Its optical and signal-analysing systems and some experimental results of flow velocity

A laser Doppler microscope, consisting of optical and signal-analysing systems, has been developed. Flow velocity can be measured with an extremely high spatial resolution over an area of up to 10μm in diameter. The optical system consists of a microscope having two types of penetrative and reflective systems. On the basis of the characteristic analysis of Doppler beat signals from the laser Doppler microscope, the signal-analysing system, which uses a tracking filter together with a digital-hold element and a time-to-pulse height converter, has been found to be the most suitable for analysing beat signals. Some experimental results obtained using the laser Dopller microscope for measuring flow velocities, both in a small square cell in a venule, and in a capillary over the web of a frog's foot are presented.

A simple method of obtaining excitation functions in digital form: application to electron impact dissociative ionization of CO 2

A method for obtaining excitation functions in digital form is described which is applicable to measurements of ion appearance potentials by electron impact in mass spectrometry. The method employs a sampling time-to-pulse height converter and synchronously pulsed operational amplifier. Excitation functions for the ions O + and C + produced by electron impact on a CO 2 gas beam are presented. An appearance potential of 19.4±0.3 eV was obtained for O +, probably corresponding to the threshold for excitation of the predissociation C 2Σ g + state of CO 2 +. The observed C + onset of 29.8±0.3 eV corresponds to total dissociation of the CO 2 molecule by the process e+CO 2 → C + + O+O+2 e.

Measurement of velocity fluctuations in laser Doppler microscope by the new system employing the time-to-pulse height converter

A new analyzing system for the laser Doppler microscope is proposed and constructed employing both the time-to-pulse height converter and the pulse height analyzer. Since it holds a sufficiently high sampling rate compared with other analyzing systems, it is very useful for measuring velocity fluctuations of the flow. By examining its properties, it is found that the envelope function of beat signals affects the dispersion of the final result for the flow velocity and that the noticeable choice of a trigger level can reject the most of noise. Some experimental results obtained by the present system are shown.

The 6+ isomer state in46Ca

Electric-quadrupole transitions between the high-spin states 6 +, 4 + of the (1/t)• configurations are of particular interest to investigatc the core polarization by valence-]~ nucleons. The high-spin states, in fact, are expected to be less affected by configurat ion mixing than thc lower ones and, in addition, the long lifetime of the 6+-levcls permits a rather precise determination of the transit ion strength. Experimental results for the (1/ 89 • nuclei a2Ca, a0Ti and 5aFe have been reviewed in ref. (1.2). In 4sCa a possible 6+-state at 2.98 MeV has been observed with the 48Ca(p, t)46Ca reaction (a-5). In the present work the decay of the cxpectcd isomer, obtained from the reaction 4sCa(p, p2n)46Ca, has been observed as a delayed activity after bombardment of a 97.2~o enriched 4sCaC0a target with 35 ~r protons. A prel iminary analysis of the present measurement has been reported (6) at the 1974 Varenna School. Measurements have been carried out at the AVF Cyclotron of Milan, which produces bursts of protons at 20.5 MHz repetition rate with a full width at half-maximum ~ 0.5 ns. The target, 10 mg/cm 2 thick, was a sandwich of 4sCaC03 powder between two stretched ~V[ylar foils. Gamma-rays were detected with a Ge(Li) counter of about 35 cm 3 volume and 3 keV resolution at 1.3 MeV. A fast-timing signal from this counter has been obtained by means of a fast amplifier and a snap-off discriminator and has been used as start for a time to pulse height converter. A fast (100 ~Hz) discriminator has been

Lifetimes of 2+ and 4+ states in 68 168 Er

The half-lives of the 2+ and 4+ states of 68 168 Er nucleus have been determined by means of the delayed coincidence method, using a magnetic double lens coincidence spectrometer and a start-stop time-to-pulse height converter coupled to a fast-slow coincidence system. The half-lives of these levels were measured to be $$\begin{gathered} T_{1/2} (2^ + \to 0^ + ) = 1.72 \pm 0.06 ns, \hfill \\ T_{1/2} (4^ + \to 2^ + ) = 106 \pm 6 ps. \hfill \\ \end{gathered} $$ , The experimental ratios ofB(E 2,4+→2+)/B(E 2,2+→0+) and some of the nuclear parameters are deduced and discussed.

Isomeric cross sections for ( n, 2 n) reactions in thallium, lead, and bismuth at 14·8 MeV

The cross sections for the 205Tl( n, 2 n) 204 m Tl, 203Tl( n, 2 n) 202 m,g Tl, 206Pb( n, 2 n) 205 m Pb , 207Pb ( n, 2 n) 206 m Pb, 208Pb( n, 2 n) 207 m Pb and 209Bi( n, 2 n) 208 m Bi reactions have been measured using the cyclic activation technique and a high-energy resolution Ge(Li) detector. The experimentally determined values of formation cross sections are 664 ± 60, 670 ± 60 and 2482 ± 220, 866 ± 77, 1017 ± 92, 1310 ± 116 and 393 ± 35 mb, respectively. The half-lives of the induced isomeric activities have been determined using a wide range time-to-pulse height converter and a multichannel analyzer.

