Study of Bohr-Weisskopf effect using low-temperature nuclear orientation

利用低温核取向研究玻尔-韦斯科普夫效应

• 批准号: 13640270
• 负责人: OHYA Susumu
• 金额: $ 2.18万
• 依托单位: NIIGATA UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640270/
• 关键词: Nuclear orientation; Bohr-Weisskopf effect; Hyperfine anomaly; Nuclear Magnetic resonance on oriented nuclei; 低温各偏極; Bohr-Weisskopt効果

The hyperfine anomaly arises from the hyperfine interaction of the finite nuclear volume of nuclear magnetization and the hyperfine field due to Fermi-contact. The difference between the point nuclear magnetic structure and the finite magnetic structure is referred as Bohr-Weisskopf effect [2], which depends on the nuclear structure. If the spin and orbital contributions to the magnetic moment have opposite sign, the large hyperfine anomaly is expected. The study of Bohr-Weisskopf effect by this project was carried on for two years from 2001.Nuclear magnetic resonance on oriented nuclei (NMR-ON) experiments on Sc isotopes (A=44, 44m, 46, 47, 48) have been performed at about 10mK. The samples were prepared by recoil implantation into Fe foils using α- beams at CYRIC cyclotron, Tohoku University. The activated part of the foil was cooled down to about 10mK by a ^3He/^4He dilution refrigerator. All NMR-ON resonances for Sc isotopes (A=44, 44m, 46, 47, 48) were observed. The values of magnetic moments except ^<48>Sc are already known by the atomic beam method. From these results, the values of the hyperfine field of ^<47>ScFe and the magnetic moment of ^<48>Sc were determined as -13, 17(5) T and 3.79(1)μ_<N_3> respectively. Comparing with ^<44m>Sc the effects of Bohr-Weisskopf were determined as; ^<44>ScΔ^<44m>Sc = -1.2(12)%, ^<46>ScΔ^<44m>Sc = 1.3(7)%, ^<47>ScΔ^<44m>Sc = -1.3(7)%. We also made the sample of ^<91g.m>YFe using the mass separator at Kyoto Univ.. The NMR-ON resonances for both isotopes were observed. From the values of the resonance frequencies versus the external magnetic fields, the effects of Bohr-Weisskopf was determined as ^<91>YΔ^<91m>Y = -1(3)%. The ^<91>Y case is that the spin and orbital contributions to the magnetic moment have opposite sign. The theoretical estimation from Fujita and Arima yields that the effect is -4-5%. Detailed analysis are now in progress.

超精细异常是由核磁化强度的有限核体积与费米接触产生的超精细场之间的超精细相互作用产生的。点核磁结构和有限磁结构之间的差异被称为Bohr-Weisskopf效应[2]，它取决于核结构。如果自旋和轨道对磁矩的贡献具有相反的符号，则预计会出现大的超精细异常。该项目对Bohr-Weisskopf效应的研究从2001年开始进行了两年。在10mK左右进行了Sc同位素（A=44、44m、46、47、48）的核磁共振定向核（NMR-ON）实验。样品是在东北大学 CYRIC 回旋加速器中使用 α 束反冲注入铁箔中制备的。通过^3He/^4He稀释制冷机将箔的活化部分冷却至约10mK。观察到 Sc 同位素 (A=44、44m、46、47、48) 的所有 NMR-ON 共振。除^ 48 Sc 之外的磁矩值通过原子束法是已知的。根据这些结果，^ 47 ScFe的超精细磁场和^ 48 Sc的磁矩值分别确定为-13、17(5) T和3.79(1)μ_<N_3>。与 ^<44m>Sc 相比，Bohr-Weisskopf 的效果确定为： ^<44>ScΔ^<44m>Sc=-1.2(12)%，^<46>ScΔ^<44m>Sc=1.3(7)%，^<47>ScΔ^<44m>Sc=-1.3(7)%。我们还使用京都大学的质量分离器制备了 ^<91g.m>YFe 样品。观察到了两种同位素的 NMR-ON 共振。根据共振频率与外部磁场的值，Bohr-Weisskopf 的影响被确定为^<91>YΔ^<91m>Y = -1(3)%。 ^<91>Y情况是自旋和轨道对磁矩的贡献具有相反的符号。 Fujita 和 Arima 的理论估计效果为-4-5%。目前正在进行详细分析。