Presentation on theme: "At the start of the 20th century, scientists have been puzzled by the fact that the air in electroscopes-instruments became charged or ionized no matter."— Presentation transcript:
At the start of the 20th century, scientists have been puzzled by the fact that the air in electroscopes-instruments became charged or ionized no matter how well the containers were insulated. It was thought that radioactivity from ground minerals was responsible. So if this were the case the effect should diminished with altitude. In 1912 the puzzle was partly solved by an Austrian physicist, Victor Hess, who took a gold leaf electroscope on a balloon flight. Discovery of cosmic rays When an electroscope is charged, its “leaves” repel. A radioactive source can ionize air molecules, which carry away charge, ending the repulsion.
Instead of observing less background as he got farther away from the ground, the only source of radioactivity then known, the amount of radiation increased with altitude. He concluded, "a radiation of very high penetrating power enters our atmosphere from above." Hess lands following a historic 5,300 meter flight. August 7, 1912 National Geographic photograph As his balloon ascended to 5300m, he observed the rate of charging in his electroscope increased with altitude. Initially Hess's theory about rays from space did not receive general acceptance, but additional observations after World War I supported it. The newly discovered radiation was dubbed “Cosmic Rays" by Robert A. Millikan in 1925.
The bulk of cosmic rays, called Galactic Cosmic Rays come from supernova explosions within our Galaxy. Fermi’s 1st order shock acceleration theory predicts a power law spectrum. Local magnetic inhomogeneities are dragged by the shock Particle acceleration occurs across the shock (1 st order Fermi Acceleration) Rest frame of a shock wave Strong shock waves are generated from Super Nova 3
6 Arriving the edge of the heliosphere, cosmic rays encounter the solar wind, a low density stream of hot plasma emanating radially from the sun. Solar magnetic field is embedded in the solar wind and carried outward becoming interplanetary magnetic field (IMF). The interplanetary magnetic field lines are not perfectly smooth, but are wavy / kinky in some places. These isolated fluctuations give rise to regions that act as a particle diffuser. The population density and amplitudes of these magnetic fluctuations vary with the solar activity cycle effecting the energy spectrum of cosmic rays at Earth This time variation in cosmic rays is referred to as Solar Modulation which 11 year cycle Trajectory of charged particle in a smooth magnetic field 11 year cycle animation (rotation rate is scaled for viewing) 4
Thule, Greenland Neutron Monitor Sun Spot Number Monthly average Long term Effect of Solar Modulation
Balloon and space measurements of proton and He ion spectra Different times / solar modulations different rigidity spectra Primary spectrum at Earth p He 6 Rigidity = momentum / electric charge = measure of resistance to deflection by a magnetic field
Primary cosmic rays must pass through the Earth’s magnetic field to enter the atmosphere. The geomagnetic field is more effective at shielding the atmosphere from cosmic rays near the equator than at the poles, producing a latitude effect. Shielding effectiveness is quantified by the Geomagnetic Cutoff Rigidity. This is the minimum rigidity (momentum/charge) a particle must have to pass through the Earth’s magnetosphere and enter the atmosphere. 7 Global contour plot of the geomagnetic cutoff rigidity
8 Atmospheric Propagation Primary galactic cosmic rays entering the atmosphere Some of these primaries are energetic enough to produce a nuclear or high energy interaction initiating a cascade of particles through the atmosphere. As the ensemble of cascades develop the particle density and the particle type distribution varies with atmospheric depth Particle fluxes at sea-level
By the time you finished reading this sentence roughly a dozen electrons, muons, neutrons and gamma rays just passed through your body. In review, this is how they got here. 1) Supernova (source/acceleration site) 2) Galactic Propagation (source to Heliosphere boundary) 3) Heliospheric Propagation (Solar Modulation) 4) Geomagnetic Propagation (Cutoff Rigidity) 5) Atmosphere Transport (TOA to ground level) 9 Cosmic Ray Gantlet
10 Measurements from the ground provide a large aperture cosmic rays making it capable to study very high energy events, however a significant amount of information is lost through the atmosphere
A significant amount of information about the structure of the Galaxy, Sources and Heliosphere can be inferred from Cosmic Ray Observations above the atmosphere
12 If the solar system composition is a template of source particle composition, one could infer the differences are the result of propagation through galaxy.
