NEW Muon Catalyzed Fusion

Introduction. Muon catalyzed fusion is the name given to a series od reactions resulting in the fusion of two hydrogen isotopes nuclei which are kept closed by a negative muon. This process firstly observed by Alvarez et al (1957). The possibility of realizing fusion-chambers based on muon catalysis is especially attractive if one considers the advantage of work with a fusion chamber that is operated relatively at low temperatures. There is a wealth of experience accumulated by nuclear community of working at these temperatures. Of course, it is almost futile to take of pure fusion reactors based on muon catalysis alone because of the unfavorable energetics associated with the production of negative mesons. However, the preliminary estimates of energy balance for muon-catalyzed fusion chambers combined with the fissionable nuclide-blanket show a net positive gain. There is another advantage in selecting muon catalyzed fusion as driver for fissionable balnkets. The muon catalyzed fusion chambers are very useful in themselves as one can investigate experimentally the validity of fusion cross-section for advanced fusion fuels like (D, D), (D, He3) (D, Li6) without bothering about the problems connected with excessive plasma temperature one requires while trying to realize thermonuclear fusion environment. Also it would be extremely useful to simulate radiation environment with muon catalyzed advanced fusion fuel for physics and engineering investigations of the likely energy extraction systems of later-day thermonuclear reactor based on advanced fusion fuels. There is also an interesting possibility of utilizing muon-catalyzed fusion to ignite usual thermonuclear reactions in an inertially confined deuterium-tritium pellet. Physics of Muonic Catalysis. The phenomenon of catalysis of nuclear reaction on cold hydrogen by µ mesons is brought about by a whole lot of atomic and nuclear process which are set into motion before hydrogen isotopes are made to fuse while keeping close company within a muonic hydrogen molecular ion by a single µ-meson. The fusion reactions of our interest among hydrogen isotopes are given earlier. Under Ordinary conditions these reactions can take place only when the reacting nuclei are imparted enough kinetic energy to tunnel significantly through the Coulomb barrier. For Example, the nuclei are heated to high temperatures in thermonuclear fusion. It is to be noted that the kinetic energy required to be supplied to the nuclei is usually much smaller than the height of coulomb-barrier. Also the probability of barrier penetration is more critically dependent on barrier width. These bring the nuclei close enough, say by chemical forces. In an ordinary hydrogen molecule, a nuclear reaction is impossible because of large distance between the two nuclei. In fact, it is easy to see this from the following relation for barrier penetration. B=exp?[(-Km)/v(m_(e^ ) )] Where K is a numerical factor around 3, m is the reduced mass of the hydrogen nuclei. me is the mass of electron, if electron could be replaced by some "electron like" heavier particle to produce chemical binding in the hydrogen molecule, B would increase. Only suitable "electron-like" particle turns out to be negative meson as it does not react with nucleus. The subnuclear µ meson is 207 times as heavy as electron with the same electric charge. This leads to vary small value of Bohr radius (aµ) for muon. Muon has got life time 2.2 x 106 sec and it decays into an electron, neutrino and antineutrino. This short lifetime of muon necessitates its utilization through fast processes. When muons are injected into some dense matter, they slow down rather quickly and at low energies are captured to form muonic atoms. For example, slowing down in a 50% D2+50% T2 medium will form muonic atoms Dµ and Tµ. These muonic atoms move around in the host medium and undergo one of the two main processes: Muon transfer from lighter to heavier nucleus, i.e. colliding with t in T2 molecule will yield T as follows: Dµ + T --> Tµ +D ... (15.7.2) The muonic molecular ion formation through interaction heavier muonic atom with lighter or equally heavy nuclei present like; Tµ + D --> DTµ ... (15.7.2) It is to be added here that the probability of formation of DT molecular ion through the collision of D and T is rather small as compared to the probability of muon transfer as shown in Eqn. (15.7.2). it can be explained from the fact that while the presence of a third particle (electron or deuteron) is necessary to transfer the binding energy released in the formation of DTµ molecular ion, the binding energy excess released in the formation of heavier muonic atom Tµ is shared by the product particles, tµ and D. After the formation of muonic molecular ion like DTµ, the heavy hydrogen nuclei present within it, namely D and T in the present case, undergo fusion almost instantaneously. It happens because of the extreme closeness of these nuclei within the muonic molecular ion-the width of the coulomb barrier is reduced drastically by the binding particle muon. The fusion of D and T within DTµ can be represented as: DTµ --> He4 + n + µ +17.6 MeV. ... (15.7.4) The energy released in the above reaction is distributed essentially between He4 and n. the muon freed in reaction (15.7.4) can repeatedly catalyze such nuclear reaction till either it decays or is captured. It is possible to give 100 (D, T) fusion events per muon. It is obvious from the foregoing discussion that the number of (D, T) fusion catalyzed by a single muon will be governed by the 'reaction rates', associated with various processes leading to formation of a "meso-molecule". In the meso-molecule a virtual photon can be absorbed by the muon thus giving (refer Fig. 15.7.1). D He3 P Fig. 15.7.1. Concept of µ catalyzes fusion by photon absorption. pDµ --> 5.4 MeV. The energy of the muon is Eµ = 5.4 MeV. Energy production from Muon catalyzed fusion. The large value of the DTµ mesomolecule formation rate has revived the idea of using muon catalyzed fusion (m.c.f) for energy generation. In this regard, petrov has proposed an indigeneous scheme, so called mesocatalytic Reactor (MR) or Hybreader, here m.c.f is used together with the electronuclear breeding in order to produce a positive energy outline. The logical scheme of the Mesocatalytic reactor is shown in Fig. (15.7.2). Light nuclei, such as D or T, are accelerated up to an energy of about 1 GeV/nucleon and hit a target where fast nucleons and p mesons (a meson is a particle equal in charge, but having greater mass than an electron or positron, and less than a neutron or proton) are produced. As p are most likely produced in n-n collisions, it is convenient to have both beam and target rich of neutrons. The fast neutrons impinge onto a U-238 blanket, where they cause the fission of uranium and produce fissile isotope (Pu). In this way one gets out heat, which can be converted into electric energy in the electric generator as well as nuclear fuel, which can be used in an atomic energy plant. Essentially, this is the scheme of electronuclear energy production. The pions, which have been trapped in a magnetic device around the target, will decay into muons and neutrinos in the converter. In principle, this system provides a source of muon which is much more economical than the standard way of producing a muon beam. Petrov and Shabelski (1981) estimate that the beam energy is necessary for the production of one negative point in a cylindrical beryllium target is about 4.5 GeV. In a suitable deuterium and tritium mixture inside the so-called synthesizer the muon will catalyze nuclear fusions. Petrov observes that, by using for electronuclear breeding the 14 MeV neutron originated from the DT fusion, it is possible to recover much more energy than the fusion energy itself. Petrov's schemes brings following two idea into the subject of m.c.f. : It presents an 'economic way' of getting a source of muons in that all the energy of the primary beam is eventually used for energy production - through channels A and B of Fig. (15.7.2), and the particle losses of the muon beam are appreciably reduced. It shows that, by a suitable use of the fusion products, it is possible to recover much more energy than the fusion itself. The theoretical predictions (later confirmed by experimental results) of a particularly high value of the (DTµ) formation rate have revived the idea of using the m.c.f for energy production. If this respect several points have to be further investigated. First, one has to clarify the formation mechanism of the (DTµ) meso-molecule and provide definite estimates on the number of possible fusions.