Two new detectors are currently under construction at the Homestake Gold Mine a 140-ton Large Area Scintillation Detector (LASD) with an upper surface area of 130 square meters, a geometry factor (for an isotropic flux) of 1200 square meters, sr, and a depth of 4200 m.w.e.; and a surface air shower array consisting of 100 scintillator elements, each 3 square meters, spanning an area of approximately square kilometers. Underground, half of the LASD is currently running and collecting muon data; on the surface, the first section of the air shower array will begin operation in the spring of 1985. The detectors and their capabilities are described

Cherry, M. L.

Corbato, S.

Daily, T.

Fenyves, E. J.

Kieda, D.

Lande, K.

Lee, C. K.

English

NASA Technical Reports Server

HE 6.1-9
246
THE HOMESTAKE SURFACE-UNDERGROUND SCINTILLATORS -- DESCRIPTION
* * * + * *
M.L. Cherry , S. Corbato , T. Daily , E.J. Fenyves , D. Kieda , K. Lande,
and C.K. Lee
Depts. of Physics and Astronomy, Univ. of Penna., Philadelphia, PA 19104
+
Dept. of Physics, Univ. of Texas, Dallas, TX 75080
Two new detectors are currently under construction at
the Homestake Gold Mine -- a 140-ton Large Area S_intilla-
tion Detector with an upper surface area of 130 m 2, a geo-
metry factor (for an isotropic flux) of 1200 m 2 st, and a
depth of 4200 m.w.e.; and a surface air shower array con-
sisting of i00 scintillator elements, each 3 m 2, spanning
an area of approximately 0.8 km 2. Underground, half of the
LASD is currently running and collecting muon data; on the
surface, the first section of the air shower array will
begin operation in the spring of 1985. We describe the
detectors and their capabilities.
I. Introduction
Underground, the Large Area Scintillation Detector will be used to
i) search for slow, massive magnetic monopoles with a combination of large
area, low dE/dx, low background, and electronic sensitivity to the entire
velocity range i0-_<_< i_ 2) study the zenith angle distribution of
neutrino-induced and penetrating muons; 3) search for neutrino bursts
from stellar collapse events in the Galaxy; and 4) serve as a prototype
for a solid, large volume scintillation detector used to search for
nucleon decay and8B solar neutrinos. The combined surface-underground
telescope will be used to 5) measure the multiplicity and transverse
momentum distributions of high-energy cosmic ray muons; 6) study the
primary cosmic ray nuclear composition near l0 Is eV; and 7) search for
cosm_9 point sources of neutrinos, gamma rays, and high-energy cosmic
rays (for example, Cygnus X-3) with very good angular resolution (3-10
mrad with the combined surface and underground detectors). We describe
the design of the detectors here; in an accompanying paper I, we discuss
the initial performance of the LASD.
II. The Underground Large Area Scintillation Detector
The Large Area Scintillation Detector is located at a depth of 4850
ft. (4200 m.w.e.) in the Homestake Mine (Fig. i). It consists of a hollow
8m x 8m x 16m box composed of 200 30cm x 30cm x 8m liquid scintillation
detectors surrounding the existing 37CI solar neutrino tank of Davis et
al. 2. The detector is sufficiently large to mount a search for magnetic
monopoles at the Parker limit (10 -15 cm -2 sec -I sr -I) in 3 years. Each of
the 200 scintillator elements is a PVC box lined with teflon (for total
internal reflection) containing a low-cost mineral oil-based liquid scin-
https://ntrs.nasa.gov/search.jsp?R=19850027822 2020-03-20T17:10:28+00:00Z
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tillator developed to have excellent light
collection and transmission Characteristics, COSMIC RAY
a light attenuation length of approximately $ PRIMARY
7 m, long-term stability, a high flash point,
and low toxicity. In addition, since the
same scintillator oil is used in the sur-
face array, the oil maintains its clarity
down to very low temperatures. Each detec-
tor element is viewed by two 5-inch photo-
multiplier tubes in coincidence, one at
each end. Fast muons passing through the
middle of one of the modules produce an SURFACE
average of 350 photoelectrons at each AIR SHOWERARRAY
photomultiplier• A particle ionizing even
at 0.01 times minimum would thus produce
3-4 photoelectrons at each photomultip-
liar and still be visible• The l?w energy
threshold is therefore set not by the
scintillator light yield, but rather by 1.6km
the background produced by the ambient i¢
radioactivity (primarily MeV gamma rays) _
from the rock walls. We have initially
set our thresholds at i/i0 minimum ioni- "_ LASD
zing, or 5 MeV. _\)
The individual detector elements
have + 1.3 ms time resolution, spatial ____resol_tion of + 15 cm, and a very low _
muon background flux Cosmic ray muons _________/___!__
• _
and neutrino-induced muons will typically _i:$I/_._i___
produce two pairs of coincident photomul- _.____._'_:_,< _ /S.._
tiplier tube pulses one pair as the muon _ _;i__
enters the detector and one delayed pair _!_i_ _/
as the muon leaves the detector. The delay
between the entering and exiting pulses _
- will be about 25 us. We can recognize
multiple muons passing through a given
module by the large pulse height and the
mismatch between time differences and Fig. i. Surface and
pulse height ratios. From the location underground Homestake
. of the entering and exiting points, the detectors•
muon direction can be determined to + 3 ° .
For a monopole, we expect a pair of slow pulses with width 1 ns/_
as the monopole enters the detector and, after a delay of 25 us/6 , a
second p_ir of slow3Pulses as the monopole, leaves. For slow monopoles
with I0- _ _ _ i0- , the delay time between the two entering and exiting
pulses will be 25-250 _s. Such long delays can only be correlated in a
very low background environment such as that available in a deep mine.
The monopole position in each box will be determined from the ratio of
pulse heights at each end of the box; the individual pulse heights are
then corrected for the position, and the monopole pulse height is deter-
HE 6.1-9
248
mined.
The electronics are designed to permit us to look at both fast
