The becquerel (Bq) is the SI unit of radioactive activity. It measures how many nuclear transformations (decays) occur per unit time. In the strict unit sense, 1 Bq = 1 decay per second.

In a unit map, Bq intentionally shares the same dimensional skeleton as hertz (Hz) because both reduce to 1/s. However, the phenomenon meaning is different: Hz is used for cyclic or periodic processes, whereas Bq is used for stochastic decay events. Fundamap keeps Bq as its own node (no aliasing) so the radiation domain remains navigable.

Dimensional Analysis

[Bq] = [1/s]

This is one of the simplest possible unit signatures: it is pure rate. What makes it “radiation” is not the dimension key but the interpretation and usage context.

What Bq is and is not

• Bq measures transformations (decays) per second, not energy deposited.
• Dose (energy per mass) is measured in gray (Gy) or sievert (Sv).
• Exposure / field intensity is a different category entirely (instrument- and medium-dependent).

Summary

The becquerel is the atomic clock-tick of radiation: a pure count-rate of nuclear events. It anchors the radiation subtree of a physics map even though it is dimensionally identical to hertz.

1) Rate interpretation

Activity A = N_decays / Δt

Units:
  [A] = 1/s = Bq
    

2) Linking activity to expected event counts

Expected decays in time t:
  N ≈ A · t
    

This is the simplest operational use: with a known activity and observation time, estimate the expected number of decays.

3) Where it appears

• Radiation source characterization (isotope activity)
• Nuclear medicine activity levels (administered activity)
• Environmental monitoring (contamination activity per sample)
• Detector calibration and count-rate modeling

4) Map edges (conceptual)

• becquerel is a radiation-specific node that shares a dimension key with hertz but should not be merged.
• Downstream “impact” nodes typically go through energy deposition (Gy) and biological weighting (Sv), which are separate units.