The new Buckland Park Air Shower Array has been producing analyzed shower data since July 1984. The array is described and some preliminary performance figures are presented

Clampa, D.

Clay, R. W.

Corani, C. L.

Dawson, B. R.

Edwards, P. G.

Elton, S. D.

Gregory, A. G.

Patterson, J. R.

Prescott, J. R.

English

NASA Technical Reports Server

OG 9.4-4
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THE BUCKLAND PARK AIR SHOWER ARRAY
R.W. Clay, C.L. Corani, J.R. Patterson, B.R. Dawson, P.G. Edwards,
A.G. Gregory, J.R. Prescott, S.D. Elton, and D. Ciampa.
Physics Department, University of Adelaide,
Adelaide, South Australia. 5000.
ABSTRACT
The new Buckland Park Air Shower Array has been producing
analysed shower data since July 1984. The array is
described and some preliminary performance figures are
presented.
1. Introduction. The Buckland Park array has recently been upgraded
with the addition of new scintillators with the result that its shower
size response has been extended to ~ i0_ particles at threshold. The
array now detects events at a mean rate of ~ 1/10s. The main purposes
of the new array are to continue the study of point sources of ultra
high energy gamma raysl, 2 in the southern hemisphere and the properties
of cosmic ray air showers with sizes less than 105 particles.
2. Array Description. The design considerations and predictions are
given in ref. 4. Briefly, the major considerations in optimizing the
rates of detection of small air
showers were the need to increase
N the ground area covered by
closely-spaced detectors and to
increase the individual detector
areas so as to minimize sampling
[]T,M_NG fluctuations.
• OENSIrY
0 NOTFINISHEO
V U
K. • • , The array consists of 27
scintillators arranged as shown
in figure i. New scintillators
L. M have been added to the old
array 3 to increase the density of
_j o o !x detectors near the centre where
_0 _ eight detectors AI, BI, C, DI,
[] Q m El, D, S and T have also been
T s _ increased in size from 1 m2 to
2.25 m2 .
The detectors are scintil-
lators of 50 mm thickness housed
G in pyramidal enclosures 4 which
are then housed in thermally
insulated galvanised iron huts.
All detectors contain a particle
Fig. 1 Array layout density measuring photo-
multiplier (RCA 8055 general
purpose 120 mm tube or
https://ntrs.nasa.gov/search.jsp?R=19850026658 2020-03-20T16:47:05+00:00Z
415
equivalent) which feeds a pre-amplifier at the detector before signal
transmission to the central laboratory. Saturation occurs at ~ 300
particle level Eleven of the detectors have, in addition, a fast timing
photo-multipller (Philips XP2040) which directly drives 50 ohm cable
(RG8) to the central laboratory. Fast timing detectors were added at
sites S and T to enable directions to be found for small showers falling
nearby and to improve the angular accuracy in the north-south plane for
medium and larger showers falling near the centre. Two further slow
detectors will soon be added as indicated in figure 1 and fast timing
introduced in X and W detectors to improve directional measurement of
showers in the east-west plane.
An event is recognized when any two of the 19 inner amplitude
measuring detectors trigger at the threshold of 2 particles, (each of
which has an individual rate ~ 0.5 Hz) and any two of the fast timing
detectors also trigger. (Their individual rates are ~ 100Hz). The slow
system thresholds are set well above those in the fast system to ensure
that, in most cases, the fast detectors trigger as closely as possible
to the start of the photomultiplier pulse and reduce timing
uncertainties associated with the fast system rise time (ot ~ 5ns). A
further result is that except for the smallest of showers, there are
normally many more than two fast detectors triggered and directions can
be found with timing redundancy. The final trigger rate is ~ 8000
events day -I.
The density measuring channels have final pulse shapes which are
