J.M. Breare

The use of neon flash tubes at high repetition rates

Abstract When flash tubes are used at high repetition rates their efficiency at long time delays between the passage of the ionizing particle and the application of the high voltage pulse decreases faster than theoretical predictions. An explanation of the phenomena is proposed in terms of clearing fields resulting from charges deposited on the inside glass surface by previous discharges. Methods of avoiding the build up of such clearing fields are discussed.

A flash tube chamber suitable for use at high repetition rates

Abstract Methods of reducing the recovery time of flash tubes by the addition of small amounts of molecular gas to the neon-helium gas mixture are described. The recovery time can be reduced from 300 ms for the tubes without additives to 0.6 ms for tubes at high pressure containing 2% of methane. The sensitive time is also reduced by the added gases, usually to times of a few microseconds, but further control of the sensitive time can be obtained by the application of alternating clearing fields. Apart from laboratory tests of the tubes using cosmic ray triggers, a flash tube chamber of 128 tubes, containing 30–70 neon-helium plus 1% methane, have been tested at rates up to 50 pulses per second in an electron beam. The digitized signals from the tubes were large enough to interface directly with a computerized Camac system. It was shown that the tubes had an internal efficiency of greater than 97% under these conditions and that they had no memory of previous events even at the highest rate tested.

Measurement of γ-ray energy using a high pressure flash tube chamber

Abstract A flush tube chamber intended for γ-ray detection is described. It uses 768 thin walled small diameter (8 mm internal diameter) tubes filled with Ne and He (70:30) and 2% methane at a pressure of 2.3 atm. The chamber contains 12 detecting modules with lead radiators between the modules. By noting the number of tubes which flash after a positron enters the chamber and also noting the position of these tubes, the energy and spatial coordinates of the particle can be obtained. Measurements have been made using a positron beam at the Daresbury Laboratory in the energy range of 0.5–3.5 GeV. An energy resolution of 43% (full width at half maximum) has been measured at 3.5 GeV using 1.8 radiation lengths of lead target between each module.

A digitised neon flash-tube chamber for γ-ray detection

Abstract A technique using flash tubes for detecting γ rays is described, in which the energy, direction, and position of the γ rays can all be obtained. The suitability of flash tubes for electron-shower detection results from the use of poorly conducting glass as the tube material. Its high resistance limits the current flowing in a tube so that all the available energy is not taken by any one tube. A chamber consisting of 8 modules, having a total of 128 tubes, was digitised, using small probes on the end of each tube. The output from the probes was fed, without amplification, along cables to CAMAC. Between each module, 1 or 2 radiation lengths of lead were placed. Tests have been carried out with an electron beam in the energy range 0.5 to 4 GeV. From measurement of the number and position of the tubes which ignited it was found that the energy of the primary electron could be estimated to ±18% at 1 GeV. From the same measurements estimates of the shower apex and axis can be made. The position of the apex can be obtained to about ±1 cm using tubes of diameter 1.6 cm. The direction of the shower axis can be measured to better than ±2°.

Charge and light gain measurements in argon-nitrogen mixtures using a gas scintillation proportional counter

Abstract This paper describes the measurements of charge and light gain in argon-nitrogen mixtures using a gas scintillation proportional counter. The factors studied here which affect light emission, are anode voltage, nitrogen concentration and anode wire diameter. Results show that around a few percent nitrogen a maximum gain is obtainable. These results are in agreement with those of other workers. It was shown that, for a given charge gain, the light gain is independent of nitrogen concentration above 4% concentration. Thicker wires are suitable for high light output requirements with minimum space charge effects.

Measurement of the drift velocity of electrons in an argon-nitrogen mixture using a gas scintillation drift chamber

Abstract A method has been discussed to measure the drift velocity of electrons in a mixture of argon and nitrogen using a gas scintillation drift chamber. The variations of drift velocities with the drift field and the nitrogen concentration have been investigated. An approximate method has been used to calculate the drift velocity in the gas mixture utilizing the data for pure argon and nitrogen. The comparison shows the similarity between the calculated and the measured variation of the drift velocity with drift field and with nitrogen concentration. A broad maximum of drift velocity has been observed at a nitrogen concentration of about 2.5%.

Rate effect on the digitisation pulse height from NeHeCH4 filled flash tubes

Abstract This paper presents the results obtained from tests carried out on small diameter, high pressure flash tubes using the positron test beam facility at the Daresbury Laboratory. The digitisation pulses obtained from the tubes were observed as a function of flashing rate and the pulse magnitude was found to be very dependent on the flashing rate of the tubes, an increase in flashing rate from 0.5 to 1.5 s−1 was found to decrease the pulse height by almost one order of magnitude. A high voltage pulsing system has now been developed which enables digitisation pulses of an almost constant amplitude to be obtained for various flashing rates up to 1.5 s−1. Preliminary results of this system are described but full details will be published in a later paper.

Some characteristics of high pressure NeHeCH4 filled flash tubes

Abstract Tests have been carried out on the recently developed high pressure NeHeCH 4 filled flash tubes. The efficiency of the tubes and the digitisation pulse heights obtained from the tubes were extensively studied for various operating conditions. The layer efficiency of the tubes was found to be very dependent on the rise time of the applied high voltage pulse. An increase in rise-time of the applied high voltage pulse from 0.1 > s to 0.5 > s resulted in a decrease in layer efficiency of the tubes from 88% to 35%. It was found that for satisfactory operation of the flash tubes an applied high voltage pulse of at least 3 > s RC time was required. The digitisation pulse heights obtained from the tubes were found to be critically dependent on the separation of the flash tubes and the ht electrode.

The application of alternate polarity ht fields to neon flash tubes

Abstract In preliminary tests on small diameter, high pressure flash tubes filled with Ne and He (70-30) and 2% of methane, using the e + test beam facility at the Daresbury Laboratory, it was found that the flash tube digitisation pulse heights decreased with increasing rate 1 ). Further investigations of the digitisation pulse height with rate have been carried out using positive and negative polarity ht pulses. The decay constants of the internal clearing field have been found to be 0.6 and 27.7 s for positive and negative applied fields respectively. The sensitive times for positive and negative applied fields have been measured to be 26.5 ωs and 7.0 ωs respectively. A new high voltage pulsing system has since been developed for applying fields of opposite polarity alternately. The tests using this new pulsing system and a 106 Ru source have been very successful and it is seen to greatly reduce the effects arising from internal clearing fields. The digitisation pulse heights are found to remain fairly constant up to a rate of 90 min −1 . The results of these tests are reported here.

A study of a gas scintillation multiwire proportional counter

A gas scintillation proportional chamber has been built to investigate its behaviour as a high-intensity low-energy X-ray detector using a gas mixture of argon and nitrogen. An X-ray source (55Fe) and an alpha -particle source (241Am) have been used to test the chamber. The scintillation pulse height has been studied for several anode voltages and for various concentrations of nitrogen. The maximum scintillation light output has been obtained for a nitrogen concentration of 2%. The energy resolution of 32.5% has been obtained using 5.9 keV X-rays for a gas multiplication factor of about 400. Very little change in the characteristics of the chamber have been observed up to rates of about 106 per second.