An experiment to search for light sterile neutrinos is conducted at a reactor with a thermal power of 2.8 GW located at the Hanbit nuclear power complex. The search is done with a detector consisting of a ton of Gd-loaded liquid scintillator in a tendon gallery approximately 24 m from the reactor core. The measured antineutrino event rate is 1976 per day with a signal to background ratio of about 22. The shape of the antineutrino energy spectrum obtained from the eight-month data-taking period is compared with a hypothesis of oscillations due to activesterile antineutrino mixing. No strong evidence of 3+1 neutrino oscillation is found. An excess around the 5 MeV prompt energy range is observed as seen in existing longer-baseline experiments. The mixing parameter sin 2 2θ14 is limited up to less than 0.1 for ∆m The mixing among three neutrinos has been well established by experiments performed in the past two decades since the discovery of neutrino oscillations [1][2][3]. Consistent measurements of the two mass differences and the three mixing angles of the standard, three-neutrino mixing model have been reported by oscillation experiments using atmospheric, solar, reactor, and accelerator neutrinos [4]. Nevertheless, the mass hierarchy, the mass of the lightest neutrino, the Dirac or Majorana nature of the neutrino, and the CP phase are yet to be determined [5].Even though the number of active light neutrinos is limited to three by Z boson decay-width measurements [6], it is still possible to have additional neutrinos if they are sterile. Sterile neutrinos can be identified by the occurrence of activesterile neutrino oscillations. A hint for this is the LSND experiment's report of an observation ofν µ →ν e mixing with a frequency corresponding to a mass-squared difference larger than 0.01 eV 2 [7]. Results from the MiniBooNE's test of the LSND signal are, however, inconclusive [8].In addition to the LSND result, there are two other anomalies that could possibly be signs of active-sterile neutrino oscillations. An apparent ν e disappearance over a baseline of a few meters in the GALLEX and SAGE gallium experiments exposed to radioactive sources was reported [9]; the ratio of the numbers of measured and predicted events is 0.88 ± 0.05. A number of short-baseline reactor antineutrino experiments established limits on the presence of neutrino oscillations with eV mass differences by shape analyses of the measured neutrino energy spectra. Among those experiments, the Bugey experimental limits on sterile neutrinos are the most stringent [10]. Mueller et al. [11] found about a 6% deficit in reactor antineutrino event rates compared with the theoretical expectations for the short-baseline reactor experiments, which is the so-called "reactor antineutrino anomaly" (RAA). It can be interpreted as an active-sterile neutrino oscillation with three active neutrinos plus one or more sterile neutrinos, i.e., a 3 + n ν scenario [12,13], compatible with the LSND result. Recent reactor experiments that measured the θ 13 mixing an...

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Among the direct searches for WIMP-type dark matter, the DAMA experiment is unique in that it has consistently reported a positive signal for an annual-modulation signal with a large (9.3σ) statistical significance. This result is controversial because if it is interpreted as a signature for WIMP interactions, it conflicts with other direct search experiments that report null signals in the regions of parameter space that are allowed by the DAMA observation. This necessitates an independent verification of the origin of the observed modulation signal using the same technique as that employed by the DAMA experiment, namely low-background NaI(Tl) crystal detectors. Here, we report first results of a program of NaI(Tl) crystal measurements at the Yangyang Underground Laboratory aimed at producing NaI(Tl) crystal detectors with lower background levels and higher light yields than those used for the DAMA measurements.