Logic electronics for a streamer chamber

Logic electronics for a streamer chamber

NUCLEAR INSTRUMENTS AND METHODS I30 (I975) 5 7 1 - 5 7 5 ; © NORTH-HOLLAND PUBLISHING CO. LOGIC E L E C T R O N I C S FOR A S T R E A M E R ...

213KB Sizes 0 Downloads 137 Views

NUCLEAR

INSTRUMENTS

AND

METHODS

I30

(I975) 5 7 1 - 5 7 5 ;

©

NORTH-HOLLAND

PUBLISHING

CO.

LOGIC E L E C T R O N I C S FOR A S T R E A M E R C H A M B E R P. R I C E - E V A N S , I. A. H A S S A 1 R I and A . K .

BETTS

Department of Physics, Bedford College (University of London), Regents Park, London N. IV. 1, England Received 23 September 1975 Logic circuits for the control o f a streamer c h a m b e r system, used to study the multiple scattering o f cosmic m u o n s in lead, are described. Also included is an account o f a fast trigger amplifier yielding 4 kV pulses.

1. Introduction In a streamer chamber experiment to study the multiple scattering of cosmic ray muons, it has been necessary to design a control system that would trigger the chamber only when a delayed electron from the decay of an arrested muon was observed. The streamer chamber and the Marx generator have been reported previouslyl'2); here we provide details of the logic e,lectronics and the trigger amplifier which have operated satisfactorily for two years. Fig. 1 shows the experimental arrangement. The passage of charged particles through the active volume of the chamber is recognised by plastic scintillation c,ounters (1) and (2) in coincidence. (A) represents

15 cm of lead to absorb the soft component of cosmic rays; (B) is a 2.5 cm slab of lead (sometimes mercury), sandwiched between the two halves of the chamber, in which multiple scattering is to be observed. (C) is a 5 cm block of lead and (E) is a l0 cm carbon block in which muons may come to rest [(D) is a lead block omitted when (E) is present.] The large plastic detector (3) serves two functions: it acts as an anticoincidence counter to preclude energetic particles which do not stop in the carbon; and it detects electrons emerging after a chosen delay, say 500 ns. With this arrangement the chamber may be activated when muons, identified by their decay electron, and having energies roughly in the range 120-140 MeV, scatter in the block (B).

ii

,

u

: I SHAPING

J -

,,.,,x

I GENERATOR

C

D

110 cm. I

D E

ELECTRON

[---r-q Fig. 1. T h e experimental a r r a n g e m e n t .

571

, AMPLIFIER

572

P.

RICE-EVANS

2. Logic control A block diagram of the control electronics is shown in fig. 2. Although the radiation environment around a streamer chamber is disturbed by fast high voltage pulses and spark discharges, it has been possible sufficiently to screen the units to allow the use of transistors and integrated circuits. Pulses from counters (I) and (2) are first shaped, and any simultaneous pulses are detected with gate 1C~. The resultant coincident pulse is inverted and delayed before being applied to N A N D l C 9. Any particle simultaneously observed with counter (3) will inhibit I C 9 and no final output will be obtained. IC s ensures a suitable dead time. For straightforward coincidence/ anticoincidence work, a fast pulse may be derived from 1C 9 and applied directly via alternative output (2) to the trigger amplifier. However, for our experiments requiring the detection of the decay electron, the logic output (1) has been employed. In this connexion, in the event of there being no prompt anticoincidence signal, the pulse from I C 9 is transferred to IC 8. Circuits IC10 and I C l l control the moment and duration of the opening of gate IC 8. If a delayed pulse appears at input (3), it may pass, via IC 8, to the main output (1) if two conditions hold: I N . I . ,7,

~-

IN.2. C

~-

et al.

that the coincidence pulse has appeared in the prior desired interval, and that no simultaneous signal is received at IC 8, from IC1, to indicate the detection of another, undesired, coincident event in counters (1) and (2).

3. Detailed circuitry Details of the pulse-shaping and logic circuits are shown in fig. 3. Negative input pulses from the photomultipliers, with amplitudes exceeding a minimum of 50 mV, are first amplified and/or limited to 5 V with a 2N3904 and then shaped with a monostable (SN 74121N) to conform with standard T T L logic. The resulting pulses have lengths of 30 ns which yield a coincidence resolving time of 60 ns. For the logic elements, the general approach has been to use Schottky integrated circuits wherever possible to minimise the transit times. The experimental requirement was to detect the decay electrons which were delayed by at least one microsecond after the initial coincidence. This delay is determined by adjustment of the 10 kf2 helipot on IC1o. In practice the electrons detected in the interval 1-3/~s were accepted - this duration being fixed by the helipot on ICll. By using delay IC3, it was ensured that the cancelling

NOT USED ~

IN.3. C

\

A"LE

o

i

5¢ II

2

Fig. 2. A block diagram of the control electronics.

