1 files changed, 23 insertions, 0 deletions
diff --git a/pdg.c b/pdg.c
new file mode 100644
index 0000000..d6a2161
--- /dev/null
+++ b/pdg.c
@@ -0,0 +1,23 @@
+#include "pdg.h"
+#include "math.h"
+
+double get_scattering_rms(double x, double p, double beta, double z, double rho)
+{
+    /* Returns the RMS width of the scattering angle for a particle deflected
+     * by many small-angle scatters after a distance `x`. `p` is the momentum
+     * of the particle in MeV, `beta` is the speed of the particle in units of
+     * the speed of light, `z` is the charge of the particle in units of the
+     * electron charge, and `rho` is the density of the water in units of
+     * g/cm^3.
+     *
+     * `x` should be in cm.
+     *
+     * Note: I'm not sure if this will work for particles other than electrons
+     * since the radiation length is only discussed in terms of an
+     * electromagnetic shower induced by electrons (see Section 33.4.2).
+     *
+     * See Equation 33.15 in
+     * http://pdg.lbl.gov/2018/reviews/rpp2018-rev-passage-particles-matter.pdf. */
+    if (x == 0.0) return 0.0;
+    return (13.6/(beta*p))*z*sqrt(x*rho/RADIATION_LENGTH)*(1+0.038*log((x*z*z)/(RADIATION_LENGTH*beta*beta/rho)));
+}