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Postgraduate Thesis: Measurement of cosmic-ray muon induced neutrons in the Aberdeen Tunnelunderground laboratory in Hong Kong
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TitleMeasurement of cosmic-ray muon induced neutrons in the Aberdeen Tunnelunderground laboratory in Hong Kong
 
AuthorsNgai, Ho-yin.
倪浩然.
 
Issue Date2012
 
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
AbstractThe Daya Bay reactor neutrino experiment aims to determine sin2 2θ13 with a sensitivity of 0.01 or better at 90% confidence level. One of the major backgrounds to neutrino measurements is the muon-induced neutrons. An ex- periment had been set up inside the Aberdeen Tunnel laboratory, Hong Kong, to study spallation neutrons induced by cosmic-ray muons in an underground environment similar to the Daya Bay experiment. The Aberdeen Tunnel laboratory is 22 m above sea level at 22:23?N and 114:6?E. The amount of overburden is approximately 235 m of rocks, which is equivalent to 611 m.w.e. Rock compositions in the Aberdeen Tunnel area is similar to that in Daya Bay. MUSIC simulation results showed that in the laboratory the mean energy of muons 〈Eμ〉= 122 GeV and the integrated muon intensity I = 9:64 X10??6 cm??2 s??1. A Bonner Spheres Neutron Spectrometer (BSS) was developed to measure the ambient neutron energy spectrum. The BSS consists of a thermal neutron detector and a set of eight polyethylene spherical shells. The overall detection efficiency of the BSS was (96:7 +3:3 ??13:1)% with a detector background rate of (1:96_0:03)_10??3 s??1. The total neutron fluence rate measured at the Surface Assembly Building (SAB) of the Daya Bay experiment was (5:20 +0:81 ??0:44) _ 10??3 cm??2 s??1, which agreed with the neutron fluence rate measured in the air/ground interface in Taiwan. The unfolded SAB neutron energy spectrum showed a clear thermal-neutron peak around 20 meV and a cascade peak around 100 MeV. Detectable number of neutrons could be seen at 1 GeV. The neutron fluence rate measured at the Aberdeen Tunnel (ABT) laboratory was significantly higher then some other underground laboratories. The unfolded ABT neutron energy spectrum showed a pronounced evaporation peak around 1 MeV, and a sup- pression in the cascade peak. Detections of muon-induced neutrons inside the Aberdeen Tunnel laboratory is achieved by a Muon Tracker and a Neutron Detector. The Muon Tracker consists of three main layers of crossed plastic scintillator hodoscopes capable of determining the incoming direction of muons. The average efficiency for most of the hodoscopes was above 95%. The Neutron Detector consists of about 760 L of gadolinium-doped liquid scintillator and sixteen photomultiplier tubes. The liquid scintillator target is shield by about 1900 L of mineral oil from external radiations. The overall average detection efficiency of muon-induced neutrons was about 16%. The measurement of muon-induced neutrons in the Aberdeen Tunnel lab- oratory started from June 2011, with a total live time of about 30 days. The average rate of the accepted muon events was 0.013 Hz. The muon-induced neutron yield was determined to be Nn = (8:5 _ 0:4(syst.) _ 1:8(stat.)) _ 10??5 neutron/(μg cm??2). This value agreed with the parametrization of FLUKA-1999 simulation results if the muon energy dependence of muon-induced neutron yields was considered.
 
AdvisorsPun, JCS
Leung, JKC
 
DegreeDoctor of Philosophy
 
SubjectNeutrons - Measurement.
Cosmic ray muons - China - Hong Kong.
 
Dept/ProgramPhysics
 
DOIhttp://dx.doi.org/10.5353/th_b4724925
 
DC FieldValue
dc.contributor.advisorPun, JCS
 
dc.contributor.advisorLeung, JKC
 
dc.contributor.authorNgai, Ho-yin.
 
dc.contributor.author倪浩然.
 
dc.date.hkucongregation2012
 
dc.date.issued2012
 
dc.description.abstractThe Daya Bay reactor neutrino experiment aims to determine sin2 2θ13 with a sensitivity of 0.01 or better at 90% confidence level. One of the major backgrounds to neutrino measurements is the muon-induced neutrons. An ex- periment had been set up inside the Aberdeen Tunnel laboratory, Hong Kong, to study spallation neutrons induced by cosmic-ray muons in an underground environment similar to the Daya Bay experiment. The Aberdeen Tunnel laboratory is 22 m above sea level at 22:23?N and 114:6?E. The amount of overburden is approximately 235 m of rocks, which is equivalent to 611 m.w.e. Rock compositions in the Aberdeen Tunnel area is similar to that in Daya Bay. MUSIC simulation results showed that in the laboratory the mean energy of muons 〈Eμ〉= 122 GeV and the integrated muon intensity I = 9:64 X10??6 cm??2 s??1. A Bonner Spheres Neutron Spectrometer (BSS) was developed to measure the ambient neutron energy spectrum. The BSS consists of a thermal neutron detector and a set of eight polyethylene spherical shells. The overall detection efficiency of the BSS was (96:7 +3:3 ??13:1)% with a detector background rate of (1:96_0:03)_10??3 s??1. The total neutron fluence rate measured at the Surface Assembly Building (SAB) of the Daya Bay experiment was (5:20 +0:81 ??0:44) _ 10??3 cm??2 s??1, which agreed with the neutron fluence rate measured in the air/ground interface in Taiwan. The unfolded SAB neutron energy spectrum showed a clear thermal-neutron peak around 20 meV and a cascade peak around 100 MeV. Detectable number of neutrons could be seen at 1 GeV. The neutron fluence rate measured at the Aberdeen Tunnel (ABT) laboratory was significantly higher then some other underground laboratories. The unfolded ABT neutron energy spectrum showed a pronounced evaporation peak around 1 MeV, and a sup- pression in the cascade peak. Detections of muon-induced neutrons inside the Aberdeen Tunnel laboratory is achieved by a Muon Tracker and a Neutron Detector. The Muon Tracker consists of three main layers of crossed plastic scintillator hodoscopes capable of determining the incoming direction of muons. The average efficiency for most of the hodoscopes was above 95%. The Neutron Detector consists of about 760 L of gadolinium-doped liquid scintillator and sixteen photomultiplier tubes. The liquid scintillator target is shield by about 1900 L of mineral oil from external radiations. The overall average detection efficiency of muon-induced neutrons was about 16%. The measurement of muon-induced neutrons in the Aberdeen Tunnel lab- oratory started from June 2011, with a total live time of about 30 days. The average rate of the accepted muon events was 0.013 Hz. The muon-induced neutron yield was determined to be Nn = (8:5 _ 0:4(syst.) _ 1:8(stat.)) _ 10??5 neutron/(μg cm??2). This value agreed with the parametrization of FLUKA-1999 simulation results if the muon energy dependence of muon-induced neutron yields was considered.
 
