Editing Cobalt bomb (section)

==Radiation levels and time==
{{Original research section|date=May 2025}}
For the type of radiation given by a cobalt bomb, the dosage measured in [[sievert]] (Sv) and [[Gray (unit)|gray]] (Gy) can be treated as equivalent. This is because the relevant harmful radiation from cobalt-60 is gamma rays. When converting between sievert and gray for gamma rays, the [[Sievert#Radiation type weighting factor WR|radiation type weighting factor]] will be 1, and the radiation will be a highly penetrating radiation spread evenly over the body so the [[Sievert#Tissue type weighting factor WT|tissue type weighting factor]] will also be 1.

Assume a cobalt bomb deposits intense fallout causing a dose rate of 10 Sv per hour. At this dose rate, any unsheltered person exposed to the fallout would receive a lethal dose in about 30 minutes (assuming a [[LD50|median lethal dose]] of 5 Sv<ref>{{cite web|url=https://www.nrc.gov/reading-rm/basic-ref/glossary/lethal-dose-ld.html|website=www.nrc.gov|access-date=2017-02-12|title=Lethal dose (LD)}}</ref>). People in well-built shelters would be safe due to [[radiation protection|radiation shielding]].

* After one half-life of 5.27 years, the dose rate in the affected area would be 5 Sv/hour. At this dose rate, a person exposed to the radiation would receive a lethal dose in 1 hour.
* After 10 half-lives (about 53 years), the dose rate would have decayed to around 10 mSv/hour. At this point, a healthy person could spend up to 4 days exposed to the fallout with no ''immediate'' effects. Long-term effects from this exposure would be increased risk to develop [[radiation-induced cancer|cancer]].<ref>{{cite journal|title=The 2007 Recommendations of the International Commission on Radiological Protection|journal=Annals of the ICRP|year=2007|volume=37|series=ICRP publication 103|issue=2–4|url=http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103|access-date=17 May 2012|isbn=978-0-7020-3048-2|author1=Icrp}}</ref> At the 4th day, the accumulated dose will be about 1 Sv, at which point the first symptoms of [[acute radiation syndrome]] may appear.
* After 20 half-lives (about 105 years), the dose rate would have decayed to around 10 μSv/hour. At this stage, humans could remain unsheltered full-time since their yearly radiation dose would be about 80 mSv. This yearly dose rate is about 30 times greater than the average [[Background radiation#Background dose rate examples|natural background radiation]] rate of 2.4 mSv/year,<ref>{{cite book |author=United Nations Scientific Committee on the Effects of Atomic Radiation|title=Sources and effects of ionizing radiation |date=2008 |publication-date=2010 |publisher=United Nations |location=New York |isbn=978-92-1-142274-0 |url=http://www.unscear.org/unscear/en/publications/2008_1.html |access-date=9 November 2012|page=4}}</ref> but within its variability. At this dose rate, causal connection to cancer incidence would be difficult to establish.
* After 25 half-lives (about 130 years), the dose rate from cobalt-60 would have decayed to less than 0.4 μSv/hour and could be considered negligible.