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The Wilson chamber
- 1. LICEO SCIENTIFICO «C. D’ASCANIO» A.S. 2020-2021 Cacciatore Giacomo, Di Giovannantonio Riccardo, Rapacchiani Luca, Tannous Sausan, Viottado Matteo Group members: The cosmic rays 1
- 2. COSMIC RAYS Cosmic rays are high-energy particles arriving from outer space. These are: Protons (nuclei of hydrogen) (89%) Nuclei of helium (10%) Heavier nuclei (1%) When the primaries reach the upper atmosphere they collide with other particles making: Neutrinos Muons PRIMARIES: observable in the upper atmosphere SECONDARIES: observable at Sea level 2 2 • https://www.youtube.com/watch?v=C3ue7cEocvI&feature=youtu.be • https://www.youtube.com/watch?v=_bKbMARsE-4
- 3. 3 MUONS The muon is a heavy particle belonging to the lepton group of particles. These are made by the collision of primaries with the nuclei of atoms in the upper atmosphere. However muons travel tens of metres below the Earth’s surface making them easily observable at sea level. 3
- 4. COSMIC ACCELERATORS 4 Pinning down the origin of the higher-energy particles is made possibile through studying high- energy gamma rays from outer space. Gamma ray: electromagnetic radiation of the shortest wavelength and highest energy. Sources of the highest energy gamma rays: Supernovae: Crab Nebula (Milky Way) Blazar: supermassive black holes How Do Cosmic Accelerators Work? 1) formation of a collimated jet of charged particles; 2) the flow of these particle in a narrow cone; 3) the acceleration of the flow to relativistic velocities. 4
- 5. CERN The Cloud The CLOUD experiment studies how ions produced by high-energy particles called cosmic rays affect aerosol particles, clouds and the climate. It uses a special cloud chamber and a beam of particles from the Proton Synchrotron to provide an artificial source of cosmic rays; It has made several important discoveries on the vapours. 5 5 • https://www.youtube.com/watch?v=fuNHm5-yFAI
- 6. CERN CLOUDy “CLOUDy” type, which studies the ice-and liquid-cloud-seeding properties of various aerosol species grown in the chamber, and direct effects of cosmic-ray ionisation on clouds. The CERN CLOUD team has built a novel generator of electrically charged cloud seeds to investigate the effects of charged aerosols on cloud formation and dynamics. 6 6
- 7. 7 CLOUD CHAMBER British physicist C.T.R. Wilson devised 1912 the cloud chamber which allows you to see the trail left by a charged particle 7
- 8. CLOUD CHAMBER How does it work? 8 IN THE LOWER PART WE FIND THE DRY ICE IN THE UPPER ONE AN ABSORBENT MATERIAL SOACKED IN PROPANOL THE PROPANOL EVAPORATES VAPOR COOLS DUE TO THE DRY ICE SUPERSATURATED ENVIRONMENT CHARGED PARTICLE IN THE CHAMBER PROPANOL CONDENSES WITHE STREAKS OF CLOUD 8
- 9. Cloud chambers are used to study charged particles, like electrons, and radioactive particles, like α and β particles. When the particles enter the chamber they create a track due to the ionization of the propanol, which is different for any particle: Heavier particles, like protons and alfa particle: release a thin, straight and defined track; Other particles, like electrons or beta particles: release a thin and twisty track due to the collisions that happens in the chamber. CLOUD CHAMBER radioactive particles 9
- 11. 2 SLIDE • https://home.cern/science/physics/cosmic-rays-particles-outer-space • https://www.britannica.com/science/cosmic-ray SITOGRAPHY 11 5-6 7/8 3 SLIDE SLIDE 4 SLIDES SLIDES 9 SLIDE • http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/cloud.html#c1 • http://www.fisgeo.unipg.it/archives/_piano_lauree_scient/Camera_Nebbia.pdf • http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/cloud.html • https://www2.physics.ox.ac.uk/accelerate/resources/demonstrations/cloud-chamber • https://home.cern/science/physics/cosmic-rays-particles-outer-space • https://heasarc.gsfc.nasa.gov/docs/cgro/epo/brochures/new_win/nw14.html • https://www.britannica.com/science/muon • https://home.cern/news/news/experiments/cosmic-rays-clouds 11
Editor's Notes
- Discovered in 1912 by the Austrian physicist Victor Hess, cosmic rays are high-energy particles arriving from outer space. When the cosmic ray “primaries” arrive at Earth, they collide with the nuclei of atoms in the upper atmosphere creating more particles, mainly pions. The charged pions can swiftly decay, emitting particles called "secondaries", such as neutrinos and muons. Unlike pions, these can travel through the atmosphere and they are observed also at sea level. To study primary cosmic rays directly, high-altitude balloons (typically reaching altitudes of 37 km) have been extensively used. Cosmic ray observations also have been made from Earth-orbiting satellites or rockets but they carry smaller payloads and remain at those altitudes for only a few minutes.Most of these particles come from sources within the Milky Way Galaxy and are known as galactic cosmic rays (GCRs). The rest of the cosmic rays originate either from the Sun or, almost certainly in the case of the particles with the highest energies, outside the Milky Way Galaxy.