dc.description.naturepublished_or_final_version
 
dc.description.thesisdisciplinePhysics
 
dc.description.thesisleveldoctoral
 
dc.description.thesisnameDoctor of Philosophy
 
dc.identifier.doihttp://dx.doi.org/10.5353/th_b4724925
 
dc.identifier.hkulb4724925
 
dc.languageeng
 
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
dc.relation.ispartofHKU Theses Online (HKUTO)
 
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.
 
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License
 
dc.source.urihttp://hub.hku.hk/bib/B47249250
 
dc.subject.lcshNeutrons - Measurement.
 
dc.subject.lcshCosmic ray muons - China - Hong Kong.
 
dc.titleMeasurement of cosmic-ray muon induced neutrons in the Aberdeen Tunnelunderground laboratory in Hong Kong
 
dc.typePG_Thesis
 
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<contributor.advisor>Leung, JKC</contributor.advisor>
<contributor.author>Ngai, Ho-yin.</contributor.author>
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<date.issued>2012</date.issued>
<description.abstract>&#65279;The Daya Bay reactor neutrino experiment aims to determine sin2 2&#952;13

with a sensitivity of 0.01 or better at 90% confidence level. One of the major

backgrounds to neutrino measurements is the muon-induced neutrons. An ex-

periment had been set up inside the Aberdeen Tunnel laboratory, Hong Kong,

to study spallation neutrons induced by cosmic-ray muons in an underground

environment similar to the Daya Bay experiment.



The Aberdeen Tunnel laboratory is 22 m above sea level at 22:23?N and

114:6?E. The amount of overburden is approximately 235 m of rocks, which

is equivalent to 611 m.w.e. Rock compositions in the Aberdeen Tunnel area

is similar to that in Daya Bay. MUSIC simulation results showed that in the

laboratory the mean energy of muons &#12296;E&#956;&#12297;= 122 GeV and the integrated muon

intensity I = 9:64 X10??6 cm??2 s??1.

A Bonner Spheres Neutron Spectrometer (BSS) was developed to measure

the ambient neutron energy spectrum. The BSS consists of a thermal neutron

detector and a set of eight polyethylene spherical shells. The overall detection efficiency of the BSS was (96:7 +3:3

??13:1)% with a detector background rate of

(1:96_0:03)_10??3 s??1. The total neutron fluence rate measured at the Surface

Assembly Building (SAB) of the Daya Bay experiment was (5:20 +0:81

??0:44) _ 10??3

cm??2 s??1, which agreed with the neutron fluence rate measured in the air/ground

interface in Taiwan. The unfolded SAB neutron energy spectrum showed a clear

thermal-neutron peak around 20 meV and a cascade peak around 100 MeV. Detectable number of neutrons could be seen at 1 GeV. The neutron fluence rate

measured at the Aberdeen Tunnel (ABT) laboratory was significantly higher

then some other underground laboratories. The unfolded ABT neutron energy

spectrum showed a pronounced evaporation peak around 1 MeV, and a sup-

pression in the cascade peak.

Detections of muon-induced neutrons inside the Aberdeen Tunnel laboratory

is achieved by a Muon Tracker and a Neutron Detector. The Muon Tracker

consists of three main layers of crossed plastic scintillator hodoscopes capable

of determining the incoming direction of muons. The average efficiency for most

of the hodoscopes was above 95%. The Neutron Detector consists of about 760

L of gadolinium-doped liquid scintillator and sixteen photomultiplier tubes. The

liquid scintillator target is shield by about 1900 L of mineral oil from external

radiations. The overall average detection efficiency of muon-induced neutrons

was about 16%.

The measurement of muon-induced neutrons in the Aberdeen Tunnel lab-

oratory started from June 2011, with a total live time of about 30 days. The

average rate of the accepted muon events was 0.013 Hz. The muon-induced

neutron yield was determined to be Nn = (8:5 _ 0:4(syst.) _ 1:8(stat.)) _

10??5 neutron/(&#956;g cm??2). This value agreed with the parametrization of

FLUKA-1999 simulation results if the muon energy dependence of muon-induced

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