Coupled-channel study of fine structure in the alpha decay of well-deformed nuclei Zhongzhou REN (任中洲) • Department of Physics, Nanjing University, Nanjing, China Outline • Introduction • Coupled-channel Schrödinger equations (1) Evaluation of interaction matrix elements (2) Pauli exclusion principle (3) Alpha-preformation factors (4) Hypothesis of Boltzmann distributions for daughter states … • Summary Introduction Proton radioactivity (Z≥51) Alpha decay (Z≥52) Cluster radioactivity (Z≥87) Spontaneous fission (Z ≥90) The study on α decay dates back to the early days of nuclear physics. It, although one of the oldest objects of study in nuclear physics, remains an attractive decay mode. There are more than 400 nuclei in the periodic table that exhibit the alpha-decay phenomenon. proton number It has been used as a reliable way to identify new synthesized elements and isomeric states. CHART OF THE NUCLIDES 1.8 ms 11.65 116 116/290 116/291 15 ms 6.3 m s 10.85 115 Pb + 50 70 115/287 115/288 32 ms 87 m s 10.59 Ti.... Zn a 114 113/283 113 113/284 0.1 s 10.12 112/277 a 112 0.48 s 114/286 a 111 0.17 s 10.37 110/269 110/267 110/270 a 110/273 110/271 a Ds a Mt 268 Mt 266 Mt 109/2 75 109/276 9.7 m s 0.72 s 9.71 10.33 Hs 264 Hs Bh 261 H s 265 Hs 266 Hs 267 Bh 262 Sg 259 Sg 260 Hs 270 Sg 261 Sg Sg 262 Sg 263 Sg 265 a 108 a Bh 264 Bh Sg 258 Hs 269 a 107/272 9.8 s 9.02 a a 105/267 105/268 1.2 h 16 h a Sg 266 a 3.6 s a 116/293 16 ms 53 ms 10.66 10.53 a 0.56 s 10.01 a a 114/289 114/288 Z = 114 2.7 s 0.63 s 9.82 9.95 a 10.00 112/282 a 0.5 m s 112/283 112/284 4.0 s 0.1 s 112/285 34 s 9.16 a a a 9.75 110/279 110/281 0.18 s 9.70 9.6 s a 108/275 a 0.15 s 9.30 107/2 71 a 111/280 114/287 0.16 s 9.54 111/279 10.74 a 116/292 10.46 10.20 111/272 Ca + 238U.... 249Cf a 117 208 48 118/294 118 a 106/271 2.4 m in 8.53 Db 256 D b 257 Db 258 Db 260 D b 261 Db 262 D b 263 Db Rf 255 Rf 256 Rf 257 Rf 258 Rf 259 R f 260 Rf 261 Rf 262 R f 263 Lr 254 Lr 255 Lr 256 Lr 257 Lr 258 Lr 259 Lr 260 Lr 261 Lr 262 N o 253 N o 254 N o 255 N o 256 N o 257 N o 258 N o 259 N o 260 Md 252 Md 253 Md 254 Md 255 Md 256 Md 257 Md 258 Md 259 Fm 251 Fm 252 Fm 253 Fm 254 Fm 255 Fm 256 Fm 257 Fm 258 Es 250 Es 251 Es 252 Es 253 Es 254 Es 255 Es 256 Cf 249 Cf 250 C f 251 Cf 252 Cf 253 C f 254 Cf 255 176 178 180 182 184 104/267 104/268 Rf 2.3 h Lr No 164 166 168 170 Fm 259 154 156 174 112/285 EC 39 s 9.15 Cf 256 E (MeV) Cf 152 172 T1/2 Fm 150 Md 260 Md Es Z/A No 262 158 160 162 neutron number SF 国内超重新核素实验265Bh (Z=107) 265Bh的实验结果与理论预言一致 Theoretical description • Phenomenological description (1) the Geiger-Nuttall law (2) the Viola-Seaborg formula (3) …… • Semiclassical approximation (WKB) (1) the shell model (2) the cluster model (3) the density-dependent cluster model (DDCM) (4) the generalized liquid drop model (GLDM) (5) the super asymmetric fission model (SAFM) (6) …… 核alpha衰变寿命计算(2006-2010), 2006-2008 建立了原子核alpha衰变的一个新模型形变的密度依赖结团模型(2006),并系统计算了从 轻核区到 超重区原子核alpha衰变寿命 (DDCM---发表了一系列论文)。 在此基础上,2009年建立了新版本的密度依赖结 团模型:纯量子模型,解准束缚态耦合薛定谔方程 (GDDCM)。 2010, 建立了多道结团模型(MCCM) 问题来源 • 量子力学源于原子物理:束缚态,散射态(教科书) • 1928,Gomov用量子力学定性解释原子核α衰变 • 不稳定原子核的特点:有限寿命—准束缚态(Q-BS) • 已有理论模型:半经典或准经典近似(WKB, BohrSommerfeld quantization) • α衰变是一个纯量子效应,应解准束缚态薛定谔方程 • GDDCM is a new version of DDCM: • 1) pure quantum version of decay • 2) wave functions are obtained by S-eq. for Q-BS. Woods-Saxon势球形核准束缚态波函数 Woods-Saxon shape nuclear potentials V0 is determined by the characteristic of the alphacluster quasibound state. 形变核alpha衰变新模型:多道结团模型(MCCM) Five-channel calculation of fine structure in the alpha decay of well-deformed nuclei Deformed system We consider a spherical alpha-particle interacts with a deformed core nucleus which has an axially symmetric nuclear shape. The decay process is described by the tunneling of the alpha particle through a deformed potential barrier, which is approximated by an axially deformed Woods-Saxon field. Schematic diagram of the alpha decay of welldeformed even-even nuclei EI I ( I 1) Key points (五耦合道计算) • The deformed potential V is expanded in spherical multipoles to order 12. • The dynamics of the core is included in evaluating the interaction matrix elements. • The Boltzmann distribution hypothesis is proposed for daughter states to simulate