Chris Collins

Tools · physics

Radiation explorer

Ionising radiation hands-on — drag shields into alpha, beta, gamma, X-ray and neutron beams (NIST attenuation data), dose from activity and distance, random decay and the natural decay chains, units and ICRP 103 weighting, a sourced dose ladder, and a clicking Geiger counter that can also read a real GQ GMC counter.

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How to use it

What radiation is, what stops it, how dose falls with distance and time, how activity changes as atoms decay, what the units mean, and how big everyday doses are — with a Geiger counter to listen to.

How to use it

  1. Types and shielding — choose alpha, beta, gamma, X-ray or neutrons and an emitter or energy. Drag shield blocks (paper, skin, aluminium, lead, concrete, water) from the tray into the beam, or tap the buttons above it, and set each thickness in millimetres. The animated stream shows what gets through, next to the expected fraction. For photons the tables give μ/ρ, μ, the half-value layer (HVL), the tenth-value layer (TVL) and how much of each material reduces the beam by any factor you choose. The examples show paper stopping alphas, aluminium stopping Y-90 betas (and why lead is the wrong first layer for betas), one HVL of lead for Cs-137, Co-60 behind concrete, neutrons going through lead but not water, and a 0.25 mm lead apron.

  2. Distance and time — pick an isotope, an activity (Bq to Ci) and a distance. You get the exposure rate, air kerma and an approximate dose rate from the gamma constant, the dose for the time you stay, how long it takes to reach 1 mSv, the "6CEN" rule of thumb as a cross-check, and a log–log plot of the inverse-square fall-off. The examples include a check source, radiography sources and a PET patient.

  3. Decay and chains — start the grid of atoms and watch the count fall: jagged and random, but inside the ±2σ band around N₀·e^(−λt). Change the half-life or the number of atoms. There is a calculator for the fraction left after any time. Under Decay chains, pick the U-238, Th-232 or U-235 series, radon and its progeny, the Mo-99/Tc-99m generator, or Sr-90/Y-90, and choose which member you start with. Then move the time slider to see each member’s activity grow in and reach secular (or transient) equilibrium.

  4. Units — converters for activity (Bq, Ci, dpm), absorbed dose (Gy, rad), equivalent dose (Sv, rem), exposure (R, C/kg) and dose rate (µSv/h, mrem/h, mSv/y). There is an explanation of absorbed, equivalent and effective dose, the ICRP 103 radiation weighting factors (with the neutron energy function) and an effective-dose calculator over the 15 tissue weighting factors.

  5. Dose ladder — about 30 everyday, medical, background, limit and acute doses on a log scale, each with its source. Filter by category. Choose your country’s background and add your own X-rays, scans and flight hours to see your year on the ladder.

  6. Geiger counter — pick a tube (SBM-20, J305, M4011, LND 712, SI-180G), a source, its activity and its distance, and press Start counting to hear random clicks. A histogram of counts per second builds up against the Poisson distribution. Below that are a CPM ↔ µSv/h converter with dead-time correction for every tube, counting statistics (√N error, how long to count for a precision, background subtraction, Currie detection limits) and Connect a real counter. That last one uses Web Serial (Chrome or Edge only) to read CPM from a GQ GMC counter.

Every input is remembered in your browser. Each tab has its own address, for example radiation/#geiger (or #shield, #distance, #decay, #units, #ladder).

Method and sources

  • Photon attenuation — total mass attenuation coefficients μ/ρ from the NIST X-Ray Mass Attenuation Coefficients tables (Hubbell & Seltzer, NIST Standard Reference Database 126, the same data as XCOM) for lead, aluminium, ordinary concrete, water and ICRU-44 soft tissue. They are interpolated log–log, with lead’s K edge at 88 keV. Paper is taken as water-equivalent per g/cm² at 0.8 g/cm³. Transmission is the narrow-beam e^(−μx). HVL = ln 2/μ and TVL = ln 10/μ. Broad beams through thick shields also deliver scattered photons (the build-up factor), so real shields need more than this. At 662 keV this gives an HVL of 5.5 mm of lead, 3.8 cm of concrete and 8.1 cm of water. At 1.25 MeV (Co-60) it gives 10.4 mm of lead.

