{
  delete gRandom;
  gRandom = new TRandom(123); // Setting the seed
  TH1F *decay = new TH1F ("decay", "Radioactive decay ^{131}I",100, 0,100);
  double mesos_xronos=11.57;
  for(int i=0; i<100000; ++i){
    double a=gRandom->Exp(mesos_xronos) ;
    decay->Fill(a);
  }
  decay->SetXTitle("t [days]"); //Monades Axona X
  decay->SetYTitle ("Events");  //Monades Axona Y
  c1=new TCanvas("c1", "Radioactive Decay", 600, 400);
  c1->cd();
  decay->Draw() ;
}