在 RIBLL 上开展的质子晕与双质子发射实验研究 中国原子能科学研究院 China Institute of Atomic Energy 林承键、徐新星、贾会明、杨峰、刘祖华、张焕乔等 中国原子能科学研究院，北京 275 信箱 10 分箱， 王建松、徐瑚珊、雷相国、胡正国、孙志宇、杨彦云等 中国科学院近代物理研究所，甘肃兰州，

内 容 一、研究背景与历史回顾 二、用透射法开展的质子晕结构研究 三、运动学完全测量进行的双质子发射研究 四、总结与展望 五、 RIBLL 合作的一些想法

一、研究背景与历史回顾 1. 国内奇特核结构（晕核）研究的兴起  1998 年之前： HI-13 串列加速器，低能重离子熔合 - 裂变研究 垒下熔合 - 裂变碎片角分布各向异性异常的实验研究与预平衡裂变模型 的理论解释 － 低能核物理实验研究跻身世界先进水平的标志。 然而，课题申请困难。。。  1998 – 2004 ： HI-13 串列加速器，激发态晕结构研究 12 B, 13 C 激发态中子晕结构研究 － (d,p) 反应， Q3D 磁谱仪 ANC 方法、核天体 (n,  ) 反应、晕核标度定律 … …  2000 年至今： HIRFL-RIBLL 装置，放射性核束，质子晕与双质子 发射研究 2000 – 2004 ： 29 S, 27,28 P ，透射法、反应截面、 Glauber 理论、质子晕 2004 年至今： 17,18 Ne, 28,29 S ，运动学完全测量、双质子关联、奇特衰变

图：目前实验发现的晕核及其种类（截至 2002 年） Z.H. Liu, C.J. Lin et al., Chin. Sci. Bull. 46, 43 (2001); Phys. Rev. C64, (2001); C.J. Lin, Z.H. Liu et al., Chin. Phys. Lett. 18, 1183 (2001); Chin. Phys. Lett. 18, 1446 (2001). Tanihata, H. Hamagaki et al., Phys. Lett. B160, 380 (1985); Phys. Rev. Lett. 55, 2676 (1985).

二、用透射法开展的质子晕结构研究 1. 实验过程： 图：典型的束流粒子鉴别谱 主束： 36 Ar, 69 MeV/u 初级靶： Be, 98.8 mg/cm 2 T2 方靶室：  Position & TOF: PPAC + Sci. + PPAC   E: Si (150  m,  20 mm)  Targets & detectors: 6-Si (300  m, 45  45 mm 2 ) 次级束：  29 S: ~ 5 pps  27 P: ~ 15 pps  28 P: ~ 30 pps

图：拟合提取反应几率的示意图 A: mass number  : density of target : Avogadro’s number  x i : thickness of  Ei  i : reaction probability, the ratio of the reaction events to the total events (gated on TOF-  E i ) Reaction cross section: [cf: R. E. Warner et al., Phys. Rev. C 52, R1166 (1995).]

2. 29 S 双质子晕的现象： 图：实验截面与理论计算的比较图：实验截面与理论计算的差别

图： 29 S 及其核芯 27 Si 反应截面的比较 Z. H. Liu et al., Chin. Phys. Lett. 21, 1711 (2004).

3. 27,28 P 质子晕与核芯增大的现象： 图： 28 P 及其核芯 27 Si 的比较图： 27 P 及其核芯 26 Si 的比较 Z. H. Liu et al., Phys. Rev. C 69, (2004). 1/2 = fm 1/2 = fm 1/2 = fm

三、运动学完全测量进行的双质子发射研究 1. Introduction – 1p & 2p radioactivity  Radioactivity (H. Becquerel, 1896)  ,  decay (P. Curie, M. Curie, and E. Rutherford, 1899)   radiation (P. Villard, 1900)  Fission (O. Hahn and F. Strassmann, 1938)  1p & 2p radioactivity: ♣ First proposed by V.I. Goldanskii & Y.B. Zeldovich in 1960 cf: V.I. Goldanskii, Nucl. Phys. 19, 482 (1960); Y.B. Zeldovich, Sov. Phys.-JETP 11, 812 (1960). ♣ 1p (Up to now, about 25 emitters were found) Isomer state – 53 Co m was observed in 1970 cf: K.P. Jackson et al., Phys. Lett. B 33, 281 (1970); J. Cerny et al., Phys. Lett. B 33, 284 (1970). Ground state – 151 Lu & 147 Tm were observed in 1982 cf: S. Hofmann et al., Z. Phys. A 305, 111 (1982); O. Klepper et al., Z. Phys. A 305, 125 (1982). ♣ 2p (3 emitters were certified – 45 Fe, 54 Zn, 48 Ni) cf: J. Giovinazzo et al., Phys. Rev. Lett. 89, (2002); B. Blank et al., ibid 94, (2005). Ground state – 6 Be, 12 O, 16 Ne, 19 Mg, 45 Fe, 48 Ni, 54 Zn …… Excited state – 14 O, 17,18 Ne, 94 Ag …… (directly 2p emitters)

