Your first calculation

Run the supplied iron example from a terminal. This example models a five-minute irradiation followed by cooling and includes the complete measured flux-spectrum shape. You do not need to clone the repository or type a 709-group vector.

1. Prepare a working folder

After installing ACTINV, create and enter an empty folder for this calculation:

mkdir actinv-example
cd actinv-example
actinv --version

2. Install data and create the problem

actinv data fetch
actinv new problem.json

new writes a complete, editable problem and refuses to overwrite an existing file. Its default data references use catalog IDs so the problem can be used on another machine with the same installed data.

3. Validate and run

actinv validate problem.json
actinv validate problem.json --hashes
actinv run problem.json result.json

The first validation checks the JSON specification. --hashes also checks the files it supports and their declared hashes; the solver checks evaluated-data compatibility during the run. A successful run writes the complete result to result.json.

The first run prepares data and can take longer than subsequent runs. If setup fails, run actinv doctor problem.json and follow Troubleshooting.

4. Inspect the final step

If you installed the Python package, inspect the JSON with:

import json
from pathlib import Path

result = json.loads(Path("result.json").read_text(encoding="utf-8"))
last = result["steps"][-1]
print("Time (s):", last["t_s"])
print("Activity (Bq/g):", sum(last["activity_Bq_per_g"].values()))
print("Decay heat (W/g):", last["heat_W_per_g"]["total"])
print("Data and calculation notes:", result["ledger"])

You can also open the result in the browser workbench to explore plots. Read your results explains the units, time steps, and diagnostic fields.

5. Adapt the example

Open problem.json in a text editor. Change the title, material composition, or schedule, then validate and run again with a new output filename. Reuse the supplied spectrum only when it represents your intended irradiation; changing the material does not make that spectrum appropriate for a different facility.

Use Describe a problem for input conventions. The measured iron case provides a fuller comparison against experimental decay-heat measurements.