Chatterjee, S D

Sastrt, R C

Sastri, R C

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J l e t i e t 5  t o  t h e  £ d i i o tThe Board of Editors does not hold itself responsible for opinions expressed in the letters published in this seU 'on, The notes containing short reports qf original invesHgaiions commu* nicated to this section should not contain many figures and should not exceed 600 words tn length. The cofitributions reaching the Secretary by the 7 ^  of any month may be expected to appear in the issue for the next month. No proof will be send to the author,1IMAGE INVERSION OF GEIGER PULSER. C. SASTRT AND S. D. CHATTERJEEJ adavpitr IJjfivERSiTY, Calciitta, 1^2, India.{Received January 25, 19C7)In a normal Geiger counter operation, it is customary to maintain the axial wire at a positive potential, as suggested in the original paper of Geiger and Muller (1928) Such an anungement yields a negative pulse at the wire due to tlu» collection of electrons. The mechanism of pulse formation due to the motion of ions in an ion-chamber or a counter and its effect on external circuits 1ms been discussi'd in some details by Curran and Craggs (1949). Curran and Reid (1948) have also described properties of some new types of counters, viz., (1) rectangular cathode with symmetrical and non-symmetrical wires and (2) circular cylindrical cathode with non-axial wire. In either case, such counters liav(' shown improved dead time and reduced coincident cosmic-ray background.Using the second typo of counter, having both an axial and a non-axial wires situated within tJic same circular cylindrical cathode, an interesting new feature has been obsiTved. The circuit arrangement is depicted in Fig. 1.J. Circuit arrangcinent for the study of image inverted pulses in a Geiger counter.Cctse A  : Negative potential is applied to""the cylinder. The axial wire has a bigger diameter (--12 mil) than that of the offset wire Aa(~4 mil). The former is connected to ground through a resistance 7? so that the pulse could bo transferred to a Tektronix oscilloscope; C is the distributed capacity of the wire147148 Letters to the E d ito rand anything altaclicd olodrically to it. Tho offset wire is normally grounded either di?’eetly or through an auxiliary battery.Tlie axial wire Juieing a relatively large tUameter, does not promote Town­send avalanche in its neighbonrliood and is in a quiescent state with a moderate cathode voltage, wlu'u the offset wire is left floating. However, when the latter is grounded, positive pidsc's simulting Geiger x>nlses appear at the terminal of tho axial wire. The rise time and dead time of these pulses are of the same order of magnitude' as of Geiger pulses, although the amplitude is correspondingly less. The latter can he varied within limits by varying the voltage of an auxiliary battery connected to the offst't wire A„. Fig. 2 gives a photographic reproduction of such positive pulses.Ficr. 2. rmfifrn irivftrtorl (^jositivo) ]>ulses at thn trrniinnl of the nnial wire.B : The operating eondition of the counter is kept the same as before, excepting that the two wires an* made iihmtical in diameter - 4iniL). Under such conditions, tin* counter app(*ars 1 o behave* as two separate counters. However, the pulses appearing at tlve axial wire (consist of both ])ositivc and negative pulses as shown in Fig. 3. 71ie reflected positive pidses look sharper, because of smaller time-constant of the offset wirejjassembly.Fig. 3. Image invortod (positive) pulsos, superimposed oa normal Geiger (negative) pulses.Ldtera to the Editor 14dWith slight modification of thci circuit parameters, the behaviour of the axial and non-axial wires can be iuad(! mutually reversible. It may, howev('r, be noted that the field-strength in the multiplicative region of lh(! non-axial wire is about 15 pt'r cent higher (Curran el al. 1948) than the field-itrength at the corresponding region of the axial wire, resulting in a lower threshoW potential of the former.Looking at the results, it seems reasonable to si^posc that ease A represents the physical situation of a charged hollow cylinder jenclosing two parallel cylin­drical conductors of same finite lengths aiid liavii|g different diameters. The axial wire is grounded through a resistor, while the* tn>n-axial one is subjected to intermittent and transient charges. Accordingly, th^ posil ive pulses may possibly be identified with image inverted pulses, whose amplitmh' depends upon image attenuation factoi's (Harm\ell, 1949).I ’ E Ji !•: X (' !■; sII. and W. lilwS, :rH. 29,r in r a n ,  S. i \  and J .  I>. Couhtliuf Tubes Arml<‘inn‘ PrcNs Inc. London,<^UTan, S. r . and Itcid, d. M. li)4S. R i e ,  S r i .  19, (>7.Ila m w i'll ,  (L  P. HUM. Prixciples of Ehxfricitif mitl EUofr(mufjueti,sm ^ Ic -(ii‘aw  H il l  Book Ho. Jno., V ork , o i l .

English

Image Inversion of Geiger Pulse

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/5013/1/Image%20inversion%20of%20geiger_RC%20Sastri.pdf

Image Inversion of Geiger Pulse

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