Differences

This shows you the differences between two versions of the page.

--- textbook:nrctextbook:chapter6 [2025-03-26 11:24]
Merja Herzig
+++ textbook:nrctextbook:chapter6 [2025-05-07 12:01] (current)
Merja Herzig
@@ Line 108: / Line 108: @@
 ;;#
+{{anchor:curie_ci}}
 ###
 Earlier //Curie// (Ci) was used as the activity unit. One Curie is  3.7×10<sup>10</sup> decays in second and thus
@@ Line 124: / Line 124: @@
 ###
+{{anchor:dps}}
+{{anchor:dpm}}
 ###
 Sometimes [[textbook:nrctextbook:chapter6#activity|activities]] are expressed as a dps unit, meaning disintegrations per second which are equal to activities presented as [[textbook:nrctextbook:chapter6#becquerel|Becquerels]]. In some instances, for example in [[textbook:nrctextbook:chapter12|liquid scintillation counting]], activity is also presented as //dpm// units (disintegrations per minute). One dpm is 1/60 dps or 16.7 mBq.
@@ Line 290: / Line 291: @@
 {{:textbook:nrctextbook:development_of_activities_no-equilibrium_fig_6_6.png |}}
 Figure VI.6. Development of activities in case of no radioactive equilibrium, in which the half-life of the parent nuclide (<sup>218</sup>Po, t<sub>½</sub> = 3 min) is shorter than that of the daughter (<sup>214</sup>Pb, t<sub>½</sub> = 26.8 min).
 Left: activity on linear scale. Right: activity on logarithmic scale. Blue: <sup>218</sup>Po . Red: <sup>214</sup>Pb.
+{{anchor:equilibria_in_natural_decay_chains}}
 ==== 6.7.4. Equilibria in natural decay chains ====
+{{anchor:long_lived_radionuclides}}
 ###
 In natural uranium and thorium [[textbook:nrctextbook:chapter4#decay_chains|decay chains]] there are individual pairs in which there would not be any equilibrium if they were present separately. An example of such pairs in the <sup>238</sup>U decay chain is <sup>234</sup>Pa parent (t<sub>½</sub> = 6.7 h) and <sup>234</sup>U daughter (t<sub>½</sub> = 245000 y). They are, however, typically in
@@ Line 301: / Line 303: @@
 ###
-In the geosphere in the natural [[textbook:nrctextbook:chapter4#decay_chains|decay chains]] beginning from <sup>238</sup>U, <sup>235</sup>U and <sup>232</sup>Th the activities of all members are the same in each series, identical with those of <sup>238</sup>U, <sup>235</sup>U and <sup>232</sup>Th, in systems which have been preserved without disturbances long enough. In such case the series is in equilibrium state. If some component of the series is removed, by dissolution for example, the equilibrium is disturbed and a disequilibrium state is created. If for example uranium is dissolved from a primary uranium-bearing mineral by oxidation the remaining radionuclides in the series will be supported by its most long-lived radionuclide which is <sup>230</sup>Th in case of <sup>238</sup>U series. If the dissolved uranium will then be precipitated somewhere out of the system a new equilibrium will start to develop. The time required to attain the equilibrium is governed by the most long-lived daughter radionuclide in the series, <sup>230</sup>Th in case of <sup>238</sup>U series. The half-life of <sup>230</sup>Th is 75000 years and this time is required to attain 50% of the equilibrium, 150000 years for 75% equilibrium, 225000 years for 87.5% equilibrium and eight half-lives, 600000 years, for 99.6% equilibrium. The disequilibria can be
+In the geosphere in the natural [[textbook:nrctextbook:chapter4#decay_chains|decay chains]] beginning from <sup>238</sup>U, <sup>235</sup>U and <sup>232</sup>Th the activities of all members are the same in each series, identical with those of <sup>238</sup>U, <sup>235</sup>U and <sup>232</sup>Th, in systems which have been preserved without disturbances long enough. In such case the series is in equilibrium state. If some component of the series is removed, by dissolution for example, the equilibrium is disturbed and a disequilibrium state is created. If for example uranium is dissolved from a primary uranium-bearing mineral by oxidation the remaining radionuclides in the series will be supported by its most [[textbook:nrctextbook:chapter4#long_lived_radionuclides|long-lived