The neutrons detection involves the use of gadolinium which has the largest thermal neutron capture cross section ever observed. The neutron capture on.
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Presentation on theme: "The neutrons detection involves the use of gadolinium which has the largest thermal neutron capture cross section ever observed. The neutron capture on."— Presentation transcript:
The neutrons detection involves the use of gadolinium which has the largest thermal neutron capture cross section ever observed. The neutron capture on Gd is followed by the emission of 3-4 gammas totalling 8 MeV. The experimental arrangement chosen for neutron detection consists in four NE110 organic plastic scintillators (one scintillator block being 18*18*200 cm 3 ). The scintillators have been tested in order to determine what is the optimum size for the neutron detector. The conclusion was that the neutrons are thermalized and captured within 18 cm inside the scintillator. The scintillators have to be large enough to detect the resulting gammas from neutron capture. At present we have a good understanding of neutron thermalization and capture in terms of Monte Carlo simulation. Interactions with different forms of radiation coming from space – gamma-rays, alpha particles, electrons and cosmic rays – are likely to swamp any signal unless extreme measures are taken. The first such precaution is to go deep underground, at least 1 kilometre, to where the rock above provides sufficient shielding against this background radiation. The UK is exceptionally fortunate in that here is one of the deepest mines in Europe. At 1.2 kilometres, the Boulby mine, operated by Cleveland Potash, not only provides the depth required but, with caverns in salt rock easy to excavate, it also offers a safe and adaptable environment in which to build underground laboratories. The Observatory for Multiflavour Neutrino Interactions from Supernovae In 1990, researchers described the use of geologic salt deposits as a neutrino to neutron converter. If a neutron detector was installed deep in a salt mine, then the expanding neutrino front from an exploding supernova would produce a burst of neutrons as it passed trough the salt. These neutrons can be used to derive signatures of supernova phenomena, such as its collapse rate and the nuclear reactions that create the heavy elements of our Universe. The objective is to observe the time profile of the neutrinos from Galactic supernova by conversion of neutrinos in salt, Pb, Fe and rock targets to produce neutrons detected by organic scintillators OMNIS detector will allow the time-of-flight measurement of neutrino mass to be done for the first time if the neutrino mass is in the cosmologically interesting range 10-100 eV. For a supernova at the centre of the Galaxy, this would produce a time separation of ~ 2s between a light neutrino and one of mass 50 eV/c 2 (after travelling 33,000 years!). If the time profile of neutrino burst shows no evidence of a mass distortion, the ν μ mass limit will be reduced by a factor 10 4 from ~100 keV to 10 eV, and the ν τ will be reduced by a factor 10 6 from ~10 MeV to 10 eV! Time Profile and Detection of Neutrino Burst Cristian Bungau, Manchester University Neutrinos that are emitted from supernovae are expected to have roughly Fermi-Dirac energy spectra, with mean energies of 11 (ν e ), 16 (ν μ ) and 25 (ν τ ) MeV. Supernovae are the most energetic events ever observed in our Galaxy. They are thought to occur roughly every 10-30 years. During the final stages of stellar evolution, the core of a massive star undergoes a catastrophic implosion followed by the emission of an energy 1000 times the total energy of our Sun over its entire 10-billion-year lifetime, but in a period of only about 10 seconds. Only about 1% of the energy released goes into the explosion itself, and about 1% of that is finally released as light…which is still enough to make a supernova as bright as entire Galaxy for a brief time. The remaining energy is released in the form of an immense flux of neutrinos. The Crab Nebula is the remnant of a supernova that exploded in 1054 AD. In 1987, a supernova was observed in the Large Magellanic Cloud (~170,000 ly from Earth). Only about 20 neutrino events were recorded, but even those were enough to confirm the basic concepts of core collapse supernova. Properties of Supernova Neutrino Burst Principles of OMNIS. Detector Development at Manchester University High Z (Pb and Fe) targets are primarily sensitive to the high energy component of the supernova neutrino flux; therefore the neutrino flavours detected are expected to be mostly muon and tau. The neutrino detection mechanism is based on the observation of neutrons emitted from NC reaction for all neutrino flavours. In addition, neutrons can arise from CC reactions The MSW conversion of ν μ or ν τ to ν e in the supernova envelope will produce ν e of high momentum and hence an enhanced charged current interaction. This produces an increase in the number of double neutron events in lead by a factor of ~60 ! Therefore OMNIS can detect MSW mixing to electron neutrinos through the increase in the charged current signal. Where would we put OMNIS