1p emission 2p emission Basic concept of 1p & 2p emission cf: B. Blank and M. Ploszajczak, Rep. Prog. Phys. 71, (2008). Meanings: 1) A good probe to extract the information of nuclear structure for the proton-rich nuclei close to or beyond the proton drip-line. 2) A good tool to study the nucleon-nucleon (like p-p) pair correlation inside a nucleus and the relative topics (such as superfluidity, BCS, BEC …) 3) A good way to investigate the astronuclear processes like (2p,  ) and ( ,2p). 4) And more …… 1S1S

2p halo structure  2p correlated emission Basic idea: 2p halo/skin 2p correlated emission 2p valence pair  above 2p emission threshold Beyond 1p drip-line2p resonance state Ground state 6 Be, 12 O, 16 Ne, 19 Mg, 45 Fe, 48 Ni, 54 Zn …… Initial state configuration BCS crossover? BEC weak link with core (decoupled) Excited state: 14 O, 17,18 Ne, 28,29 S, ……

Our interesting points Light emitters: 6 Be, 12,14 O, 16,17,18 Ne, 19 Mg … ( A < 20 ) Low Coulomb barrier Ground state or lowly excited state Short lifetime (~ keV order) Online complete-kinematics measurement Heavy emitters: 39 Ti, 42 Cr, 45 Fe, 48,49 Ni, 54 Zn … ( A > 40 ) High Coulomb barrier Ground state Long lifetime ( > ps) Offline decay measurement Intermediate emitters: Si, S, 31,32 Ar, 34 Ca… ( 20 < A < 40 ) Medium Coulomb barrier Ground state, lowly or highly excited state Short lifetime (~ fs/keV/MeV order) Online complete-kinematics measurement Z N

Two-proton halo/skins in S Figure: Density distributions of valence particlesFigure: Contributions of valence particles For the proton-rich sulfur isotopes, Z=16, 2p in the 2s 1/2 orbit. Calculated by single-particle potential model. c.f. C.J. Lin et al., Phys. Rev. C 66, (2002). S 2p = 0.9 MeV 2p

2. RIBLL Experiment 2005 – – 29 S+ 28 Si Collimators:  30mm  &  20mm.  E: 150  m Si  E detector, combined with TOF (upstream) for particle identification. 12 C: target, 300  m. X1, Y1, X2, Y2 : 300  m Si strip  E detectors, 18 strips each, 1.2mm/strip with 0.1 mm interval. Stop: 300  m Si  E detector, for stopping all the heavy fragments. CSI: CSI(Tl)+PIN array, 24 segments, for light particle (p, d, etc.) identification.

CIAE-RIBLL-2005 detector array  自制的硅条探测器、 CsI 闪烁体阵列和电荷灵敏前置放大器；  首次实现参数达 200 余路的运动学完全测量。

Secondary beam identification 29 S 28 P 27 Si 26 Al 25 Mg 24 Mg 25 Al 26 Si 27 P 23 Na 22 Ne 28 Si 29 P 30 S 27 Al Primary beam: 36 Ar 80.4 MeV/u Secondary beam: 29 S 46.8 MeV/u intensity: ~ 10 pps Purity: 1% 1  S was accumulated

Proton removal cross sections 29 S:  1p = 3.15  0.32 b  2p = 1.85  0.20 b 28 P:  1p = 2.13  0.22 b IMP data: without any coincidence, M. Wang et al., High Energy Physics and Nuclear Physics 26, 803 (2002). CIAE data: coincide with heavy fragments this work. Yields of light particles in 28 P, 29 S+ 12 C( 28 Si) reactions preliminary

2p relative momentum2p angular correlation q = |p 1 -p 2 |/2 2p singlet s state 2p sequentially emitted C.J. Lin et al., INPC2007 口头报告, Nucl. Phys. A805, 403 (2008)

3. RIBLL Experiment 2007 – – 17,18 Ne+ 197 Au Complete-kinematics measurement

Primary beam: 20 Ne, 78.2 MeV/u; Primary target: 9 Be, 1590  m Degrader: 27 Al, 1024  m; Secondary target: 197 Au, 200  m Secondary beam: 17 Ne, 50.0 MeV/u, Secondary beam: 18 Ne, 51.8 MeV/u, intensity  200 pps, purity  10% intensity  800 pps, purity  40% Identifications of the secondary beams

Identification of heavy fragments 17 Ne 18 Ne

Identification of light particles 17 Ne 18 Ne

17,18 Ne results Excitation-energy spectra Preliminary F. Jia, C. J. Lin, H. Q. Zhang et al., Chin. Phys. Lett. 26, (2009).

