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Development of a method for positron annihilation lifetime measurement in thin polyethylene films using a Na-22 source

Na-22線源を用いたポリエチレン薄膜の陽電子消滅寿命測定法の開発

山脇 正人*; 上杉 直也*; 岡 壽崇  ; 長澤 尚胤*; 安藤 太一*; O'Rourke, B. E.*; 小林 慶規*

Yamawaki, Masato*; Uesugi, Naoya*; Oka, Toshitaka; Nagasawa, Naotsugu*; Ando, Hirokazu*; O'Rourke, B. E.*; Kobayashi, Yoshinori*

15$$mu$$mから2000$$mu$$mの厚みを持つポリエチレンの陽電子消滅寿命測定を行った。試料厚がNa-22からの陽電子の飛程よりも薄い場合、陽電子はポリエチレン試料を突き抜けてしまい、精確な陽電子寿命測定が行えない。そこで、試料の裏にアニールしたSUS基板を配置し、SUS基板中で消滅した陽電子を計測することで、薄膜ポリエチレン試料中での陽電子消滅を分析する手法を開発した。この手法を延伸ポリエチレン試料に適用したところ、延伸に伴う自由体積空孔のサイズの減少と、自由体積空孔内で消滅する陽電子の割合の増加が測定できた。

Positron annihilation lifetime measurements were performed on polyethylene films with thickness of 15$$mu$$m - 2000$$mu$$m using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

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