Cold fusion reaction products

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 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. 

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... 

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... 

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-... 

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. 

Fig. 3 Cross sections for " Ca-induced 3n- and 4n-evaporation channels to produce superheavy nuclides, plotted against the atomic number of the compound nucleus. For purposes of comparison, the fit to the cold-fusion data from Fig. 2 is included as a solid line. The " Ca-induced cross sections do not follow a simple exponential trend, and there are significant advantages over cold-fusion reactions for production of Z > 112 isotopes...

Denisov, V.Yu., Hofmann, S. Production of superheavy elements in cold fusion reactions. Acta Phys. Pol. B31, 479 84 (2000)... 

Smolanczuk, R. Excitation functions for the production of superheavy nuclei in cold fusion reactions. Phys. Rev. C61, 011601(4) (1999)... 

Palladium hydride is a unique model system for fundamental studies of electrochemical intercalation. It is precisely in work on cold fusion that a balanced materials science approach based on the concepts of crystal chemistry, crystallography, and solid-state chemistry was developed in order to characterize the intercalation products. Very striking examples were obtained in attempts to understand the nature of the sporadic manifestations of nuclear reactions, true or imaginary. In the case of palladium, the elfects of intercalation on the state of grain boundaries, the orientation of the crystals, reversible and irreversible deformations of the lattice, and the like have been demonstrated. 

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

These three elements were all first synthesized by the cold fusion method at GSI, Darmstadt, using a very sophisticated set of techniques. For element 107 (1981) an accelerated beam of ionized Cr atoms was made to impinge on a thin ° Bi foil the reaction recoils were separated in flight from the incoming beam and from the unwanted products of transfer reactions by a velocity filter consisting of a combination of magnetic and electric fields. This facility is known by the acronym SHIP,... 

Element 113 has been discovered at RIKEN in the reaction B Zn, n) 113 (Morita et al. 2004d). In an irradiation time of 79 days with a projectile dose of 1.7 x 10 the a-decay sequence of one atom had been observed. In a second experiment (Morita et al. 2007b) one more chain was found (O Fig. 19.4). The production cross section is 30 fb, the smallest cross section ever measured for the production of a heavy element. The value is 11.68 MeV and the half-life, 0.24 ms (Morita 2008). The isotope 113 has been produced in the reaction Np( Ca, 3n) (Oganessian et al. 2007), while the isotopes with masses 283 and 284 appear in the decay chains of element 115. The half-lives of the four isotopes range from 0.24 ms to 0.48 s. Element 113 is presently at the experimental limit for heavy-element production by cold fusion, because of the required beam time. A simple extrapolation would require a beam time of the order of 1 year for one atom of element 114. To go beyond, new concepts are needed. 

The production cross sections of cold heavy-ion fusion by In evaporation, and Ca-induced reactions in 3n evaporation channels are displayed in fig. 19.19 and O Table 19.1. The cross sections for cold fusion drop steeply fi-om the order of 1 pb for nobelium to 0.03 pb for element 113, which is more than six orders of magnitude. The Ca data do not follow this trend. They stay constant around 1 pb from copemicium to element 118. 

Abstract The Island of Stability of spherical superheavy nuclides exists at the extreme limit of the Chart of the Nuclides, beyond regions of nuclear stability associated with deformed nuclear shapes. In this chapter, the reactions that are used to synthesize these transactinide nuclides are discussed. Particular emphasis is placed on the production of nuclides with decay properties that are conducive to a radiochemical measurement. The cold- and hot-fusion reactions that lead to the formation of evaporation residues are discussed, as are the physical techniques that have been used in production experiments. Recent results from " Ca-induced fusion reactions are included. Speculative methods of producing the more neutron-rich nuclides that populate the approaches to the center of the Island of Stability are also presented. 

Pb( V,n) reaction [239]. The isotope Db Jy2 = 2.5 s) is produced in the Bi( Ti,2n) reaction with a cross section of 2 nb [251] and in the Pb( V,n) reaction [239]. An isomeric state, Db Tiri = 0.9 s), has also been observed in the Bi( i,2n) reaction [248, 252]. The isotope Db Ty2 = 1.6 s) is produced in the Bi( °Ti,3n) reaction with a cross section of 0.2 nb [248] and in the ° Bi(" Ti,2n) reaction [239]. Dubnium isotopes also result from the a decays of bohrium isotopes (see below), but with smaller cross sections than for their direct production. While some of the cold-fusion isotopes have half-lives in excess of one second, the production of longer lived nuclides in other reactions is of more interest to the radiochemisL... 

Darmstadtium (Z = 110) was first synthesized in 1994 at GSI with the SHIP apparatus, used to isolate Ds (ri/2 = 180 ps), produced in the Pb( Ni,n) reaction with a cross section of 2.6 pb [267]. Later, the heavier IV = 161 isotope Ds (ri/2 =1.1 ms) was produced using the Pb( Ni,n) reaction [195]. Here, an increase in the neutron number of the projectile enhanced the production cross section by a factor of 5 to 15 pb. This work has been confirmed [270, 279, 280] as has the existence of a second a-decaying state with Ty2 — 70 ms, which is probably an isomer [67, 270]. The intermediate even-even isotope Ds (Ti/2 = 100 ps) was produced in the reaction Pb( Ni,n) reaction with a cross section of 13 pb [281]. This nuclide may have a high-spin two-quasiparticle K isomer with Ty2= 6 ms [281, 282], which has interesting implications for structure effects on nuclear stability [98,283]. Production of a single atom of Ds (Ty2 = 3 ps) via the Bi( Co,n) reaction was reported tentatively in 1995 [284] the unusual decay sequence proposed for the isotope needs further experimental elucidation. The a decay of Cn results in Ds (Ty2 =170 ps) [190, 263, 271]. All cold-fusion darmstadtium isotopes have very short half-Uves, though the isomeric state in Ds has a hatf-Ufe approaching 0.1 s [270]. 

As mentioned above, there is an exponential downward trend in cold-fusion evaporation-residue cross sections with increasing atomic number of the product, attributed more to an increase in dynamical hindrance to fusion than to a decrease in < rjFf> [105, 108, 227, 232, 235, 236, 296]. For the transactinides, representative cross sections for In-channel cold-fiision reactions [198, 201, 246] are plotted in Fig. 2. In going from Z = 105 to Z = 113, the cross section decreases... 

Simple addition of protons and neutrons in the reactants indicates that the transactinide products of " Ca-induced fusion reactions derive the same advantage in neutron number over cold-fusion products that was observed in more asymmetrical hot-fusion reactions (see Sect. 2.2). In reactions that produce copemicium (Z = 112), the switch from the cold-fusion Pb( n,n) Cn reaction to the hot-fusion U(" Ca,3n) Cn reaction effectively adds 6 neutrons to the evaporation residues. In terms of exploring Z,N space toward the center of the Island of... 

Regardless of the asymmetry of the reaction, production of superheavy recoils is not significantly increased by increasing the target thickness beyond 2 mg/cm. In practice, the momentum acceptance criteria of on-line separators (see Sect. 3.4) are significantly more strict. The areal densities of lead and bismuth targets in online cold-fusion physics experiments are usually on the order of 0.5-1.0 mg/cm ... 

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