<Detection efficiency>
At the electron impact energy of 120 eV the overall efficiency 􏰑ions per incident atom􏰀 is estimated to be somewhat greater than 10􏰖6, increasing with decreasing atom beam velocity. ---efficiency 매우 낮음 (2000-PRA-wieland)
<Background>
Four differentially pumped vacuum stages between the grating and detector chamber reduce the total pressure in the latter chamber to less than 1 􏰗10􏰖11 mbar corresponding to a background count rate of typically 4 counts/s.

3.3 Awing analysis - appanalysis 

adjust, analyse, calibrate, estimate, compensate// beam size 50 um: near field// fresnel number 

3.4 Data analysis

4. Results and Discussion

4.1 Comparison of He and D2