diff --git a/NUCE_2113/lab6/exercise6_4.png b/NUCE_2113/lab6/exercise6_4.png
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diff --git a/NUCE_2113/lab6/quick_maths.py b/NUCE_2113/lab6/quick_maths.py
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+print("Experiment 6.1\n")
+measured_activity = 5.2e-6  # curies
+elapsed_time = 193.92  # s
+sigma_u1 = 35331  # counts
+background_time = 193.94  # s
+sigma_b = 558  # counts
+
+R = sigma_u1 / elapsed_time - sigma_b / background_time
+print(f"R: {R:.3e} counts / s")
+print(f"R: {R/3.7e10*1e6:.3e} microcurie")
+eps_ip = 0.101  # from figure 6.2
+f = 0.6617
+
+d = 100  # mm
+r = 38 / 2  # mm
+
+G = r**2 / 4 / d**2
+
+A = R / eps_ip / G / f
+
+print(f"G: {G:.3e}")
+print(f"A: {A:.3e} decays / s")
+print(f"A: {A/3.7e10*1e6:.3e} microcurie")
+
+A = 4.5 * 3.7e10 / 1e6
+eps_ip_est = R / A / G / f
+print(f"eps_ips: {eps_ip_est:.3e}")
+
+sigma_u1 = [10122, 11763, 14464, 17476, 22073, 28268, 38084]
+sigma_b = 130
+d = [100, 90, 80, 70, 60, 50, 40]
+t = 60  # s
+
+import numpy as np
+
+n = len(sigma_u1)
+R = np.empty(n)
+G = np.empty(n)
+eps_ip = np.empty(n)
+
+for i, value in enumerate(sigma_u1):
+    print(i, value)
+    R[i] = (value - sigma_b) / t
+    G[i] = r**2 / 4 / d[i] ** 2
+    eps_ip[i] = R[i] / A / G[i] / f
+
+print("R")
+print(R.transpose())
+print("G")
+print(G.transpose())
+print("eps_ip")
+print(eps_ip.transpose())
+
+import matplotlib.pyplot as plt
+
+plt.plot(d, eps_ip, ".b")
+plt.xlabel("Distance [mm]")
+plt.ylabel("$\epsilon_{ip}$")
+plt.grid("both")
+plt.savefig("exercise6_4.png")
+plt.show()