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Improvement of Gamma-Resonant Spectroscopy

#1825


Method Development of Essential Increase of Gamma-Resonant Spectroscopy Resolving Power and of New Type Gamma-Sources Design for Use in This Field

Tech Area / Field

  • PHY-ANU/Atomic and Nuclear Physics/Physics
  • PHY-OPL/Optics and Lasers/Physics
  • PHY-PFA/Particles, Fields and Accelerator Physics/Physics
  • PHY-SSP/Solid State Physics/Physics

Status
3 Approved without Funding

Registration date
22.03.2000

Leading Institute
ITEF (ITEP), Russia, Moscow

Supporting institutes

  • All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow\nMoscow State Technical University of Radioengineering, Electronics and Automation, Russia, Moscow\nVNIIEF, Russia, N. Novgorod reg., Sarov

Collaborators

  • Old Dominion University / College of Science, Department of Physics, USA, VA, Norfolk\nCEA / DAM / Centre d'Etude de Bordeaux-Gradignan, France, Gradignan\nYoungstown State University / Department of Physics and Astronomy Ward Beecher Planetarium, USA, OH, Youngstown\nKatholieke Universiteit / Departement Nauurkunde / Institut voor Kern- en Staungsfysica, Belgium, Heverlee

Project summary

The most part of the works in г-resonant spectroscopy is being performed in present by means of Mössbauer effect with resolving power of spectrometers corresponding by an order of magnitude to the ratio of natural г-line width, Г, to the energy of г-rays, Eг. For the most widely used Mössbauer nuclide 57Fe the value of Г/Eг is equal to ~ 3.110-13 . In spite of such small value of this ratio it is not possible in many cases to resolve the components of hyperfine structure of measured spectrum. In other branch of г-resonant spectroscopy operating with г-rays of higher energy which are being emitted and absorbed with recoil the difficulties exist in creation of г-sources permitting to compensate by some means the г-ray energy losses via recoils of emitting and absorbing nuclei. It is proposed in the present project to perform the works directed to both the increase of the resolving power of Mцssbauer spectroscopy and the development of г-sources of new type for use in both branches of г-resonant spectroscopy.

The experimental study will be performed of the possibility of Mössbauer г-spectrometer design on the base of long-living nuclear isomers such as 109Ag. This nuclide has an excited state with energy of 88 keV and mean life time of 57 s. The ratio Г/Eг = ~ 1.310-22 for this nuclide. This value is more than 9 orders of magnitude less than the corresponding ratio for 57Fe. The experiments performed in recent years show that in the single crystals of silver the Mцssbauer г-line of 109Ag may turn out to be comparatively small broadened. In the frames of present project the experiments will be performed by means of which the value of broadening factor for this г-line will be determined unambiguously. On the base of this result one could judge about possibility of use 109Ag in Mössbauer spectrometers of high resolution. The first step experiments will be performed with a set-up permitting to measure simultaneously three effects from which one could extract the data about the broadening factor. These effects are the following: a) the temperature dependence of 109Ag г-ray selfabsorption in the г-source which is a single crystal silver plate with embedded parent nuclide 109Cd, b) the influence of gravitational red shift of г-ray energy on the resonant г-ray absorption. To reveal this influence the yields of г-rays from the source will be measured in horizontal and vertical directions by two germanium detectors, and c) the influence of outer magnetic field direction on the resonant г-ray absorption. This will be done by periodical compensation of vertical component of Earth's magnetic field by means of Helmholtz rings. As a result the synchronous modulation of г-ray intensity will take place the scale of which depends on г-line broadening. The additional control nonresonant г-source will be used simultaneously with the main one. For the г-rays of control г-source all the resonant effects must be absent expected for silver г-rays.

Some alloys will be studied of Ag (Ag-Be, Ag-Si, Ag-Ge) with a goal to find the substance with larger Debye temperature than that of pure silver. If the alloy with suitable properties will be found then it will be used in the experiments on the search for г-resonant absorption.

The next step of the experiments will be connected with resonant excitation of initially nonactive single crystal silver absorber by г-rays of sufficiently strong gamma-source and with measurement of inducted activity by means of detectors shielded from the direct г-radiation of the source. Such experiment will permit to measure the г-line broadening factor if it will turn out to be too large to be measured by г-ray selfabsorption. The totality of these experiments would permit (if positive results will be obtained) to design the spectrometer in which the measurement of Mцssbauer spectrum may be performed by the gravity influence at the rotation in vertical plane of an assembly consisting of г-source, absorber and detector or by means of weak magnetic field influencing upon the г-source under the conditions of compensated Earth magnetic field. Mössbauer spectrometers of such type will be adopted both in the studies of very small admixture influence on the structure and properties of superhigh-pure substances and in the design of high-sensitive magnetometers and gravimeters. The latter may be used in geological prospecting. Note that the positive results of these experiments would permit to undertake the experiments on the observation of induced г-emission using the long -living nuclear isomers. As regards to basic science, one has to say the experimental proof of small broadening of 109mAg Mцssbauer γ-line would require for change of modern conceptions about the forming mechanism of г-resonance of long-living isomers in solids.

The ITEP group is engaged in the experiments on Mцssbauer excitation of long-living isomeric nuclear states during a long time. Just this group performed some time ago the first successful experiments on resonant excitation of 107Ag and 109Ag nuclei by г-rays of strong sources in polycristallic samples. These works are quoted till now in Russia and abroad.

New principles will be studied of design of monochromatic radiation sources for use in г-resonant spectroscopy. Narrow г-lines may be obtained not only by means of Mцssbauer effect but also using the cooled beams of ions (atoms) which nuclei are excited. The cooling, which may be reached both kinetically (by means of ion acceleration to the energies about hundred keV) and by means of optical lasers, leads to the equilization of longitudinal ion (atom) velocities. As a result narrow г-lines are being emitted along the forward and backward directions with regards to the beam. The energies of these г-lines differ from the nuclear transition energy by the sum of corresponding Doppler shifts connected with moving of emitting nuclei in the beam and with nuclear recoils via г-emission. Changing the ion velocity one can regulate smoothly the г-ray energy. The main circle of problems to be solved is the following: the selection of suitable nuclides and the choice of ion source rational design for them, the time shortening of laser cooling of the beam, the possible design of mass-separator if this device would turn out to be necessary. MIREA group, which will work on this problem in collaboration with ITEP and ARSRIEP groups, has a large experience of theoretical and computing work both in physics of atomic and electromagnetic radiation and in the field of task solution, connected with charged particle optics.

Important contributions in project performing will be brought by participant groups from ARSRIEP and ARSRIIM. The first of these groups has to develop the technology of 241Am atoms embedding into the surface layer of г-source plate. Gamma-rays of americium do not interact resonantly with silver nuclei and therefore all resonant effects expected for 109mAg г-rays must be absent for 241Am г-quanta. The presence of resonant and nonresonant г-sources in the same silver sample permits to perform in one experiment the main and control measurements simultaneously. ARSRIEP group has a large experience of work in the field of ionic implantation using the available set-up.

ARSRIIM group will work on the fabricating of silver alloys with Be, Si and Ge and on the study of their physical properties. The goal of this work is the receipt of the samples for preparation of г-sources with better Mössbauer properties than those of silver metal. This group has sufficiently high qualification for performing of such work.

Present project corresponds to the ISTC goals because the specialists are recruited to its performing from ARSRIEP, ARSRIIM and ITEP bearing a relation to the works on the nuclear weapon.

The role of foreign collaborators will consist in the consultations and discussions of experimental methods and of theoretical interpretation of its results.


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