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half-lives and these
Some of these elements, notably thorium ( atomic number 90 ) and uranium ( atomic number 92 ), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our solar system.
All of the heavy elements that are derived solely through artificial means are radioactive, with very short half-lives ; if any atoms of these elements were present at the formation of Earth, they are extremely likely to have already decayed, and if present in novae, have been in quantities too small to have been noted.
Some of these elements, notably thorium ( atomic number 90 ) and uranium ( atomic number 92 ), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our Solar System.
All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute.
All of the remaining radioactive isotopes have half-lives that are less than 2. 5 hours, and the majority of these have half-lives that are less than 5 minutes.
All the remaining radioactive isotopes have half-lives shorter than 4. 7612 years, and the majority of these have half-lives shorter than 12. 2 seconds.
All of the remaining radioactive isotopes have half-lives that are less than, and the majority of these have half-lives that are less than 4 minutes.
The majority of these have half-lives of less than 24. 6 seconds.
Most of the remaining radioactive isotopes have half-lives that are less than 24 hours, and the majority of these have half-lives less than 1 minute.
All of the remaining radioactive isotopes have half-lives that are less than 97 minutes, and the majority of these have half-lives that are less than 5 minutes.
All of the remaining radioactive isotopes have half-lives that are less than three hours and the majority of these have half-lives that are less than one minute.
All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds.
All of the remaining radioactive isotopes have half-lives that are shorter than eleven days, and the majority of these have half-lives that are shorter than 70 seconds.
All of the remaining radioactive isotopes have half-lives that are less than 4. 5 days, and the majority of these have half-lives that are less than 50 minutes.

half-lives and metastable
As a result, the term " metastable " is usually restricted to refer to isomers with half-lives of 10 < sup >− 9 </ sup > seconds or longer.
All other radioisotopes have half-lives not greater than 1. 117 days in their ground states ( although the metastable < sup > 166m </ sup > Ho has a half-life of about 1, 200 years ), and most have half-lives under 3 hours.

half-lives and theoretical
These " theoretical radionuclides " have half-lives at least 100 million times longer than the estimated age of the universe.

half-lives and radionuclides
Even the number of long-lived radionuclides is uncertain ( to a lesser degree ), because many " stable " nuclides are calculated to have half-lives so long that their decay has not been experimentally measured.
In addition, there exist about 650 radionuclides that have been experimentally observed to decay, with half-lives longer than 60 minutes ( see list of nuclides for this list ).
Including artificially produced nuclides, more than 3300 nuclides are known ( including ~ 3000 radionuclides ), many of which (> ~ 2400 ) have decay half-lives shorter than 60 minutes.
This list expands as new radionuclides with very short half-lives are characterized.
Primordial radionuclides, such as uranium and thorium, originate mainly from the interiors of stars and are still present as their half-lives are so long they have not yet completely decayed.
They have shorter half-lives than primordial radionuclides.
Trace radionuclides are those that occur in tiny amounts in nature either due to inherent rarity, or to half-lives that are significantly shorter than the age of the Earth.

half-lives and are
The longest half-lives are observed for < sup > 247 </ sup > Bk ( 1, 380 years ), < sup > 248 </ sup > Bk ( 9 years ) and < sup > 249 </ sup > Bk ( 330 days ); the half-lives of the other isotopes range from microseconds to several days.
Moreover, in geriatric medicine, if benzodiazepines are necessary, those with short half-lives ( e. g. lorazepam & oxazepam ) are preferred, as they do not require hepatic oxidation.
The half-lives of elements 41 through 82 are so long however that their radioactive decay has yet to be detected by experiment.
DDT and DDE are very resistant to metabolism ; in humans, their half-lives are 6 and up to 10 years, respectively.

