Coincidence Circuit Research Articles

A Chronotron for Relativistic Neutron Time-of-Flight Measurements

Neutrons in pulses produced at a 19 mc rate by the circulating beam of the 184-inch cyclotron striking an internal target have kinetic energies from 100 to 800 mev. Circulating-beam bunching limits the time duration of each neutron pulse. Reference signals are produced by a Cherenkov-radiator internal target or the radio-frequency voltage on the cyclotron dee. The chronotron coincidence circuits, capable of a resolving tine of less than 10-9 second, are spaced with increasing time intervals to reduce reflection reinforcement. Saturation of coincidence circuits minimizes the dependence on signal amplitude. The 125-Ω cable is matched at sampling points by a series inductance tapped by tube input capacity.

Vernier Chronotron

The instrument described is a multichannel time interval analyzer with digital output for use in the millimicrosecond region. The analyzer consists of two circulating transmission lines with a single fast coincidence circuit between them and associated gating circuits. Each circulating line is a precisely trimmed coaxial cable with its ends joined by a two-stage noninverting saturating amplifier. A circulating pulse delivers time marks to the input of the coincidence circuit. By making the circulation periods of the two lines slightly different, the time marks are made to arrive at slightly different frequencies. The instrument is a true vernier. To measure an interval it is only necessary to count the number of circulations before coincidence and multiply by the difference in circulation period of the lines. A commercial 256-channel magnetic core memory is used for storage. The circuit of the instrument is described. A method is described for predicting circulation threshold, growth to equilibrium, and equilibrium amplitude of a circulating pulse from the amplifier transfer characteristic. Data are presented which indicate the linearity, stability, and time resolution of the instrument.

25-Minute Isomer ofSe83

BS>Se/sup 83/ was produced by irradiation of a selenium sample, enriched to 75% in Se/sup 82/, in the Pennsylvania State University research reactor. The gamma-ray spectrum of the 25-minute isomer was investigated by means of a 3-in. thick x 3-in. diameter NaI(Tl) crystal scintillation spectrometer. Gamma rays of 2.294 sintering time (0.833 sintering time 0.005, 0.712 sintering time 0.010, 0.524 sintering time 0.012, 0.358 sintering time 0.005, and 0.225 sintering time 0.005 Mev were found. The beta-ray spectrum was investigated by means of a plastic scintillator. In order to eliminate a competing activity from Se/sup 81/ it was found essential to restrict the observation of beta rays to those in coincidence with the Se/sup 83/ gamma spectrum. A coincidence circuit of 0.25microsecond resolving time was developed for this purpose. The beta spectrum was found to be complex with end-point energies of approximately 0.45, 1.0, and 1.7 Mev. From these data, together with gammagamma coincidence measurements, a decay scheme is proposed. (auth)

The level scheme of 112Cd

The level scheme of 112Cd has been investigated by studying the gamma ray spectrum from the decay of 112Ag which excites levels in this nucleide. A source of 112Pd 112Ag in equilibrium was used. Gamma rays of 615, 690, 785, 855, 980, 1090, 1210, 1310, 1400, 1490, 1620, 1810, 1930, 2110, 2240, 2300, 2520, 2540, 2680, 2710, 2830, 2950, 3100 and 3280 keV were found to follow the decay of 112Ag. The summing spectrum was examined using a well type NaI(Tl) crystal with the source in different geometries; summing peaks of 3560, 3300, 3130, 2830, 2710, 2450, 2230, and 2050 keV were observed. Gamma-gamma coincidences were performed using a conventional fast-slow coincidence circuit. The results of these coincidence measurements are listed in table I. A level scheme for 112Cd, based on the intensity values of the various gamma rays following the decay of 112Ag and on the summing and gamma-gamma coincidence measurements is presented in fig. 6.

