As the first stage of the future huge array, the Akeno air shower array was expanded to about 20 sq. km. by adding 19 scintillation detectors of 2.25 sq m area outside the present 1 sq. km. Akeno array with a new data collection system. These detectors are spaced about 1km from each other and connected by two optical fiber cables. This array has been in partial operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984. 20 sq m muon stations are planned to be set with 2km separation and one of them is now under construction. The origin of the highest energy cosmic rays is studied

Hara, T.

Hatano, Y.

Hayashida, N.

He, C. X.

Honda, M.

Ishikawa, F.

Kamata, K.

Matsubara, Y.

Ohoka, H.

Teshima, M.

English

NASA Technical Reports Server

430 OG 9.4-8
Akeno 20km2 Air Shower Array (Akeno Branch)
M.Teshima*, H.Ohoka, Y.Matsubara*, T.Hara, Y.Hatano, N.Hayashida,
C.X.He**, M.Honda, F.Isbikawa, K.Kamata, T.Kifune, M.Mori*, M.Nagano,
K.Nishijima***, Y.Ohno and G.Tanahashi
Institute for Cosmic Ray Research, University of Tokyo, Tokyo, 188 Japan
*Department of Physics, Kyoto University, Kyoto, 606 Japan
**Institute of High Energy Physics, Academia Sinica, Beijing, China
***The Graduate School of Science and Technology,Kobe University,Kobe,657
As the first stage of the future huge array we have expanded the
Akeno air shower array to about 20km2 b_ adding 19 scintillation detectors
of 2.25m2 area outside the present Ikm_Akeno array with a new data
collection system. These detectors are spaced about Ikm from each other
and connected by two optical fiber cables. This array has been in partial
operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984.
20m 2 muon stations are planned to be set with 2km separation and one of
them is now under construction.
I. Introduction
The origin of the highest energy cosmic rays is an interesting
problem. We have a chance to connect their sources with the astronomical
objects, because their propagation becomes simpler than that of lower
energies and the possible sources may be limited to some kinds of active
astronomical objects. The observation of giant air shower (GAS) produced
by cosmic rays above 1019 eV have been made at Volcano Ranch[l], Haverah
Park[2], Narabrai[3] and Yakutsuk[4]. But there still remain the
discrepancies among experiments not only in their energy spectrum but also
in their arrival direction distribution. A814
In order to clarify the
present ambiguities on the ABIB Ikm2AKENO crrcy
experiments and to extend the AS41 AS4
observation to higher energy, A847
a plan of huge surface array
of area over 100km2 is AB12 A825 A844
currently under discussion in A842ABa2 AB45
Japan. In this report we
describe about the "Akeno AB11
Branch" which is just AS51 AS43b
constructed at Akeno with the AB32 .XDAB56
intention of being a part of Sthe huge array.
A824 155
2. Array of .Akeno Branch" to AI
The detector arrangement
of the "Akeno Branch" is shown toBI m
in fig.1. The open circles _53
are the scintillation
detectors of 2.25m2 each, i t I |
located at about Ikm o 5oo _oo _oo.
separation. The closed A852
circles are scintillation Fig.1 The detector arrangement of
counters of Im2 area of the the "Akeno Branch".
https://ntrs.nasa.gov/search.jsp?R=19850026662 2020-03-20T16:47:12+00:00Z
431 OG 9.4-8
existing "Ikm2 Akeno array"[5]. The four large ones are also connected to
the present new recording system. The open square is a much detectors of
20m2 area under construction and the closed ones will be arranged within a
few years. Each detector is connected to the next one with two optical
fiber cables successively on a string as shown by a solid line. One cable
is used for sending the control commands to each module of the detector
from the center, and the other is for data transmission.
Inside the Ikm2 array, there are unshielded detectors of total area
of 169m2, shielded detectors of 225m2 (IGeV for vertical traversing muons)
and 75m2 (0.5GeV), and 53 fast timing channels of 10nsec resolution.
These are effective to measure the properties of the large showers at far
from the core.
3. Data acquisition system
In each station there is a module called Detector Control Unit (DCU)
which is designed with one board micro computer(Z-80A). DCU consists of 3
major parts; communication part, data processing part and detector monitor
and control part. Several DCU's are tied to a common string which
consists of two directional optical fibers. One fiber of outgoing
direction from the center is used to send commands, clock pulses for the
timer of DCU and timer frame (clear pulse for the timer). Another one is
used to accept the status information of each detector for the trigger
conditions and to collect shower data and monitor data from DCU's at the
center. The communication data rates on strings are 625kb/s.
Every DCU has a timer which synchronizes to that of the center with
20nsec accuracy. All signals from the detector are digitized and stored
in the ring-image-memory of DCU with the incident time of 20nsec accuracy.
Each DCU sends the information to the center in every 3.2 _sec period
