diff --git a/include/openmc/material.h b/include/openmc/material.h
index 3497d0f387..6a3461e0b1 100644
--- a/include/openmc/material.h
+++ b/include/openmc/material.h
@@ -95,7 +95,7 @@ public:
   std::unique_ptr<Bremsstrahlung> ttb_;
 
 private:
-  //! Calculate density effect correction
+  //! Calculate the collision stopping power
   void collision_stopping_power(double* s_col, bool positron);
 
   //! Initialize bremsstrahlung data
@@ -113,14 +113,14 @@ private:
 //==============================================================================
 
 //! Calculate Sternheimer adjustment factor
-double sternheimer_adjustment(std::vector<double>& f, std::vector<double>&
-  e_b_sq, double e_p_sq, double n_conduction, double log_I, double tol, int
-  max_iter);
+double sternheimer_adjustment(const std::vector<double>& f, const
+  std::vector<double>& e_b_sq, double e_p_sq, double n_conduction, double
+  log_I, double tol, int max_iter);
 
 //! Calculate density effect correction
-double density_effect(std::vector<double>& f, std::vector<double>& e_b_sq,
-  double e_p_sq, double n_conduction, double rho, double E, double tol, int
-  max_iter);
+double density_effect(const std::vector<double>& f, const std::vector<double>&
+  e_b_sq, double e_p_sq, double n_conduction, double rho, double E, double tol,
+  int max_iter);
 
 //! Read material data from materials.xml
 void read_materials_xml();
diff --git a/src/material.cpp b/src/material.cpp
index 277a568ea5..7b000db7d2 100644
--- a/src/material.cpp
+++ b/src/material.cpp
@@ -573,7 +573,7 @@ void Material::init_bremsstrahlung()
     double sum_density = 0.0;
 
     // Get the collision stopping power of the material
-    this->collision_stopping_power(&stopping_power_collision(0), positron);
+    this->collision_stopping_power(stopping_power_collision.data(), positron);
 
     // Calculate the molecular DCS and the molecular radiative stopping power using
     // Bragg's additivity rule.
@@ -948,9 +948,9 @@ void Material::to_hdf5(hid_t group) const
 // Non-method functions
 //==============================================================================
 
-double sternheimer_adjustment(std::vector<double>& f, std::vector<double>&
-  e_b_sq, double e_p_sq, double n_conduction, double log_I, double tol, int
-  max_iter)
+double sternheimer_adjustment(const std::vector<double>& f, const
+  std::vector<double>& e_b_sq, double e_p_sq, double n_conduction, double
+  log_I, double tol, int max_iter)
 {
   // Get the total number of oscillators
   int n = f.size();
@@ -993,9 +993,9 @@ double sternheimer_adjustment(std::vector<double>& f, std::vector<double>&
   return rho;
 }
 
-double density_effect(std::vector<double>& f, std::vector<double>& e_b_sq,
-  double e_p_sq, double n_conduction, double rho, double E, double tol, int
-  max_iter)
+double density_effect(const std::vector<double>& f, const std::vector<double>&
+  e_b_sq, double e_p_sq, double n_conduction, double rho, double E, double tol,
+  int max_iter)
 {
   // Get the total number of oscillators
   int n = f.size();
diff --git a/src/physics.cpp b/src/physics.cpp
index 6e76200204..8a16c2ae6a 100644
--- a/src/physics.cpp
+++ b/src/physics.cpp
@@ -271,10 +271,8 @@ void sample_photon_reaction(Particle* p)
     if (E_electron >= settings::energy_cutoff[electron]) { 
       double mu_electron = (alpha - alpha_out*mu)
         / std::sqrt(alpha*alpha + alpha_out*alpha_out - 2.0*alpha*alpha_out*mu);
-      double uvw[3];
-      std::copy(p->coord[0].uvw, p->coord[0].uvw + 3, uvw);
-      rotate_angle_c(uvw, mu_electron, &phi);
-      p->create_secondary(uvw, E_electron, electron, true);
+      Direction u = rotate_angle(p->u(), mu_electron, &phi);
+      p->create_secondary(u, E_electron, Particle::Type::electron, true);
     }
 
     // TODO: Compton subshell data does not match atomic relaxation data