,~ O U T P U T ( 1 ) (TO TRIGGER AMPLIFIER)

..r

lr

|

E ,,

is,(

,~o

I

"

GATE GATE GATE MIS

.pE

: : : :

SN74G1iN SNT4SI4N SN?4S11N SN?4121N

IEK

~

I~ED

L

I

I

,

|

I

I I I

I

.

.

.

.

.

It4

.

.

.

.

.

.

.

.

Ht

.

_ _ _ _ .

.

SlpF

I

.

.

Fig. 3. Detailed circuits for the pulse s h a p i n g a n d logic.

t

i

1

:

i

e+Sv~

,.,~,1

I

p .

.

.

.

.

.

.

.

.

.

.

.

.

.

s

~m

| S 4 pF

DELAY

.

Ig$

! ~,.-I~

J

i I !

I !

I IoK ! ! !

1

2

OUT

~°.

I !

I 1OK

,,,

E|

÷Sv

c~

© Z

t"

©

574

n. RICE-EVANS et al.

4oo~H W SI00pF 400pH

0"001 F INPUT :

||

':::

-

+.

I

r

iv

,I -150v 75K z +300v 0.'lp F

+

i SCALER OUT

1"5K

DI L2. 1;1 L4. 1:5

D 7. FX1598

F CAMERA 'eOU T

1N 914

J,.._

,,

--

iS8pF

T • -15Ov

Fig. 4. The fast trigger amplifier.

pulse from any anticoincidence signal arrived a t ] C 9 10ns in advance of any coincidence pulse. Monostable IC 5 ensures the cancelling lasts for 50ns. To eliminate events triggering counters (1), (2) and (3), which appear within the delay interval during which the decay electron is expected in (3), the direct pulse from IC~ can veto IC 8. The delay IC7 ensures the prior arrival of this veto pulse. The shortest delay between the input and the alternative output (2) is 50ns; comprising 35 ns in the initial pulse shaper and 15 ns in the logic. Care was taken to ensure that the integrated circuits were effectively shielded against the high radiation fields of the Marx generator and the unscreened streamer chamber only 1 m away. This was achieved by mounting the limiters in their own metal box, the logic circuit in an adjacent box, and the whole assembly in a closed bin module.

4. Fast trigger amplifier To trigger the spark gap lying in front of the Marx generator, it is necessary to amplify the 4 V pulse to 4 kV with a minimum delay. In the circuit of fig. 4, the first stage is a buffer with amplification unity, designed to protect the preceding

integrated circuit logic from destruction through pulse feedback. L2 is a 1:1 pulse transformer. The second stage is a fast avalanche transistor which produces 50 V when switched on. L4 is a I : 5 pulse transformer, which effectively produces 180 V on the anode of the third stage diode, and also on the camera-driving triode. The purpose of the diode stage is to lengthen the pulse to suit the final EL 360 pentode. The 180 V input pulse here results in an output of 4000V, with a 10 ns rise time. To enstire the satisfactory operation of the triggered spark gap (not shown) a dc bias of 2 kV is continuonsly applied to the trigger electrode1). Thus the actual trigger breakdown voltage is 6 kV. The delay in this four stage amplifier amounted to 25 ns, meaning an overall delay from the scintillation counter outputs to the triggered spark gap of less than 80 ns, when direct triggering via alternative output (2) is used. Additional pulses obtained from the triode EAC 91 were 2.5 V to drive a counter, and a 40 V, 1 ,us length pulse to drive the camera mechanism. In normal operation Lecher wires are used for the high voltage pulse shaping3). Good linear tracks are always obtained. The difference between tracks

LOGIC ELECTRONICS o b t a i n e d via alternative o u t p u t (2), a n d tracks obtained via o u t p u t (1) with the i m p o s e d delay o f at least one m i c r o s e c o n d before the registration of the decay electron, is barely perceptible. The circuits described in this p a p e r are inexpensive; the c o m p o n e n t s are easily available, and in our experience they are reliable. W e are pleased to t h a n k Prof. E. R. D o b b s for his support. A n d we are grateful to Messrs W. A. Baldock,

575

F. Grimes, A. King, J. Sales a n d B. Pashley for their technical assistance.

References 1) p. Rice-Evans and S. R. Mishra, Nucl. Instr. and Meth. 67 (1969) 337. 2) p. Rice-Evans, Spark, streamer, proportional and drift chambers (Richelieu Press, London, 1974). 3) p. Rice-Evans and I. A. Hassairi, Nucl. Instr. and Meth. 106 (1973) 345.