超極化3He稀有氣體之核磁共振研究
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2006
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我們建構了一套雷射光激發系統。此系統利用雷射光激發法（optical pumping）與原子的自旋交換法（spin exchange）製造能加強核磁共振影像訊號之超極化氣體。我們使用含有硼矽酸鹽的Pyrex玻璃自製填裝超極化氣體之極化腔（Cell）。我們自製的極化腔具有耐高壓、可重複填充使用、價格低廉、可大量製造之優點。由其他學者的研究可知，極化氣體與極化腔器壁的碰撞、極化腔內壁是所含磁性物質多寡造成自旋鬆弛（spin relaxation）的主要因素。因此在清洗極化腔內壁時，我們特別加入鹽酸的步驟以去除極化腔內壁的鐵離子。填充預極化氣體之前，必須先用機械幫浦將填充氣體管路與極化腔抽氣至10-3 torr以下，之後在充滿氮氣的手套箱內填入約300 mg光激發所要用到的銣金屬原子。然後再回到預極化氣體填充系統，填充氮氣與3He混合氣體。目前我們只做1大氣壓內的混合預極化氣體，並且利用已知特性的極化腔做比較。我們自製極化腔所產生的極化氣體在關掉雷射光僅依靠外加磁場保存的情形下可以維持10分鐘。
We have fabricated a set of pre- polarized gas filling system. With the optical pumping method and the spin exchange method, we can get hyperpolarized 3He gas. The hyperpolarized gas can enhance the intensity of NMR signals. We use borosilicate (Pyrex) glass to make up our hand- made cells. Our hand- made cells have the advantages of standing for high- pressure, refillable using, inexpensive, and large number output. By other scholars’ research, we can know there are two important factors to decrease the polarization of hyperpolarized gas: one is the wall relaxation, and the other is the magnetic impurities content of Pyrex glass. So we added the hydrochloric acid (HCL）cleaning into the cleaning steps in order to eliminate the iron ions (Fe+2 and Fe+3). The hade-made cells have to be prepared under high vacuum (below 10-3 torr) using oil- free mechanical pump, filled of Rubidium metals (about 300 mg) under nitrogen in glove box, and mixed gas (contained of N2 and 3He) with pre-polarized gas filling system. Up to now, we just study the mixed gas pressure smaller than 1 atm, and compare the physical properties of our hand- made cells with the known cells. Our hand-made hyperpolarized 3He gas can maintain about 10 minutes under 30 Gauss without laser light.
We have fabricated a set of pre- polarized gas filling system. With the optical pumping method and the spin exchange method, we can get hyperpolarized 3He gas. The hyperpolarized gas can enhance the intensity of NMR signals. We use borosilicate (Pyrex) glass to make up our hand- made cells. Our hand- made cells have the advantages of standing for high- pressure, refillable using, inexpensive, and large number output. By other scholars’ research, we can know there are two important factors to decrease the polarization of hyperpolarized gas: one is the wall relaxation, and the other is the magnetic impurities content of Pyrex glass. So we added the hydrochloric acid (HCL）cleaning into the cleaning steps in order to eliminate the iron ions (Fe+2 and Fe+3). The hade-made cells have to be prepared under high vacuum (below 10-3 torr) using oil- free mechanical pump, filled of Rubidium metals (about 300 mg) under nitrogen in glove box, and mixed gas (contained of N2 and 3He) with pre-polarized gas filling system. Up to now, we just study the mixed gas pressure smaller than 1 atm, and compare the physical properties of our hand- made cells with the known cells. Our hand-made hyperpolarized 3He gas can maintain about 10 minutes under 30 Gauss without laser light.
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核磁共振, 光激發, 極化氣體, 氦3, NMR, optical pumping, polarized gas, 3He