A new underground cosmic ray station has been opened at Matsushiro, Japan, and a multidirectional (17 directional channels) muon telescope has been installed at an effective vertical depth of 220 m.w.e. The counting rates are; 8.7 x 10,000/hr for the wide vertical component and 2.0 x 10,000/hr for the vertical component. Continuous observation has been performed since March 22,1984. Some details of the telescope and preliminary analyzed results of the data are presented

Akahane, S.

Chino, K.

Higuchi, T.

Ichinose, M.

Mori, S.

Ozaki, M.

Sagisaka, S.

Yasue, S.

English

NASA Technical Reports Server

506 SH 9.1-14
NEW MATSUSHIRO UNDERGROUND COSMIC RAY STATION
(220 M.W.E. IN DEPTH)
Mori, S., S. Yasue, S. Sagisaka, K. Chino, S. Akahane, T. Higuchi,
M. Ozaki and M. Ichinose*
Department of Physics, Faculty of Science and Faculty of Liberal
Arts*, Shinshu University, Matsumoto 390, Japan
ABSTRACT
A new underground cosmic ray station has been opened
at Matsushiro, Japan and multi-directional (17 directional
channels) muon telescope has been installed at an effec-
tive vertical depth of 220 m.w.e. The counting-rates are;
8.7x104/hr for the wide-vertical component and 2.0×104/hr
for the vertical component. The continuous observation
has been performed since March 22, 1984. Some details of
the telescope and preliminary analyzed results of the data
are presented.
I. Introduction
More than a dozen of the underground cosmic ray stations have been
actively operated, and invaluable data have been accumulated. Based on
those data, a great deal of investigation has been performed on the
cosmic ray modulation in the heliosphere, cooperated with small air
shower measurements (e.g., Nagashima and Mori, 1976). Complete pictures
of the modulation have not yet been established in the rigidity range of
i011_i014 eV, therefore more accumulation of the data of high counting-
rates with multi-directional channels would be mostly acknowledged.
2. Underground Site and Muon Telescope
Matsushiro is located in Nagano-city, Nagano Pref., Japan and _40 km
northeast of our Cosmic-Ray Lab. of Shinshu University in Matsumoto-city.
A new station is very close to our elder one (_4 km in distance) (Yasue
et al., 1981; also in this issue). Locality of the present station is;
36.53°N and 138.02°E in geographic coordinate and 360 m in altitude.
Fig. l(a) shows the contour map of the underground site and Fig. l(b)
illustrates one of the cross-sections along the line AB in Fig. l(a).
NATSUSHIRO UNDERGROUND COSMIC BAY OBSERVATORY
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_.-.../ ,/,'< :_._4o.t_ _ -
(a) (b)
Fig. 1 (a) Contour map of tunnel area and (b) Cross-section along AB
https://ntrs.nasa.gov/search.jsp?R=19850026816 2020-03-20T16:49:39+00:00Z
507 SH 9.1-14
The vertical rock depth is 92.8 m, and the rocks overburden are
mostly andesite (Ad) and shale (Sh), its average density _2.65 g/c m3,
therefore _240 m.w.e. The depth is somewhat different in each direction,
and the effective vertical depth is estimated at _220 m.w.e.
The temperature inside the tunnel is 14%15°C, almost constant
throughout the year (precise temperature variations on the daily and
seasonal bases have not yet been measured). Both observation room
(10xl0 m 2 in area) and recording room have been heated up to _19°C, and
the humidity has been kept as <50%.