The level scheme of 112Cd

The level scheme of 112Cd has been investigated by studying the gamma ray spectrum from the decay of 112Ag which excites levels in this nucleide. A source of 112Pd112Ag in equilibrium was used. Gamma rays of 615, 690, 785, 855, 980, 1090, 1210, 1310, 1400, 1490, 1620, 1810, 1930, 2110, 2240, 2300, 2520, 2540, 2680, 2710, 2830, 2950, 3100 and 3280 keV were found to follow the decay of 112Ag. The summing spectrum was examined using a well type NaI(Tl) crystal with the source in different geometries; summing peaks of 3560, 3300, 3130, 2830, 2710, 2450, 2230, and 2050 keV were observed. Gamma-gamma coincidences were performed using a conventional fast-slow coincidence circuit. The results of these coincidence measurements are listed in table I. A level scheme for 112Cd, based on the intensity values of the various gamma rays following the decay of 112Ag and on the summing and gamma-gamma coincidence measurements is presented in fig. 6.

Multiple fast coincidence unit

A fast diode coincidence unit which can be driven by photomultiplier pulses is described. The coincidence circuit can be changed from a double to a triple or quadruple by a switch. A resolving time, τ, of about 3 mμsec with 100% efficiency can be achieved. The dead time following non-coincident and coincident input pulses are about 16 and 70 mμsec respectively.

Measurement of Time of Flight in the Millimicrosecond Region

The Hanford system for measurement of neutron time of flight differs from conventional techniques only in the use of a vernier chronotron for time interval measurements. The chronotron consists of two circulating transmission lines with a single fast coincidence circuit between them. The line lengths are adjusted to give slightly different circulation periods. By counting the number of circulations necessary to bring two noncoincident pulses into coincidence, a number is obtained which is a measure of the time interval in terms of the difference in circulation periods. This number is used as the channel address for storage in a Radiation Counter Laboratories 256 channel analyzer. Discussion of the vernier chronotron includes: 1) The factors determining channel width, stability and uniformity, 2) use of the RCA 6810 for starting circulation directly, 3) performance of the system as determined with prompt gamma ray cascades, and 4) performance of the instrument in conjunction with the other components of the time of flight system.

Differential Elastic Scattering of 14 MeV Neutrons in Aluminum, Iron, Lead and Bismuth for Large Angles

The absolute differential cross sections for the elastic scattering of 14 MeV neutrons in Al, Fe, Pb and Bi have been measured for large angles up to 170°. The neutrons generated by 3 T( d , n ) 4 He reactions were scattered by the disk-shaped scatterer, and counted by the n -α coincidence circuit with the resolving time of 4 ns. An anticoincidence method was used to reduce the accidental coincidences between the α-particles and the neutrons which run directly to the detector from the target. Except for the lighter nucleus, the angular distributions obtained fit fairly well with distributions based on the optical model theory employing a surface imaginary part and a real spin-orbit coupling term.

THE DECAY OF Os191 AND Os193

The beta- and gamma-ray spectra of Os191 and Os193 have been studied with a magnetic beta-ray spectrometer, scintillation spectrometers, and coincidence circuits. The 14-hour isomer of Os191 decays via a 0.0742-Mev (M3) transition. Gamma rays of energy 0.0418 (100%, E3), 0.0809 (1%, M1 + E2), 0.1287 (100%, M1 + E2), and 0.1858 (0.1%) Mev have been found to be associated with the 14.6 ± 0.3 day decay of Os191 and an extension of the accepted decay scheme proposed. The following 19 transitions have been associated with the 31.5 ± 0.5 hour decay of Os193: 0.0730 (14%), 0.1068 (~1%), 0.1393 (10%), 0.180 (0.3%), 0.196 (0.1%), 0.243 (~0.2%), 0.2485 (0.3%), 0.2514 (0.4%), 0.278 (0.6%), 0.2810 (1.6%), 0.2885 (0.3%), 0.2994 (0.4%), 0.314 (0.3%), 0.3218 (1.7%), 0.3620 (0.6%), 0.3878 (1.6%), 0.4604 (4.1%), 0.4857 (0.3%), and 0.5585 (2.2%). The internal conversion coefficients for all the stronger transitions suggest that they are M1 + E2 in character. The decay energy of Os193 is 1.132 ± 0.005 Mev. Fermi analyses and beta–gamma coincidence experiments have established excited states of Ir193 at 0.073, 0.139, 0.281, 0.362, 0.460, and 0.559 Mev above the ground state. Six otherwise unclassified weak gamma rays can be accommodated if levels at 0.247, 0.315, and 0.613 Mev are included in the decay scheme.The activation cross sections of Os184 and Os190 are (2.2 ± 0.5) × 103and 5.3 ± 2 barns respectively, relative to Seren's value of 1.6 ± 0.4 barns for Os192.

