At an altitude of 1890m, a pre-test with an Air shower (AS) core selector and a small acoustic array set up in an anechoic pool with a volume of 20x7x7 cu m was performed, beginning in Aug. 1984. In analyzing the waveforms recorded during the effective working time of 186 hrs, three acoustic signals which cannot be explained as from any source other than AS cores were obtained, and an estimation of related parameters was made

Du, S.

Gao, X.

Liu, Y.

English

NASA Technical Reports Server

838
HE 7.I-4
ACOUSTIC DETECTION OF AIR SHOWER CORES
Gao Xiaoyu
Physics Dept. Yunnan University, Kunming, Yunnan, P.R.C."
Liu Yongyue
Institute of High Energy Physics, BeiJing, P.R.C.
Du Songlin
Physics Dept. Yunnan University, Kunming, Yunnan, P.R.C.
ABSTRACT
At an altitude of 1890m, a pre-test with an As core
selector and a small acoustic array set up in an
anechoic pool w&th a volume of 20xTx7m _ was per-
formed, beginning from Aug. 1984. In analysing the
waveforms recorded during the effective working time
of 186 hrs, three acoustic signals which can not be
explained as from any sources other than AS cores were
obtained and the estimation of connective parameters
was made.
I. Introduction. Up to now, the only way of studying VH en-
ergy phenomena is by means of air shower. But, as the AS
energy becomes higher and higher, the sensitive area needed
to detect it becomes larger and larger. Limited finances
make it difficult to perform the experiment. The suggested
scheme of accoustic detection of AS cores (I) (2) will be
not only less costly, but also able to determine the core
energy and the accurate position at which the high trans-
verse momentum may be shown. And furthermore, some topics
associated with astrophysics can be studied by determining
" the directions along which AS's ar_ive. The experiments on
acoustic signals caused by proton beams (5) have proved it
is feasible to detect acoustic signals caused by high energy
particles passing through water. Our preceding work (4), in
which the influences of the duration of heating pulses and
of the transient responses of hydrophones on the time
structures and the amplitudes of acoustic pulses were studi-
ed in particular, indicated that the energy threshold of the
acoustic detection calculated from the data of accelerato_
experiments, without taking into account the effect of spill
time of the proton beam, was much too high. How-ever, the
acoustic signals are still weak because of the verz. small
energy transformation ratio (10 -? -10-/°). The low S/N ratio
has been remaining the main difficulty in the application of
the acoustic detection. Particularly, in a natural water
body (such as an ocean or a lake) background noises from
the surface conditions (wind, waves, boats) and from animal
life will greatly reduce the S/N ratio. In order to accumul-
ate experiences for designing a largescale acoustic detector,
the pre-test was performed with an anechoic pool whose back-
grot]n4 noises were very low.
https://ntrs.nasa.gov/search.jsp?R=19850027845 2020-03-20T17:10:04+00:00Z
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HE 7.1-4
8. Methods. The experiment arrangement is schematically shown
in Fig. I. The AS core selector, which consisted of four
counters with active area of 0.33m 2 each set up on the cor-
ners of the pool,was
r 1254[_ vvvv arranged to select
! H _ _ E_1Or_ev events"
When there was a
fourfold coincidence
pulse coming out of
- c AS cor selector,
__ allbrator I the fourst p s air-
__ case wave generator
was triggered once
and produced three
simultaneous outputs.
__ , One of the outputswas used to triggerthe double-beam
Fig. I Schematic of experimental oscilloscope and the
arrangment and electronics_ other two were fed
respectively to the
two signal channels so as to increase the effective breadth
of the screen by four times. The sweep speed of the oscil-
loscope was 0.2ms/em, so that about two and a half timebase
lines were enough to display the events happening at any spot
in the pool, and the rest part of timebase lines which had no
information relative to AS cores on it was used for compari-
son.
The four PZT-5 spherical hydrophones used in the experi-
ment are essentially the same, and their frequency response
are flat up to 50 KHz. In each signal channel, acoustic sig-
nals with the same phase coming from the two hydrophones set
up very closely together were amplified and then added to-
gether to improve the signal-to-electric-noise ratio. The
ou_ut terminals of the two signal channels were connected
respectively to the two input terminals of the oscilloscope.
According to the most propable spectrum distribution of
signal and the influence of the response of hydrophones on
the time structures of acoustic signal and the consideration
on minimum BW with tolerable distortion, we employed filters
' , l i l with a pass-band of 3KHz to
reldyne/c_.Hz_ 30KHz to limit noises as much
as possible. It was shown by
-7o-_ --_----- our simulating experiment with
Q-switch laser beams that
these filters did not cause
-so- serious distortion. The ane-
choic pool used in the e_peri-
