Hot fusion

A combined team of scientists from the Lawrence-Livermore National Laboratory (LLNL) in California, and from the laboratory in Dubna, Russia, reported the following hot fusion reaction ... 

Crawford. M. "Hot Fusion A Mclldown in Polmcul Support," Science, 15.M (March 10. 19901. 

In Figure 15.4, we show current measurements (filled squares) of the cross sections for cold fusion reactions as a function of the atomic number Z of the completely fused system. (The cold fusion point at Z = 118 is an upper limit.) Also shown (as open circles) are the cross sections for hot fusion reactions. Clearly, future efforts will have to focus on experiments at the 0.1- to 1.0-pb cross-section level or lower. Current technology for cold fusion reaction studies would require 12 days to observe one event at a cross-section level of 1 pb. Similarly, a cross section of 1 pb in a hot fusion reaction would require 6—19 days to observe one event. From examining the data in Figure 15.4, it would also appear that hot fusion reactions might be the reactions of choice in pursuing future research in this area. 

Figure 15.4 Plot of the observed cross sections for the production of heavy elements by cold and hot fusion reactions.

The saga of cold fusion, more properly called low-energy nuclear reactions, has a fascinating history in the United States. A few years after the initial announcement of the discovery of cold fusion, this author had collected over 3000 papers from over 200 laboratories in exactly 30 countries. Over 600 of these papers reported successful replications or improvements on the original Fleischmann-Pons discovery [34]. However, due to a well-conceived, well-funded, and well-conducted effort by adherents to the hot-fusion technology, cold fusion in the U.S. has been discredited [35]. 

In the following sections a detailed description is given of the set-ups of the physical experiments used for the investigation of SHEs. (The instrumentation based on chemical methods for the study of heavy elements is presented in subsequent chapters of this book.) Experiments are presented, in which cold and hot fusion reactions were used for the synthesis of SHEs. 

Table 1. Nuclides from hot fusion reactions [50] used in chemical investigations.

The effect of Coulomb repulsion on the cross section starts to act severely for fusion reactions to produce elements beyond fermium. From there on a continuous decrease of cross section was measured from microbams for the synthesis of nobelium down to picobarns for the synthesis of element 112. Data obtained in reactions with Pb and Bi for the In-evaporation channel at low excitation energies of about 10-15 MeV (therefore named cold fusion) and in reactions with actinide targets at excitation energies of 35-45 MeV (hot fusion) for the 4n channel are plotted in Figure 7a and b, respectively. 

The cross sections for elements lighter than 113 decrease by factors of 4 and 10 per element in the case of cold and hot fusion, respectively. The decrease is explained as a combined effect of increasing probability for reseparation of projectile and target nucleus and fission of the compound nucleus. Theoretical consideration and empirical descriptions, see e.g. [61,62], suggest that the steep fall of cross sections for cold fusion reactions... 

The experimental work of the last two decades has shown that cross sections for the synthesis of the heaviest elements decrease almost continuously. However, recent data on the synthesis of element 114 and 116 in Dubna using hot fusion seem to break this trend when the region of spherical superheavy elements is reached. Therefore a confirmation is urgently needed that the region of spherical SHEs has finally been reached and that the exploration of the island has started and can be performed even on a relatively high cross section level. 

This kind of reactions would offer the possibilty of fusion at relatively low temperatures ( cold fusion ) of about 10- K in contrast to hot fusion at about 10 K (section 8.12). 

Irradiation of actinides with ions of relatively low atomic numbers (e.g. Z = 5 to 16). In general, these reactions lead to high excitation energies of the compound nuclei ( hot fusion ). 

High excitation energies (hot fusion) lead with high probability to immediate fission. 

The unusual interaction of hydrogen with palladium-based membrane materials opens up the possibility of oxidative hydrogen pump for tritium recovery from breeder blankets. The feasibility for this potential commercial application hinges on the hot-fusion and cold-fusion technology under development [Saracco and Specchia, 1994]. At first, Yoshida et al. [1983] suggested membrane separation of this radioactive isotope of hydrogen followed by its oxidation to form water. Subsequently, Hsu and Bauxbaum [1986] and Drioli et al. [1990] successfully tested the concept of combining the separation and reaction steps into a membrane reactor operation. 

The characteristic circular-shape of the tokamak reactor is clearly seen here. The reactor uses strong magnetic fields to contain the intensely hot fusion reaction and keep it from direct contact with the interior reactor walls. 

For element 114, gas-phase chromatography experiments similar to those for element 112, are also planned for the near future by the PSI/GSI collaboration. A long-lived isotope 114 (3 s) will be produced in the hot -fusion reaction from Pu with a Ca beam. Element 112, a decay product of element 114, will be studied on its volatility in relation to that of Hg using the same technique as described above. In this way, the Z number of element 114 will be proven in an indirect way. 

Ariza, Luis Miguel. Burning Times for Hot Fusion. Scientific American 282 (March 2000) 19-20. This article focuses on efforts of researchers to develop methods to produce electricity from D-T fusion. 

In order to make isotopes of new elements having high N/Z ratios, there has been more recent interest in hot fusion reactions involving nuclei such as and Es as targets and light ions... 

In 1998, Yuri Oganessian and his research group in Dubna obtained isotopes from Lawrence Berkeley National Laboratory and accelerated a Ca beam into a Pu target in a hot fusion experiment. Calcium 48, with Z = 20 and N = 28, is doubly magic and Pu is the most neutron-rich plutonium isotope. The JINR observed two isotopes of element 114 (ununquadrium or Uuq) uq, = 27 s and Uuq, V, = 2 s. The... 

In February 2004, tbe Dubna and Berkeley groups announced their collaborative discovery of elements 113 (ununtrium or Uut) and 115 (ununpentium or Uup). Using hot fusion the researchers fired Ca at a target with formation of both Uup (expulsion of 4 neutrons) and Uup (expulsion of 3 neutrons). The lifetimes of these two nuclei were tens of milliseconds and they each ejected an a-particle to form Uut and Uut respectively with half-lives of tens of milliseconds. The results, published in a respected journal, are not yet confirmed by the JWP. The researchers also very tentatively noted the observation of one possible decay event from element 118 and, in 2006, corroborating evidence was obtained in the United States and in Russia. 

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