Recoil/-energy

In collisions where =M2 at 0 = 180° tlie incident particle is at rest after the collision, with all the energy transferred to the target atom. For 2.0 MeV helium ions colliding with silicon the recoil energy 2 is 0.88 MeV and from palladium is 0.28 MeV. 

Henrich and WolP have studied the formation of Mo(CO)5 by catching Mo and Mo recoils in Cr(CO)g. The Molybdenum isotopes were produced in several different reactions, so that the recoil energy varied over a wide range. It was found that the yields of Mo(CO)g with the two isotopes differed from each other, but varied only slightly as a function of initial recoil energy. These authors were also able to show that the isotope effect of about 8% is nearly insensitive to radiation received by the sample (and catcher) during the bombardment. They argued that there remains only one possible cause of this isotope effect, that is, differences in the de-excitation schemes of the product nuclei. 

Bi decays by emission of n, = 1.16meV with no y-transition. Thus, the only influences are those of mechanical recoil from the fj emission (maximum recoil energy 3.5 eV) and the ionization due to collective electron excitation (shakeoff). 

Chemical effects of nuclear decay have been studied in Germanium through the use of Ge and Ge. Ge decays to Ga with a 275 day half-life by 100% electron capture with no y quanta emitted. Ge is a P emitter which decays to As with a 11.3 h half-life, by three jS transitions having maximum energies of 710 keV (23%), 1379 keV (35%) and 2196 keV (42%). From this are calculated maximum recoil energies of 1.7 eV, 4.5 eV and 10.2 eV, respectively. 

When nuclear decay is a pure )S-emission or by p with low energy, unconverted gamma-transition recoil energy is unimportant, and electronic... 

When a single y-ray of known energy is emitted, the recoil energy given to the atom is calculated from the conservation of energy and momentum. The result is... 

This recoil energy is so large compared to chemical energies that there seems to be no question about the atom s breaking loose from its bonds and travelling a considerable distance before coming to rest. The effect observed by Szilard and Chalmers is thus readily explained. 

Attempts have been made to calculate the recoil energy spectrum using an assumed statistical distribution of y-energies and direction. Notably, Hsiung et al. (39) have done this calculation for C1 produced by CCI4 (n,y). While the results of the calculation were in reasonble agreement with experimental data, the complexity of the necessary assumptions makes the agreement seem perhaps fortuitous. 

Experimental determination of the recoil energy spectrum from neutron capture has not been reported. 

It is evident that, since primarily only low-energy transitions are converted, the ultimate recoil energy will not be much affected whether a given transition is converted or not. The effect is felt in another way, however. 

The process of j3-decay in some respects offers simpler radiochemical consequences than do neutron capture and other reactions, because (a) the nuclear recoil energy is very low and (b) the decay schemes, and thus the probability of Auger cascades, are generally well known. Despite this, no clear mechanisms have been worked out. 

Recognizing that the maximum recoil energy is about 0.04 eV, we see that the molecule must be preserved intact in most instances, to dissociate subsequently. 

What are the relative roles of kinetic recoil energy and of electronic effects in leading to the observed products ... 

The Mossbauer effect can only be detected in the solid state because the absorption and emission events must occur without energy losses due to recoil effects. The fraction of the absorption and emission events without exchange of recoil energy is called the recoilless fraction, f. It depends on temperature and on the energy of the lattice vibrations /is high for a rigid lattice, but low for surface atoms. 

Recoil Energy Loss in Free Atoms and Thermal Broadening of Transition Lines... 

Suppose the nucleus was at rest before the decay, it takes up the recoil energy... 

Since r is very small compared to Eq, it is reasonable to assume that Ey Eq, so that we may use the following elementary formula for the recoil energy of a nucleus in an isolated atom or molecule ... 

Hence, nuclear resonance absorption of y-photons (the Mbssbauer effect) is not possible between free atoms (at rest) because of the energy loss by recoil. The deficiency in y-energy is two times the recoil energy, 2Er, which in the case of Fe is about 10 times larger than the natural line width F of the nuclear levels involved (Fig. 2.4). 

The arguments seen in section 2.3 suggest that resonant y-absorption should decrease at very low temperatures because the Doppler broadening of the y-lines decreases and may even drop below the value of the recoil energy. In his experiments with solid sources and absorbers, however, R.L. Mossbauer ([1] in Chap. 1) observed on the... 

Total internal conversion coefficient Recoil energy (in 10 eV)... 

The high atomic mass yields small recoil energies and thus a large recoU-free fraction even at room temperature (/300 0.95 for Ta metal [175]) this allows measurements of the resonance effect to be made over a wide temperature range up to about 2,300 K. 

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