Grid

θmin[n_, s_, h_] := ArcTan[n s/h];

θmax[n_, s_,  h_]  :=          ArcTan[(n + 1) s/h];

θmin[2, 0.3, 2]  // N

nn[θ_, h_, s_] :=
         Floor[(h/s) Tan[θ]];

Plot[nn[a, 2, 0.3], {a, 0,  2 Pi}]

T[θ_, h_, s_,
         t_,  μ_] := (1/
             s) (((nn[θ, h, s] + 1) s  -                    h Tan[θ]) Exp[-nn[θ, h, s] μ t/
                     Sin[θ]]  + 
   (h Tan[θ]  -  nn[θ, h,
                       s] s) Exp[-(nn[θ, h, s]  +
                         1) μ t/Sin[θ]])

attenuation coefficient for lead is 60 cm^-1

Plot[
       T[θ, 0.2, 0.03, 0.005, 60], {θ, 0,
         1}, {PlotRange -> All,
         PlotStyle -> Thickness[0.01]}]

vary the height

Plot3D[
       T[θ, h, 0.03, 0.005, 60], {θ, 0, 1},  {h, 0.05,
         0.5}, {PlotRange -> {0, 1},
         PlotPoints -> {64, 64}}]

DensityPlot[
       T[θ, h, 0.03, 0.005, 60], {θ, 0, 1},  {h, 0.05,
         0.5}, {PlotRange -> {0, 0.5}, PlotPoints -> {64, 64},          Mesh -> False}]

Vary the separation

Plot3D[
       T[θ, 0.2, s, 0.005, 60], {θ, 0, 1},  {s, 0.0075,
         0.2}, {PlotRange -> {0, 1},
         PlotPoints -> {64, 64}}]

DensityPlot[
       T[θ, 0.2, s, 0.005, 60], {θ, 0, 1},  {s, 0.0075,
         0.2}, {PlotRange -> {0, 0.5}, PlotPoints -> {64, 64},          Mesh -> False}]

vary thickness

Plot3D[
       T[θ, 0.2, 0.03, t, 60], {θ, 0, 1},  {t, 0.001,
         0.02}, {PlotRange -> {0, 1},
         PlotPoints -> {64, 64}}]

DensityPlot[
       T[θ, 0.2, 0.03, t, 60], {θ, 0, 1},  {t, 0.001,
         0.02}, {PlotRange -> {0, 0.5}, PlotPoints -> {64, 64},          Mesh -> False}]

vary the attenuation coefficient

Plot3D[
       T[θ, 0.2, 0.03, 0.005, μ], {θ, 0, 1},  {μ, 1,
         100}, {PlotRange -> {0, 1},
         PlotPoints -> {64, 64}}]

DensityPlot[
       T[θ, 0.2, 0.03, 0.005, μ], {θ, 0, 1},  {μ, 1,
         100}, {PlotRange -> {0, 0.5}, PlotPoints -> {64, 64},          Mesh -> False}]