Disintegrations per second to Terabecquerel

Because dps is literally what the instrument measures — a detector counts individual nuclear decay events over time. Calling it "dps" keeps the language grounded in what physically happened. Calling it "Bq" applies an SI label to the same number. Old lab protocols, standard operating procedures written before 1975, and some US-centric equipment manuals still use dps because nobody rewrote the paperwork. Numerically, 1 dps = 1 Bq, so the conversion is trivially multiplying by one.

Counts per second (cps) is what the detector actually registers; disintegrations per second (dps) is how many decays actually occurred. No detector catches every decay — some radiation misses the detector, some is absorbed before reaching it, and some types of radiation are invisible to certain detectors. The ratio of cps to dps is the detection efficiency, which can range from under 1% (for low-energy beta emitters in a Geiger tube) to over 90% (for gamma emitters in a well counter). Getting from cps to dps requires careful calibration.

The sample is dissolved in a scintillation cocktail — a solvent containing fluorescent molecules. Each beta particle or electron excites the cocktail, producing a flash of light detected by photomultiplier tubes. But chemical impurities in the sample absorb some of that light (a phenomenon called quenching), so the counter sees fewer flashes than decays. The instrument runs an internal or external standard to measure the quench level, then applies a correction curve to convert raw cpm to true dpm, which you divide by 60 to get dps.

Not numerically — they are identical. But contextually, "dps" emphasizes the physical measurement process and appears in lab protocols where you are calculating detector efficiency: "the source emits 10,000 dps and the detector reads 3,200 cps, so efficiency is 32%." Writing that sentence with Bq would be technically correct but odd, like referring to your morning coffee temperature in kelvin. The unit name signals what kind of work you are doing.

Before the becquerel was adopted in 1975, there was no named SI unit for radioactivity — scientists just said "disintegrations per second" or used the curie. The CGPM gave the name "becquerel" to one disintegration per second to honor Henri Becquerel and to bring radioactivity into the SI naming system alongside the gray and sievert. The dps description never went away; it just lost its status as the primary label. Think of it like saying "cycles per second" instead of "hertz" — correct, but dated.

The total release from Chernobyl Unit 4 is estimated at 5,200 petabecquerels (5.2 × 10⁶ TBq), though figures vary by source and isotope accounting. Of that, about 1,760 TBq was iodine-131 and 85 TBq was caesium-137. For perspective, the entire global nuclear weapons testing era released roughly 2.6 × 10⁸ TBq — so Chernobyl was devastating but still a fraction of Cold War fallout. Fukushima released about 520 TBq of Cs-137, roughly one-sixth of Chernobyl.

To sterilise food, you need to deliver 1–10 kilograys of absorbed dose in minutes across conveyor belts of product. That requires an enormous photon flux, which only a multi-hundred-TBq cobalt-60 source can provide. A typical facility starts with 500–1,000 TBq and replenishes as the Co-60 decays (5.27-year half-life). The food never becomes radioactive — gamma photons do not induce radioactivity in stable atoms at these energies. Over 60 countries have approved food irradiation for spices, meat, and produce.

Nuclear medicine staff literally call it a "moly cow." A generator arrives with ~150 TBq of Mo-99 adsorbed onto an alumina column. Mo-99 decays (66-hour half-life) into Tc-99m, which is washed off the column with saline — "milking" the generator. Fresh Tc-99m accumulates between milkings, reaching peak yield about every 23 hours. A single generator supplies a hospital for about a week before the parent Mo-99 activity drops too low. It is one of the cleverest supply chains in medicine.

Fresh spent fuel is extraordinarily active — a single assembly registers in the petabecquerel range, dominated by short-lived fission products like I-131, Xe-133, and Ba-140. Within a year, activity drops by about 99% as these burn out. After 10 years it drops another 90%, leaving mainly Cs-137 and Sr-90 (both ~30-year half-lives). After 300 years those are gone too, and the remaining activity comes from transuranics like plutonium — far less active per gram but with half-lives of thousands to millions of years.

Permanently, no — radioactivity decays by definition. Practically, it depends on the isotopes deposited and the cleanup threshold. Chernobyl's exclusion zone still restricts habitation 40 years later because Cs-137 (30-year half-life) contaminated the soil at levels above 1,480 TBq/km² in the worst spots. Parts of Fukushima were decontaminated and reopened within years because the deposition was lower. The real question is not whether an area recovers, but whether society is willing to wait — or pay for aggressive decontamination.