The telescope under construction is mainly for the purpose of locating the arrival directions of energetic particles and quanta which generate air showers of sizes 10 to the 5th power to 10 to the 6th power. Both fast timing method and visual track method are incorporated in determining the arrival directions. The telescope is composed of four stations using scintillators and neon flash tubes as detectors. The system directional resolution is better than 1.5 deg

Chan, S. K.

Ng, L. K.

English

NASA Technical Reports Server

252 HE 4.5 - 14
Construction of a Cosmic Ray Air Shower Telescope
L.K. Ng and S.K. C_an
Physics Department, University of Hong Kong
Hong Kong
Abstract
The telescope under construction is mainly for the
purpose of locating the arrival directions of energetic
particles and quanta which generate air showers of sizes
105 - 5.106 . Both fast timing method and visual track method
are incorporated in determining the arrival directions. The
telescope is composed of four stations using scintillators
and neon flash tubes as detectors. The system directional
resolution is better than 1.5 ° .
i. Introduction. Applicatio6 of medium-size shower arrays
in astronomical observations is exemplified by the Kiel
experiment I in the detection of high energy gamma rays from
Cygnus X-3. This type of continuous observation using ground
-base air shower arrays may yield more fruitful results, if
it is participated by more stations spreading out at various
latitudes. For long term observations, such telescope could
be less elabourate than Kiel's. The requirements may just be
high directional resolution and ability to measure the
muon/electron density ratios of individual showers, in
addition to the usual determination of lateral distributions
and age parameter. This paper reports a simple air shower
telescope which meets the above requirements.•
2. Detection system. It consists of four detector
assemblies (a required minimum), which are at sea level and
arranged as shown in figure i.
N
• Flash-tube tray
- I Scintillation i
T "
,. 'L_ _ _ _2¢m CONCRETE
__\ [ 'I ¢_ Flash-tube trays I
I _ I 103Cm _I
I occr)" [x-)coI -
Fig. 1 _e Shower Array. Fig. 2 _e Detector Assembly.
Each detector assembly has a soft roof and contains a
plastic scintillator, 4 trays of neon flash tubes and an
absorber medium as shown in figure 2. The scintillator has
https://ntrs.nasa.gov/search.jsp?R=19850027723 2020-03-20T17:05:18+00:00Z
253 HE 4.5 - 14
a minimum geometry of 0.5m x 0.5m x 0.05m and is viewed by
two 2" photomultipliers in contact with the scintillator.
For precise arrival time determination, anti-jitter preamp-
lifiers described in another conference paper (HE 4.7 - 9)
are used.
Each of the four flash-tube trays consists of 48 c]ose
packed tubes. Each tube has a geometry of 2m x 1.9cm did.
and when it fires, its output electromagnetic signal is
picked up by a latch. There are 4 x 48 latch units in an
assembly providing 24 bytes of data per shower per assembly.
Clearly, the top tray is for shower density measurement and
the bottom three trays are for much density and direction
measurements.
3. Electronics. For each shower, data required from the
system include information from the flash tubes, the
particle arrival times, and the event time and date. Block
diagram of the electronic system is given in figure 3.
Communication between each assembly and the central
processing station is linked by transceiver buses through-
out. A master pulse is produced by 4-fold coincidence of the
scintillator outputs (2_s window). The master pulse is used
to reset the flash-tube latches, to fire the flash tubes by
triggering the UHT pulsing unit, and to start the data
acquisition subroutine in the microcomputer.
I decoder
difference Micro- H ' Address _-_ latches
=it computer ___ decoder 4__ for
L"I°I isystemI l tebufferlr"lIAsse=lles
Scintill, I _ A, B, C, H
Pre_pl i
4-fold Nster pulse cable I _T pulsing
• J )I mite for
coincidence _ A, B, C, H
Fig. 3 Block diagr_ of the electronic system.
However, the key part of the electronic system is the
