Nuclear Instruments and Methods in Physics Research A337 (1993) 221-223North-Holland

A setup for determination of EAS parametersD. Nath, B. Das, M.J . Deb, G.K.D . Mazumdar and K.M. PathakDepartment of Physics, Gauhati University, Guwahati 781014, Assam, India

Received 20 July 1993

A new experimental setup has been developed at the Cosmic Ray Research Laboratory of Gauhati University to study thecomplex characteristics of large extensive air showers. The system consists of particle detectors, Cherenkov light detectors, radiopulse detector, necessary electronics and microprocessor based data acquisition system . The versatility of this setup has beendescribed in this paper.

1. Introduction

The distribution of electrons and muons in theshower front, their correlation with Cherenkov pulseresponse have become a very important factor to studythe EAS core location (Xo, Yo), size (N), primaryenergy (EP), age parameter (S) and primary masscomposition over a certain energy range [l-3]. Studieson possible production of heavy, long lived particles inEAS need measurement of arrival time difference ofmuons and electrons [4,5] . Precise measurement of thearrival time distribution of shower front electrons isuseful to study the arrival direction of primary particles[6] . The structure of the shower front can be studiedfrom lateral distribution of the full width at half maxi-mum (FWHM) of Cherenkov pulses [7]. This paperpresents in detail the setup developed, the determina-tion of shower parameters and some experimental find-ings .

2. Experimental set up

Eight particle detectors, each detector having oneplastic scintillator block (50 cm x 50 cm x 5 cm), onePMT (XP2050) and a preamplifier (PA), two Cherenkovdetectors (CD), each consisting of one light reflector,one PMT (XP2050) and a preamplifier and one radiopulse detector (RD) having a rod antenna fitted withband pass filter (BPF) are located in the GauhatiUniversity air shower array (latitude 26°10'N, longi-tude 91°45'E, altitude 51 .8 m a.s .I ., declination 1°2'W).The counter arrangement is shown in fig. 1.

The experimental arrangement includes fourteenindividual channels connected to a microprocessor (In-tel 8085A) based data acquisition system . The system is

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controlled by a control unit which is triggered by amaster pulse (MP) generated by the coincidence unit[8,9] . Out of fourteen channels, eleven are for pulseheight measurement. Each of these channels is drawnfrom either particle or Cherenkov or radio pulse detec-tor followed by a main amplifier (MA), integrator(TNT), peak detector (PD) and sample and hold (S/H)units. PD and S/H units are triggered by the sameMP. The remaining three channels are for the mea-surement of arrival time differences of shower particles[9] . These three channels, taken from three particledetectors, are connected with a three channel time-to-amplitude converter (TAC).

50mA2

loom

NUCLEARINSTRUMENTS& METHODSIN PHYSICSRESEARCH

SectionA

50m

0a

aa

A6

A5

A4

Fig . 1 . Array diagram of detectors . A 1 _ ß =Particle detectors,A 3 , = shielded particle detector, C8,9 = Cherenkov detectors,

RIO = radio pulse detector .

222

The flow diagram of the experimental setup withthree channels, one each for particle, Cherenkov andradio, associated with coincidence and TAC units isshown in fig . 2.

One storage oscilloscope (DSO 4072, 100 MHz) isbeing used to record the pulse shape. Selection ofparticle detectors both for coincidence and TAC unitshave been made as follows:

Coincidence : (1, 3, 4), (1, 3, 5), (1, 3 6), (3, 2, 4),(3, 6, 4)

TAC:

(3, 3', 1), (3, 3', 4), (3, 3', 6)

3. Data collection and applications

The digital outputs of the data acquisition systemrepresent the amplified pulse height from each detec-tor. Outputs of the particle detectors are convertedinto particle densities using the most probable pulseheight from the single particle calibration . Outputpulses of Cherenkov counters are calibrated in unit ofvertical equivalent of penetrating muons (p c ) [1] . Ar-rival time difference between muons and electrons arecalculated from relative amplitude difference betweenTAC channels connected with 3 and 3' detectors . Therelative amplitude difference between TAC channelsconnected with detectors 3 and any one of 1, 4 or 6gives the arrival time distribution of shower front elec-trons.

