Kilocurie to Rutherford

In 1987, scrap metal scavengers in Goiânia, Brazil broke open an abandoned caesium-137 teletherapy source containing about 1,375 Ci (50.9 TBq). The glowing blue Cs-137 powder fascinated locals — they rubbed it on skin, gave it to children, and spread it across multiple homes. Four people died, 249 were contaminated, and the cleanup produced 3,500 m³ of radioactive waste. The incident became the textbook case for why sealed sources must be tracked and securely stored throughout their entire lifecycle, and why the IAEA created its Code of Conduct on the Safety and Security of Radioactive Sources.

Yes, multiple times. In Ciudad Juárez, Mexico (1983), a stolen Co-60 teletherapy source was sold as scrap and melted into rebar, contaminating 4,000 tonnes of steel and exposing thousands. In Samut Prakan, Thailand (2000), a junked Co-60 source killed three scrap workers who pried it open. In Yanango, Peru (1999), a welder pocketed an Ir-192 industrial radiography source and carried it in his pocket for hours — his leg was amputated. The IAEA documents over 30 serious radiation accidents involving orphaned or stolen sources since the 1960s, collectively killing dozens and injuring hundreds.

Cobalt-60 has a 5.27-year half-life, so a 500 kCi source drops to 250 kCi after five years and becomes too weak for industrial throughput after about 15–20 years. The spent source pencils are returned to the manufacturer (typically in Canada or Russia) for reprocessing or secure storage. Transport uses heavily shielded Type B casks certified to survive a 9-meter drop and 30-minute fire. The manufacturer often offers a swap program: deliver fresh sources and take back decayed ones in the same shipment, minimising the number of high-activity transports.

The Fukushima Daiichi disaster released an estimated 10–30 PBq (10,000–30,000 TBq) of caesium-137 directly into the Pacific Ocean between March and July 2011 — the largest single marine radioactive release in history. For comparison, the Sellafield reprocessing plant in the UK discharged about 40 PBq of Cs-137 into the Irish Sea over decades of operation (1952–2000). Soviet dumping of entire reactor compartments from nuclear submarines in the Arctic added further inventory. Despite these numbers, ocean dilution is vast: Pacific Cs-137 levels from Fukushima peaked at about 50 Bq/m³ near the plant and dropped below 2 Bq/m³ within a few hundred kilometers.

This is exactly why the IAEA, NRC, and national agencies track high-activity sources so aggressively. A kilocurie Cs-137 or Co-60 source dispersed by conventional explosives would contaminate a few city blocks — not causing acute radiation casualties (the blast itself is deadlier) but creating a costly, panic-inducing cleanup lasting months. The actual health risk to the public would be low, but the economic and psychological damage would be enormous. Post-9/11 programs like the US GTRI (now NNSA OSRP) have recovered or secured thousands of orphaned high-activity sources worldwide.

The rutherford was proposed in the 1940s when the curie was the only game in town and was inconveniently large for many lab measurements. At 10⁶ dps (1 MBq), the rutherford sat in a useful range. But the 1975 SI reform chose the becquerel (1 dps) as the base unit with standard SI prefixes — kBq, MBq, GBq — which covered every scale. Having both the rutherford and the megabecquerel for the same quantity was redundant. The scientific community picked one, and the rutherford quietly disappeared from everything except unit conversion tables and physics trivia.

Rutherford discovered the atomic nucleus by firing alpha particles at gold foil (1911), identified alpha and beta radiation as distinct particle types, and performed the first artificial nuclear transmutation — turning nitrogen into oxygen — in 1917. He won the Nobel Prize in Chemistry in 1908, which famously annoyed him because he considered himself a physicist. His students went on to split the atom (Cockcroft and Walton) and discover the neutron (Chadwick). Nearly every branch of nuclear science traces back to his Manchester and Cambridge laboratories.

Several. The stat (1 disintegration per second, identical to the becquerel but proposed earlier), the eman (used for radon concentration in water, equal to 10⁻¹⁰ Ci/L), and the mache unit (another radon measure used in Austrian and German spa water literature) are all effectively extinct. The curie itself is technically obsolete under SI but persists through sheer institutional momentum in the US. The pattern is typical of measurement science: every era invents its own units, and standardisation eventually consolidates them.

Unlikely in practice because the rutherford disappeared from active use by the 1970s, before the megabecquerel entered common parlance in the 1980s. You would only encounter the rutherford in papers from roughly 1946–1970, primarily in European nuclear physics journals. If you see "Rd" in a modern unit conversion tool, it is there for completeness and historical interest, not because anyone is publishing in rutherfords. The real risk of confusion in old literature is between the curie and the becquerel, where a missing prefix can mean a billionfold error.

The "sunshine unit" — officially the strontium unit — was coined by the US Atomic Energy Commission in the 1950s to describe strontium-90 concentration in bones and milk during nuclear weapons testing. One sunshine unit equalled 1 picocurie of Sr-90 per gram of calcium. The name was a deliberate PR choice to make fallout contamination sound cheerful and harmless. It backfired spectacularly when journalists mocked it as Orwellian doublespeak, and the term was quietly dropped in favor of pCi/g Ca. It remains a cautionary tale about naming units for political rather than scientific reasons.