Notes on a fast time-to-amplitude converter

A time-to-amplitude converter with a full resolution width of 8.5 × 10 −10 sec is described. The circuit is based on the 6BN6 gated beam tube operated at unusually low electrode voltages. An additional supervisory fast coincidence circuit ensures that output pulses are produced only when the pulse delay lies within the desired time interval, thus avoiding the double-valued time-to-amplitude conversion inherent in such systems. Examples of the performance of the apparatus are shown for prompt coincidences and for the delayed coincidence distribution observed when positrons annihilate in fused quartz. The time-to-amplitude converter is easily added to an existing fast-slow coincidence assembly.

PHOTON CORRELATION IN COHERENT LIGHT BEAMS

Experiments have been carried out in an attempt to detect any correlation between photons in coherent light rays using a coincidence circuit of resolving time 2τ = 8 ×10 −9 second. A Hg 198 electrodeless discharge tube under rf excitation was used to provide an intense monochromatic source of narrow line width (0.006 Å and 0.009 Å) at 5461 Å. A positive correlation was detected and compared with theoretical predictions.

Stable Multichannel Positive Pion Detector

A π-μ decay counter has been designed and used to count positive pions in several synchrotron and cyclotron experiments. Utilizing an improved gate generator and coincidence circuit, the detector possesses a very stable efficiency for counting pions in several energy intervals. The detector is readily adaptable to the addition of extra counters to permit the detection of pions in the presence of large backgrounds.

Investigation of the statistical distribution of spontaneous U238 fission acts according to the energies of the two fragments

Using an apparatus consisting of a double pulse ionization chamber, two amplifying channels, a coincidence circuit and a two-beam pulsed oscillograph, we measured the kinetic energy of each of the two fragments formed during nuclear fission. 780 cases of spontaneous U238 fission and about 4500 cases of U235 fission by slow neutrons were recorded. Using these data we plotted the statistical distributions of acts of spontaneous fission and fission with slow neutrons according to the energies of the two fragments. These distributions gave the following curves for the two fission methods: a) the energy spectrum of all fragments and that of light and heavy fragments separately; b) the distribution of acts according to the total kinetic energy of the two nuclear fragments; c) the distribution of fission fragments according to mass; d) the relation of the average total kinetic energy of the two fragments to the ratio of their masses; and e) the relation of the average kinetic energy of light and heavy fragments to their total kinetic energy. The results of the two methods of fission are quite similar. It was found that the total kinetic energy of the two fragments in spontaneous U238 fission was, on the average, 4 Mev less than the energy in U235 fission by slow neutrons.

Total cross sections for fast neutrons by a time of flight method

A time of flight method for the determination of total cross sections for fast neutrons has been realized by detecting neutrons twice along their path by stilbene scintillation counters. The time interval between the pulses of the two counters is measured by a delayed coincidence circuit and determines the energy of the neutrons between the counters. The experimental arrangement and its properties with respect to efficiency, energy resolution and background are discussed. The time resolution was limited by the low efficiency of the coincidence circuit for resolving times smaller than 4 nanoseconds. The method has been tested by measuring with an average energy resolution of 20% the total cross section of sulphur between 400 and 1200 keV. The results are compared to earlier measurements and to the optical model. Further possibilities of the method are discussed.