whether the detector is hit by a particle or not. With this status
information, coincidence requirements can be set at the center. 6 folds
coincidence of neighbouring detectors is required for the trigger. When
GAS hits over the array, central unit recognizes coincidence of signals
from many detectors and knows its occurence time. Then the central unit
issues a command for all DCU's to search for the GAS data in the ring
memory with the time information of coincidence. Each DCU which has
accepted this command, stops data acquisition and searches for the all
corresponding data recorded within 100 _sec before and after the
coincidence. Central unit commands DCU's to send the picked out data one
by one. These data are sent to micro-computer(NEC 16bit PC9801) at Akeno
central laboratory through RS232C line of optical fiber and stored in the
10MB Hard Disk.
With this system not only the air shower data and monitor data are
acquired but also detector conditions can be controlled at the center.
Supplied voltage to the phototube, temperature, counting rate and pulse
height distribution of detectors are monitored periodically. The
discrimination level of the amplifier and the high voltage to the
, phototube can be controlled on request from the center. These functions
enable us to maintain the detectors stable for long term and make data
reliable. The details of this system are described in Ohoka and
Teshima[6].
4. Array response
The response of the present array was examined by analyzing the
artificial showers which were simulated by the Monte Carlo method. The
432 Og %]I-8
fluctuationsof electron density and 3 | I t
the shower front structure at core \
distances between 500m and 3000m of \1018-1019eV EAS observed at Frequecy
4km2/2Okm 2 array[7] were used for _2 \ 1_km2 -
the present simulation. 7= t _ \
The threshold energy of detect- _ _ \
able air shower is found to be about _ E°=lO_ev __\
I017.5eV and the recording 51 I, _ 2
efficiency reaches 100% at I018-5eV L _, _=
as shown in fig.2. The histograms e_ \_
show the response and effective area
for the showers hit inside the array. _ 0 -100
The broken line shows the area for =
all events including outside the _ aLtevents ...-
array. The sensitivity for shower _ _ .--°"" Il_km2 .-
size and arrival direction in case _-I ,/ I0
of showers hat inside the array are
shown in flg.3(a),(b) respectively, inside
We can determine the electron size area
with 30% accuracy, arrival direction _I.0
with 3 degree and core position with _ /80m. However for the showers outside
the array, these are 150%, 9 degree E°='O_eV Iand 150m, we need much caution to -: 0.1
use the outer showers for the dis- 8.0 9.0 10.0
cussion of primary energy spectrum LOGNe
and their arrival directions. Fig.2 The detection efficiency
of EAS with "Akeno Branch".
150 _.e 150
25_
9.0
2es LOG Ne=8. LOG Ne=9.5
IOO IO0 &e=4.66 Ae=_.51 &e=_62
50 50
.
0
• 8.5 9_ 9.5 0 5 10 15 0 5 10 15 0 5 10 15
8.0 LOG(Ne) &# (degree)
(a) (b)
Fig.3 The sensitivity for shower size(a) and arrival dlrection(b)
in the case of showers whose core hit inside of array.
433 OG 9.4-8
5. Conclusion and future plan
The observation of ultra high energy cosmic rays has started at
Akeno. In order to determine their origin, the expansion of array to
100km2 is under planning. The technical problems for expansion is already
solved through the experience under the construction of Akeno Branch.
The schematic diagram of recording system of the future array is
shown in fig._. The whole array is divided into several Branches. Each
Branch is managed by BCU(Branch Control Unit) which is connected
successively to the next one with two optical fiber cables "String". This
structure is exactly the same as that inside Branch. The commands from
the center and data from the Branch are put on this "String". The clock
pulse is supplied from the central unit SCU(System Control Unit) to each
DCU(Detector Control Unit) via BCU (Branch Control Unit). Since the timer
of every DCU synchronizes to the central timer, we can manage the GAS hit
in the boundary gap between branches, in the same way as ones hit inside a
Branch.
_ withICRI o" I._ anotherstation
SUPERII#IJ
MINICOMjIM I , I AI > I A2 I1_ #IIIAKENOBRANCH >
L_ BCU J ;
BI ! > ! B2 i--*-Yr
I I---'_-)'BCU ' c i BCU J
E]l H H j[_u [ ] [ [
DCU""e[ i
[
[
Fig.4 The data acquisition system of future surface array.
Acknowledgements
The authors wish to thank the participants of GAS workshops held in
Japan for their fruitful discussions. The simulation was carried out with
FACOM M380 at the computer room of Institute for Nuclear Study, University
of Tokyo.
Reference
[I] J.Linsley, Proo. 8th ICRC, Jaipur _ (1963) 295.
[2] D.M.Edge et al., J. Phys. A_ (1973) 1612.
[3] C.J. Bell et al., J. Phys. A X (1974) 990.
[4] O.S. Diminstein et al., Proc. 15th ICRC, Plovdiv _ (1977) 154.
[5] T.Hara et al., Proc. 16th ICRC, Kyoto_ (1979) 135.
[6] H.Ohoka and M.Teshima, to be appeared.
[7] M.Teshima et al., This conf. HE 4.7-3


Akeno 20 km (2) air shower array (Akeno Branch)

Akeno 20 km (2) air shower array (Akeno Branch)

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