8 decay half-lives, neutron-rich

Pu. The isotope Pu is the longest-lived of the plutonium- isotopes, with a half-life of 8 X 10 years. It can be produced by neutron absorption in Pu, but because of the short half-life and low concentration of Pu only minute quantities of Pu, of the order of 10" percent, are present in reactor-produced plutonium [K2]. Small quantities of Pu, as well as Pu and Pu, are present in the residues from nuclear explosions, resulting from the decay of the neutron-rich uranium isotopes and formed by multiple neutron capture in the high neutron... 

We can continue our survey of the lightest nuclei with A = 3. Only the combinations of two protons and one neutron, 3He, and one proton with two neutrons, 3H, are bound, while the combinations of three protons, 3Li, and three neutrons are unbound. Again we see a balance between the numbers of neutrons and protons with the extreme cases being unbound. The nuclear spins of both bound A = 3 nuclei are j indicative of a pair of nucleons plus one unpaired nucleon three unpaired nucleons would have had a total spin of. In the A = 3 system the more neutron-rich nucleus, tritium, 3H, is very slightly less stable than 3He and, it decays by (3 emission with a 12.3-y half-life. 

In this paper, we discuss several categories of decay data which have contributed to low-energy nuclear physics, indicate some of the ways they are useful in solving problems in other areas and identify needs for further measurements. Illustrations include half-life and emission-probability data of actinide nuclides important for reactor technology and useful as reference standards for nuclear-data measurements. Decay data of highly neutron-rich fission-product nuclides are important in such diverse areas as astrophysics and reactor-safety research. Some of these data needs and experimental approaches suitable for satisfying them are presented. 

In conclusion thre first half-life measurements of light neutron rich nuclei using the MSU Reaction Product Mass Separator has resulted in the measurement of eight half-lives,two of which represent first time measurements and three of which are second measurements.The RPMS coupled with fast beam switching has proven to provide a very clean environment in which to study the decays of neutron rich nuclei. 

Chemical studies were not possible until 1970 with the synthesis of longer-lived Lr (ti = 26 s). The even more stable neutron-rich Lr with a half-life of 3.6 hours is now known. At the time, though, there seemed few prospects of extending the Periodic Table into another series and in any case it was also not clear what chemical properties were expected for these elements, nor how they might be studied. Experience with the actinides had shown that half-lives for a-decay of each element were steadily growing shorter as the atomic number increased, whilst the drop in half-lives for spontaneous fission was even more dramatic. Extrapolation to elements with atomic numbers around 107-108 indicated that half-lives would be so short t = 10 s) that it would be impossible to isolate further elements. 

Radioactive decay by proton emission is a very seldom observed decay mode for very neutron deficient nuclides because decay by /S or EC normally has a very much shorter partial half-life ( 4.14). Decay by p" has been observed for " 0 E 1.55 MeV, ti/ 0.25 s, -1.5%). However, jS decay sometimes leads to a proton-unstable excited state which immediately (< 10 s) emits a proton. Several 0 emitters from to Ti with N = Z — 3 have /S delayed proton emission with half-lives in the range 10 — 0.5 s. Also radioactive decay by simultaneous emission of two protons has been observed for a few proton rich nuclides, e.g. Ne, 6 10 ° s. 

Al-26 comes in two forms -- one with a 6.4 second half-life and one with a 7 million year half-life. Some radioisotopes have three different half-lives. So, for radioactive isotopes, we sometimes have to add to our symbol to tell which decay mode we mean. In the case of Al-26, the 6.4 second activity is a "higher energy state" and is called Al-26m. In class we will discuss decay schemes of radioisotopes we encounter at UWNR are produced by absorbing a neutron in a stable element and are "neutron rich" — which... 

Carbon exists in five isotopic forms. That is to say there are atoms of carbon with five different nuclear characteristics, specifically with different numbers of neutrons. These variations are denoted as carbon-11 (C-11), carbon-12 (C-12), carbon-13 (C-13), carbon-14 (C-14) and carbon-15 (C-15) in which the numbers of neutrons vary ftom 5 to 9 respectively. Of these isotopes, C-12 and C-13 are stable while the others are imstable and radioactive. In order to achieve stability, radioactive decay occurs involving the emission of particles from the nucleus. This occms at a constant rate for each isotope for C-11 the half-life, i.e. the time required for half the original number of atoms to decay is 20.3 minutes, for C-15 it is 2.5 seconds and for C-14 it is 5730 years. The long half life of the latter isotope allows it to be used as a means of estimating the age of carbon-rich substances that have been preserved through bmial in enviromnents that prohibit decomposition. The approximate age is determined by comparing the amount of radioactive carbon in the preserved sample with that in a modem sample. While the physical properties of the isotopes vary in this way, their chemical properties are the same, as reflected by their atomic munber of six. 

---