muons and slow monopoles. The muon circuitry is currently running on the
southern half of the detector. The range of interesting times is from
1 ns to 250 _s. The system is therefore equipped with a fast clock (2.5
ns resolution) which covers the first 500 ns and a slow UTC clock (0.2
_s resolution) to cover the time span thereafter. A 16-pulse (or event)
deep memory buffer is associated with each photomultiplier so that
multiple pulses for each event can be recorded.
The monopole circuitry is presently being built. It provides the
functions of a transient recorder for each photomultiplier, using fast
flash ADC's (7 bits, 20 MHz) associated with 2048-byte memories. Five
parallel ADC-memory channels are associated with each tube, displaced
in time by i0 ns each. When a trigger is seen, the memories are read out
for every phototube which fires, giving a record of pulse heights in
intervals of i0 ns over a duration of up to i00 _s for a single wall.
Individual walls of the detector are triggered independently, so that
the total length of the_event can be 300 _s, sufficiently long to see
slow monopoles (_ _ i0- ) or low-energy neutrons. A fast (i0 us) muon
pulse can then be clearly distinguished from a slowly rising (i/ B us)
monopole pulse; in addition, we measure the flight time across the
room, and the individual pulse heights.
The mechanical work on the underground detector is essentially
finished. The southern half of the detector has been filled with liquid
and turned on. Since Jan. 1985, we have collected 2 x i0 4 muon events
which are currently being analyzed. We are now installing the north-
side electronics and filling the remaining detector modules with oil.
The detector is expected to be fully operational (including the monopole
electronics) in the fall of 1985.
III. The Surface-Underground Telescope -- Composition
and Point Sources of Cosmic Rays
The surface array will consist of approximately i00 scintillation
detectors, spaced by 15 - 200 m and deployed over an area of about2
0.8 km over the underground chamber. The individual detector elements
consist of reinforced concrete boxes 4 ft x 8 ft x 2 ft high with 3"
thick side walls, covered on top by a 24 gauge galvanized tin cover
plate. The inside of the box is lined with styrofoam insulation and an
aluminum light reflector. The active detector is 4" of liquid scintilla-
tor, designed to have a high flash point and to remain clear at low
temperatures. The scintillator is viewed by two 5" photomultiplier tubes
operating in coincidence. Twenty-seven detector elements are presently
in position and ready to begin operation.
The telescope can operate either in a "prompt" mode in which only
the surface elements fire, or in a "delayed" mode in which a trigger
pulse from the underground detector arrives approximately 14 _s after
the surface array signals. The 14_ s delay is the result of £he 5 _s
muon flight time from the surface to the underground detector plus the
9 9s signal propagation time along the cable connecting the underground
HE6.1-9
249
detector and the surface array.
The location of the shower core will be calculated from the
locations, pulse heights, and arrival times seen by those detectors
firing in the shower. We expect to locate shower cores to within 4 m in
the central section of the array and i0 - 20 m in the outer part. Under-
ground, the liquid scintillator elements make it possible to resolve
tracks separated by 1 ft; however, the final underground position uncer-
tainty of 2.5 m is determined primarily by scattering in the rock. The
angular resolution of the combined surface-underground telescope is then
3 - i0 mrad. The expected surface-underground coincidence rate will be a
few hundred per year.
By combining the large air shower array on the surface with the
underground detector, we can measure the cosmic ray composition between
i0 I_ and 1016 eV. Measuring the total electron number N on the surface
(i.e., the total energy/nucleus) and the multiplicity o_ high energy
(E9 _ 2.7 TeV) muons underground (i.e., the energy/nucleon) permits
discrimination between primary species in a way that depends essentially
on energetics. In order to reach our depth, muons must have roughly 2.7
TeV at the surface of the earth. Such muons can be produced by proton
primaries with energies in excess of i013 eV or, for example, by iron
primaries with energies above a few times I0 I_ eV. A proton generally
gives rise to a single high energy muon while an iron, consisting of a
superposition of 56 separate nucleons, has a large probability of multiple
muon production, particularly above i0 ±s eV. Our data will thus consist
of muon multiplicity and separations underground, and shower size at the
< 15
surface. For small showers (E _ i0 eV) we expect to observe sing_ muons
primarily from cosmic ray protons, while for large showers (E >i0 eV)
we expect a mix of single and multiple muons from protons and heavy
(nominally iron) primaries.
The combined surface-underground detectors can also be used as a
high angular resolution telescope to look for intense point sources of
cosmic gamma rays or neutrinos i.
Funding for the Homestake scintillator experiments is provided by
the U.S. Department of Energy. The assistance and generous cooperation
of the Homestake Mining Company are deeply appFeciated. We are especially
indebted to A. Gilles and J. Dunn. In addition, we appreciate the advice,
assistance, and participation of T. Ashworth, K. Brown, B. Cleveland,
R. Davis, I. Davidson, J. Lloyd-Evans, R. Reid, E. Marshall,
R. Steinberg, and A. Watson.
References
i) M.L. Cherry, S. Corbato, T. Daily, D. Kieda, K. Lande, and C.K. Lee,
19th Intl. Cosmic Ray Conf., La Jolla, paper HE 5.1-3 (1985).
2) J.K. Rowley, B.T. Cleveland, and R. Davis, Jr., Solar Neutrinos @nd
Neutrino Astronomy, ed. by M.L. Cherry, K. Lande, and W.A. Fowler,
AIP Conf. Proceedings No. 126, AIP, New York (1985).


The homestake surface-underground scintillations:  Description

The homestake surface-underground scintillations: Description

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