B.C. Nandi

Precise measurement of the vertical muon spectrum in the range 20-500 GeV/c

The 300 ton cosmic ray spectrograph (MARS) has been used to measure the vertical momentum spectrum of cosmic ray muons in the momentum range 20-500 GeV/c at sea level.

Mars II: The operation and elements of the spectrograph

Abstract The method of operation of the spectrograph - MARS - is described. The limitations of the triggering system, and of the method of storage of data from the flash-tubes are discussed. The momentum selector incorporated in the spectrograph is considered in detail, and it is shown that there is no rejection of events by the device due to the production of bursts in the iron blocks or to air showers incident upon the apparatus. The events are also considered by equipment which, if the data in the event is suitable, calculates the deflection of the particle traversing the spectrograph using the information available from the momentum selector.

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.

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.

The flash tube discharge mechanism from a study of the digitization pulse output

Abstract The digitization pulse obtained from the flash tube has been found to follow the characteristics of the discharge mechanism. Two types of digitization pulses have been observed corresponding to Townsend and streamer discharge mechanisms. The streamer breakdown fields have been found for three different gas compositions: (1) Ne:He (70:30); (2) Ne:He (98:2) and (3) Ne:He (70:30) plus 1% CH 4 . An attempt has been made to estimate the induced clearing field and its decay with time from a study of the streamer discharge probability with rate. The digitization pulse heights for both streamer and Townsend discharge mechanisms have been investigated as a function of the applied field and the rate of flashing. No significant difference has been found in operation of the tubes for positive and negative applied fields.

The performance of a gas scintillation counter at high count rates

Using a gas mixture of 10% N2 in argon in a gas scintillation counter with a thick wire anode of 400 μm, the energy resolution and the mean pulse height from the photomultiplier were studied at rates up to 10 MHz. A shift of the pulse heigth o only 10% was measured for a rate of 6 MHz, with an energy resolution of 56% for 6.9 keV X-rays.