  • Alphas — approximate NIST ASTAR CSDA ranges at 5.5 MeV, scaled with Geiger’s rule R ∝ E1.5 (about 4 cm of air, 45 µm of water).

  • Betas — the Katz–Penfold maximum range, the empirical absorption coefficient μ = 17·Emax−1.14 cm²/g, and the bremsstrahlung fraction ≈ 3.5×10⁻⁴·Z·Emax (Cember & Johnson, Introduction to Health Physics).

  • Neutrons — fast-neutron removal cross-sections ΣR built from elemental ΣR/ρ (after Chilton, Shultis & Faw, Principles of Radiation Shielding). These are only a rough guide.

  • Dose rate — Γ·A/r² with rounded textbook exposure-rate constants in R·cm²/(mCi·h) (Co-60 13.2, Cs-137 3.3, Ir-192 4.8, Na-22 12.0, F-18 5.7, I-131 2.2, Tc-99m 0.78, Ra-226 8.25). Exposure is converted with 1 R = 8.76 mGy air kerma (W/e = 33.97 J/C), and air kerma is taken as roughly equal to dose in Sv.

  • Decay chains — half-lives from NNDC/ENSDF, rounded; branches under 0.1 % are left out. The activities solve dN/dt = A·N with a matrix exponential (scaling and squaring, recomputing the diagonal exactly at each step), which matches Bateman’s equations and stays accurate from Po-214 (164 µs) to U-238 (4.5 × 10⁹ y).

  • Units and weighting — ICRP Publication 103 (2007): wR (photons and electrons 1, protons 2, alphas 20, neutrons a continuous function of energy) and the tissue weighting factors.

  • Dose ladder — RadiologyInfo.org (ACR/RSNA) for medical exams, UNSCEAR 2000 and 2008 for background, flights and high-background areas, NCRP Report 160 for the USA, UKHSA, STUK, BfS and ARPANSA for national figures, the US NRC and ICRP 103 for limits, IAEA/CDC guidance for acute effects, NASA for the ISS, and xkcd’s Radiation Dose Chart for the banana and other small doses. Medical doses are typical adult values and vary by a factor of two or more.

  • Geiger tubes — the commonly published Cs-137 conversion factors in CPM per µSv/h: SBM-20 175.43, J305 123.147, M4011 153.8, LND 712 108 (from its datasheet’s 18 cps per mR/h), and SI-180G 575. The SI-180G is poorly documented; users report 321–575. Dead time is 190 µs for the SBM-20 and 90 µs for the LND 712; for the others 190 µs is assumed, and you can enter your own. The non-paralysable model is used: m = n/(1 + nτ), corrected with n = m/(1 − mτ). These are approximations: GM tubes over-respond to low-energy photons, and thin-window and pancake tubes count betas too.

  • Counting statistics — Poisson σ = √N, the optimal gross/background time split tg/tb = √(Rg/Rb), and Currie’s (1968) LC = 2.33√B and LD = 2.71 + 4.65√B.

  • GQ GMC serial — the documented GQ-RFC1201/RFC1801 commands <HEARTBEAT0>>, <GETVER>> and <GETCPM>>. The CPM reply is 2 bytes on the GMC-300/320 and 4 bytes on the GMC-500/600/800. The baud rate is 57600 on older units and 115200 on newer ones.

For learning. These are idealised models, not a radiation-safety assessment. Real shielding, dosimetry and survey work need calibrated instruments and a qualified radiation-protection adviser.

Sharing

Share link (under the title) copies a URL that reopens this tool exactly as you have it — every tab’s inputs, with the current tab selected. Opening such a link replaces the inputs this browser had saved for the tool.

Runs entirely in your browser; nothing you type leaves this page.