Half-life daughters

Nuclear Reaction Radionuclide Half-Life Daughter (Half-life)... 

Parent (Half-Life) Daughter (Half-Life)... 

Nuclide Half-life Daughter Yield (atoms/decay) Comments... 

All certificates must contain information that identifies the physical, chemical, and radiological properties of the SRM. Physical properties include density and mass. Chemical properties identify composition such as chemical form, acidity, and salt content. Radiological properties are the name of the radionuclide, the decay scheme, half-life, daughter radionuclides, reference time for calculating decay, and radionuclide impurity amounts. The most important information is the radionuclide activity or concentration and the uncertainty of this value. Details must be provided about the technique used to determine activity and the basis for the uncertainty value. Technical information such as the production method also may be given on the certificate. 

Element 106 was created by the reaction 249Gf(180,4N)263X, which decayed by alpha emission to rutherfordium, and then by alpha emission to nobelium, which in turn further decayed by alpha between daughter and granddaughter. The element so identified had alpha energies of 9.06 and 9.25 MeV with a half-life of 0.9 +/- 0.2 s. 

Radon-222 [14859-67-7] Rn, is a naturally occuriing, iaert, radioactive gas formed from the decay of radium-226 [13982-63-3] Ra. Because Ra is a ubiquitous, water-soluble component of the earth s cmst, its daughter product, Rn, is found everywhere. A major health concern is radon s radioactive decay products. Radon has a half-life of 4 days, decayiag to polonium-218 [15422-74-9] Po, with the emission of an a particle. It is Po, an a-emitter having a half-life of 3 min, and polonium-214 [15735-67-8] Po, an a-emitter having a half-life of 1.6 x lO " s, that are of most concern. Polonium-218 decays to lead-214 [15067-28A] a p-emitter haviag = 27 min, which decays to bismuth-214 [14733-03-0], a p-emitter haviag... 

Parent Daughter P-Decay energy, keV Mode Half-life PP-Decay energy, keV... 

The radioisotopes Tc and I (see Table 16) are often used for medical purposes. Tc has a half-life of only 6 h, which would normally make it difficult to transport from a production facility to the medical facility. However, one can supply the longer-lived 2.7-d Mo in a chemical form that allows one to separate out, generate or milk, the daughter iTc when the latter is needed. 

The nature of the radioactive decay is characteristic of the element it can be used to fingerprint die substance. Decay continues until bodi die original element and its daughter isotopes are non-radioactive. The half-life, i.e. die time taken for half of an element s atoms to become non-radioactive, varies from millions of years for some elements to fractions of a second for odiers. 

Francium is produced by the a decay of Ac, which decays mostly by /3 emission. However, ca. 1% of the decays are by a emission, giving Fr, the isotope with the longest half life (t,/2 = 1260 s). Rapid separation techniques are necessary to isolate this short-lived species from the complex mixture. One way is to separate the Th and Ra daughters from the Ac mother and then separate the monovalent Fr from the trivalent Ac. Other major isotopes of Fr have even shorter lifetimes. 

One of the behaviors of the system not easy to grasp is why the return to equilibrium is mostly controlled by the half-life of the daughter nuclide This can be investigated by considering the Ra/ °Th system ( °Th decays to form Ra with a half-life of 1599 years). If fractionation by some process results in an activity ratio greater than 1 at time t = 0, the equation describing the return to equilibrium, as shown above, is ... 

Figure 3. Parent daughter disequilibrium will return to equilibrium over a known time scale related to the half-life of the daughter nuclide. To return to within 5% of an activity ratio of 1 requires a time period equal to five times the half-life of the daughter nuclide. Because of the wide variety of half-lives within the U-decay-series, these systems can be used to constrain the time scales of processes from single years up to 1 Ma.

Figure 1. (a) Schematic representation of the evolution by radioactive decay of the daughter-parent (N2/N1) activity ratio as a function of time t after an initial fractionation at time 0. The initial (N2/Ni)o activity ratio is arbitrarily set at 2. Time t is reported as t/T2, where T2 is the half-life of the daughter nuclide. Radioactive equilibrium is nearly reached after about 5 T2. (b) Evolution of (N2/N1) activity ratios for various parent-daughter pairs as a function of time since fractionation (after Williams 1987). Note that the different shape of the curves in (a) and (b) is a consequence of the logarithmic scale on the x axis in (b). 

One other highly useful chronometer is measurement of °Po- b disequilibria. °Po has a half-life of 138.4 days making the chronometer active for 2 yrs. °Po- °Pb fractionation is based on Po but not Pb partitioning into volatiles during degassing (Gill et al. 1985). Ey repeat analysis of °Po, Rubin et al. (1994) constrained the time of eruption of several samples from 9°N EPR to windows of-100 days. These dates are consistent with eruption windows based on submersible observation. Thus, this technique can provide critical age constraints for other U-series parent-daughter pairs but requires that samples be collected and analyzed as soon as possible after eruption. 

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