A practical and simple method for burst rejection is applied to the digitized data of cosmic ray ion chambers at Mt. Norikura, Tokyo and Kochi. As a result of burst rejection, the burst size frequency distributions in the digitized data at mountain altitude and sea level ion chambers is obtained. Results show that there are no significant differences between the digital and analog data processing in burst rejection

Chuang, L. S.

Kudo, S.

Kusunose, M.

Wada, M.

English

NASA Technical Reports Server

486
SR 9.1-9
BURST SIZE DISTRIBUTIONS IN THE DIGITIZED DATA OF
THE ION CHAMBERS AT MT.NORIKURA AND SEA LEVEE STATIONS
M. Kusunose, M. Wada*, S. Kudo*, and L. S. Chuang**
Department of Physics, Kochi University,
Akebono-cho 2-chome, Kochi 780, Japan
* Cosmic Ray Laboratory, Institue of Physical and Chemical Research,
Kaga 1-chome, Itabashi-ku, Tokyo 173, Japan
** Department of Physics, The Chinese University of Hong Kong,
Shatin, New Territories, Hong Kong
ABSTRACT
A practical and simple method for burst rejection was applied to
the digitized data of cosmic ray ion chambers at Mt. Norikura,
Tokyo and Kochi. As a result of burst rejection, the burst
size-frequency distributions in the digitized data at mountain
altitude and sea-level ion chambers were obtained. The results
show that there are no significant differences between the
digital and analog data processing in the burst rejection.
1. Introduction
COsmic ray ion chambers have been used for the continuous
observation since the early days of cosmic ray studies. Five sets of
Nishina-type ion chambers were built during the period from 1935 to
1941. 1,2) COntinuous recording by those Nishina-type ion chambers had
been started at Tokyo in 1948, Mr. Norikura in 1955, Hong Kong in 1970
and Kochi in 1979. At present, the digital recording systems for cosmic
ray-ion chambers 3,4) are in operation (see Table I).
The burst distribution in ion chamber records is recognized from an
abrupt change in charge up voltage. It is generated from a bremsstrahlung
of muon or some nuclear interaction in lead absorber which covers the
chamber to avoid undesirable radiation around the apparatus. Since the
size of a burst sometimes exceeds total voltage variation in an hour, it
should be rejected to reduce fluctuations. In this paper, we discuss on
the burst rejection and the burst size distribution in the digitized data
at Mt. Norikura, Tokyo and Kochi.
Table 1. List of Nishina type ion chambers in Japan
Station Mr. Norikura Tokyo Kochi
Cutoff rigidity (GV) 11.38 11.50 12.88
Altitude (m) 2770 20 30
Atmospheric depth (g/cm 2 ) 740 I030 I030
Nishina type ion chamber No.I No.5 No.4
Argon gas pressure (kg/cmZ ) 39 30 39
Electrometer output range (V) 30 10 10
Thickness of roof (g/cm_) 20 10 120
Thickness of lead shield (cm) 10 10 10
19th Int. Cosmic Roy Conf., ka Jolla, 1985, SH9.1-9
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2. Method of burst rejection
There is no a priori way of rejecting the burst data, since smaller
bursts can not be distinguished from ordinary statistical fluctuations.
As a method of burst rejection, Wada et al. _) proposed to chose the
threshold from the distribution, so that the average is not change.
Kusunose eta/. 5) presented a practical method to separate bursts
from the ordinary cosmic ray data on the assumption that the frequency of
burst number per hour follows the Poisson distribution. We reduced the
procedure of burst rejection, where the principle is the same as the
previous method. The threshold of burst rejection is taken as knon
(a=l,2 ....), where on are standard deviations and k, are constants, which
are determined so that the frequency of burst obeys the Poisson
distribution. In the previous report, R was taken up to 10, now we reduce
it to 3.
z2-test of the Poisson distribution was applied to the distribution
of the burst frequency per hour. The results show fairly good fitness to
the Poisson distribution except for a few cases. The distributions of one