- The muon is a heavy particle discovered in 1936. Because of its mass, it was at first thought to be the particle predicted to explain the strong force that binds protons and neutrons together in atomic nuclei. However, a muon is correctly assigned as a member of the lepton group of subatomic particles with electrons and taus. A muon is relatively stable compared to other particles, with a lifetime of only 2.2 microseconds before it decays into an electron and two kinds of neutrinos. Because muons are charged, before decaying they lose energy by displacing electrons from atoms (ionization). At high-particle velocities close to the speed of light, ionization dissipates energy in relatively small amounts, so muons in cosmic radiation are extremely penetrating and can travel tens of metres below the Earth’s surface.
- Pinning dowm the origin of the higher-energy particles is made possible through studying high-energy gamma rays from outer space. Gamma ray are electrically neutral, generate showers of secondary particles that can be detected on Earth and that point back towards the point of origin of the gamma rays. Sources of the highest energy gamma rays in our own galaxy, the Milky Way, include the remnants of supernovae, such as the famous Crab Nebula; other sources are a class of active galaxies termed "blazars". These class of active galaxies emit narrow, intense jets of gamma-rays andare among the most powerful and least understood objects in the Universe. The principals process of particle acceleration are the formation of a collimated jet of charged particles, the flow of these particle in a narrow cone, and the acceleration of the flow to relativistic velocities.
- The CLOUD experiment studies how ions produced by high-energy particles called cosmic rays affect aerosol particles, clouds and the climate. It uses a special cloud chamber and a beam of particles from the Proton Synchrotron to provide an artificial source of cosmic rays. All experimental conditions can be controlled and measured, including the “cosmic ray” intensity and the trace atmospheric vapours in the chamber. CLOUD has shown that aerosols can form purely from biogenic vapours emitted by trees, and that their formation rate is enhanced by cosmic rays by up to a factor 100.
- The run that has just started is of the “CLOUDy” type, which studies the ice- and liquid-cloud-seeding properties of various aerosol species grown in the chamber, and direct effects of cosmic-ray ionisation on clouds. At the moment CLOUD uses the most comprehensive array of instruments ever assembled for CLOUDy experiments, including several instruments dedicated to measuring the ice- and liquid-cloud-seeding properties of aerosols over the full range of tropospheric temperatures. In addition, the CERN CLOUD team has built a novel generator of electrically charged cloud seeds to investigate the effects of charged aerosols on cloud formation and dynamics.
- In the lower part we find dry ice, in the upper one an absorbent material soaked in propanol. The propanol evaporates, the vapor cools due to the dry ice and a supersaturated environment is created. When a charged particle passes through the chamber, the propanol molecules acquire a polarization and are ready to condense and do so in the form of droplets, which appear in the form of white streaks along the path of the particles.
- The cloud chamber is used to study electrons and α and β particles typical of radioactive elements. To study the radioactive particles, bars of radioactive elements are used, such as isotopes of strontium (90 Sr), potassium, thorium or uranium, placed in the machine which, once activated, shows trails that vary from particle to particle: α particles and protons have a wide straight path; electrons and b particles have a luminous and twisted trace due to collisions; gamma particles a poorly defined and linear trace. Sr 90 is a radioactive isotope with a half-life of about 64 hours and decays into yttrium 90 (90 Y) which is equally radioactive; these two isotopes are very dangerous and represent a practically pure source of β particles.