-
富集钕-150同位素在核工业、科学研究等领域有着重要应用。基于高效高选择性多步电离路径，原子蒸气激光同位素分离法能够实现钕同位素分离，但现用路径第二步跃迁的同位素位移几乎为零，导致产品中Nd-150丰度偏低。本文基于密度矩阵理论建立了通用的三步电离路径选择性光电离模型，模型中综合考虑了同位素位移、超精细结构等原子参数和频率、功率、线宽、偏振等激光参数，可在磁子能级级别计算原子与激光的相互作用过程。基于上述模型，通过与文献数据对比获得了现用路径分支比的最优拟合值，评估了现用路径在不同线宽下的Nd-150丰度水平；在仅改变第二步跃迁的前提下构造假定电离路径，开展所有钕同位素的电离率计算，评估不同同位素位移、超精细结构下的Nd-150丰度，指导后续原子光谱实验。数值计算发现J3=6,IS23,148 ≥ 300 MHz时，在b12≤ 0.5 GHz,b23 ≤ 1.0 GHz,平行线偏振的典型激光参数下可实现与电磁法相当的Nd-150丰度（>95%）。在此基础上压窄激光线宽，能够在保持电离率的同时获得超过电磁法的Nd-150产品。后续原子光谱实验应着重寻找同位素位移IS23,148≥ 300 MHz、第二激发态角动量J3=6的第二步跃迁，第二步跃迁的约化电偶极矩达到现用路径的30%即可满足丰度要求。The enriched neodymium-150 (Nd-150) isotope plays a critical role in nuclear industry and basic scientific research. The Nd isotope separation could be conducted by Atomic Vapor Laser Isotope Separation (AVLIS), where the target isotope is selectively ionized through the λ1 = 596 nm → λ2 = 579 nm → λ3 = 640 nm photoionization scheme, and non-target isotopes remain neutral due to the frequency-detuned excitation; subsequently an external electric field is applied to extract the ions in the laser-produced plasma. The Nd-150 abundance in the product cannot meet the requirement of the application, attributed to the nearly negligible isotope shift of the λ2 = 579 nm transition, which causes the excess ionization of non-target isotopes. A new high-selectivity photoionization scheme is desirable to address this limitation, and its expected parameter values could be determined through numerical calculations prior to the time-consuming atomic spectroscopy experiment. In this study, a three-step selective photoionization model is established based on the density matrix theory, with the consideration of the hyperfine structures and magnetic sublevels. This model allows flexible adjustments of atomic parameters (e.g., branching ratios, isotope shifts, hyperfine constants) and laser parameters (e.g., frequency, power density, bandwidth, polarization), while the ionization probabilities of magnetic sublevel transitions could be quantitatively predicted. For the existing scheme, the branching ratios are determined by the comparison between literature data and numerical results, and the Nd-150 abundances under different laser bandwidths are evaluated. Further, we numerically explore an alternative scheme under the assumption that the first transition remains unchanged and the second transition has a more significant isotope shift and a less branching ratio, and the Nd-150 abundances under different combinations of isotope shifts, hyperfine structures, and laser bandwidths are evaluated with all the natural Nd isotopes included. From the numerical results, a scheme with the angular momentum of the second excited state J3 = 6, the isotope shift between Nd-148 and Nd-150 IS23,148 ≥ 300 MHz, and a lower reduced dipole matrix element of the second transition reaching approximately 30% of that of λ2 = 579 nm, could produce the high-abundance Nd-150 (>95%, equivalent to that of the electromagnetic separation method) under the bandwidth b12 ≤ 0.5 GHz, b23 ≤ 1.0 GHz, and parallel linear-polarized lasers. Higher abundance, superior to the electromagnetic separation method, could be achieved with the narrower-bandwidth lasers. The expected high-abundance Nd-150 could be attributed to the combined effects of multi-factors: the larger isotope shift between Nd-150 and Nd-148 compared with that between other isotope pairs, the unsignificant hyperfine splitting of odd isotopes, as well as the match between narrow-bandwidth lasers and Nd I spectroscopic parameters. These parameter values could serve as helpful benchmarks for experimental parameter selection in the forthcoming high-precision spectroscopy experiments.
