Kamioka Liquid Scintillator Antineutrino Detector
The Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) is an electron antineutrino detector at the Kamioka Observatory, an underground neutrino detection facility in Hida, Gifu, Japan.
The device is situated in a drift mine shaft in the old KamiokaNDE cavity in the Japanese Alps.
The device is sensitive up to an estimated 25% of antineutrinos from nuclear reactors that exceed the threshold energy of 1.8 megaelectronvolts (MeV) and thus produces a signal in the detector.
If neutrinos have mass, they may oscillate into flavors that an experiment may not detect, leading to a further dimming, or "disappearance," of the electron antineutrinos.
KamLAND is located at an average flux-weighted distance of approximately 180 kilometers from the reactors, which makes it sensitive to the mixing of neutrinos associated with large mixing angle (LMA) solutions to the solar neutrino problem.
The KamLAND detector's outer layer consists of an 18 meter-diameter stainless steel containment vessel with an inner lining of 1,879 photo-multiplier tubes (1325 17" and 554 20" PMTs).
Its second, inner layer consists of a 13 m-diameter nylon balloon filled with a liquid scintillator composed of 1,000 metric tons of mineral oil, benzene, and fluorescent chemicals.
A 3.2 kiloton cylindrical water Cherenkov detector surrounds the containment vessel, acting as a muon veto counter and providing shielding from cosmic rays and radioactivity from the surrounding rock.
Electron antineutrinos (νe) are detected through the Inverse beta decay reaction
> is the average neutron recoil energy, which is only a few tens of kiloelectronvolts (keV).
The neutron is captured on hydrogen approximately 200 microseconds (μs) later, emitting a characteristic 2.2 MeV γ ray.
This delayed-coincidence signature is a very powerful tool for distinguishing antineutrinos from backgrounds produced by other particles.
flux due to the long baseline, KamLAND has a much larger detection volume compared to earlier devices.
As part of the Kamland-Zen double beta decay search, a balloon of scintillator with 320 kg of dissolved xenon was suspended in the center of the detector in 2011.
KamLAND-PICO is a planned project that will install the PICO-LON detector in KamLand to search for dark matter.
PICO-LON is a radiopure NaI(Tl) crystal that observes inelastic WIMP-nucleus scattering.
[4] Improvements to the detector are planned, adding light collecting mirrors and PMTs with higher quantum efficiency.
The shape of this energy spectrum carries additional information that can be used to investigate neutrino oscillation hypotheses.
Statistical analyses in 2005 show the spectrum distortion is inconsistent with the no-oscillation hypothesis and two alternative disappearance mechanisms, namely the neutrino decay and de-coherence models.
[7][citation needed] It is consistent with 2-neutrino oscillation and a fit provides the values for the Δm2 and θ parameters.
Since KamLAND measures Δm2 most precisely and the solar experiments exceed KamLAND's ability to measure θ, the most precise oscillation parameters are obtained in combination with solar results.
Precision combined measurements were reported in 2008[8] and 2011:[9] KamLAND also published an investigation of geologically-produced antineutrinos (so-called geoneutrinos) in 2005.
These neutrinos are produced in the decay of thorium and uranium in the Earth's crust and mantle.
New results in 2013, benefiting from the reduced backgrounds due to Japanese reactor shutdowns, were able to constrain U/Th radiogenic heat production to
KamLAND-Zen uses the detector to study beta decay of 136Xe from a balloon placed in the scintillator in summer 2011.
[3] KamLAND-Zen plans continued observations with more enriched Xe and improved detector components.
An improved search was published in August 2016, increasing the half-life limit to 1.07×1026 yr, with a neutrino mass bound of 61–165 meV.
[16] The KamLAND-Zen 800 experiment started data taking in January 2019 and first results were published in 2020.
No neutrinoless double-beta decay was observed, and the established lower bound for half-life was T >
yr corresponding to upper limits on the effective Majorana neutrino mass of 36 – 156 meV.
