Add attenuation interpolator

src/pg_rad/physics/attenuation.py

@@ -0,0 +1,15 @@
+from importlib.resources import files
+
+from pandas import read_csv
+from scipy.interpolate import interp1d
+
+
+def get_mass_attenuation_coeff(
+        *args
+        ) -> float:
+    csv = files('pg_rad.data').joinpath('attenuation_table.csv')
+    data = read_csv(csv)
+    x = data["energy_mev"].to_numpy()
+    y = data["mu"].to_numpy()
+    f = interp1d(x, y)
+    return f(*args)