Complex sentence: The collision that occurs causes sputtering of atoms from the sample surface, and of these atoms only a small amount will undergo ionization; these become the secondary ions, which are then detected after transfer through the mass spectrometer.
Split into simpler sentences: The collision that occurs causes atoms to sputter from the sample surface, and of these atoms only a small amount will undergo ionization. These become secondary ions, which are then detected after transfer through the mass spectrometer.