ASYMPTOTICLATITUDEAND LONGITUDE(MTSUSHIRO:37,53"N,138,02°E) Fig, 2 shows the aS-
LATITUE(°) ymptotic directions for 17
9o _,2 ,3 component telescopes calcu-
N /Tsoov lated for the rigidities of
607s°_ 750, 450, 350 and 250 GV
75oov \,_ (Inoue, personal communica-
w v tion).
,so s9 s _E \B3 The median primary.- ...... , rigidity is estimated at
6o 120 ,8o 24o 3oo _600 GV, using the response
_2 LONGITUDE (°)
_ function given by Murakami
75[
-30 et al. (1981). The corre-
sponding Lamore radius for
6 nT of the IMF strength is
Fig. 2 Asymptotic orbit for 13 comp. Js.
_2 AU.
The muon telescope consists of 50 plastic scintillation detectors
in all, as shown in Fig. 3, arranged in two layers spaced by 150 cm.
AR_NDE_NTOFCOSMIC_Y DETECTORS The detectors are exactly the same
ANDTEEIRNU_ERINO
as those of our elder Matsushiro
.........._' ...._- station (Yasue et al., 1981); each
iiii iii[ii _I having i×i m 2 in area, 4 plastic
.... ....... _' scintillators (50×50xi0 cm3), and
"_- ......... _] viewed with double photomultipliers......... (5" in diameter) as shown in Fig. 4
i...._....l...._....:.._.___-_. . . .......
! to obtain good S/N ratio and high
; ! detection efficiency.i . I -- CONST_UCTEOi
_ _ _icos.xc _, ..... P_z"Q 1°6 WV-coMp,
--_-,I''_LLI
s _ -_ -COMP.
Fig. 3 Arrangement of detectors _os
MAIN _P, _ _ _
104 _itag _ "
PHOTO-MULTIPLIER _ rae
i i I , I _ I , I j__
L 10500 600 700 800 900 looo
H,V. SUPPLIED (VOLTS)
Fig. 4 Cosmic ray detector Fig _ 5 High-voltage characteristic
/ 508
_ .... SH 9.1-14
Based on this arrangement, 17 component telescopes are constructed
by taking an appropriate 2-fold coincidence between the detectors in
upper and lower trays. In Fig. 5, high-voltage characteristics of some
telescopes are plotted of real counts vs. high-voltage supplied for the
upper (US) and the lower (LS) trays, the wide-vertical component (WT; 2-
fold coincidence between US and LS) and the vertical component (V). The
continuous observation has been performed since March 22, 1984 and the
hourly counts have been recorded. In the followings, some preliminary
analyzed results of the data are presented.
3. Data and Their Analysis
3.1 Atmospheric effect
Barometric pressure effect was examined; one for a short time-period
of 6 days when transient large atmospheric pressure change was observed
in a range of _30 mb and the other for a long time-period of about 6
months (Mar.,_Oct., 1984). Single correlation between the pressure and
the counting-rate was taken. Barometric coefficients were obtained as;
8_-0.01%/mb for the former short-period and _-0.04%/mb for the latter
long-period. These are in good agreement with our previous results and
can be well explained by taking accounts of the upper atmospheric tempera-
ture effect (Sagisaka et al., 1983).
3.2 Cosmic ray north-south asymmetry (N-S asymmetry)
Among 17 component telescopes, some telescopes (e.g., N, N2, ...)
view rather northern latitude, while some (e.g., S, S2, ...) view rather
Ns_ ....._Tsus,_....,_,0 southern latitude or equatorial plane,
as shown in Fig. 2. Using the daily
_ • mean values of these directional
intensities (%60×10_/day), N-S asym-
/ ./ _ metry was evaluated daily as
: /5_. _=(N+N2+N3+NE+NW)'(S+S2S3+SE+SW)*
_':"" " where * indicates the normalized
0_3 t
M
... counts between these two groups (Mori
and Nagashima, 1979). Also IMF-sense
dependence of this N-S asymmetry was
examined by referring to Toward (T)-
