Turn counts into efficiency with reliable corrections fast. Compare absolute and intrinsic detector performance easily. Export tables to share, archive, and report results clearly.
First compute measured count rates:
Optional dead-time correction depends on the selected model:
Then compute the net (corrected) count rate:
With emission rate E = A × f, efficiencies are:
Uncertainty uses counting statistics (σₙ ≈ √N) and standard propagation with optional relative uncertainties for A, f, and g.
| Ns | ts (s) | Nb | tb (s) | A (Bq) | f | g | τ (s) | εabs (%) | εint (%) |
|---|---|---|---|---|---|---|---|---|---|
| 18500 | 120 | 320 | 120 | 37000 | 1.00 | 0.12 | 0.00018 | 0.41 | 3.43 |
| 9200 | 60 | 180 | 60 | 14800 | 0.85 | 0.10 | 0 | 0.72 | 7.24 |
| 5400 | 180 | 210 | 180 | 7400 | 1.00 | 0.08 | 0.00012 | 0.37 | 4.58 |
Efficiency links what your instrument counts to how many emissions are actually available to be detected. A Geiger tube can register only a fraction of photons or particles because of window losses, gas gain limits, and electronic thresholds. Reporting efficiency makes surveys comparable across setups.
Absolute efficiency uses the net count rate divided by the emission rate (activity multiplied by emission yield). Intrinsic efficiency removes geometry by dividing absolute efficiency by the geometry factor g. This separation helps you judge detector quality independent of distance, shielding, or collimation.
Background is best treated as a rate, not a raw count, because source and background runs often use different times. The calculator converts counts to cps, subtracts the corrected background rate, and warns when the net rate becomes non‑positive. Longer background runs reduce uncertainty without changing the mean rate.
The geometry factor describes what fraction of emissions reach the detector. For point sources, it is often driven by solid angle and can drop quickly with distance. Scattering, shielding, and source encapsulation can also reduce it. Use a consistent measurement jig and document distance and alignment when estimating g.
At high rates, pulses can overlap, causing undercounting. Typical Geiger systems have dead times on the order of 100–300 µs, but you should use your instrument’s specification. The non‑paralyzable model applies R = r/(1-r\tau), while the paralyzable model accounts for extended losses near saturation.
Counts follow Poisson behavior, so the standard deviation is approximately \sqrt{N}. This calculator propagates those rate uncertainties through the net subtraction and then combines them with optional relative uncertainties for activity, emission yield, and geometry. Increasing counting time improves precision roughly with the square root of time.
Efficiency is energy dependent. Thin‑window tubes respond better to lower‑energy beta particles, while gamma response is often limited and highly dependent on photon energy and tube construction. If you change radionuclide, shielding, or source encapsulation, do not reuse an old efficiency value without re‑measuring or recalculating geometry and corrections.
For professional reporting, include the net count rate, activity reference date, emission yield used, geometry assumptions, and whether dead‑time correction was applied. Saving a CSV provides a clean audit trail for spreadsheets and lab notebooks. Printing a PDF snapshot supports calibration records and compliance documentation.
Intrinsic efficiency divides out geometry. If your detector is far from the source or heavily shielded, geometry can be small, so absolute efficiency falls while intrinsic stays comparatively higher.
Use the fraction of decays that produce the emission you are counting. If every decay produces one relevant emission, enter 1. Otherwise use the published branching ratio for that line or particle.
Use a fixed distance and alignment, then approximate solid angle for a point source, or determine g empirically with a calibrated reference. Keep units consistent and document shielding and holder dimensions.
Apply it when rates approach the instrument’s specified linearity limit or when you know dead time is non‑negligible. At low rates, correction has little effect and can add unnecessary uncertainty.
If background rate is close to or greater than the source rate, subtraction can yield a net rate near zero. Increase counting time, improve shielding, reduce distance uncertainty, or confirm the source is positioned correctly.
Yes, as long as activity and emission yield match what your detector is sensitive to. The physics of the tube and window strongly affects response, so efficiency values are not interchangeable across radiation types.
It varies widely with geometry and radiation type. Gamma absolute efficiency is often well below a few percent, while certain beta configurations can be higher. Use this tool to quantify your specific setup.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.