  It is commonly assumed that reaction measurements for astrophysics should be
preferably performed in the direction of positive Q value to minimize the
impact of the stellar enhancement factor, i.e. the difference between the
laboratory rate and the actual stellar rate. We show that the stellar effects
can be minimized in the charged particle channel, even when the reaction Q
value is negative. As a demonstration, the cross section of the astrophysically
relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 <
Ec.m. < 3.96 MeV and the astrophysical reaction rate for (p,n) as well as (n,p)
is directly inferred from the data. The presented arguments are also relevant
for other alpha and proton-induced reactions in the p and rp processes.
Additionally, our results confirm a previously derived modification of a global
optical proton potential.
