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Positrons and Positroniu m in Grainy and Porous Solids

100%

Kajcsos Z., Liszkay L., Duplâtre G., Varga L., Lázár K., Pál-Borbély G., Beyer H., Lohonyai L., Caullet P., Patarin J.

Acta Physica Polonica A

2001

vol. 99

issue 3-4

399-406

Systematic investigations have been performed using positron annihilation techniques on micrograins of crystalline powders (e.g., MgO, Al_2O_3, SiO_2) and on various zeolites (e.g., silicalite 1, Na-X, Na-Y, ZSM-5, mordenite) aiming at a better under standing of the formation and decay of the long-lived ortho-positronium states. The techniques were lifetime spectroscopy, Doppler-effect measurements and the recording of the full energy distribution of the annihilation radiation. The influences of heat treatment, sample evacuation and presence of gases were investigated. Lifetimes over 130 ns and o-Ps fractions of about 30% were found. A strong correlation of positron annihilation technique data with a water content of the samples was evidenced. Possible pictures of the formation and decay of ortho-positronium in porous media are discussed.

Positron and Positronium Trapping in Heat Treated Zeolites (Ceramics), the Effect of Swift Heavy Ion Irradiation

81%

Major P., Kajcsos Z., Liszkay L., Zalán P., Kosanović C., Bosnar S., Subotić B., Lázár K., Skuratov V., Havancsák K., Gordo P., Ferreira Marques M.

A systematic study of zeolite precursor gels, zeolites, and products of their recrystallization to ceramics was carried out in presence of various alkali ions. The investigation of radiation damage induced by high-energy ion beam irradiation with swift heavy ions (Bi ions at 670 MeV energy with 4×10^{12} ion/cm^2 fluence) was also included. The shortening of lifetimes found after irradiation in ceramics might probably be ascribed to interactions of o-Ps with free radicals and other quenching agents created through the ion irradiation. These lifetime-shortening interactions probably partly hide the o-Ps trapping in free volume sites.

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies

72%

Kajcsos Z., Liszkay L., Duplâtre G., Varga L., Lohonyai L., Pászti F., Szilágyi E., Lázár K., Kótai E., Pál-Borbély G., Beyer H., Caullet P., Patarin J., Azenha M., Gordo P., Lopes Gil C., de Lima A., Ferreira Marques M.

Acta Physica Polonica A

2005

vol. 107

issue 5

729-737

Positron annihilation techniques are used for the structural investigation of solids but the interpretation of results in grainy and porous media is still unclear. A unique picture can be obtained assuming that the dominant process is Ps trapping in competing "extended free volume" sites. In samples with a large amount of free volumes near-saturation Ps trapping will rule the lifetime pattern, and very long lifetimes of over 100 ns might arise from o-Ps trapped in mesopores. It is shown that lifetime parameters must be corrected for the 3γ/2γ counting efficiency ratio. The results demonstrate the high sensitivity of Ps to mesopores in zeolites but also that Ps-trapping poses limitations on the applicability of lifetime to structural investigation in porous systems. The evolution of the lifetime spectra upon changes in the sample and measuring conditions should be considered in a complex way, observing not only changes in some selected components but in the whole lifetime pattern simultaneously.

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3 Acta Physica Polonica A

1 2008

1 2005

1 2001

3 Kajcsos Z.

3 Liszkay L.

3 Lázár K.

2 Beyer H.

2 Caullet P.

2 Duplâtre G.

2 Ferreira Marques M.

2 Gordo P.

2 Lohonyai L.

2 Patarin J.

2 Pál-Borbély G.

2 Varga L.

1 Azenha M.

1 Bosnar S.

1 Havancsák K.

1 Kosanović C.

1 Kótai E.

1 Lopes Gil C.

1 Major P.

1 Pászti F.

1 Skuratov V.

1 Subotić B.

1 Szilágyi E.

1 Zalán P.

1 de Lima A.

Search results

Positrons and Positroniu m in Grainy and Porous Solids

Positron and Positronium Trapping in Heat Treated Zeolites (Ceramics), the Effect of Swift Heavy Ion Irradiation

Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies