Nuclear resonance fluorescence

The NRF explosive detection technology is much more immature than are the NRA, PFNA, and NQR approaches. Whereas PFNA and NQR have prototype systems and are examining engineering trade-offs for specific applications, NRF is at the stage where basic physics experiments are being performed in science laboratories. 

The first term in Equality (4.1) describes the change of y-quantum energy due 

The perfect resonance, which corresponds to total overlap of natural im-perturbed emission and absorption lines at an energy Eq is thus disturbed by the recoil caused by the emission line displaced from the resonance energy Eq by an amount Er. For a y-ray with energy of lOkeV, Pr is in the millielec- 

Er-Eo/21V1 Nucleus of mass M and 7 Mean energy E at rest 

Iron volt (meV) range. Although the recoil energy is of the order of 10 to 10 eV yet it is sufficient to destroy the resonance in isolated atoms. 

The second perturbation, namely the thermal motion of emitter nuclei, produce a Doppler-effect broadening of the emission line and causes it to extend in part beyond the energy Eq even though centered at Ey (= Eq—Er). The y-ray energy will be broadened into a distribution by the Doppler-effect energy, E = MvV, which is proportional to the initial velocity, Vx. from the random thermal motion of the atom, and v from the recoil of the nucleus. 

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Resonant y-ray absorption is directly connected with nuclear resonance fluorescence. This is the re-emission of a (second) y-ray from the excited state of the absorber nucleus after resonance absorption. The transition back to the ground state occurs with the same mean lifetime t by the emission of a y-ray in an arbitrary direction, or by energy transfer from the nucleus to the K-shell via internal conversion and the ejection of conversion electrons (see footnote 1). Nuclear resonance fluorescence was the basis for the experiments that finally led to R. L. Mossbauer s discovery of nuclear y-resonance in ir ([1-3] in Chap. 1) and is the basis of Mossbauer experiments with synchrotron radiation which can be used instead of y-radiation from classical sources (see Chap. 9). 

Ti ossbauer spectroscopy is the term now used to describe a new ana-lytical technique which has developed using y-ray nuclear resonance fluorescence or the Mossbauer effect. For most of the time since Rudolf Mossbauer s discovery in 1958 it was the physicist who utilized this new tool. Starting approximately in 1962 some chemists realized the potential of this new technique. Since then they have applied Mossbauer spectroscopy to the study of chemical bonding, crystal structure, electron density, ionic states, and magnetic properties as well as other properties. It is now considered a complimentary tool to other accepted spectroscopic techniques such as NMR, NQR, and ESR. 

X 10 for up to 202 mms for Re. They are all very small when compared with the tremendous velocities ( 7 x 10 mm s ) used by Moon in 1950 to detect nuclear resonance fluorescence without recoilless emission, and show dramatically that the Mossbauer technique eUminates both recoil and thermal broadening. The Heisenberg relation means that an excited state with a shorter half-life has a greater uncertainty in the y-transition energy and hence a broader resonance line. 

Rudolph Mossbauer discovered the phenomenon of recoil-free nuclear resonance fluorescence in 1957-58 and the first indications of hyperfine interactions in a chemical compound were obtained by Kistner and Sunyar in 1960. From these beginnings the technique of Mbssbauer spectroscopy rapidly emerged and the astonishing versatility of this new technique soon led to its extensive application to a wide variety of chemical and solid-state problems. This book reviews the results obtained by MSssbauer spectroscopy during the past ten years in the belief that this will provide a firm basis for the continued development and application of the technique to new problems in the future. 

Data from inelastic scattering of different particles and data obtained by NRF Nuclear Resonance Fluorescence method can be found at the end of the data-hne or between these two groups of transfer reaction data. In some cases we preserve notations used in papers. Wigner units IW.u.(Ml) = 1.79/i and IW.u.(El) = 1.28e fm were used in several cases. In Table 2 different reactions are given approximately in the same order as they appear in data-hnes of Vol. I/19B2. 

This state was strongly excited in NRF (Nuclear Resonance Fluorescence Method) experiment [03Fr02]. 

Ratio r /r=229(25) meV for this level was obtained by nuclear resonance fluorescence (NRF) method in [90He03],... 

Fig. 4.1. (a) The effect of recoil of the nucleus on the energy of y-rays and (b) schematic of the phenomenon of nuclear resonance fluorescence... 

Principle and Experimental Conditions of Recoil-free Nuclear Resonance Fluorescence... 

Figure 1. Schematic representation of nuclear resonance absorption of y-rays (MOssbauer effect) and nuclear resonance fluorescence...

After resonance absorption, the excited nucleus will decay by either emitting isotropically a y-quantum (as in the primary y-ray emission of Figure I) or a conversion electron e , preferentially from the K-shell. This phenomenon is termed nuclear resonance fluorescence and may be used in Mossbauer scattering experiments (surface investigations). 

The photons emitted by the de-excitation of nuclear levels that are populated in the course of radioactive decays can be resonantly scattered. Nuclear resonance fluorescence experiments can give information on the velocity distribution of recoil atoms and the chemical modifications following transmutations and on the slowing-down process of hot atoms. This technique can be applied in gaseous, liquid, and solid systems, giving an advantage over Mossbauer spectroscopy. Nuclear resonance fluorescence has been reviewed, with particular reference to the following systems ... 

Nuclear resonance fluorescence scattering provides evidence for Coulomb fragmentation of P Xe molecules following decay in II. The chemical behaviour of carrier-free radio-iodine, produced by beta decay, has been studied. ... 

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