Experimental determination of W for oxygen ions in nitrogen

'Differential' and integral measurements were made of the W value (average energy required to form an ion pair) for oxygen ions in nitrogen gas. A variable pressure cylindrical ionization chamber with a differential pumping section was employed. The average energy deposited per particle in the chamber was determined by integrating the energy spectrum measured with a heavy ion solid state detector. In the integral measurement of W, the particle was completely stopped in the chamber and the total ionization produced in the chamber was measured. The integral W value for 34-5 MeV oxygen ions was found to be 38-6 +/- 0-54 eV per ion pair. For 'differential' measurements, the pressure in the chamber was raised to 0-003, 1, 5, 15 and 20 Torr; and measurements of ionization currents and average energy deposited per particle were made at each pressure. From differences between these measurements 'differential' W was found. The average value of fifteen 'differential' W values was found to be 38-6 +/- 1-16 eV per ion pair.