gamma rays

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Across
  1. 2. the first letter of the Greek alphabet
  2. 4. the shortest distance between any two points in phase
  3. 5. the second letter of the Greek alphabet
  4. 7. can be observed in the sky around once a day
  5. 8. due to their high penetration power, they can damage ______ and internal organs.
  6. 9. gamma rays can be used to treat ______
Down
  1. 1. the name of a kind of radio surgery that is directed at brain tumours to kill cancer cells
  2. 3. gamma rays are a form of ________ radiation
  3. 6. risky, dangerous)