From the study of the annihilation at rest pp →K ± K 0 m i s s π π + π - the production rates of the η(1440) → K ± K 0 L π were obtained for three different hydrogen target densities: liquid, gaseous at NTP and at low pressure (5 mbar). The rate values are: f η ( 1 4 4 0 ) (LH) = (6.0 ± 0.5) 10 - 4 , f η ( 1 4 4 0 ) (NTP) = (2.9 ± 0.4) 10 - 4 and f η ( 1 4 4 0 ) (5 mbar) = (1.0 ± 0.2) 10 - 4 . From these results, the density dependence of the annihilation fraction from the 1 S 0 protonium level can be extracted directly.