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+// Scilab code: Ex4.2 : Width of the potential barrier: Pg: 125 (2008)
+A = 222;    // Atomic weight of radioactive atom
+Z = 86;    // Atomic number of radioactive atom
+eV = 1.6e-19;    // Energy required by an electron to move through a potential barrier of one volt, joules
+epsilon_0 = 8.854e-012;    // Absolute electrical permittivity of free space, coulomb square per newton per metre square
+e = 1.6e-19;     // Charge on an electron, coulomb
+r0 = 1.5e-015;    // Nuclear radius constant, m
+r = r0*A^(1/3);    // Radius of the radioactive atom, m
+E = 4*eV*1e+06;    // Kinetic energy of an alpha particle, joule
+// At the distance of closest approach, r1, E = 2*(Z-2)*e^2/(4*%pi*epsilon_0*r1)
+// Solving for r1, we have
+r1 = 2*(Z-2)*e^2/(4*%pi*epsilon_0*E);    // The distance form the centre of the nucleus at which PE = KE
+a = r1 - r;    // Width of the potential barrier, m
+printf("\nThe width of the potential barrier of the alpha particle = %5.2e m", a);
+// Result
+// The width of the potential barrier of the alpha particle = 5.13e-014 m
+\ No newline at end of file