diff --git a/scripts/docker/ci/launch-testing.sh b/scripts/docker/ci/launch-testing.sh
index 9d550210d9..d22a4675c0 100755
--- a/scripts/docker/ci/launch-testing.sh
+++ b/scripts/docker/ci/launch-testing.sh
@@ -1,11 +1,11 @@
-#!/bin/sh -ex
+#!/bin/sh -e
 
 if [ -z "$1" ]; then
   echo "Usage: $0 pull-request-id" 1>&2
   exit 2;
 fi
 
-CONTAINER=$(docker run -t -d celeritas/ci-cuda11:latest)
+CONTAINER=$(docker run -t -d celeritas/ci-cuda11:2021-01-27)
 echo "Launched container: ${CONTAINER}"
 docker exec -i $CONTAINER bash -l <<EOF || echo "*BUILD FAILED*"
 set -e
@@ -16,5 +16,6 @@ git checkout mr/$1
 SOURCE_DIR=. BUILD_DIR=build entrypoint-shell ./scripts/build/docker.sh
 EOF
 docker stop --time=0 $CONTAINER
-echo "To resume:  docker exec -i -e 'TERM=xterm-256color' $CONTAINER bash -l"
-echo "To delete:  docker rm -f $CONTAINER"
+echo "To resume: docker start $CONTAINER \\"
+echo "           && docker exec -it -e 'TERM=xterm-256color' $CONTAINER bash -l"
+echo "To delete: docker rm -f $CONTAINER"
diff --git a/src/base/Collection.hh b/src/base/Collection.hh
index 691b8983fd..951ae5e43a 100644
--- a/src/base/Collection.hh
+++ b/src/base/Collection.hh
@@ -121,11 +121,11 @@ class Collection
 
     // Construct from another collection
     template<Ownership W2, MemSpace M2>
-    inline Collection(const Collection<T, W2, M2, I>& other);
+    explicit inline Collection(const Collection<T, W2, M2, I>& other);
 
     // Construct from another collection (mutable)
     template<Ownership W2, MemSpace M2>
-    inline Collection(Collection<T, W2, M2, I>& other);
+    explicit inline Collection(Collection<T, W2, M2, I>& other);
 
     //!@{
     //! Default assignment
@@ -133,13 +133,13 @@ class Collection
     Collection& operator=(Collection&& other) = default;
     //!@}
 
-    // Assign from another collection in the same memory space
-    template<Ownership W2>
-    inline Collection& operator=(const Collection<T, W2, M, I>& other);
+    // Assign from another collectio
+    template<Ownership W2, MemSpace M2>
+    inline Collection& operator=(const Collection<T, W2, M2, I>& other);
 
-    // Assign (mutable!) from another collection in the same memory space
-    template<Ownership W2>
-    inline Collection& operator=(Collection<T, W2, M, I>& other);
+    // Assign (mutable!) from another collection
+    template<Ownership W2, MemSpace M2>
+    inline Collection& operator=(Collection<T, W2, M2, I>& other);
 
     //// ACCESS ////
 
diff --git a/src/base/Collection.i.hh b/src/base/Collection.i.hh
index 9b44366b23..730c7a8097 100644
--- a/src/base/Collection.i.hh
+++ b/src/base/Collection.i.hh
@@ -37,12 +37,12 @@ Collection<T, W, M, I>::Collection(Collection<T, W2, M2, I>& other)
 
 //---------------------------------------------------------------------------//
 /*!
- * Assign from another collection in the same memory space.
+ * Assign from another collection.
  */
 template<class T, Ownership W, MemSpace M, class I>
-template<Ownership W2>
+template<Ownership W2, MemSpace M2>
 Collection<T, W, M, I>&
-Collection<T, W, M, I>::operator=(const Collection<T, W2, M, I>& other)
+Collection<T, W, M, I>::operator=(const Collection<T, W2, M2, I>& other)
 {
     storage_ = detail::CollectionAssigner<W, M>()(other.storage_);
     detail::CollectionStorageValidator<W2>()(this->size(),
@@ -52,12 +52,12 @@ Collection<T, W, M, I>::operator=(const Collection<T, W2, M, I>& other)
 
 //---------------------------------------------------------------------------//
 /*!
- * Assign (mutable!) from another collection in the same memory space.
+ * Assign (mutable!) from another collection.
  */
 template<class T, Ownership W, MemSpace M, class I>
-template<Ownership W2>
+template<Ownership W2, MemSpace M2>
 Collection<T, W, M, I>&
-Collection<T, W, M, I>::operator=(Collection<T, W2, M, I>& other)
+Collection<T, W, M, I>::operator=(Collection<T, W2, M2, I>& other)
 {
     storage_ = detail::CollectionAssigner<W, M>()(other.storage_);
     detail::CollectionStorageValidator<W2>()(this->size(),
diff --git a/test/physics/em/LivermorePE.test.cc b/test/physics/em/LivermorePE.test.cc
index f327fa4bd3..3e8453ed39 100644
--- a/test/physics/em/LivermorePE.test.cc
+++ b/test/physics/em/LivermorePE.test.cc
@@ -505,8 +505,10 @@ TEST_F(LivermorePEInteractorTest, model)
     EXPECT_EQ(1, grid_storage.size());
 
