사이언스 올제

읽고 생각하는 과학문제

1. If the annihilation of an anti-electron (e+) with an electron (e-) at rest results in two gamma ray each of energy 511 keV, what is the mass of e+ ?

A. zero

B. 0.255 MeV

C. 0.511 MeV

D. 1.022 MeV

E. 938 MeV

2. A very high energy gamma ray into the LAT can produce an e+e-pair by "pair production in the Coulomb field of a high-Z nucleus".The incident gamma ray is zero mass and the photon contributed by the nucleus is very low energy. Therefore, what is the angle between the produced e+ and e- ?

A. nearly zero degrees

B. a few degrees

C. 45 degrees

D. 90 degrees

E. 180 degrees

3. A violation of Special Relativity could be suspected if the speed of light were measured to be a function of photon energy. The resolving time of GLAST is 10 microsec, how small would the gamma- emitting region have to be in order to measure a meaningful arrival time difference between gamma rays of different energy?

A. 3 meter

B. 3 km

C. 3000 km (approx. size of Earth)

D. 3 x 10^5 km (one light-second)

E. 3 x 10^8 km 9100 light-seconds)

4. GLAST-LAT will measure 30 million photons per year. How many is this per second?

A. 1 per second

B. 10 per second

C. 100 per second

D. 1000 per second

E. 10,000 per second