Teaching Physics with the Physics Suite

Edward F. Redish

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Anti-matter ion cosmic rays

An international consortium is presently building a device to look for anti-matter nuclei in cosmic rays to help us decide if there are galaxies made of anti-matter. Anti-matter is just like ordinary matter except the basic particles (anti-protons and anti-electrons) have opposite charge from ordinary matter counterparts. (Anti-protons are negative, and anti-electrons are positive.)

A schematic of the device is shown at the right. A cosmic ray -- say a carbon nucleus or an anti-carbon nucleus -- enters the device at the left where its position and velocity are measured. It then passes through a (reasonably uniform) magnetic field. Its path is bent in one direction if its charge is positive, in the opposite direction if its charge is negative. Its deflection is measured as it goes out of the device.

  1. On the figure shown, what is the direction of the magnetic field?
    How do you know?
  2. What is the path followed by each particle in the device? Why?
  3. If you were given the magnetic field, B, the size of the device, D, the amount of charge on the incoming particle, q, and the mass of the incoming particle, M, would this be enough to calculate the displacement of the charge, d? If so, describe briefly how you would do it (but don't do it). If not, explain what additional information you would need (but don't estimate it).

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Page last modified October 19, 2002: MG04