time-difference unit which determines the relative arrival
time of particles falling at the scintillators. The arrival
time is precisely related to the leading edge of the output
pulse from the anti-jitter preamplifier. This leading edge
o is free from distortion during transmission, because the
signal cable is terminated by a matched pair of driver/
receiver.
The time-difference unit contains three sets of time-
to-amplitude converter(TAC) and analogue-to-digital
converter(ADC). The leading edge of an input pulse from one
254 HE 4.5 - 14
of the assemblies A, B, C is compared with a common time
reference, and the difference is then digitized by the TAC
and ADC. The TAC and time reference circuits are shown in
figure 4.
Flip-flop ---------OE'-_ or CA'--_
74S00
' " __eL c ?
e----- .# ( s_c ---r-'°_7_[ 1 _
_ _i L
0-tu n
Cin Bin Ain Fig. 4 The time-to-_plitude converter.
The TAC is a sample/hold chip (Teledyne Philbrick 4856)
with a charging rate _1.5 V/ps and a drift rate _0.8 mV/s at
the hold state, using a low leakage capacitor C of 0.027 pf.
The hold pulse (at SHC) is generated by a fast flip-flop as
shown. Its leading edge Tr is the time reference
corresponding to the latest leading edge of the three input
pulses Ain , Bin , Cin (after triple coincidence). Its falling
edg____eTf corresponds to either the end of ADC conversion
(EOC) or the end of computer processing (CA---_),whichever is
the last. When the chip is at the sample state, the
capacitor C is being charged up starting from 0 V at time Ts
, the leading edge of the input pulse. If there is a shower
event, the hold pulse opens the switch at the reference time
T_. Hence C stores a voltage amplitude corresponding to the
time difference (Tr- Ts). It is held until the falling edge
Tf sets in, and the chip starts to sample again.
Digitization is done by a slow but high precision ADC
(MC14514) with a reference voltage +2.48 V provided by a
chip MC1403. Th_s together with the TAC gives a full range
of 1999 corresponding to a time difference of 1768 ns. Hence
the time resolution is better than 1 ns. The unit is
calibrated by using a fast CRO and a signal generator. The
various fixed time delays are also determined similarly.
From the geometry in figure i, _ time difference of
2.9ns corresponds to _i ° zenith angi_, Hence the directional
resolution is mainly determined by the time fluctuation in
the scinhillation counters, including photomultipliers and
preamplifiers. The fluctuation is not expected to exceed
4ns. Therefore, the directional resolution is better than
1.5 ° .
255
HE 4.5 - 14
4. Shower rate and efficiency. The minimum trigger density
at each scintil_or _s 4 m :_. Using the differential
intensity spectrum 2 ,
j(N) = 1.95.106N -2"7 ,
The shower rate is estimated by the expression,
_-2--_-_c_+2f j(N)A(N)dN, with c_ = 8.6 at sea level,
and is presented below.
---2.7
Shower size (N - N+6N) A(_) N A(_)_N
9.2 E4 - 1 E5 1.0 E1 0.03 E-7
1 E5 - 2 E5 3.0 E2 4.87 E-7
2 E5 - 3 E5 2.05 E3 6.31 E-7
3 E5 - 4 E5 4.10 E3 4.76 E-7
4 E5 - 5 E5 6.10 E3 3.47 E-7
5 E5 - 6 E5 8.00 E3 2.61 E-7
6 E5 - 7 E5 1.05 E4 2.16 E-7
7 E5 - 8 E5 1.24 E4 1.73 E-7
8 E5 - 9 E5 1.47 E4 1.46 E-7
9 E5 - 1 E6 1.67 E4 1.22 E-7
1 E6 - 2 E6 2.40 E4 7.78 E-7
2 E6 - 3 E6 4.20 E4 2.58 E-7
3 E6 - 4 E6 5.70 E4 1.32 E-7
4 E6 - 5 E6 6.80 E4 0.77 E-7
Total 41.07 E-7
Hence the shower rate is ¢ (>9.2.104 ) = 4.7 hr -I .
" The effective area of each flash-tube tray is 1.73 m2
and the expected efficiency of the tubes is _85%. Hence on
the average, the minimum number of shower particles recorded
. from each tray is 4 x 1.73 x 0.85 = 5.9. The directions of
the muon tracks in a muon-rich shower can be used to check
the shower direction obtained by the time-difference method.
. 5. Acknowledgement. The authors are grateful to Professor
D.J. Newman for his support and encouragement.
" References.
i. Samorski M and Stamm w, Ap.J. Lett. 268 (1983) LI7.
2. Hillas A Met al, Phys. Reports, 20C (1975) 79.


Construction of a cosmic ray air shower telescope

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