3.1 . Determination of (Xo , YO ), S and N

Particle densities at the four detectors are sufficientfor the determination of these parameters . The calcu-

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D. Nath et al. /A setupfor determination ofEAS parameters

lation based on Chi square minimisation procedure isdone by using a computer program.

3.2. Calculation of N,, and EP

Total number of muons (NP )mined by the equation

Fig . 2 . Flow diagram of experimental setup .

pw (r)21Trôe

\

o)m-Z,

in a shower is deter-

where pN(r) = muon density at a distance r from thecore, ro is constant for given altitude . Primary energy(EP) is calculated with the equation from ref. [10] givenby

EP = 1016

[eV] .

3.3. Determination of zenith angle (0)

Calculation of 0 have been done considering fig. 3and using the equation,

(At xc, ,B=si I

1In

-1d

where At = arrival time difference of shower frontelectrons between two detectors A and B. d= distancebetween A and B, c = velocity of light.

4. Experimental findings

The showers recorded are divided into differentenergy groups (10 15 eV to 10 17 eV). The age param-

PA

A 3

CD

RD BPF

MA

MA

MA

MA

MA

MA

DISC

DISC

DISC

TA

c

PD

PDIMLFM=w1r®PD

UNIT

xF-WW FW Z

0W o

U

TO MUX

TO MUX

.2

A t

D. Nath et al. / A setup for determination ofEASparameters

Fig . 3 . Inclined shower geometry .

eter calculated for these showers ranges from 0.8to 1 .4. The size is found to be varied from _ 105 forEP = 1015 eV to _ 107 for EP = 1017 eV .

Arrival time difference of muons over electrons fallwithin the range 10-15 ns with r ranging from 30 to

1015

1016

1017EP(eV)

Fig . 4. pw /p c vs EP curve for r = 70 m, 30'_< 0 S 45° .

100 m and not much more dependent on EP and 0 .Fig. 4 shows sharp increase of muon content in theshowers with EP close to 1016 eV .

5. Conclusion

The setup described above has been found to beuseful to study almost all the parameters of large EAS.The dynamic range of the time analyser is 220 ns andmeasuring step is 3.5 ns which is sufficient to measurethe inclination even greater than 60°. Fig. 4 reflectsthat there may be a change in primary mass composi-tion near EP = 1016 eV .

Acknowledgement

The authors are thankful to ASTEC, Assam forfunding the research project . We wish to thank Prof.A.W. Wolfendale of Durham University, UK for hiskind visit to the concerned laboratory and his valuablesuggestions.

References

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[1] P.R . Blake et al ., Proc. 20th ICRC, 6 (1987) p. 21 .[2] A.V. Glushkov et al ., Proc. 21st ICRC 9 (1990) p. 122.[3] K. Boruah et al ., Indian J. Pure and Appl. Phys . 28

(1990) 628.[4] G.B . Khristiansen et al ., Proc . 21st ICRC 9 (1990) p. 150.[5] Y. Toyoda et al ., Proc. 20th ICRC 6 (1987) p. 370.[6] A.W. Wolfendale, Cosmic Rays (George Newnes Ltd.,

Tower House, London, 1963).[7] John Linsley, Phys . G. Nucl . Phys . 12 (1986) 51 .[8] G.K.D . Mazumdar et al ., Proc . Nat. Symp . on Nucl .

Electr. and Instr . (1989) p. 637.[9] D. Nath et al ., Nucl . Instr . and Meth . A 330 (1993) 293.

[10] H.R . Allan, Prog . Elem . Part and C.R . Phys. 10 (1971)172.