http://stdjns.scienceandtechnology.com.vn/index.php/stdjns <p><span class="" lang="en"><span title="Tạp chí đã được phát hành tại các thư viện của các đơn vị thành viên của ĐHQG-HCM, các Sở Khoa học Công nghệ của các tỉnh thành trên cả nước và được Hội đồng học hàm Giáo sư Nhà nước đánh giá cao."><strong>VNUHCM Journal of</strong>&nbsp;<strong>Natural Science</strong> <strong>(STDJNS)</strong> (<strong>2588-106X</strong>) is the official journal of Viet Nam National University Ho Chi Minh City, Viet Nam, published by Viet Nam National University Ho Chi Minh City, Viet Nam. STDNS has been developed and separated from section of <strong>Nature Sciences</strong> of <strong>Science &amp; Technology Development Journal</strong> (<strong>STDJ</strong>) (<strong>1859-0128</strong>). From 2017, this section became a dependent journal with title <strong>VNUHCM</strong>&nbsp;<strong>Journal of</strong>&nbsp;<strong>Natural Sciences.&nbsp;</strong></span></span></p> <p><span class="" lang="en"><span title="Tạp chí đã được phát hành tại các thư viện của các đơn vị thành viên của ĐHQG-HCM, các Sở Khoa học Công nghệ của các tỉnh thành trên cả nước và được Hội đồng học hàm Giáo sư Nhà nước đánh giá cao."><strong>VNUHCM Journal of</strong>&nbsp;<strong>Natural Sciences</strong></span></span> is a multiple discipline scientific journal covering from all fields of natural sciences including&nbsp; mathematics and computer science, chemistry, physics and engineering physics, biology and biotechnology, environment, geology, information technology, electronics and telecommunications, materials science and technology.</p> <p><span class="" lang="en"><span title="• Khoa học Trái đất và Môi trường"><span id="result_box" class="" lang="en">&nbsp;</span></span></span></p> Viet Nam National University Ho Chi Minh City en-US VNUHCM Journal of Natural Sciences 2588-106X <p>Copyright The Author(s) 2018. This article is published with open access by Vietnam National University, Ho Chi Minh city, Vietnam. This article is distributed under the terms of the&nbsp;<a href="https://creativecommons.org/licenses/by/4.0/" target="_blank" rel="noopener">Creative Commons Attribution License (CC-BY 4.0)</a> which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.&nbsp;</p> http://stdjns.scienceandtechnology.com.vn/index.php/stdjns/article/view/1438 <p>This study evaluates the influence of gas environments and adsorbed water on the pick-off annihilation process of ortho-positronium (o-Ps) lifetime in zeolite Silicalite-1 and ZSM-5. The results indicate that short-lifetime components (<em>τ₁, τ₂, τ₃</em>) are minimally affected, whereas long-lifetime components (<em>τ₄, τ₅</em>) and annihilation intensity (<em>I₄, I₅</em>) vary significantly depending on the gas environment. Vacuum conditions are optimal for analyzing pore structures, while air significantly reduces o-Ps lifetime due to quenching by O₂. Inert gases such as Ar and N₂ have a lesser impact and can serve as alternatives when vacuum conditions are not available. The effect of adsorbed water is categorized into three drying temperature stages, primarily influencing the <em>τ₅</em> and <em>I₅</em> components. Below 200°C, retained water decreases o-Ps lifetime. Between 200°C and 250°C, rapid water desorption from the pores leads to a notable increase in <em>τ₅</em> and <em>I₅</em>. Beyond 250°C, water is nearly eliminated, and these parameters reach a saturation state. Additionally, Silicalite-1 exhibits higher o-Ps lifetime and annihilation intensity than ZSM-5, reflecting differences in pore size and density between the two materials. These findings highlight the crucial role of environmental conditions in zeolite structure analysis. Vacuum remains the optimal choice for ensuring measurement accuracy, while the influence of adsorbed water must be controlled to prevent measurement deviations.</p> Luu Anh Tuyen Pham Thi Hue Nguyen Thi Ngoc Hue Dinh Thi Hai Ha ##submission.copyrightStatement## http://creativecommons.org/licenses/by/4.0 2025-12-07 2025-12-07 9 4 3466 3472 10.32508/stdjns.v9i4.1438 title description none g