Inhibition of positronium formation and its quenching reactions in binary solid solutions and mixtures of metal tris-2,2,6,6-tetramethyl-3,5-heptanedionate (dpm) complexes

Porto, A.O.; Magalhães, W.F.; Machado, J.C.

doi:10.1016/s0009-2614(97)00013-4

Cited by 12 publications

(6 citation statements)

References 17 publications

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“…These values were taken as the maximum of the probability density function, but it should be pointed out that the lifetime spectra is in fact a distribution, as shown in the figure. These half-lives are in excellent agreement with those published in the literature, 9 which are, respectively, 0.12 ns, 0.35 ns and 1.62 ns. Another important quantity for the positron annihilation lifetime spectroscopy is the area under the curves.…”

Section: Resultssupporting

confidence: 90%

“…The area contribution for the species p-Ps, free positron and o-Ps are, respectively, 13%, 32%, 55%, whereas the literature values 9 correspond to 19.9%, 24.1% and 56.0%. The halflives and areas in reference 9 were obtained in an approximate way, by fitting the logarithm of c(t) to a set of three linear equations. From this consideration, it is believed that the present results are more reliable, since it handles the data directly, giving the distribution of halflives and its respective areas.…”

Section: Resultsmentioning

confidence: 99%

“…Instead of dealing with simulated data, the present work will handle laboratory data for the Al(dpm) 3 system. 9 The singular value decomposition method will be used, which has been proved to be very useful while inverting data in simulated data, both in positronium annihilation 8 and in thermodynamics 10 . Effects not considered before, the experimental noise in the data and the choice of zero time channel, will be also discussed.…”

Section: Introductionmentioning

confidence: 99%

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Probability density function from experimental positron annihilation lifetime spectra

Viterbo

Sebastião

Monteiro

et al. 2005

J. Braz. Chem. Soc.

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A inversão de espectro experimental de vida média de aniquilação de pósitron foi realizada com o intuito de se obter a função densidade de probabilidade. A resolução do aparelho, juntamente com ruído experimental foram considerados na resolução deste problema mal-colocado. O método de decomposição em valores singulares, movendo-se o limite entre os subespaços foi a formulação teórica empregada para calcular a função densidade de probabilidade. O complexo Al(dpm) 3 , sistema considerado no presente trabalho, apresenta três picos no espectro invertido, indicando a presença de para-positrônio, pósitron livre e orto-positrônio. As posições previstas foram 0,1042 ns, 0,3542 ns e 1,3958 ns, respectivamente. Como o presente método fornece a distribuição das espécies, é possível também prever a relativa importância de cada espécie no espectro. As áreas obtidas foram: 13%, 32%, 55%. Ambos resultados, posição dos picos e áreas relativas, bem como a distribuição dos tempos de meia-vida, podem fornecer informações importantes para experimentalistas.Inversion of experimental positron annihilation lifetime spectra was carried out to obtain the probability density function. Apparatus resolution together with experimental noise was taken into consideration while solving this ill posed problem. The singular value decomposition approach, moving the boundary between the subspaces was the theoretical formulation to calculate the probability density function. For the system considered, the Al(dpm) 3 complex, three peaks will be presented in the inverted spectra, indicating the presence of the para-Positronium, the free positron and the orthoPositronium. The predicted positions were, 0.1042 ns, 0.3542 ns and 1.3958 ns, respectively. Since the present approach gives the distribution of the species, it was possible also to predict the relative importance of each species in the spectra. The areas found correspond to: 13%, 32%, 55%. Both these results, position of the peaks and the areas, together with the half-life distribution can provide important information for experimentalists.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Probability density function from experimental positron annihilation lifetime spectra

Viterbo

Sebastião

Monteiro

et al. 2005

J. Braz. Chem. Soc.

Self Cite

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“…Spin conversion of o-Ps is a process that o-Ps exchanges its electron with another electron from the surface of the pore, which has an opposite spin, and then converts into p-Ps and finally annihilates just as p-Ps does. However, both of the two above processes will lead to the shortening of o-Ps lifetime, and in case of the chemical quenching effect, inhibition of the positronium formation happens most of the time, which also causes decrease in o-Ps intensity [16][17][18] . Therefore, the positron lifetime measurement itself cannot clarify between chemical quenching and spin conversion process.…”

Section: Resultsmentioning

confidence: 99%

“…As for the decrease of its intensity I 4 , this is due to the inhibition of the positronium formation caused by Cr 2 O 3 . Most often the inhibition of positronium formation occurs accompanying the chemical quenching effect [16][17][18] . According to the spur reaction model [19] , formation probability of positronium depends on the number of excess electrons created by the incident positrons at the end of spur.…”

Section: Resultsmentioning

confidence: 99%

Chemical quenching and inhibition of positronium in Cr2O3/Al2O3 catalysts

Huang

Dai

Zhang

et al. 2011

Wuhan Univ. J. Nat. Sci.

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The pore structure of Cr 2 O 3 /Al 2 O 3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening (CDB) measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ 4 and τ 3 are attributed to ortho-positronium (o-Ps) annihilation in large pores and microvoids, respectively. With increasing Cr 2 O 3 content, both τ 4 and its intensity I 4 show sharp decrease, while τ 3 and its intensity I 3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr 2 O 3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium (p-Ps) intensity also decreases with increasing Cr 2 O 3 content. This indicates that the change of o-Ps lifetime τ 4 is due to

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Positron annihilation studies in binary solid solutions and mechanical mixtures of lanthanide dipivaloylmethanate complexes

et al. 2015

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Inhibition of positronium formation and its quenching reactions in binary solid solutions and mixtures of metal tris-2,2,6,6-tetramethyl-3,5-heptanedionate (dpm) complexes

Cited by 12 publications

References 17 publications

Probability density function from experimental positron annihilation lifetime spectra

Probability density function from experimental positron annihilation lifetime spectra

Chemical quenching and inhibition of positronium in Cr2O3/Al2O3 catalysts

Positron annihilation studies in binary solid solutions and mechanical mixtures of lanthanide dipivaloylmethanate complexes

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