quite long (rise ~ lOOns, fall ~ 5Bs) and these pulses are fed to CAMAC
Peak-sensing ADCs (LeCroy 2259A) which are gated by the array trigger.
The array data is calibrated and partly analyzed (for angles of
incidence) by a Nova minl-computer system. Output is presently recorded
on magnetic tape for later analysis and one 2400 foot tape lasts about
five days. The resolved single particle peaks of all detectors are
monitored regularly, normally when each tape is changed.
The relative times of arrival of the fast timing pulses are
measured with ~ i ns bit resolution using a CAMAC Time to Digital
Convertor (LeCroy 2228A). Our previous practice had been to start the
TDC off using a discriminator output from the central detector, the
others being delayed a fixed amount to act as stops. With our more
loose coincidence system we now do not specify any particular fast
channel to be the TDC start channel. Instead the fast coincidence
output triggers the TDC start. In order to ensure that all pulses will
be within the range of the TDC, there is a further monostable delay of
N 200 ns in each channel after the discriminator and before the TDC
stop. These delays appear to be inherently quite stable and do not
suffer from any bandwidth limitations of delay cable.
Any combination of fast timing detectors may trigger on a given
event. We need to find one timing detector which has been triggered and
calculate all usable (non-collinear) time differences after subtraction
of the known delays. It is then straightforward to calculate the zenith
and azimuth angles for the shower axis. At the same time, right
ascension, declination and Julian time are calculated for the event.
The chi-square fitting parameter for a planar shower front is consistent
OG 9.4-4
416
with a directional accuracy ~ 2.5/c0s 8 degrees where most detectors are
triggered. The worst cases wlll be for small showers triggering only
our inner 2.25 m2 detectors. In these cases, we have a detector spacing
of only 8m and directions are expected to have uncertainties > I0°.
3 Preliminary Results. The array detects showers wlth analysed sizes
down to I0_ particles and with our present preliminary shower analysis
we have a median shower size ~ 0.9x105 particles. Figure 2 shows a
preliminary graph of the size distribution for analysed showers over the
whole array and compares it to the performance of the old array. We are
beginning to develop our directional analysis system and Table 1 shows a
sky map with the accumulation Of events for several sidereal days in
which only showers with at least five measured times are used. The map
shows the extent of sky coverage available from Buckland Park.
w
= Flg. 2 Size Distribution for
1_8 all events accepted by whole
_ array. The events are analysed
using the NKG function and
MINUIT 5 program package.
10_ 10s 106
Ne ( pnrtides)
References
I. Protheroe, R.J., Clay, R.W. and Gerhardy, P.R., 1984, Ap. J.
(Lett.) 280, L47.
2. Protheroe, R.J. and Clay, R.W., (1985) Nature (in the press)
3, Crouch, P.C., Gerhardy, P.R., Patterson, J.R., Clay, R.W. and
Gregory, A.G. (1981) Nucl. Inst. Meth., 179, 467.
4. Clay, R.W., Corani, C.L., Dawson, B.R., Gregory, A.G., Patterson,
J.R., and Prescott, J.R., (1983) Proc. 18th Int. C.R.C. •
(Bangalore), 6__ 257.
5. James, F. and Roos, M., 1975, Computer Phys. Comm. IO, 343.
OG 9.4-4
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0 0 3 5 14 ' 33 43 103 141 187 335 2?2 257 268 340 197 151 100 66 24 10 7 8 1 0 0 1 1
0.5 0 0 10 16 23 70 109 144 178 231 245 308 23? 235 161 152 93 70 33 14 "5 3 1 0 0 0 0
1.0 0 2 4 15 29 56 100 136 186 318 _?0 29_ 269 256 197 139 102 66 37 36 7 6 2 1 0 0 0
1.5 0 2 4 20 31 07 96 143 303 330 253 36_ 257 356 199 153 91 61 37 10 9 2 0 1 0 0 0
2.O 0 1 13 6 31 39 102 150 182 239 250 374 255 266 2OO 137 93 68 24 17 "7 4 2 1 0 0 0
3,5 0 3 6, 8 36 58 115 153 174 173 253 285 279 237 316 140 113 57 37 13 ;9 3 0 1 0 0 0
