Actinide isotopes, longest half-lives

All of the actinides through Cf have isotopes with half-lifes of hundreds to thousands of years. The longest half-lifes of Es and Fm are measured in tens of days Md and higher atomic number elements exist for only hours or less (102). Because of the radioactive decay, these latter elements are not considered for normal laser applications. Other concerns for practical lasers are (1) the presence of radioactive isotopes which may cause radiation damage and undesirable absorption bands in the host and (2) the cost and availability of adequate quantities of the required isotope. 

The other actinides have been synthesized in the laboratory by nuclear reactions. Their stability decreases rapidly with increasing atomic number. The longest lived isotope of nobelium (102N0) has a half-life of about 3 minutes that is, in 3 minutes half of the sample decomposes. Nobelium and the preceding element, mendelevium (ioiMd), were identified in samples containing one to three atoms of No or Md. 

The element was generated by bombardment of californium with boron in a linear accelerator. The priority is debated. Isotopes of the elements were observed both by the group of Glenn T. Seaborg and by that of G. N. Flerov in Dubna. IUPAC proposed that the priority be shared. The longest-lived isotope has a half-life of 200 minutes. Lawrencium ends the series of actinides, as the 5f level is fully occupied with 14 electrons. 

Although in a strict sense not a member of the actinide series, actinium is included here for completeness as lanthanum is frequently included in the lanthanide series. The longest lived isotope of actinium is with a half-life of 21.8 years. It occurs in nature from the decay... 

Symbol Lr atomic number 103 atomic weight 262 a transuranium inner-transition actinide series element a synthetic radioactive element electron configuration [RnjTs b/ Sdi valence +3 six isotopes of masses 255 to 260 have been synthesized longest-lived known isotope Lr-260 has half-life of 3 minutes. 

Table Longest-lived isotopes of actinides Atomic no. Element Isotope Half-life... 

Figure 14.10. Logaritlim of the half-life [y] of the longest-lived isotopes of the actinides as a function of the atomic number Z.

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