     // Test cross sections calculated from tables
+    Collection<double, Ownership::const_reference, MemSpace::host> real_ref{
+        real_storage};
     celeritas::XsCalculator calc_xs(
-        grid_storage[ValueGridInserter::XsIndex{0}], real_storage);
+        grid_storage[ValueGridInserter::XsIndex{0}], real_ref);
     EXPECT_SOFT_EQ(0.1, calc_xs(MevEnergy{1e-3}));
     EXPECT_SOFT_EQ(1e-5, calc_xs(MevEnergy{1e2}));
     EXPECT_SOFT_EQ(1e-9, calc_xs(MevEnergy{1e6}));
diff --git a/test/physics/grid/NonuniformGrid.test.cc b/test/physics/grid/NonuniformGrid.test.cc
index a73c8a352d..c0abe000a5 100644
--- a/test/physics/grid/NonuniformGrid.test.cc
+++ b/test/physics/grid/NonuniformGrid.test.cc
@@ -26,11 +26,16 @@ class NonuniformGridTest : public celeritas::Test
     {
         auto build = celeritas::make_builder(&data);
         irange     = build.insert_back({0, 1, 3, 3, 7});
+        ref        = data;
     }
 
     celeritas::ItemRange<int> irange;
     celeritas::Collection<int, celeritas::Ownership::value, celeritas::MemSpace::host>
         data;
+    celeritas::Collection<int,
+                          celeritas::Ownership::const_reference,
+                          celeritas::MemSpace::host>
+        ref;
 };
 
 //---------------------------------------------------------------------------//
@@ -39,7 +44,7 @@ class NonuniformGridTest : public celeritas::Test
 
 TEST_F(NonuniformGridTest, accessors)
 {
-    GridT grid(irange, data);
+    GridT grid(irange, ref);
 
     EXPECT_EQ(5, grid.size());
     EXPECT_EQ(0, grid.front());
@@ -50,7 +55,7 @@ TEST_F(NonuniformGridTest, accessors)
 
 TEST_F(NonuniformGridTest, find)
 {
-    GridT grid(irange, data);
+    GridT grid(irange, ref);
 
 #if CELERITAS_DEBUG
     EXPECT_THROW(grid.find(-1), celeritas::DebugError);
diff --git a/test/physics/grid/ValueGridBuilder.test.cc b/test/physics/grid/ValueGridBuilder.test.cc
index d5b152b39e..f96992ae5e 100644
--- a/test/physics/grid/ValueGridBuilder.test.cc
+++ b/test/physics/grid/ValueGridBuilder.test.cc
@@ -40,9 +40,11 @@ class ValueGridBuilderTest : public celeritas::Test
         {
             b->build(insert);
         }
+        real_ref = real_storage;
     }
 
     Collection<real_type, Ownership::value, MemSpace::host>  real_storage;
+    Collection<real_type, Ownership::const_reference, MemSpace::host> real_ref;
     Collection<XsGridData, Ownership::value, MemSpace::host> grid_storage;
 };
 
@@ -75,13 +77,13 @@ TEST_F(ValueGridBuilderTest, xs_grid)
     // Test results using the physics calculator
     ASSERT_EQ(2, grid_storage.size());
     {
-        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_storage);
+        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_ref);
         EXPECT_SOFT_EQ(0.1, calc_xs(Energy{1e1}));
         EXPECT_SOFT_EQ(0.2, calc_xs(Energy{1e2}));
         EXPECT_SOFT_EQ(0.3, calc_xs(Energy{1e3}));
     }
     {
-        XsCalculator calc_xs(grid_storage[XsIndex{1}], real_storage);
+        XsCalculator calc_xs(grid_storage[XsIndex{1}], real_ref);
         EXPECT_SOFT_EQ(10., calc_xs(Energy{1e-3}));
         EXPECT_SOFT_EQ(1., calc_xs(Energy{1e-2}));
         EXPECT_SOFT_EQ(0.1, calc_xs(Energy{1e-1}));
@@ -106,7 +108,7 @@ TEST_F(ValueGridBuilderTest, log_grid)
     // Test results using the physics calculator
     ASSERT_EQ(1, grid_storage.size());
     {
-        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_storage);
+        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_ref);
         EXPECT_SOFT_EQ(0.1, calc_xs(Energy{1e1}));
         EXPECT_SOFT_EQ(0.2, calc_xs(Energy{1e2}));
         EXPECT_SOFT_EQ(0.3, calc_xs(Energy{1e3}));
@@ -133,7 +135,7 @@ TEST_F(ValueGridBuilderTest, DISABLED_generic_grid)
     // Test results using the physics calculator
     ASSERT_EQ(2, grid_storage.size());
     {
-        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_storage);
+        XsCalculator calc_xs(grid_storage[XsIndex{0}], real_ref);
         EXPECT_SOFT_EQ(0.1, calc_xs(Energy{1e1}));
         EXPECT_SOFT_EQ(0.2, calc_xs(Energy{1e2}));
         EXPECT_SOFT_EQ(0.3, calc_xs(Energy{1e3}));