NASA Balloon Program The primary objective of the NASA Balloon Program is to provide high altitude platforms for scientific and technological investigations. These investigations include fundamental scientific discoveries that contribute to our understanding of the Earth, the solar system, and the universe. The platforms also provide demonstration opportunities of potential new instrument and spacecraft technologies
ANITA Antarctic Impulsive Transient Antenna AESOP Anti-Electron Sub-Orbital Payload LEE Low Energy Electrons University of Delaware Department of Physics and Astronomy Balloon Program Active Projects Astrophysics Ultra High Energy Neutrinos Space Physics and Astrophysics Positrons and Electrons Geomagnetic and Space Physics Electrons and X-rays
The LEE Payload LEE detects electrons with – Plastic scintillators T1, T3 and G (anticoincidence) – Gas Cherenkov detector T2. It measures the electron energy with – Cesium iodide (T4) calorimeter – Lead glass (T5) calorimeter Scintillator T6 assists in particle identification and energy determination by counting the number of particles that escape the calorimeter. 25
LEE Balloon observations of electrons with the LEE begun in 1968 at the University of Chicago and has continued at the UD-Bartol Research Institute since 1984. The data from these balloon flights have been used to study solar modulation of electrons with energies up to ~ 20GeV. Flight Log for LEE
Outward flowing solar wind and solar rotation produce a spiral geometry of the interplanetary magnetic field lines. A+ is shorthand for the case where the dipole has a positive projection on the solar rotation axis is positive whereas the opposite projection is termed A-. Reversals of the solar magnetic field occur every 11 years. q>0q<0 q>0 Drift Directions Particles moving on a curved magnetic field line experience a centrifugal force due to the field curvature that makes the guiding center drift perpendicular to both the centrifugal force and B -- either toward or away from neutral current sheet depending on the particle charge sign and polarity epoch.
Response of electrons and nuclei to changing conditions in interplanetary space is qualitatively similar but quantitatively different. Fluxes are low when the sun is active and high when the sun is inactive, however particles with opposite sign to the polarity state reveal a narrower time profile than those with like charge-sign. 1.2GV Electrons 1.2GV Helium Time profile of helium and electron fluxes at a rigidity of ~1.2 GV: Filled Symbols Open Symbols Magnetic Polarity Observations have shown cosmic ray electrons and nuclei respond differently to solar modulation
19 LEE instrument also provides a means to study the Magnetosphere Without the Sun, our magnetosphere would resemble a dipole structure In the presence of the Solar Wind, however the magnetosphere structure is distorted into a teardrop shape
High Energy Nucleons above the local cutoff Atmospheric Splash Albedo Electrons below the local cutoff Primary Electrons below local cutoff Atmospheric Splash Albedo Electrons escape Primary Electrons Night Time Day Time Night Day Electron Flux Time
The LEE payload was launch May 16, 2009 from Esrange, Sweden and accumulated roughly 100 hours at float before terminated in Northern Canada.
AESOP AESOP detects electrons with plastic scintillators (T1, T3), anticoincidence)(G) and a gas Cherenkov detector (T2). It measures the electron energy in a lead glass (T5) calorimeter. A final scintillator (T6) assists in particle identification and energy determination by counting the number of particles that escape the calorimeter. A permanent magnet and a digital optical spark chamber hodoscope (SC 1,2,3) determine the charge sign and momentum of the electrons. The AESOP instrument was designed and built specifically for this goal… To measure the positron abundance in electrons from 200MeV to 5GeV over a full 22 year cycle. (Chickens can fly)
Vertical axis: Energy measured in the Pb-Glass calorimeter Horizontal: Deflection in the magnet in units of inverse rigidity. Curve represents the ideal instrument response for positrons (positive side) and electrons (negative side). Red symbols are events tagged as high energy protons Particle ID and energy of each event are assigned using a likelihood analysis AESOP 2006 Flight Trajectory
Time dependence of positron abundance (black) and anti-proton ratio (red) at a rigidity of roughly 1.3GV. Black line is a Positron abundance prediction based on the analysis of Clem et al. (1996). Red line is an antiproton/proton ratio model Bieber et al. (1999). Dashed lines are the predicted results for future observations. Anti-protons were measured by the series of BESS flights
27 Cosmic Ray Spectrum The cosmic microwave background (CMB) is the thermal radiation left over from the "Big Bang" These UHCR Interact with doppler- shifted cosmic microwave background radiation limiting the distance that these particles can travel before losing energy; this is known as the GZK limit. These interactions can produce very high energy neutrinos
The ANITA experiment: New high-energy neutrino limits and detection of ultra-high energy cosmic rays University of Delaware John Clem and David Seckel ANtarctic Impulsive Transient Antenna
Goal of ANITA is to explore beyond the Galaxy Is anybody out there??