Reduction of the counting losses in a time analyser by the use of an intermediate memory

In the analysis of time-of-flight experiments the counting losses due to the various counting components may cause serious disturbance to the spectral data obtained. The dead time of the time analyser contributes most to the counting losses. A theoretical formula was introduced to estimate the correction for counting losses in the case of constant counting rates in all the analyser channels. Experimental checking of the spectrum distortion at constant pulse rates at the analyser input has been investigated. The time analyser used in this experiment is composed mainly of a time-to-pulse height converter and a multi-channel pulse height analyser. To reduce counting losses, we have used an additional pulse height analyser in parallel with the main analyser to act as an intermediate memory. It was found that this method helps to reduce appreciably the counting losses of the time analyser.

A pulse delay generator

The principle of operation of the Pulse Delay Generator (PDG), the circuitry and results of measurements of the parameters are described. Special attention was concentrated on the effect of the counting rate increase on the PDG performance, and it was found that the PDG may be combined with the Time to Pulse Height Converter (TPHC) in life-time measurements. The instrument can be used in delay ranges from 50 ns to 8 ms. It is found especially useful for the delay times above 1 μs.

Convertisseur temps→amplitude à compensation pour détecteurs Ge(Li)

A time to pulse height converter, including an adjustable device which compensates the timing errors due to leading edge variations of PIN detectors stop pulses, is described. Its start and stop inputs are gated by a medium speed parallel channel. Some factors interfering with the resolution time of the circuit are analyzed. Experimental results in a 350 keV to 2.75 MeV range are reported. At 1.33 MeV the full width at half maximum of the prompt resolution curve obtained with a scintillation counter and a 18 cm 3 Ge(Li) detector is 2.2 ns.

Angle information with a gridded ionization chamber and its applications

The characteristics of a gridded ionization chamber were studied, that is the angle information by rise time analysis. An improvement was made to the alpha spectrum, demonstrating the effectiveness of the technique. The following was revealed by the study: a) The technique can give angle information for nuclear reactions and also serve a neutron spectrometer with a thin radiator. b) Improvement of the alpha spectrum is fairly high in energy resolution, alpha background continuum, beta background, and background from the surrounding materials. c) The information obtained can be varied by change in the setting of a rise time to pulse height converter (RHC).

Spectrum measurements of intermediate energy neutrons by an organic scintillator

The pulse height distribution was obtained experimentally for monoenergetic neutrons having energies from 566 keV to 52 keV with a newly developed gamma-ray pulse shape discriminator, the risetime to pulse height converter (RHC), in conjuction with an NE-213 scintillator. The gamma-ray rejection and the discrimination loss of 52 keV neutrons were estimated to be 99.4% and 13%, respectively, and the estimated neutron energy corresponding to the cut-off of the pulse height distribution was 20 keV. The light outputs of the NE-213 scintillator for neutrons (protons) to the energies are also shown in 60Co light units.

A long period time-to-pulse height converter and new calibration methods

A time-to-pulse height converter (TPC) suitable for the measurement of nuclear half-lives in the range of microseconds to seconds is described. The apparatus, based on an oscilloscope sweep unit, is capable to convert the time delays of all pulses accepted within the selectable fixed conversion period. The differential conversion linearity obtained is better than 1.5% Versatile methods of high accuracy are proposed for pulse delay measurements and TPC calibration covering the region of about 10 −7s to 1 s. Corrections of experimental time spectra due to multichannel analyzer deadtimes are discussed in detail.

Measurement of photon emission due to atomic rearrangement following nuclear decay

An apparatus for the detection of single photons (2–5 eV) is described. Low noise cooled photomultipliers are used, the amplitude spectrum of which is measured with incident low intensity light (single electron peak); it is compared with the noise spectrum. A tunneldiode discriminator for the standardization of the photomultiplier pulses and the determination of its optimum threshold is described. The quantum efficiency of the photomultipliers used is about 25%, the following electronic circuitry has a detection efficiency of almost 100%. The effect of noise background is decreased by the application of the coincidence method. For this purpose an atomic relaxation process is used: Delayed single photons are emitted after atomic adaption to the new nuclear charge following a β-decay. The coincidence signals and their mutual delay (optical lifetime) are measured by means of a time to pulse height converter of the start-stop-principle and a multichannel analyzer. The time resolution of the fast-fast circuit alone is 6 nsec. The excitation of the daughter-ion is primarily due to the sudden change of nuclear charge; excitation by direct collision with charged particles can be neglected. The relative intensities of three emission lines and the lifetimes of the two 5 p( 1 2 1 2 0 - and 5 p( 3 2 case3 2) 0) − Rb + -states populated by the 85Kr-decay are measured as a function of krypton-gas pressure. The undisturbed lifetimes of these states are measured to be τ 0 = 8.0±0.6 nsec and τ 0 = 9.4 ± 0.4 nsec, respectively; the corresponding cross-sections for deexciting collisions ( Rb +∗− Kr) are σ ∗ = 5.5 ± 0.6 × × 10 −15 cm 2 and σ ∗ = 4.8 ± 0.5 × 10 −15 cm 2 .

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.

A simple method for stabilizing a time-of-flight neutron spectrometer

A simple but effective method of digital stabilization of a fast neutron time-of-flight spectrometer is described. Only a commercially available digital stabilizer and an “OR” circuit are added. Two fast outputs of a neutron detector, one being delayed by a definite time and fed to a time-to-pulse height converter through the “OR” circuit, are used as the start and stop signals for reference pulse. The long-term stability is considerably improved.