Disintegrations per second to Millicurie

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.

Yes, and it creates real problems. If a patient who received therapeutic I-131 (30–200 mCi) dies within days, the body can trigger radiation alarms at funeral homes and crematoria. Cremation is the bigger concern — burning the body aerosolises the isotope, contaminating the crematorium and potentially exposing workers. Most radiation safety programs require a waiting period before cremation, or direct burial with notification to the funeral director. In 2019, an Arizona crematorium unknowingly cremated a patient with residual lutetium-177, contaminating the facility. Hospitals are supposed to flag these cases, but the system is imperfect.

The radiopharmacist draws the Tc-99m solution into a syringe, places it in a dose calibrator (a pressurized argon ionisation chamber), and reads the activity in mCi or MBq. Because the isotope is decaying constantly — Tc-99m loses half its activity every 6 hours — the calibrator reading must be decay-corrected to the planned injection time. If the scan is at 2pm and the dose is drawn at 10am, the pharmacist dispenses more than the prescribed 20 mCi, knowing it will decay to exactly 20 mCi by injection. Timing is everything.

The Tc-99m bone scan, with about 20–25 mCi (740–925 MBq) injected intravenously. Technetium-99m accumulates in areas of high bone turnover — fractures, infections, metastases — and emits 140 keV gamma rays that a gamma camera images. The scan itself takes 2–3 hours (allowing time for the tracer to distribute), and the patient's radioactivity drops to negligible levels within 24–48 hours. Over 30 million Tc-99m procedures are performed worldwide each year, making it by far the most-used medical radioisotope.

Technically yes, but radiation detectors at airports, borders, and government buildings may alarm for days after certain scans. A patient who received 10 mCi of I-131 can trigger a portal monitor for up to 3 months. Most nuclear medicine departments provide a wallet card explaining the procedure, isotope, and date — TSA and customs agents are trained to recognize these. The actual radiation risk to fellow passengers is negligible; the issue is entirely about security system sensitivity, not safety.

Hyperthyroidism treatment aims to kill just enough thyroid tissue to normalize hormone production — typically 5–15 mCi (185–555 MBq) of I-131. Thyroid cancer ablation aims to destroy every remaining thyroid cell after surgery and kill any metastases — that takes 30–200 mCi (1.1–7.4 GBq). The higher doses require inpatient isolation and more aggressive radiation safety precautions. Some oncologists are exploring whether lower ablation doses (30 mCi) work as well as high ones (100+ mCi) for low-risk cancers — the evidence is surprisingly close.