radionuclide]]  which is <sup>230</sup>Th in case of <sup>238</sup>U series. If the dissolved uranium will then be precipitated somewhere out of the system a new equilibrium will start to develop. The time required to attain the equilibrium is governed by the most long-lived daughter [[textbook:nrctextbook:chapter4|radionuclide]] in the series, <sup>230</sup>Th in case of <sup>238</sup>U series. The [[textbook:nrctextbook:chapter6#half_life|half-life]] of <sup>230</sup>Th is 75000 years and this time is required to attain 50% of the equilibrium, 150000 years for 75% equilibrium, 225000 years for 87.5% equilibrium and eight half-lives, 600000 years, for 99.6% equilibrium. The disequilibria can be utilized in dating geological events. If for example, the <sup>230</sup>Th/<sup>238</sup>U ratio is 0.5 in a uranium mineral we may calculate that this uranium mineral was precipitated 75000 years ago.
-utilized in dating geological events. If for example, the <sup>230</sup>Th/<sup>238</sup>U ratio is 0.5 in a uranium mineral we may calculate that this uranium mineral was precipitated 75000 years ago.
 ###
 ###
-To calculate activities of all members in a series manually is a cumbersome task. Computer programs for this purpose have been fortunately developed. One of them is the Decservis-2 program developed at the Laboratory of Radiochemistry, University of Helsinki, Finland. An example of such calculation carried out by Decservis-2 is shown in Figure VI.6. Here, we assume separation of <sup>226</sup>Ra (1 Bq) from the system and development of equilibrium between<sup> 226</sup>Ra and its progeny in
+To calculate [[textbook:nrctextbook:chapter6#activity|activities]] of all members in a series manually is a cumbersome task. Computer programs for this purpose have been fortunately developed. One of them is the Decservis-2 program developed at the Laboratory of Radiochemistry, University of Helsinki, Finland. An example of such calculation carried out by Decservis-2 is shown in Figure VI.6. Here, we assume separation of <sup>226</sup>Ra (1 Bq) from the system and development of equilibrium between<sup> 226</sup>Ra and its progeny in 10000 years. We have to assume that the gaseous <sup>222</sup>Rn, the daughter of <sup>226</sup>Ra, is not escaped from the system. In the first phase, up to about a month, the equilibrium is attained with <sup>222</sup>Rn, <sup>218</sup>Po, <sup>214</sup>Pb, <sup>214</sup>Bi and <sup>214</sup>Po and the time required for equilibrium is governed by the most long-lived member of these, <sup>222</sup>Rn with a half-life of 3.8 days. In the second phase, up to about 200 years, the equilibrium is attained with <sup>210</sup>Pb, <sup>210</sup>Bi and <sup>210</sup>Po and the time required for equilibrium is governed by the most long-lived member of these, <sup>210</sup>Pb with a half-life of 22 years. The half-life of<sup> 226</sup>Ra is 1600 years and decrease in its activity and correspondingly activities of its progeny can be seen after about 1000 years.
-years. We have to assume that the gaseous <sup>222</sup>Rn, the daughter of <sup>226</sup>Ra, is not escaped from the system. In the first phase, up to about a month, the equilibrium is attained with <sup>222</sup>Rn, <sup>218</sup>Po,
-<sup>214</sup>Pb, <sup>214</sup>Bi and <sup>214</sup>Po and the time required for equilibrium is governed by the most long-lived member of these, <sup>222</sup>Rn with a half-life of 3.8 days. In the second phase, up to about 200 years, the equilibrium is attained with <sup>210</sup>Pb, <sup>210</sup>Bi and <sup>210</sup>Po and the time required for equilibrium is governed by the most long-lived member of these, <sup>210</sup>Pb with a half-life of 22 years. The half-life of<sup> 226</sup>Ra is 1600 years and decrease in its activity and correspondingly activities of its progeny can be seen after about 1000 years.
 ###

CINCH NucWik

Sidebar

Differences

A-CINCH Consortium

CINCH NucWik

User Tools

Site Tools

Sidebar

Differences

Page Tools

A-CINCH Consortium