diff --git a/pyproject.toml b/pyproject.toml
index 133f573..6d5ef05 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,3 +42,6 @@ skip-string-normalization = true
 [tool.isort]
 skip_gitignore = true
 profile = "black"
+
+[tool.ruff.format]
+quote-style = "preserve"
diff --git a/src/tof/source.py b/src/tof/source.py
index 38896de..9b2b603 100644
--- a/src/tof/source.py
+++ b/src/tof/source.py
@@ -226,6 +226,9 @@ def __init__(
                     "time": pulse_params["time"],
                     "wavelength": pulse_params["wavelength"],
                     "speed": pulse_params["speed"],
+                    "id": sc.arange("event", pulse_params["time"].size, unit=None).fold(
+                        "event", sizes=pulse_params["time"].sizes
+                    ),
                 },
             )
 
@@ -270,6 +273,9 @@ def from_neutrons(
                 "time": birth_times,
                 "wavelength": wavelengths,
                 "speed": wavelength_to_speed(wavelengths).to(unit="m/s", copy=False),
+                "id": sc.arange("event", birth_times.size, unit=None).fold(
+                    "event", sizes=birth_times.sizes
+                ),
             },
         )
 
@@ -326,6 +332,9 @@ def from_distribution(
                 "time": pulse_params["time"],
                 "wavelength": pulse_params["wavelength"],
                 "speed": pulse_params["speed"],
+                "id": sc.arange("event", pulse_params["time"].size, unit=None).fold(
+                    "event", sizes=pulse_params["time"].sizes
+                ),
             },
         )
         return source