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Great Observatories

Fermi Gamma ray Space Telescope (2008). Large Area Telescope. Gammas hit thin metal sheets, converting to electron-positron pairs via PP.

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Great Observatories

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  1. Fermi Gamma ray Space Telescope (2008) Large Area Telescope • Gammas hit thin metal sheets, converting to electron-positron pairs via PP. • Positron and electron pass through interleaved layers of silicon microstrip detectors, causing ionization which produces detectable tiny pulses of electric charge. • Path of the particles can be determined, each particle creating an inverted "V" that points back to gamma origin. • After passing through tracker, electron and positron enter scintillator crystals and total energy of the particles is measured. The photo shows the LAT stack of metal sheets. Great Observatories

  2. Herschel Space Observatory (ESA) Launched in 2009, will exceed Spitzer in the far-infrared and is capable of seeing the coldest and dustiest objects in space; for example, dusty galaxies just starting to bulk up with new stars. Great Observatories It has a lifetime of 3 years and uses a helium cooled infrared CCD.

  3. Future Observatories Hubble expected to function until at least 2014. Its successor, the James Webb Space Telescope (JWST) is due to be launched in 2014. Goal to observe most distant objects in the Universe beyond the reach of Hubble by observing in infrared penetrating dust. It will continue some of Spitzer capabilities whilst some Hubble capabilities will be lost. Great Observatories 6.5 m mirror and an IR camera and spectrograph

  4. Future Observatories Constellation-X (2016) To perform 50 times more sensitive X-ray observations than Chandra also extending further into hard X-ray regions, giving it abilities of CGRO. One role for Constellation-X will be to take X-ray spectra from matter as it falls into supermassive black holes via Doppler shift. Great Observatories Wolter telescope and CCD.

  5. Elementary particle, travels close to the speed of light, electrically neutral, and is able to pass through ordinary matter almost undisturbed. Member of the lepton family (electrons, muons, taus, electron neutrinos, muon neutrinos, tau neutrinos and the corresponding antiparticle of each). Neutrinos have a very small, but non-zero mass which is yet to be accurately measured. Neutrinos Tau 3,500 mass of electron Lifetime 2.9×10-13 s Muon 200 mass of electron Lifetime 2.2×10-6 s Electron

  6. Most neutrinos passing through the Earth originate from the Sun, and more than 50 trillion solar neutrinos pass through an average human body every second. Neutrinos are clearly extremely difficult to detect. In this course we will concentrate on two main sources: (i) Stars and (ii) Supernovae Neutrinos

  7. Stellar neutrinos In β− decay, In β+ decay, Neutrinos Which process occurs to make deuterium below ? Which process occurs to make beryllium below ?

  8. Stellar neutrinos Neutrinos are emitted at many stages of a star’s life. The main reaction sequences are : Neutrinos 10 MK – 14 MK >23 MK 14 MK – 23 MK

  9. Stellar neutrinos We can calculate how much energy is evolved following each reaction… Mass of proton = 1.00728u Mass of electron = approx zero Mass of neutron = 1.00867u Mass of electron = approx zero Mass of deuterium = 2.0141u u = 1.661 × 10-27 kg Neutrinos e.g. Mass before: 2 × 1.00728u = 2.01456u Mass after: 2.0141u Mass difference: 4.58 × 10-4u = 7.61 × 10-31 kg. Energy emitted: Δmc2 = 6.845 × 10-14 J = 0.43 MeV. How is this energy shared between particles ?

  10. Stellar neutrinos Below is predicted stellar neutrino energy spectrum. Depending on the number of reaction products we either get a spike or a continuum. Neutrinos Once we’ve made a prediction we must build detectors to try to observe it…

  11. Supernova neutrinos When stars go supernova they radiate energy in the form of neutrinos in the range 10-30 MeV. There are two main processes... 1) Electrons and protons are forced together to interact through the weak force: Neutrinos Inverse beta decay

  12. Supernova neutrinos 2) A more important neutrino source is the thermal energy (100 billion kelvin) of the newly formed neutron core, which is dissipated via the formation of neutrino-antineutrino pairs of all flavours. Most of the energy produced in supernovas is thus radiated away in the form of an immense burst of neutrinos. Neutrinos The first experimental evidence of this phenomenon came in 1987, when neutrinos from supernova 1987A were detected. This again gave a direct insight into the core of a supernova.

  13. Detecting neutrinos Bad news No charge Nearly no mass Interaction cross section so low that we require 1017 m thickness of steel to ensure 50% of the incident neutrino flux are captured!!!!! Neutrinos Good news Fortunately it is also true that lots are produced.

  14. Detecting neutrinos There are four main approaches to detecting neutrinos. Two we will meet now and the other two will be covered when discussing the SNO detector. Neutrinos 1. Neutrino capture reactions If neutrino collides with a neutron in atom it can interact via negative beta decay. This changes the atom to a different one. For example

  15. 1. Neutrino capture reactions So take a big container of chlorine and watch to see if any argon is produced. Homestake solar neutrino experiment has been taking data since 1970 using a target containing 600 tonnes of tetrachloroethylene (dry cleaning fluid) placed 1.5 km underground in a gold mine in South Dakota. Neutrinos Argon isotope accumulates for a month and is then filtered out. The number of argon atoms present is calculated from the activity rate as it decays. http://www.youtube.com/watch?v=bSW_xwhCP48 http://www.youtube.com/watch?v=1IORLpKzfp0&feature=related

  16. 1. Neutrino capture reactions Even with such a big target the production rate is less than one argon atom per day and it is a huge experimental challenge to detect a few tens of atoms in 1031. Neutrinos Disadvantages: Not real-time data, labour intensive, low rate, only flux.

  17. 2. Neutrino scattering Neutrinos scatter off electrons in a target giving them high recoil energy. These fast moving electrons produce Cherenkov light providing information on energy and direction of neutrino. Neutrinos Interaction is sensitive to all neutrino flavours, but the scattering probability of an electron-neutrino is about a factor of six larger than the scattering probability of the two other neutrino types.

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