Alan R. Baldwin

The response of NE-228A, NE-228, NE-224, and NE-102 scintillators to protons from 2.43 to 19.55 MeV

Abstract The response of NE-228A, NE-228, NE-224, and NE-102 scintillators to protons from 2.43 to 19.55 MeV has been measured relative to electrons. The NE-228A scintillator has the same high hydrogen content (CH 2.11 ) as NE-228; but it has a 30% higher light output. Proton recoils in this energy range were obtained by elastically scattering (20.76±0.13) and (26.08±0.06) MeV neutrons from protons in the scintillators through angles of 20°, 30°, 45°, and 60°. The neutrons were obtained from the T(d, n)α reaction. The measured response (in units of electron energy) for protons above 5 MeV in NE- 102 is about 8% higher than that assumed in popular computer programs for calculating the neutron detection efficiency of plastic scintillators. The response of NE-228A is equivalent to that of NE-228. The response of NE-224 differs from that of either NE-102 or NE-228.

An analog mean-timer circuit for use with large-volume scintillation counters

Abstract A self-contained modular instrument determines the average of the transit times of photons from a scintillation event to the photomultiplier tubes attached to the ends of a long scintillator. The mean-timer circuit described here generates a mean-timing pulse that is a true analog computation of the mean arrival time of the two input pulses. The mean timer circuit performs this computation in approximately 50 ns followed by a dead-time of about 75 ns. The measured timing error in generating the mean-timing signal is less than 1.5% the absolute time difference between the two input trigger pulses for absolute time differences up to 20 ns.

A two-parameter spectrometer for unidirectional neutrons from about 5 to 200 MeV☆

Abstract A two-parameter spectrometer has improved background discrimination capabilities over the previously reported one-parameter version for measuring unidirectional neutrons in the region from about 5 to 200 MeV. While both versions measure the time-of-flight of a neutron scattered elastically between two scintillation counters, the two-parameter spectrometer measures also the pulse-height of the recoil proton from a neutron-proton elastic scattering event in the first scintillator. The electronic system is capable of measuring recoil-proton pulse-heights over a dynamic range of 200 to 1. Measurements of thick-target neutron spectra in the region from 5 to 95 MeV with 4″ thick first detectors reveal that the combined backgrounds from neutron-carbon and plural-scattered neutrons constitute about 50% of the total events observed in a “good geometry” arrangement.

A radio-frequency phase-drift compensator for neutron time-of-flight measurements

Abstract A device is described that compensates variations at the target in the time of arrival of the external cyclotron beam relative to a fixed phase on a radio-frequency signal from the cyclotron. The rf timing compensator permits achieving long-term stability in time resolution for neutron time-of-light measurements at the Indiana University Cyclotron Facility.

A temperature-stable linear gate for nanosecond signals and an optional stretcher circuit

Abstract A temperature-stable linear gate with an optional stretcher circuit has been developed for gating nanosecond signals from photomultipliers. Stabilization of the gate circuit results in a baseline drift at a 50 Ω output of less than a millivolt for a 50° C change in temperature from 0 to 50 °C. In addition to good temperature stability and linearity, this direct-coupled circuit switches in less than 5 ns with small switching transients; moreover, it is unaffected by the gating rate or duty cycle. Gate intervals from 30 ns to any larger interval are possible. The responsible is linear to within 2% over 30:1 range of input pulse heights. A linear dynamic range of 300:1 has been achieved with a combination of two circuits. The optional stretcher circuit integrates the gated pulse from the photomultiplier anode and generates a stretched analog signal which is proportional to the total charge of the gated signal.

A high-voltage pulse generator for spark chambers in space

Abstract The design and performance characteristics of a high-voltage pulse generator for use with spark chambers in space are described. In order to minimize power consumption, the pulse generator is designed around a cold-cathode thyratron. The complete pulse generator consists of a thyratron pulser and an avalanche-transistor switching circuit. Included also is a simple means for applying a steady clearing field to the spark chambers. The pulse generator can be triggered at uniform repetition rates up to about 100 per second to produce negative pulses with a peak amplitude of typically 2 kV. The observed rise-time is about 5 ns with only stray capacitance loading. It increases with the capacitance loading introduced by a spark-chamber at the output of the pulser. The total delay-time from the input trigger pulse to the output pulse is about 140 ns. The pulse decays exponentially with a time constant of the order of a microsecond. Pulse amplitudes up to 4 kV are possible with the particular thyratron selected for this application. The particular high-voltage pulse generator described in this paper provides 2100 V to three spark-chambers each with a capacitance of 150 pF. The power consumption of this generator with a single power supply is typically 0.5 W at low pulse repetition rates, 1.2 W at a pulse repetition rate of 20 per second, and 3.3 W at 100 pulses per second; alternatively, the power consumption of a pulse generator with multiple power supplies may be reduced to typically 0.1 W at low repetition rates, 0.8 W at 20 pulses per second and 2.9 W at 100 pulses per second. In laboratory tests, several krytrons have been pulsed from 275 to 385 million times before failure.

A portable spark-chamber range spectrometer and data acquisition system☆

Abstract A portable spark-chamber range spectrometer and electronic data acquisition system is described for acquiring spectral data on energetic charged particles. The instrument system consists of a uni-directional spark-chamber range telescope with pulse-height analysis of the specific energy loss ( d E d x of a charged particle that passes through a triggering telescope. The range telescope consists of a stack of sealed double-gap spark-discharge modules with absorbers sandwiched between them. A Cherenkov counter discriminates against electrons and muons. Cherenkov and d E d x signals are gated by the coincidence circuit. Data, either telemetered or recorded in situ, include the number of coincidences, a clock signal, system voltage levels, and the d E d x , Cherenkov, and spark-discharge module signals. Power consumption of the self-contained system is about 10 W at an event rate of 20 per second and 17 W at an event rate of 100 per second. The standby power is about 8 W. This instrument system can measure primary protons and alphas at balloon altitudes and secondary protons at lower altitudes. A particular configuration with a geometric factor of about 1 cm2 sr has been assembled for measuring atmospheric proton intensities and spectra in the range from MeV to 300 MeV and at altitudes ranging from the altitude of high-flying aircraft to balloon altitudes near the top of the atmosphere.

Evolution of c-axis resistivity in Y1−xPrxBa2Cu3O7−δ single crystals

We report on the systematic study of the evolution of the in-plane (ρab) and out-of-plane (ρc) resistivities of fully oxygenatedY1−xPrxBa2Cu3O7−δ single crystals. ρc(x) exhibits a non-monotonic behavior: at low to moderatex, ρc(x) and the anisotropy ρc(x) increase, reaching a maximum at x≈0.42; for higherx,x, ρc and ρc/ρcab decrease, while ρab continues to increase monotonically. These results, along with the coexistence of metallic ρab(T) and semiconducting ρc(T), are consistent with the presence of a gap in the energy spectrum of the chains, leading to tunneling through both valence and conduction bands of theCuO chains.

A useful 350 MHz scaler

A single decade 350 MHz scaler has been designed and used to extend the pulse rate capability of present scaling instruments. The scaler counts fast negative pulses and has a pulse pair resolution of less than 3 nsec. The complete circuit and operating characteristics are described.