and Away (A)-sense given by Stanford
Fig. 6 Correlation between group (Solar-Geophysical Data, NOAA,
Matsushiro and Misato. 1985). Fig. 6 shows the correlation
between derived N-S asymmetries of the present station and Misato (34
m.w.e, in depth). Table 1 gives the numerical values on T and A of
these two stations for the period
Station T(%) A(%)
Mar.22_Oct. 31, 1984. From this
Matsushiro 0.02 -0.05 result, some indication may be noted
Misato 0.066 -0.060 that even such high rigidity parti-
cles (_600 GV) observed at 220 m.w.e.
Table 1 N-S asymmetries on T and A
underground station, are influenced
by the IMF-sense.
3.3 Daily intensity variation
The hourly data (without corrected for barometric effect) were har-
monically analyzed in solar (SO), sidereal (SI) and anti-sidereal (AS)
5 0 9 SH 9o1-14
time for full one-year (Apr. 1984 Mar. 1985). Fig. 7 shows one of month-
to-month variations of SO(ist) for V-comp. The monthly vectors move
counterclockwise systematically, indicating the at deep undergrouns sta-
tion SI(ist) may be more significant in the ist harmonics. Fig. 8 illust-
rates some of the harmonics for 13 component telescopes (V, N, S, E, W,
NE, NW, SE, SW, N2, S2, E2 and W2); si(ist) in (a), AS(Ist) in (b) and
SO(2nd) in (c). In the figure, errors are derived from counting-rates.
We may note that from their directional dependence, almost of them are
significant.
0H
0H
sl(lstl ...... 9 s2 _sl]st)
0,05
oH _TSUS.XRO _'_:': ._V W /"\ S
I V-C_p. ".'. \ S i _2
, _ _ i _, , _
18H _0105 I'.. _#s. I , "'O's2 _ ' %6H
Q.O5
0.O5.
i 6H (a) % (b)
18_ o.1_ 12H o_1o
OH E2Q......
'... " .......... ..
SO{2nd) _ CORRECTED ",
• Sl(iscl ".,
_J_._ s 0.05 % 18H /" ""'_ n,n, 6H
c ) _o._5
Fig. 7 Monthly movement 6" 12"
of SO(ist) for V-comp.
Fig. 8 Harmonics of; (a) SI(ist), (b) AS(Ist),
(c) SO(2nd) and (d) corrected SI(Ist)
In a case, where SO(2nd) is observed significantly, as developed by
Nagashima et al. (1983), space anisotropy of 2nd order responsible for
the observed SO(2nd) produces the spurious SI(ist) and AS(Ist) having
equal amplitude and due phase. As in Fig. 8 (b), AS(lst) may be signifi-
cant. Based on Nagashima correction (1983), the observed SI(ist) should
be, at least, corrected for the above spurious SI(Ist) by utilizing the
observed AS(ist). Fig. 8 (d) shows the corrected SI(ist) thus derived.
We may summarize that i) these results are consistent with those so far
, reported; almost of them lie in the direction 3-5 hr LST. And 2) some of
SI(ist)'s, e.g., S2-comp. is rather larger (_0.13% in ampltude) than
others, which is consistent with that of Ueno et al. (1984) at Sakashita.
4. Acknowledgement
The authors express their aapreciation to Prof. K. Nagashima for his
kind discussion.
References
Mori, S. and K. Nagashima, (1979), Plant. Space Sci., 27, 34.
Murakami, K. et al., (1981), Rep. CR-Lab., Nagoya Univ., No. 6.
Nagashima, K. and S. Mori, (1976), Int. CR-Symp. (Tokyo), p326.
Nagashima, K. et al., (1983), Nuovo Cimento, 6__C, 550.
Sagisaka, S. et al, (1983), 18th ICRC (Bangalore), iO0, 237.
Ueno, H. et al., (1984), Int. CR-Symp. (Morioka), p349.
Yasue, S. et al., (1981), 17th ICRC (Paris), 4, 304.
Yasue, S. et al., (1985) in this issue (SH 4.4-9).


New Matsushiro underground cosmic ray station (220 M.W.E. in depth)

New Matsushiro underground cosmic ray station (220 M.W.E. in depth)

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