Lifetime of the first rotational state of Gd 156

The half-life of the 89 keV state of Gd 156 has been measured by means of a fast-slow coincidence circuit. From the observed value T 1 2 = (1.9 ± 0.1) × 10 −9 sec the reduced E2 transition probability can be calculated. One finds B(E2; I 0 → I f) : e 2 = (5.1±0.3) × 10 −48 cm 4 in good agreement with the Coulomb excitation result of Ramšak et al. 4).

COINCIDENCES CAUSED BY COMPTON BACKSCATTERING OF GAMMA-RAYS

With slight improvement of ordinary Rossi circuit, a coincidence circuit of resolving time of 1.5×10-7 sec. has been built. Using this instrument, the annihilation radiations of small component β+-rays emitted by Zn65 have been investigated under various experimental conditions. The experiments demonstrate that the 0.21 Mev γ-rays found previously by some authors in Zn65 may be the backscattered γ-rays due to large component 1.12 Mev γ-rays of Zn65. Moreover, the coincidence rate of collimated annihilation radiations gives the percentage of β+-decay of Zn65 per total disintegration as (1.56 ±0.16)%.

25-channel time analyzer for the mμs-range and a simple time to pulse-height converter

A multi-channel system is described which consists of 25 equal coincidence circuits. The time separation is carried out by a lumped delay-line. Because the delay-line can easily be exchanged, the arrangement can be used in a wide time-range. A simple time-to-pulse-height converter is described which is a variant of the above 25-channel analyzer.

A fast coincidence circuit

A coincidence circuit is described with an improved rejection ratio to non coincident pulses. In the coincident condition, information is gathered during a large part of the time of overlap of the applied signals, not merely from the coincidence of the leading edges. The resolving time is comparable with that obtained using conventional circuits.

Fast Read-Out Chronotron System

A new electronic read-out system has been devised which enables one to obtain a fast answer from a chronotron to be used with accelerator beams of particles. It allows for an analysis of time delay with variable and continuous time intervals. The timing is pulse-height independent with an accuracy increasing for large pulses. The recovery time is in the range of one microsecond. With delay-line clipped coincidence pulses from two photomultipliers being fed into a 12-channel chronotron with a 30-mμsec range, a time resolution with half-width at half maximum of 1.2 mμsec was readily obtained. Using only 4 channels, with a range of 10 mμsec, a half-width at half maximum of 6×10−10 sec was observed. A simplified version with only three channels has made a useful fast coincidence circuit.

THE DECAY OF Os185

A study of the decay of Os185 with a magnetic beta-ray spectrometer, scintillation counters, and coincidence circuits reveals radiations of the following energies (in Mev.), intensities, and multipolarities: K-shell X-rays (65%), 0.0716 (0.4%, M1 + E2), 0.1255 (2.5%, M1 + E2), 0.1626 (1%, M1), 0.2334(1.4%, E2), 0.5920 (1.1%, E2), 0.6458(80%, E2), 0.7177 (4.1%, M1 + E2), 0.8720 (7.1%, M1 + E2), and 0.8789 (7.5%, M1 + E2). These transitions are interpreted in terms of a decay scheme involving the following levels in Re185: 0(5/2+), 0.1255(7/2+), 0.6458(1/2+), 0.7176(3/2+), 0.872(3/2+), and 0.879(3/2+) Mev.The ratio of L-capture to K-capture considering decay to all levels of Re185 is 0.38 ± 0.07. The ratio of L-capture to K-capture to the 0.872 and 0.879 Mev. levels is 1.04 ± 0.04. This implies that the Os185-Re186 atomic energy difference is 0.985 ± 0.007 Mev. The half-life of Os185 was found to be 93.6 ± 0.5 days.