This is a borrowed answer from my friend, DP.
"The activity level produced depends on the target and beam strike area. The target design must be such that the water being bombarded can circulate for cooling and thus the water will stay in the beam strike area. If the transmission is very high,Â
(> ~92%) the beam will keep the water pushed to the sides of the target cavity and can bore through the water to the back of the target cavity = less yield and damage to the target. If the beam transmission if low (<~60%) the water will have equal heat (from beam energy) dissipated across the water and it will not circulate for cooling and the pressure inside the target will increase to a possible failure of target window (foil).
The correct transmission, with the beam hitting slightly low on the water, will produce the most activity per beam energy and time. Every cyclotron - target combination has to be tuned for best target production. Even the beam shape itself will determine production capability.Â
For example, a cracked stripper foil will produce a beam that is unequal across the target area and thus a hot spot is produced that causes erratic water beam strike and bad yields. Must learn characteristics of a cyclotron to get best production."