Question: How do I optimize this function in Maple?

I am new to Maple and need assistance optomizing the following function F with respect to t:

F := int(f, [yip = -infinity .. infinity, xip = -infinity .. infinity, tp = 0 .. t])

Where: f := exp(-(xip^2+yip^2)*(1/2))*exp(-((2*Pe*tp+x-xip)^2+(y-yip)^2+z^2)/(4*(t-tp)))/((4*Pi^(3/2))*(t-tp)^(3/2))

and

Pe := 10; x := 0; y := 8/10; z := 1/18

I have a plot of F from 0 to approximately 1/2 and I know what the shape of the function is:

Is is clear that there definitely is a maximum within this range of t (i.e. t=0 to 1/2). When I right click on the function F and click the "Optomization" tab, then "Maximize (local)" maple results in the following pink text "Error, (in Optimization:-NLPSolve) integration range or variable must be specified in the second argument, got HFloat(1.0) = 0 .. HFloat(1.0)"

Any help fixing the error and optimizing the function F will be appreciated. Thank you!