half-lives and so
The very heaviest elements ( those beyond californium, atomic number 98 ) undergo radioactive decay with half-lives so short that they do not occur in nature and have to be synthesized.
The very heaviest elements ( those beyond californium, atomic number 98 ) undergo radioactive decay with half-lives so short that they do not occur in nature and have to be synthesized.
Synthetic elements are radioactive and decay rapidly into lighter elements — possessing half-lives so short, relative to the age of the Earth ( which formed 4. 54 billion years ago ), that any atoms of these elements that may have existed when the Earth formed have long since decayed.
Naturally occurring tungsten consists of five isotopes whose half-lives are so long that they can be considered stable.
Many naturally-occurring radioisotopes ( another 51 or so, for a total of about 339 ) exhibit still shorter half-lives than 80 million years, but they are made freshly, as daughter products of decay processes of primordial nuclides ( for example, radium from uranium ) or from ongoing energetic reactions, such as cosmogenic nuclides produced by present bombardment of Earth by cosmic rays ( for example, carbon-14 made from nitrogen ).
These peptides have relatively long half-lives in the brain ( about 20 minutes in the CSF ), and they are released in large amounts in the supraoptic nucleus, and so they are available to diffuse through the extracellular spaces of the brain to act at distant targets.
< sup > 149 </ sup > Pm and < sup > 151 </ sup > Pm have half-lives of only 53. 08 and 28. 40 hours, so are not found in spent nuclear fuel that has been cooled for months or years.

half-lives and long
Calcium has four stable isotopes (< sup > 40 </ sup > Ca, < sup > 42 </ sup > Ca, < sup > 43 </ sup > Ca and < sup > 44 </ sup > Ca ), plus two more isotopes (< sup > 46 </ sup > Ca and < sup > 48 </ sup > Ca ) that have such long half-lives that for all practical purposes they also can be considered stable.
Some NSAIDs ( typically oxicams ) have very long half-lives ( e. g. 20 – 60 hours ).
Their naturally occurring isotopes have very long half-lives, on the order of billions of years.
C 67 ( 2003 ) 014323 .</ ref > The stable isotopes make up only 33. 2 % of the naturally occurring tellurium ; this is possible due to the long half-lives of the unstable isotopes.
In a similar way, the alpha emitting actinides and radium are considered very harmful as they tend to have long biological half-lives and their radiation has a high relative biological effectiveness, making it far more damaging to tissues per amount of energy deposited.
When looking at long term radioactive decay, the actinides in the SNF have a significant influence due to their characteristically long half-lives.
Most naturally occurring nuclides are stable ( about 253 ; see list at the end of this article ); and about 35 more ( total of 288 ) are known radioactives with sufficiently long half-lives ( also known ) to occur " primordially.
Many isotopes that are classed as stable ( i. e. no radioactivity has been observed for them ) are predicted to have extremely long half-lives ( sometimes as high as 10 < sup > 18 </ sup > years or more ).
At lower excitation energy ( see neutron evaporation ), the effect of the shell will be enhanced and ground-state nuclei can be expected to have relatively long half-lives.
A less moderated neutron energy spectrum does worsen the capture / fission ratio for < sup > 235 </ sup > U and especially < sup > 239 </ sup > Pu, meaning that more fissile nuclei fail to fission on neutron absorption and instead capture the neutron to become a heavier nonfissile isotope, wasting one or more neutrons and increasing accumulation of heavy transuranic actinides, some of which have long half-lives.
A meltdown is considered very serious because of the potential, however remote, that radioactive materials with long half-lives could breach all containment and escape ( or be released ) into the environment, resulting in radioactive contamination and fallout, and leading to radiation poisoning of people and animals nearby.
Due to the long half-lives of Fluoxetine and Fluvoxamine this effect may persist.
There are a few exceptions with relatively long half-lives and high decay energy, such as:
Unbihexium, having a magic number of protons, is predicted to be more stable than other elements in this region, and may have nuclear isomers with very long half-lives.
Some of the nuclei resulting from the fission are radioactive isotopes with short half-lives, and nuclear reactions among them release additional neutrons after a long delay of up to several minutes after the initial fission event.

0.737 seconds.