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The energy transported by particle radiation depends in large measure upon their kinetic energy and hence the velocity of the particles. Particles such as protons are a major constituent of cosmic radiation. Some of these protons arrive in the solar system from distant sources in the galaxy. The majority however are arriving at the earth from the solar wind. The graphs below show the kinetic energy of protons as a function of their velocity. |
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1. Using the graph to the left determine the kinetic energy of a proton moving at 20% the speed of light. Express your answer in MeV. 2. Using the graph to the left determine the kinetic energy of a proton moving at 40% the speed of light. Express your answer in MeV. 3. A proton is brought to rest by colliding it with atoms inside a very sensitive calorimeter. The proton releases 25MeV of energy. What was its initial impact velocity?
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4. A substance absorbs a beam of 1011 protons. If the beam
is monochromatic1 (i.e. all protons have exactly the same energy) and the velocity of the protons is 35% the speed of light (0.35c), how much energy in MeV is absorbed?
1The term monochromatic, when used in particle physics, refers to the energy of an ensemble of particles, meaning they all have exactly the same energy. The term has been "borrowed" from optical physics. 5. Calculate the rate of energy transfer (power in watts) of the beam in question (4) if the protons are all absorbed within 10-5 seconds. (recall 1eV=1.60x10-19J and 1W=1J/s) |
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6. Using the graph to the left determine the kinetic energy of a proton moving at 60% the speed of light. Express your answer in MeV. 7. Using the graph to the left determine the kinetic energy of a proton moving at 98% the speed of light. Express your answer in MeV. 8. A proton is brought to rest by colliding it with atoms inside a very sensitive calorimeter. The proton releases 6GeV of energy. What was its initial impact velocity? 9. What factors, other than impact velocity, do you think determine the total amount of energy deposited by particle radiation when it irradiates a substance? |
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10. Astronauts in space are subject to particle radiation from various celestial sources including the sun which ejects a high velocity stream of protons into space.
The solar proton flux is highly variable and has the potential to deliver lethal doses of
radiation to both humans and electronic equipment aboard various spacecraft. Suggest several ways by which one might protect oneself and sensitive electric equipment from dangerous solar radiation. |