Mesonic X-rays

Mesonic atoms can be regarded as new types of nuclear probes in material science dealing with chemical aspects. In this section, capture ratio problems in binary systems as well as X-ray intensity patterns in mesonic transitions are briefly described. 

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Some uses of mesonic X-rays for analytical purposes have been published". However, only in a system in which the capture ratio is well known, would a quantitative determination be practical. 

The fact that mesonic X-ray intensity patterns are sometimes dependent on chemical environments is an interesting topic in mesonic chemistry. When the relative line intensities of mesonic X-rays are considered in such cases, systematic differences are found between different compounds of the same element. The chemical effect on muonic X-ray patterns was first discovered by Zinov et al. and by Kessler et al. 

An explanation for the chemical effects on the mesonic X-ray intensity patterns (H-capture by Cr in CrjOj and in CrOj) has been given by Schnewly et al. taking... 

Initiation by Fission Fragments. All attempts to initiate explosives by nuclear fission fragments such as a-particles, protons, Ar or Hg ions, 7-rays, X-rays, mesons and pions have resulted in failures [Bowden Yoffe quoted above, J. Cerny J.V.R. Kaufman,... 

Recent years have seen a considerable extension of the experimental methods used in quantum chemistry and in investigations of the nature of chemical bonds in crystals. It is worth mentioning methods based on the studies of the elastic and the inelastic scattering (by crystals) of X rays, electrons, neutrons, protons, mesons, a and other particles, as well as the x ray spectroscopic methods. Methods based on the use of positron annihilation are also of considerable interest. 

Investigations of the scattering of x rays, electrons, mesons, and neutrons, carried out under suitable conditions, can provide hi ly accurate information on the atomic scattering functions, and on the electron and spin densities in crystals. 

The n" and [T mesons will go from continuum states into bound atom states with the accompan3dng emission of X-rays. They thus temporarily form what are known as "mesic atoms . The X-rays from these transitions have been the observable manifestation of the existence of these mesic atoms. The / -mesic atoms have been useful in providing data on the charge distribution of nuclei. The results agree with those obtained from electron scattering experiments. 

This formulation is not limited to the scattering of X-rays, but it should apply to any weak interactions in which plane waves constitute a reasonable approximation and the initial and final states of the nucleus are the same. Gp[d) is then changed to the cross-section appropriate for the process. Processes where it is convenient to think in terms of form factors include the elastic scattering of electrons (from low Z nuclei), elastic photon scattering, fji meson scattering, IJL meson pair production, and the scattering of those K mesons which have a weak nuclear interaction. The nuclear form factor is also a convenient first... 

In more detailed papers, Wheeler stressed the possibility of obtaining the size of the charge distribution of the nucleus from measurements of the energy of these X-rays from [jl mesonic atoms. 

The most precise values of the energies of the X-rays from [ji-mesic atoms are those obtained by Fitch and Rainwater . They used negative x-mesons from... 

K X-rays are observed only for light nuclei, the yield of such X-rays (per pion stopped) decreases rapidly with Z. This is attributed to an increasing probability for nuclear capture from the 2p state and is in agreement with a known attractive interaction between a nucleon and a meson in a state. The yield of K X-rays for Z = 8 is down to about 3% of all pions that have stopped L X-rays have a yield of about 8% for Z = 26. 

Most laboratories with n meson beams have such investigations underway, and more effort is being devoted presently to studies of zr-mesic X-rays than to studies of [x-mesic X-rays. 

Studies of the volmne effect yield information on the charge distribution in the nucleus. Hyperfine structure and isotopic shifts are of the same order of magnitude. Isotopic shifts can be studied in the visible region as weU as in the X-ray region. Particularly prominent isotopic shifts are obtained for muonic atoms, in which, for example, a p meson (m = 209me) has taken the place of an electron. The classical radius of the orbit is reduced by a factor of 209, and thus the nuclear influences are much greater than those pertaining to the electrons. Isotope shifts and their interpretation have been discussed m [2.57-2.59J. 

An important modality in cancer treatment is that of radiotherapy, either alone or in combination with chemotherapy. Indeed, the first treatment of cancer by X-rays followed within a year of their discovery by Rontgen [1] and it is estimated that today approximately half of all cancer patients receive radiation in some form. Conventional sources such as X-rays and Co-y rays are now supplemented with particles such as protons, neutrons and mesons [2] and also by internal delivery (brachytherapy) using various implanted isotopes [3]. 

Conditions in the universe almost immediately after the big bang were not favorable for the formation of electrons. At that point in time, gamma rays, photons, and neutrinos had very large amounts of energy, much more than was needed to produce electrons. Instead, conditions favored the creation of much more massive particles with large energy equivalents. Among these particles were the muon and the proton. A muon (also known as a mu meson) is a much more massive relative of the electron. It has amass of 1.870 x 10"25 g, about 2,000 times that of an electron. A proton is even heavier, with a mass of about 1.660 x 10 24 g, nearly 3,000 times that of an electron. 

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