{
  "ran": "2026-10-14T14:37:26.697Z",
  "how": "kit/ionchamber.mjs. Ion pairs per second q = A·f·E/W. Without smoke every ion reaches a plate: I0 = q·e. With N smoke particles per m³ an ion either reaches a plate within transit time tau or attaches to a particle first (rate beta·N), so I = I0/(1 + beta·N·tau). The same current is also found step by step from dn/dt = q − n/tau − beta·N·n and must match within 1 %. Well-mixed approximation: an ion's time to reach a plate is exponential with mean tau.",
  "sources": {
    "activity": "NRC, Smoke Detectors (ADAMS ML17114A491): \"Most units sold today use one microcurie or less of americium-241.\" 1 µCi = 37 000 Bq; the upper bound is used.",
    "alphaEnergy": "NNDC NuDat 3, 241Am decay: main alpha line 5485.56 keV (84.8 %); 5442.80 keV (13.1 %) and weaker lines are left out.",
    "mechanism": "NRC ML17114A491: plates attract the ions, a small steady current; smoke interrupts it.",
    "particleSize": "NIST, How Do Smoke Detectors Work? (updated 20 Feb 2026): ionization alarms detect small soot particles from flaming fires more quickly because they are produced in greater numbers."
  },
  "assumptions": {
    "wEv": "34.44 eV per ion pair: ICRU Report 90 value for protons in dry air; ICRU 90 gives no value for alpha particles",
    "deposit": "0.15: fraction of alpha energy left in the chamber air (half the alphas go into the source backing, the other half leave about 30 percent of their energy in the air before the wall: 0.5 × 0.3 = 0.15)",
    "tau_s": 0.08,
    "beta_m3_per_s": 1e-12,
    "d0_m": 1e-7,
    "betaGrowsLinearlyWithDiameter": true,
    "alarmDrop": 0.25,
    "smokeDensity_kg_m3": 1000
  },
  "derived": {
    "pairsPerSecond": 883997038,
    "cleanCurrent_A": 1.4163e-10,
    "alarmCount_per_m3": 4166700000000,
    "at_0_1_mg_per_m3": {
      "small_0_1um_fraction": 0.985,
      "large_1um_fraction": 0.9998
    }
  },
  "ok": true
}