diff --git a/McGenerator.py b/McGenerator.py
index 59fe2f8..444c4b0 100644
--- a/McGenerator.py
+++ b/McGenerator.py
@@ -72,23 +72,26 @@ def parameterization():
     c.SetTopMargin(0.05)
     c.SetRightMargin(0.05)
 
+    ### using regional fitting from 0.2 to arr_t[0] - 0.2
+    ### 0.2 is to avoid the too sharp rise edge at the beginning for low-energy X-rays, where the statistics is low and the fitting is not stable. (Low propability given the shorter attenuation length for low-energy X-rays.)
+    ### arr_t[0] - 0.2 is to avoid the drop at the end for high-energy X-rays due to the absorption of holes by the anode for the intial strong repuslsion effect. (Low propability given the longer attenuation length for high-energy X-rays.)
     global gr_AlphaT, gr_BetaT
     pad2 = c.cd(1)
     gr_AlphaT = TGraphErrors(len(arr_z0), arr_t, arr_alpha, array('d', np.zeros(len(arr_z0))), arr_alphaUncert)
     gr_AlphaT.SetTitle(';Approximated Drift Time [ns];#alpha')
-    func_alpha = TF1('func_alpha', '[0] + [1] * sqrt((x)) + [2] * x + [3] * x^2')
+    func_alpha = TF1('func_alpha', '[0] + [1] * sqrt((x)) + [2] * x + [3] * x^2', 0.2, arr_t[0] - 0.2)
     func_alpha.SetLineColor(kRed+1)
-    gr_AlphaT.Fit(func_alpha, '')
+    gr_AlphaT.Fit(func_alpha, 'R')
     # set fit line color
     gr_AlphaT.Draw()
     print(f'Alpha fitting chi2/NDF = {func_alpha.GetChisquare()/func_alpha.GetNDF()}')
 
     c.cd(2)
     gr_BetaT = TGraphErrors(len(arr_z0), arr_t, arr_beta, array('d', np.zeros(len(arr_z0))), arr_betaUncert)
-    func_betaT = TF1('func_betaT', '[0]*(x-[1])^[2]+ [3]*exp([4]*x) + 2')
+    func_betaT = TF1('func_betaT', '[0]*(x-[1])^[2]+ [3]*exp([4]*x) + 2', 0.2, arr_t[0] - 0.2)
     func_betaT.SetParameters(1.3, -4, -0.4, -0.6, -4.)
     func_betaT.SetLineColor(kRed+1)
-    gr_BetaT.Fit(func_betaT, '')
+    gr_BetaT.Fit(func_betaT, 'R')
     gr_BetaT.SetTitle(';Approximated Drift Time [ns];#beta')
     gr_BetaT.Draw()
     print(f'Beta fitting chi2/NDF = {func_betaT.GetChisquare()/func_betaT.GetNDF()}')