Cold fusion reactions

Calculate the energy release in kilocalories per mole (kcal/mol) of He for the cold fusion reaction... 

Element 111 was synthesized and characterized by the same group during the period 8-17 December 1994 using the analogous cold-fusion reaction, ° Bi( Ni,n) lll, followed by observation of up to five successive cc-emissions which could be assigned to the chain ... 

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. 

In this section, we present results dealing with the discovery of elements 107 to 112 using cold fusion reactions based on lead and bismuth targets. A detailed presentation and discussion of the decay properties of elements 107 to 109 and of elements 110 to 112 was given in previous reviews [15,20,21], Presently known nuclei are shown in the partial chart of nuclides in Figure 2. 

Fig. 3. Two decay chains measured in experiments at SHIP in the cold fusion reaction 70Zn + 208Pb —> 278112. The chains were assigned to the isotope 277112 produced by evaporation of one neutron from the compound nucleus. The lifetimes given in brackets were calculated using the measured a energies. In the case of escaped a particles the alpha energies were determined using the measured lifetimes.

Actinides served already as targets, when neutron capture and subsequent P decay were used for the first synthesis of transuranium elements. Later, up to the synthesis of seaborgium, actinides were irradiated with light-ion beams from accelerators. At that time it was already known that cold fusion reactions yield higher cross sections for heavy element production. 

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... 

Fig. 7. Measured cross sections (a) for reactions with 208Pb and 209Bi targets and In evaporation and (b) for reactions with actinide targets and 4n evaporation. At the right ordinate cold fusion reaction yields are given which are obtained with the presently available technology. The values (N-Z)/2 denote the projectile isospin.

Locally an increase of the cross section by a factor of 5.8 was measured for element 110 in cold fusion reactions when the beam was changed from 62Ni to f>4Ni. It was speculated that this increase could be due to the increased value of the projectile isospin. However, the assumption could not be confirmed in the case of element 112 which was synthesized using the most neutron rich stable zinc isotope with mass number 70. 

The main features of cold fusion reactions with the spherical nuclei of Pb or ° Bi as targets are low excitation energies of the compound nuclei (Ex w 15 to 20 MeV) with the consequence of emission of only one or two neutrons, low probability of fission, and relatively high fusion cross sections otus- On the other hand, the reaction products have relatively small neutron numbers and short half-fives. Suitable projectiles are neutron-iich stable nuclei, such as " Ca, Ti, " Cr, Fe, Ni, Zn, and Kr. 

Smolanczuk, R. 2001b. Formation of superheavy elements in cold fusion reactions. Phys Rev C 63, 044607-1-8. 

A cold fusion reaction is one that takes place under ambient conditions using simple equipment. Such a fusion reaction would be extremely desirable, since it could allow for a simple and efficient means of energy production. 

Evidence for different isotopes of element 110 was reported by several groups of scientists in 1995-1996. Ghiorso et al. (1995a, b) reported production of a single atom of 110 in the ° Bi( Co,n) cold fusion reaction, Lazarev et al. (1996) reported evidence for decay of... 

After many improvements to SHIP, an international team led by S. Hofmann conducted experiments at GSI in 1995 and claimed discovery of element 110 (Hofmann et al. 1995a) produced in the cold-fusion reaction Pb( Ni,n) l 10. They reported observation of 110 based on four chains that decayed by alpha emission to known daughter nuclides. They proposed the name darmstadtium (Ds), which was approved by the lUPAC in August 2003. The second chain could not be found in subsequent re-examination of the data (Hofmann et al. 2002), but lUPAC ruled that the remaining three chains constituted adequate proof... 

Direct production of two different isotopes of element 113 has also been reported. Morita et al. (2004b, 2007b) reported production of two events of 113 via the Bi( Zn,n) cold fusion reaction with the extremely small production cross section of only about 31 fb in two separate experiments at a beam energy of 353 MeV at the Riken Linear Accelerator Facility. These were attributed to 113 based on alpha-decay to the previously reported isotopes Bh... 

Beyond Element 106 The Cold Fusion Reactions of Heavy Ions... 

In the superheavy elements, the cold-fusion evaporation residues with the highest cross sections are the result of (HI,n) and (HI,2n) reactions. Evaporation of particles other than neutrons in a cold-fusion reaction is unlikely [192, 198, 201, 238, 239]. The same arguments that were made above for suppression of proton and a-particle emission from hot-fusion compound nuclei apply even more strongly to cold-fusion products. The height of the Coulomb barrier to charged-... 

In spite of the lower excitation energies obtained in cold-fusion reactions, hot-fusion reactions produce evaporation residues that are more neutron rich, a consequence of the bend of the line of fi stability toward neutron excess. For the purposes of studying nuclei whose stability is more strongly influenced by the spherical 184-neutron shell clostrre, hot fusion is the more viable path. If nuclei were constrained to be spherical, or deformed into simple quadrupole shapes like those that influence the properties of the actinide isotopes with N — 152, one would expect cold-fusion reactions to quickly veer into ZJ space where nuclides would be characterized by very short partial half-lives for decay by spontaneous fission. In fact, there is a region of nuclear stability centered at Z = 108 and N — 162 [12, 19-21], removed from the line of fi stability toward proton excess, where the nuclei derive a resistance to spontaneous fission from a minor shell closure associated with complicated nuclear shapes, making a emission their most probable decay mode [133, 240]. 

Cn is produced in the Pb( Zn,n) cold-fusion reaction with a cross section of 0.5 pb. While the indirect production of Hs proceeds with a cross section that is an order of magnitude lower than that for the direct process, in specific cases there may be disadvantages to the direct method involving, for example, reaction kinematics and radioactive target handling that might make the indirect overshooting reaction attractive in some applications. 

Rutherfordium (Z = 104), first synthesized by hot fusion (see Sect. 2.2), has also been produced in cold-fusion reactions. Early cold-fusion work was focused on demonstrating the disappearance of the effect of the TV = 152 shell closure on the spontaneous fission half-life systematics of the heavy elements [198]. Rutherfordium isotopes are produced in reactions between Pb targets and Ti projectiles. The most neutron-rich cold-fusion Rf isotope is Rf (J a — 4.7 s), produced in the ° Pb( °Ti,n) reaction with a cross section of 5 nb [210, 246, 247]. 

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