Mirion Technologies (MIR) Surges 10.87% on $600M Volume Spike, Ranks 150th in Market Activity

On September 26, 2025, Mirion Technologies (MIR) surged 10.87% to close trading, driven by a 126.48% jump in daily trading volume to $600 million, ranking it 150th in market activity. The abnormal liquidity spike suggests strong institutional or algorithmic interest, though underlying fundamentals remain unannounced.

Analysts note the volume surge exceeds typical volatility patterns, with no publicly disclosed catalysts such as earnings reports, product launches, or partnership announcements. The stock’s technical profile shows no pre-existing momentum patterns, indicating the rally may be event-driven or speculative in nature.

To run this back-test rigorously I need to make sure we both agree on a few practical details that aren’t completely specified: Universe - "Top 500 stocks by daily trading volume" can be interpreted several ways. Do you want the whole U.S. equity universe (NYSE + NASDAQ + AMEX), or a subset (e.g., only S&P 500 constituents, only Russell 3000, only stocks above a certain price)? Is ADR volume acceptable, or do you prefer U.S. common stocks only (share class “.A” / “.B” consolidated)?

Weighting & sizing - Equal‐weight across the chosen 500 names each day? Or volume-weighted / dollar-volume-weighted? Transaction assumptions - Slippage and commissions: should we assume zero, a flat 1 bp each side, or another value? Are fractional shares allowed (typical for model portfolios)? Rebalancing calendar - Rebalance every trading day at the day’s close, then hold until the next day’s close (i.e., 1-day holding period)?

Data frequency & survivorship bias - Intraday prices aren’t required for this test (we can use daily OHLCV). Is it acceptable to use a survivorship-bias-free universe (i.e., including delisted names), or is a “live today” universe sufficient? Once these choices are nailed down, I’ll generate the data-retrieval plan, pull the required volume and price data, build the daily signal files, and feed them to the back-testing engine.