Cosmic Rays, Protons & Electrons, Heavies, Origins Flashcards
What did the findings of Pacini and Hess conclude about CRs?
Source is above the atmosphere.
What does the latitude effect tell us about CRs?
CRs are charged particles. Mostly positive.
Which direction are positive low energy CRs partially blocked by the Earth?
East.
How are low-energy CRs detected?
Small detectors on satellites or balloons. Can detect primary CRs. Measure charge and mass directly.
How are high-energy CRs detected?
Use Earth’s atmosphere. Head on collisions between CR and nucleons. Cascade of high energy particles. Detect Cherenkov of incoming secondaries and primaries (intermediate E).
How can the energy spectrum of CRs be described?
Power law. p~3
What is the ratio of stripped nuclei and electron CRs?
98%:2%
What are the relative abundances within stripped nuclei CRs?
87% protons, 12% alpha, 1% heavier elements.
What abundances of CRs differ from ISM?
less Li, Be, B and elements below Fe, Pb. (elements below most common enhanced) Interactions chip away at nuclei. -> spallation
What does the rigidity of high-energy CRs tell us about their origin?
Most CRs are of Galactic origin.
There are energy breaks in the e- spectrum. What are the primary energy loss mechanisms in each region?
ionization loss, escape, IC and synch.
What do the energy breaks in the CR spectrum tell us?
They imply the residence time is 10^7 yrs.
What does the abundance of positrons tell us?
10% of e+/- are e+. steeper spectrum than e-.
they are secondary.
Why can’t protons be observed directly for E<1GeV?
At lower energies, they suffer solar modulation.
What is the main energy loss mechanism of protons?
strong interactions with ISM H nuclei. produce mainly pions, then e+/- or neutral pions produce gamma rays.
What is the effect of the energy loss of protons (producing gamma rays)?
bump in local gamma-ray spectrum.
What does the gamma ray emission along the Galactic plane tell us?
the density of CRs is proportional to the density of the ISM. CRs protons are produced where ISM is denser.
What is the aim of the ‘diffusion-loss equation for nuclei’?
to explain higher CR abundances of light elements (Li,Be,B) with spallation.
How do we describe the diffusion component?
nuclei travel through some volume of ISM to reach us. The number of nuclei varies as they enter and leave the volume. Treat Galaxy as a finite volume, allow CRs to escape (diffuse like a gas, scattering).
What two components of spallation must be considered?
loss and gain.
In the Leaky box model, what assumptions are made?
sources uniformly distributed
particles diffuse from source to observer.
possibly escape the volume
Assume steady state.
Why is the energy loss component of diffusion loss and leaky box equations ignored?
For heavier elements, energy loss is negligible.
Since speeds are ~c, how can we adapt diffusion loss and leaky box equations?
Replace t with x. Write distances as density-weighted distances.
How can Leaky box model be used to understand CR abundances?
adopt solar system value for Q’_j to find x_0
adopt values for x_0 to estimate Q’_j