the internal effect of nuclear states on alpha-cluster formation. • A more realistic description of alpha decay has been achieved. The total wave function of the system JM ( )r 1 unJ I (r ) Y (rˆ) I JM I The set of coupled equations for the radial components 2 d2 ( 1) 2 Q0 EI u (r ) 2 r 2 dr V ' (r )u ' (r ) 0, [ (n I )] ' The multipole expansion of the interaction potential max V (r ) (r ) Y 00 0 The coupling potential between channels α and α’ (1) V , ' (r ) (r ) 4 (2 ' 1)(2 I 1)(2 1) ' 00 0 W ( ' JI ; I ') I I ' For rotational nuclei, the reduced matrix elements are assumed as I I ' (2 1)(2I ' 1) I ' K 0 IK 4 (2I 1) Coupled-channel wave functions (1) The potential depth V0 is adjusted to make all channels reproduce the experimental QJd values. (2) The Wildermuth condition G 2n 4 g i 1 i (3) Boundary conditions for different channels un j (r 0) 0; un j (r ) N j G (k J d r ) iF (k J d r ) . Alpha-cluster formation • A constant preformation factor is used for all even-even nuclei (Pα =0.36). This value is not only consistent with the experimental data of open-shell nuclei but also supported by the microscopic calculation. • The hypothesis of Boltzmann distributions ρ(EI) is proposed for daughter states, as Einstein did for molecules with a set of discrete states. This implies that there is a gradual decline in the Pα factor with increasing daughter spins. The total decay width representing the tunneling through the deformed barrier { I } P ( EI ) I The partial decay width corresponding to the decay into a core state I | un I ( R) |2 I G ( k I R) 2 F ( k I R) 2 2 kI The alpha-decay half-lives and branching ratios (BR) are expressed as T1/ 2 ln 2 / BR P ( EI ) I 100% Sensitivity of the calculated half-lives and branching ratios to the decay Q0 value for the alpha decay of 244Cm, showing the crucial effect on half-lives. Sensitivity of the calculated branching ratios to the energy spectrum of daughter nuclei The decrease of BR with increasing the E2 value is more evident as we proceed to higher-spin states. There is an increase in the half-life by about 28% as the E2 value is varied from 40 to 80 keV. Sensitivity of the calculated branching ratios and halflives to the deformation β2 values of daughter nuclei The comparison of experimental alpha-decay half-lives with theoretical ones for well-deformed emitters 2 1 i i 0.19 log10 Texpt Tcalc i 1 34 35 Calculated results for two isotopes of Pu 240Pu Exp. (%) Cal. (%) 242Pu 4.6×10-5 4.6×10-6 + 8 0.00106 0.00147 0.084 0.048 27.1 27.73 6+ 4+ Exp. (%) Cal. (%) --- 2.6×10-6 0.00086 0.00232 0.0307 0.0341 23.48 23.85 72.22 0+ T1/2(s) 2.07×1011 2.74×1011 6+ 4+ 2+ 72.8 8+ 2+ 76.49 76.12 0+ T1/2(s) 1.18×1013 1.93×1013 Calculated results for two isotopes of Cm 242Cm Exp. (%) Cal. (%) 244Cm 2.0×10-5 3.8×10-5 + 8 0.0046 0.0053 0.035 0.077 25.92 31.04 6+ 4+ Exp. (%) Cal. (%) 4.0×10-5 2.8×10-5 + 8 0.00352 0.00733 0.0204 0.0479 23.1 28.60 4+ 2+ 74.08 68.87 0+ T1/2(s) 1.41×107 1.32×107 6+ 2+ 76.9 71.34 0+ T1/2(s) 5.72×108 5.68×108 Calculated results for two isotopes of Cf 250Cf Exp. (%) Cal. (%) --- 5.8×10-5 ~0.01 0.010 0.3 0.66 15.0 22.73 252Cf 8+ 6+ 4+ Exp. (%) Cal. (%) 6.0×10-5 7.9×10-5 + 8 0.002 0.24 15.7 0.0089 0.95 4+ 19.76 2+ 84.7 76.60 0+ T1/2(s) 4.13×108 3.09×108 6+ 2+ 84.2 79.29 0+ T1/2(s) 8.61×107 8.87×107 Calculated results for two isotopes of Fm 252Fm Exp. (%) Cal. (%) --- 3.8×10-4 0.023 0.022 0.97 1.45 15.0 21.60 254Fm 8+ 6+ Exp. (%) Cal. (%) --- 4.8×10-4 0.0066 0.0126 0.82 4+ 20.30 2+ 2+ 84.0 76.93 0+ T1/2(s) 9.14×104 4.70×104 6+ 1.41 4+ 14.2 8+ 85.0 78.28 0+ T1/2(s) 1.17×104 7.95×103 The comparison of experimental branching ratios with theoretical ones for well-deformed emitters Summary We present a five-channel calculation of fine structure in the alpha decay of deformed nuclei within the multichannel cluster model. • Well consider the internal effect of daughter states, the coupling effect of various channels, Pauli exclusion principle, nuclear deformation. • Agree well with the experimental data; good prediction for half-lives and branching ratios. • The alpha transition to high-spin states is a powerful tool to probe nuclear structure properties of daughter nuclei. 致谢 • 感谢各位同行对我们工作的支持 • 感谢shen, Li, Zhang, Yu …老师对本次会 议召开的辛勤工作