minute values as differences from averages of respective hours are shown
in Fig. l. Curves A's are the distribution of one minute values due to
ionization current of cosmic rays detected in the chamber, and B's are
the distribution of the rejected burst values. As shown in the figures,
both curves are separated each other reasonably.
05 i I I I I I I I I I" f" I I I !
Mt. Norikura Tokyo Kochi
_ A
m 104
-" I
,, I
o i0a B
/ ?
m
_- 102
(a) (b)
I01 i , , , ,I , , , ,. , , i , ,
-40 0 -40 0 40 -40 0 40
ONE MINUTE VALUE (bit)
Fig. I. Distribution of one minute values as deviation from the averages
of respective hours at the period from May 24, t980 to May 9, 1981.
488
SH 9.1-9
10-6
i I I I I i
x x xx X
x
x
ooo >_
x
x
•.-- _ \
, x
10_7
I "_- ×
>-
¢_ (C)
,, i0-8 _
OO
r.- (a) Mt. Norikura (Oct.79 - Jan.83)
(b) Tokyo (Nov.80 - NOV.83)
(C) Kochi (May 80 - Jan.84)
i0-9 , I [ I I
i0 20 50 i00 200 500 i000
B U R S T S IZ E (particle)
Fig. 2. Burst size-frequency distribution.
3. Burst size distribution
The integral size-frequency distributions of bursts thus obtained
are shown in Fig. 2, where (a), (b) and (e) are those of Mr. Norikura,
Tokyo and Kochi ion chamber respectively. In the figure, the burst size
is represented in unit of particle that means the number of incident
charged particles in a ion chamber. The frequencies of the bursts are
indicated in the number of bursts divided by the time of total duration
and by the horizontal cross-sectional area of the chamber.
The frequencies of the bursts at a point where the burst size is 200
particles, are shown as, 6.0x10 -8 cm-Zsec-I at Mt. Norikura, 1.83xi0 -8
at Tokyo, and i 35×10 -8 at Kochi. The burst frequency at Mt. Norikura is
3.3 times that of Tokyo. According to Kameda and Wada8), it means that
considerable parts of the total bursts at sea level are t_ose induced by
N-components. The ratio of Tokyo to Kochi is found as _1.3. It will be
489
SH 9.1-9
explained by the difference in the cutoff rigidities and the thickness of
roof materials.
The burst frequency spectrum can be expressed partly by the form of
power function ass -_ , where S is the burst size in unit of particle. We
calculated the power 7 in the range of burst size from 150 to 220
particles by the least square method. The results are 7=2.07±0.01 at Mt.
Norikura, 7=2.09±0.01 at Tokyo, and 7=2.09±0.01 at Kochi. There is no
significant difference among them.
4. Summary
In summary, we separated one minute data of cosmic ray ion chamber
into the ordinary cosmic ray data and the burst data by the statistical
way under the assumption that the number of bursts in one hour follow the
Poisson distribution. The merit of this method is capable of testing the
appropriateness of burst rejection by application of z2-test on the
Poisson distribution.
As a result of the burst rejection, the distributions of burst
size-frequencies were obtained. The differences of burst size spectrum
bwteen Mr. Norikura and sea level ion chambers are generally in
coincidence with the results of Kameda and Wada.
5. Acknowledgments
The observations at Mr. Norikura were made in cooperation with the
staffs of the Norikura Cosmic Ray Station <by Prof. I. Kondo) of the
Institute for Cosmic Ray research, University of Tokyo. The compilation
of the data of Tokyo-Itabashi was performed by Mrs. K. Imai. Computer
works were performed by using M-380, M-140F, and F270-30.
References
I) Ishii,C, (1944), Bull. I. P. C. R. <in Japanese), 23, 535.
2) Miyazaki, Y., (1954>, J. Sci. Res. Inst., 48, 80.
3) Chung, L. S. e_ al., (1981), Proc. 17_h In_. Cosmic Ray Conf., Paris,
8, 154.
4) Wada, M. ef el., (1982), Nucl. Instr. Meth., 200, _57.
5) Kusunose, M. et al., (1984), Hem. Fac. Sci., Kochi Univ., Set. B, 5,
• 15.
6) Kameda, T. and M. Wada, (1952), Prog. Theor. Phys., 7, 1.


Burst size distributions in the digitized data of the ion chambers t Mt. Norikura and sea level stations

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