Alkali background banishment

When I started this project, the background count rates for the alkali, in ppm equivalets, were:
Li: 87
Na: 623
Rb: 0.090
Cs: 0.037

After a year of belittling the backgrounds, the machine can now generally achieve:
Li: 0.5
Na: 161
Rb: 0.022
Cs: 0.005

I'd say that result is good enough for a conference in New Zealand. I'm going to bed now.