ment had low background nois-
I es. Fig. 2 shows the noise
-901• 3 _0 30 50 _z spectrum for the whole deter-
, tion system (including ambient
Fig. 2 Noise spectrum for wno±enoise, noises Qf hydrophones
• detection system, and amplifiers), the noise
'855 HE 7.1-4
lever is 1.5x10-4#/b/Hz=at a freqency of 30KHz. The water
termperature was 18.5_C during the experiment.
5. Results and Discussion. In sweeping and analysing all of
the traces recorded during the effective working time of 186
hr. The acoustic signals of three events which had the
following characteristics in common were obtained.
I. The signals from the two channels are both bipolar
pulses and have the same shape except the amplitudes.
The caculation (5) from thermoacoustic model and the
experiments (5) (4) with proton beams and laser beams have
shown that when a beam of charged particles passes through
water, the acousticsignal caused by the sudden thermal
expansion of water is a bipolar pulse. AS cores produce this
type of event.
2. The positions at which {_le signal pulses appear on the
timebase lines, whlch are determined by the propagation times
of the sound wave from the source to the hydrophones in
water, are accordant wi_h the geometrical confiquration of the
pool and the location of hydrophones in it.
3. The attenuation of the signals obeys the propagation.
law of the cylindrical wave, i.e. pocq/v/_ .
Fig. 5 Gives the copy of event acoustic signal No. KY 5.
The three characteristics mentioned above are only the
necessary requirements that acoustic signals caused by AS
cores must satisfy. On the other
hand, the possibilities that the
same results may be caused by other
factors have to be considered and
eliminated one by one.
(a) If any eletric interference
was picked up, its waveforms from
the two signal channels would appear
" at exactly the same position on the
u__ • * corresnonding timebase lines. We did
Fig. 3 The copy of event saw these waveforms. But it was very
acoustic signal easy to identify and ignore them.
Mo. KY 3. Scale is One kind of interference which must
200%(s/cm. be considered is the noises from the
electric equipment themselves. After
they had worked continuously for
8hr., we short-circuited their inputs and observed the noise
waveforms, it was seen that a large number of which were
unipolar pulses emerging at random. No bipolar pulses were
observed.
(b) If any acoustic disturbance was recieved by the hydro-
phones, its waveforms would be of damped oscillation form but
bipolar pulses in general. Even if bibopar pulses had appear-
ed, •their ampli_/des would not have varied as I/_ as re-
quired in the near field configuration. We did not find any
886
HE 7.1-4
possibility in the exi 'stance, of _ cylindrical source besides
AS cores in the pool.
(c) If any other interferences were present, no matter at
regular time or at random their waveforms would appear on
every timebase line with the same probability, because the
oscilloscope was triggered by the coincidence output of the
AS core selector which occurred at random. In order to obtain
sufficient record of the background noises, we triggered the
oscilloscope manually at various intervals between different
stages of the experiment and all of the timebase lines
obtained had no information from AS cores on it, (we call them
background lines).The number of all background lines (includ-
ing the last one and a half lineaobtained when the oscillos-
cope was triggered by the coincidence output of the AS core
selector) were larger than that of the lines information on
it. But no signals whose characteristics are the same as any
one of the three event signals appear on the background
lines. Therefore this kind of possibility can be eliminated.
From about, the three acoustic signals can not be explained
as from any sources other than AS cores. The experiment date
are listed in the following table in which the subscripts I
and 2 indecate channels one and two respectively. From the
table, it is can be seen that the values of the effective :
diameter of the cores causing acoustic effect are not incon-
sistant with the expected ones
P, (_(b) Px (_b) d(cm), fc (KHz) [ _ I T -I
_riY-1'iEvent -t(_S)50"0.25 ......[ -0.37 .... 7.5.......20 I 1.66"I"Ii;_ ....i
I 14. [........................iKY 3 40 I
Key: t--Duration of acoustic pressure pulse
P--Acoustic_pressure d--Effective diameter #
. f--mid-frequency R--Distance from source
to hydrophones
/_l__ We would like to thank Prof. Yan Guigong
(Yunnan University) for his encouragement and Engineer Jiang
Weiluan, Gong Wending, Associate Engineer Huang Aiyong and
Wong Liyan for their helps with this experiment.
References
I. Bowen, T. et. al.,"A lake Detection for High Energy Air
Shower Near the Fly's Eye" Proc. of Air Shower Workshop,
•" 1 979.
2. Liu Yongyue, Gao Xiaoyu, (1981), Physics (Chinese), I0,
p690.
3. Sulak, L., et. al., (1979), Nuci. Inst, & Meth. 161, p203.
&. Gao Xiaoyu_ Liu. Yongyue,(1983), 18th ICRC, 8, p166.
5. Boweb, T. (1977), 15th ICRC, p277.


Acoustic detection of air shower cores

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