3.O 0 3 5 9 35 68 106 143 177 246 2_1 273 346 218 2O5 136 104 57 2O 3 _0 1 1 1 0 1 0
3.5 0 1 8 16 36 62 37 149 197 237 239 388 350 250 186 143 80 07 25 16 !6 2 1 1 0 0 0
4.0 0 1 6 30 36 42 30 144 187 310 253 335 362 359 133 182 99 69 29 13 _8 2 0 0 1 0 0
4.5 0 0 5 17 26 50 101 131 194 223 283 248 234 238 I34 160 98 53 _2 17 _8 4 1 0 0 0 0
5.O 1 2 7 13 35 51 g5 140 305 253 254 264 294 245 182 156 104 57 39 22 10 3 ) 1 0 0 0
3._ 1 4 5 12 3_ 67 88 141 193 358 346 261 369 329 19L 148 88 83 29 14 4 3 1 2 0 0 0
a,O 0 1 3 18 39 43 " 95 137 310 94O 276 391 278 244 181 144 98 59 37 e 11 4 1 0 1 3 0
6.5 0 2 3 14 _6 77 01 141 teo 2_4 245 2O9 356 22_ 2)_ 1_5 96 B_ 27 12 6 I 2 1 0 0 !
7,O 0 3 6 13 39 55 87 153 2O9 32O 27_ 304 355 356 313 1_9 84 61 3O 13 6 5 1 ! 0 0 1
7.5 1 3 3 18 25 50 102 146 198 363 R08 261 259 339 191 1_5 108 54 37 12 8 5 1 0 0 0 0
3.0 0 2 6 1_ 32 58 10_ 12g 190 243 275 376 248 344 183 1_6 96 _5 3O 15 13 ! 1 0 0 0 0
8.B 0 1 8 10 28 63 96 119 2O3 222 _74 205 _81 330 _11 147 IO0 78 4O ls 12 3 1 0 0 1 0
9.O 0 2 2 18 35 65 87 138 192 327 263 265 277 342 21_ 159 96 63 3O 16 6 0 0 3 0 1 0
g._ 0 2 3 13 28 50 100 122 161 328 _5 314 266 243 199 145 83 57 29 12 4 5 1 1 0 0 0
10.0 1 3 5 10 34 56 100 1_9 20_ 230 263 25? 260 2_0 102 Z61 _4 04 26 12 5 2 0 0 0 0 0
10.5 0 2 4 13 26 57 37 144 191 327 383 280 _44 313 138 105 _2 37 13 3 _ 9 1 1 0 0_71
C_
_:_ 11.0 0 1 1 18 22 68 106 154 200 22S 261 283 280 260 191 148 90 65 43 13 7 3 0 0 1 0 0
,-]
11.5 0 5 2 10 29 64 100 146 188 308 280 276 334 265 317 156 98 43 31 14 3 1 0 1 0 0 3
13,0 0 8 3 / 13 29 48 87 183 174 333 a73 249 350 338 104 148 103 41 26 34 8 3 1 0 1 0 "0
Pl
_2_ 13.8 0 3 a 13 37 80 92 134104 238 255 253 303 325 106 175 104 50 25 15 3 4 0 1 0 1 1
13.0 0 3 4 10 30 88 93 144 100 100 268 283 260 318 193 139 100 00 33 L7 5 3 2 3 0 0 0
13,5 0 0 4 17 39 48 108 144 103 341 274 288 281 330* 199 131 101 53 34 15 7 3 1 0 1 0 0
165 229 266 380 373 385 210 134 107 83 38 20 6 3 1 1 0 0 114.0 0 3 e 13 36 63 74 133
14,8 0 2 0 13 34 63 102 151 _91 310 244 387 340 246 202 150 ' 92 58 3? 16 6 3 1 0 0 1 0
r/) 18,0 0 1 2 32 39 88 90 133 207 289 273 304 282 353 310 146 114 64 34 19 8 2 0 0 1 1 0
18.5 0 0 7 36 30 81" 104 142 187 205 203 376 202 237 198 144 103 84 31 I1 ? 6 3 O 0 0 0
16.0 0 1 11 22 30 69 108 139 307 334 333 269 293 246 182 157 100 84 33 18 6 8 3 1 0 0 0
16,5 0 0 8 16 24 55 96 147 203 238 253 267 264 248 109 148 99 80 33 13 1 3 1 0 0 0 0
17,0 0 0 7 10 33 50 103 142 188 231 277 378 284 228 317 167 108 63 36 30 4 3 3 0 1 0 0
17.5 3 3 ? 15 24 85 90 133 203 233 383 282 248 237 310 144 90 70 31 18 0 8 1 1 0 0 0
18.0 0 2 4 14 28 83 100 134 178 212 271 203 257 227 LO0 142 EL 68 37 12 3 4 2 0 0 0 2
18.8 0 3 8 8 31 48 03 156 163 326 268 289 280 227 188 154 93 @0 35 18 7 1 2 0 0 0 0
10.0 0 3 8 _17 36 ?0 84 136 196 233 33? 283 200 253 190 154 107 60 40 13 6 7 0 2 0 0 0
19.3 0 1 ? 9 39 63 102 141 160 243 267 370 268 341 200 161 109 65 33 12 2 3 1 0 1 0 0
30.0 1 3 0 13 31 58 98 148 170 216 350 310 391 333 301 141 98 84 23 0 ? 3 1 0 0 0" 0
20.3 0 2 7 13 24 81 90 129 165 337 340 361 250 249 308 180 110 69 39 14 8 3 2 0 0 0 0
21.0 2 0 6 17 28 53 83 142 193 316 281 2?9 372 23_ 197 148 101 58 24 19 8 4 0 0 0 2 Q
91.8 1 1 2 14 32 88 105 100 106 233 253 271 251 233 194 161 100 72 37 19 8 4 8 1 0 0 0
22.0 0 3 7 16 31 84 27 147 194 338 380 202 271 321 188 147 113 44 40 22 4 7 0 0 0 l 0
22.5 0 5 ? 12 38 21 110 137 188 342 202 360 332 221 219 183 115 87 31 30 4 2 0 I 0 0 b
23.0 2 1 3 19 30 80 108 138 190 213 2_9 344 289 201 205 145 22 61 28 12 ? 2 1 0 0 1 0
23.8 0 1 6 18 27 03 09 128 196 205 248 301 283 347 103 151 104 50 21 18 7 3 3 0 0 0 0
-20 -85 -80 -78 -?0 -08 -00 -88 -80 -48 -40 -35 -30 -28 -20 -15 -10 -8 0 8 10 15 30 25 30 35 40
DECLINATION (DEGREES)
TABLE 1
Sky map showing typical coverage of the southern sky.
The median shower size is 0.9XI0 5 particles.


The Buckland Park air shower array

The Buckland Park air shower array

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