-
Keywords:
- Nd-150 /
- selective photoionization /
- isotope shift /
- hyperfine structure
-
[1] Akhmedzhanov R A, Gushchin L A, Nizov N A, Nizov V A, Sobgayda D A, Zelensky I V 2024 JETP Letters 119 834
[2] Liang P J, Liu X, Li P Y, Zhou Z Q, Li C F, Guo G C 2020 J. Opt. Soc. Am. B 37 1653
[3] Broderick K, Lusk R, Hinderer J, Griswold J, Boll R, Garland M, Heilbronn L, Mirzadeh S 2019 Appl. Radiat. Isot. 144 54
[4] Hu F, Cutler C S, Hoffman T, Sieckman G, Volkert W A, Jurisson S S 2002 Nucl. Med. Biol. 29 423
[5] Committee A 2015Standard Practice for Analysis of Spent Nuclear Fuel to Determine Selected Isotopes and Estimate Fuel Burnup
[6] Suryanarayana M V 2022 Sci. Rep. 12 11471
[7] Barabash A S, Belli P, Bernabei R, Boiko R S, Cappella F, Caracciolo V, Cerulli R, Danevich F A, Fang D L, Ferella F, Incicchitti A, Kobychev V V, Konovalov S I, Laubenstein M, Leoncini A, Merlo V, Nisi S, Niţescu O, Poda D V, Polischuk O G, Shcherbakov I B K, Šimkovic F, Timonina A, Tinkova V S, Tretyak V I, Umatov V I 2025 Eur. Phys. J. C 85 174
[8] https://www.isotopes.gov/products/neodymium
[9] Letokhov V, Ryabov E (Trigg G L ed) 2004Encyclopedia of Applied Physics (New York: Wiley) pp1015-1028
[10] Babichev A P, Grigoriev I S, Grigoriev A I, Dorovskii A P, D'Yachkov A B, Kovalevich S K, Kochetov V A, Kuznetsov V A, Labozin V P, Matrakhov A V, Mironov S M, Nikulin S A, Pesnya A V, Timofeev N I, Firsov V A, Tsvetkov G O, Shatalova G G 2005 Quantum Electron. 35 879
[11] Grigoriev I, Diachkov A, Kovalevich S, Labosin V, Mironov S, Nikulin S, Pesnia A, Firsov V, Shatalova G, Tsvetkov G 2003 Proc. SPIE Int. Soc. Opt. Eng. 5121 406
[12] D'Yachkov A B, Kovalevich S K, Labozin V P, Mironov S M, Panchenko V Y, Firsov V A, Tsvetkov G O, Shatalova G G 2012 Quantum Electron. 42 953
[13] Kramida A, Ralchenko, Yu., Reader, J. and NIST ASD Team 2024NIST Atomic Spectra Database (Gaithersburg, MD: National Institute of Standards and Technology)
[14] Miyabe M, Iwata Y, Tomita H, Morita M, Sakamoto T 2024 Spectrochim. Acta Part B At. Spectrosc. 221 107036
[15] van Leeuwen K A H, Eliel E R, Post B H, Hogervorst W 1981 Z Physik A 301 95
[16] Zyuzikov A D, Mishin V I, Fedoseev V N 1988 Opt. Spectrosc. 64 287
[17] D'Yachkov A B, Gorkunov A A, Labozin A V, Mironov S M, Panchenko V Y, Firsov V A, Tsvetkov G O 2018 Quantum Electron. 48 75
[18] Zhang J Y, Xiong J Y, Wei S Q, Li Y F, Lu X Y 2023 Acta Phys. Sin. 72 193203(in Chinese) [张钧尧, 熊静逸, 魏少强, 李云飞, 卢肖勇2023 72 193203]
[19] Campbell P, Moore I D, Pearson M R 2016 Prog. Part. Nucl. Phys. 86 127
[20] Yang X F, Wang S J, Wilkins S G, Ruiz R F G 2023 Prog. Part. Nucl. Phys. 129 104005
[21] Lu X Y, Wang L D 2023 Chin. Phys. B 32 53204
[22] Lu X Y, Wang L D 2024 Appl. Radiat. Isot. 210 111334
[23] Demtröder W (Demtröder W ed) 2008Laser Spectroscopy: Vol. 1 Basic Principles (Berlin: Springer) pp5-60
[24] Greenland P T 1990 Contemp. Phys. 31 405
[25] Axner O, Gustafsson J, Omenetto N, Winefordner J D 2004 Spectrochim. Acta Part B At. Spectrosc. 59 1
[26] Agarwal G S 1970 Phys. Rev. A 1 1445
[27] Lambropoulos P, Lyras A 1989 Phys. Rev. A 40 2199
[28] Blagoev K B, Komarovskii V A 1994 At. Data Nucl. Data Tables 56 1
[29] Childs W J, Goodman L S 1972 Phys. Rev. A 6 1772
[30] Shen X P, Wang W L, Zhai L H, Deng H, Xu J, Yuan X L, Wei G Y, Wang W, Fang S, Su Y Y, Li Z M 2018 Spectrochim. Acta Part B At. Spectrosc. 145 96
[31] Lu X Y, Wang L D 2025 J. Phys. B: At., Mol. Opt. Phys. 58 025001
[32] Wakasugi M, Horiguchi T, Guo Jin W, Sakata H, Yoshizawa Y 1990 J. Phys. Soc. Jpn. 59 2700
计量
- 文章访问数: 29
- PDF下载量: 0
- 被引次数: 0
下载:
