Emission of γ rays by x-ray electron-nuclear transitions

Olariu, Silviu; Olariu, Agata; Zoran, V.

doi:10.1103/physrevc.56.381

Cited by 7 publications

(9 citation statements)

References 31 publications

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“…The indirect nuclear decay of an isomeric level can be very efficient. This paper is an application of the ideas of Olariu [31][32][33] in a context where it had not been considered previously: a hot plasma where the excitation is ruled by thermal free electrons and LTE atomic levels. The indirect isomer decay process in the plasma is identical in its principle to the two-step ␥-ray transition from isomeric states described by Olariu, where the indirect decay is induced by an intense photon flux at the appropriate energy.…”

Section: B Enhanced Nuclear Decay Of Isomersmentioning

confidence: 97%

Enhanced nuclear level decay in hot dense plasmas

Gosselin

Morel

2004

Phys. Rev. C

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A model of nuclear level decay in a plasma environment is described. Nuclear excitation and decay by photon processes, nuclear excitation by electron capture, and decay by internal conversion are taken into account. The electrons in the plasma are described by a relativistic average atom model for the bound electrons and by a relativistic Thomas-Fermi-Dirac model for the free electrons. Nuclear decay of isomeric level may be enhanced through an intermediate level lying above the isomer. An enhanced nuclear decay rate may occur for temperatures far below the excitation energy of the transition to the intermediate level. In most cases, the enhancement factor may reach several decades. PACS number(s): 23.20.NxIn a hot dense plasma, either laser heated or of astrophysical interest [1-3], nuclei in an isomeric state may have a decay rate different from the laboratory value. The large number of photons and free electrons modifies the environment in which the nucleus naturally decays under laboratory conditions through spontaneous emission and internal conversion (IC). In the plasma, the IC decay rate can be modified by the lower number of available electrons in the partially ionized atom. Moreover, new decay modes also appear such as induced photon emission, free electron scattering, or bound internal conversion.Furthermore, indirect decay channels may be opened, if there exists a nuclear level lying above the isomeric level that may be excited from the isomeric state, and then decay down to the ground state. At first glance, one may expect that this indirect decay mode may become significant when the temperature is around the energy difference between the isomeric level and the upper level. However, if the multipolarities of the excitation transition of the intermediate level and of its decay are more favorable than that of the isomeric transition, one may expect that the indirect decay mode becomes predominant at a lower temperature.This indirect process would be a valuable tool for investigating nuclear excitation in plasmas. In a laser heated plasma, it could provide experimental conditions allowing tests of the nuclear transition rate model as well as the ability to reach significantly populated higher energy nuclear levels. These studies are critical for nuclear energy storage on an isomeric level and its release mechanism.If these hot plasmas are maintained for a long enough duration at the thermodynamic equilibrium at a temperature T, the different nuclear level populations reach an equilibrium given by the Boltzmann law where the ratio between any two populations N i and N f is easily calculated:where k B is the Boltzmann constant, E i and E f the excitation energies, and J i and J f the spins of lower initial state i and the upper final state f.One remarkable feature of the thermodynamic equilibrium is that the populations can be calculated without any explicit knowledge of the detailed excitation and decay processes. However, in the case of plasmas where only the nuclear populations are not at equilibrium, i...

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Section: B Enhanced Nuclear Decay Of Isomersmentioning

confidence: 97%

Enhanced nuclear level decay in hot dense plasmas

Gosselin

Morel

2004

Phys. Rev. C

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“…The power levels required by the photon approach to the problem of induced gamma emission studied in this work are comparable to the power levels required by the XENDT approach described in [1]. The choice of isomeric nuclei was restricted in this work by the upconversion condition E γ > 2E ni , and it was restricted to intermediate states of known energy and known spin and parity.…”

Section: Discussionmentioning

confidence: 64%

“…In a recent work it has been shown that the lifetime of isomeric nuclear states can be influenced by X-ray electron-nuclear double transitions (XENDT's), which are processes in which a transition effected by an inner atomic electron takes place simultaneously with a nuclear electromagnetic transition [1]. The rate of deexcitation of isomeric nuclei induced by XENDT's was calculated for the case when the holes in the atomic shells are produced by incident ionizing electrons and it was found that the induced nuclear deexcitation rate becomes comparable to the natural decay rate for ionizing electron fluxes of the order of 10 14 W cm −2 .…”

Section: Introductionmentioning

confidence: 99%

Induced emission ofγradiation from isomeric nuclei

Olariu

1998

Phys. Rev. C

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We study the possibility to influence the lifetime of nuclear isomeric states with the aid of incident fluxes of photons. We assume that a nucleus initially in an isomeric state |i first absorbs an incident photon of energy E ni to reach a higher intermediate state |n , then the state |n decays to a lower state |l . In favorable cases the two-step induced emission rates become equal to the natural isomeric decay rates for incident power densities of the order of 10 10 W cm −2 .

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“…[3] Electron activated γ-ray sources could also be of interest for Mössbauer experiments in cases where the half-life of conventional radioactive sources is too short to be practical. For example, among the cases listed in Table I Although the cross sections of X-ray electron-nuclear double transitions discussed in [1] and the cross sections for the direct excitation of nuclear transitions are not very large, these processes appear to be of real interest for the development of electron-activated sources of γ-ray photons of narrowly defined energy.…”

mentioning

confidence: 99%

“…It has been shown [1] that if a beam of incident electrons produces holes in the atomic shell of certain atomic species, this atomic excitation can be transferred to the nucleus. The nucleus thus raised in an excited state then decays by the emission of Mössbauer gammaray photons.…”

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confidence: 99%