17 Ne Main results from relative momenta & opening angles 1) No obvious 2 He emission from 17 Ne, at present. 2) 2 He emission from 6.15 MeV state of 18 Ne was confirmed. Preliminary X10

momentum correlation functions and HBT analyses 17 Ne Exc: fm Inc: fm 18 Ne Exc: fm Inc: fm 17 Ne: NPA733, 85(2004) BCS or BEC ? p opening angel 74.5  BCS/BEC crossover 17 Ne Preliminary

Complete-kinematics measurements Secondary target: 197 Au, 100 µm SD: Silicon detectors, 325, 1000 µm SSSD: Single sided Silicon Strip Detectors, 300 µm, 24 strips with 2 mm in the width and 0.1 mm in the interval for the construction of the particle trajectories CsI(Tl) array: 6×6 lattices, each 15×15×20 mm, read out through PIN photodiodes Detector array for 28,29 S experiment 4. RIBLL Experiment 2007 – – 28,29 S+ 197 Au

FaceBack

Identifications of the secondary beams 29 S: 49.2 MeV/u Intensity:  200 pps Purity:  3% Dose: ~ 2.5  S: 48.0 MeV/u Intensity:  30 pps Purity:  1% Dose: ~ 3  10 6

29 S time window Si-isotope band Events induced only by 29 S Selection of heavy fragments Eliminate the contamination of 26,27 Si directly from the secondary beam and the accidental coincidences.

In this way, the unmixed 29 S  27 Si+p+p events are selected. blue dots: single-hit events red dots: double-hit events Selection of light particles

Trajectory tracking – selection of reactions in the target Cross point of trajectories before and after reaction 29 S  28 P+p events 29 S  27 Si+p+p events

Three extreme decay modes MC simulations, sampling in phase space, no FSI. Experimental results, likely 2 He cluster decay. 2 He cluster decay 3-body democratic decay 2-body sequential decay Results: Monte-Carlo simulations

Strong p-p correlations 2 He cluster decay ? 3-body simultaneous decay ? 2-body sequential decay ? or more complicated mode ? Invariance mass 3-body system of the final state Excitation-energy spectrum of 29 S reconstructed by 27 Si+p+p Relativistic-kinematics reconstruction for 29 S  27 Si+p+p events Relative momentum, q pp = |p 1 -p 2 |/2 Opening angle,  pp cm Feature 2: small  pp cm (< 90  ) Feature 1: small q pp (~ 20 MeV/c)

Experimental evidences of 2 He emission from the 10 MeV excited states of 29 S

More evidences… Relative energy of two protons, E pp Resonance of 2 He quasi-bound states ? Precise theoretical description is required ! C. J. Lin et al., Phys. Rev. C 80, (2009).

X. X. Xu, C. J. Lin, H. M. Jia et al., Phys. Rev. C 81, (2010). 2p emission from 28 P 2p correlated emission Large deformation? 2p intrinsic configuration?

2  emission from 28 P 2  uncorrelated emission or correlated ( 8 Be) emission? X. X. Xu, C. J. Lin, H. M. Jia et al., Phys. Rev. C 82, (2010).

cf: C.J. Lin et al., Phys. Rev. C 66, (2002). 2p BCS/BEC 2p halo Decay with large Spectroscopic factor cf: K. Hagino et al., Phys. Rev. Lett. 99, (2007). Link between 2p halo and 2p emission 1. 2p halo and 2p emission 四、总结、展望与感想

2. Outlook Pay attention to:  The link between 2p halo and 2p emission & pygmy resonance.  Explore the ground-state emitter: 26 S, 30 Ar, 34 Ca, 38 Ti, 48 Ni, 59 Ge, 63 Se, 67 Kr …  Precise theoretical descriptions embedded in the MC simulations.

RIBLL Experiment 2012 – – 34,35,36,37 Ca Directly 2p emission &  -delayed 2p emission SD0,1,2 (Silicon detectors, 300 µm) SD3,4 (Silicon detectors, 1500 µm) DSSD (Double sided Silicon Strip Detectors,500 µm, 16 strips ) PPAC2PPAC1SD0 Scint2. DSSD SD3,4 34, 35 Ca SD2 Scint1. T 1 SD1 T 2 Clover ToF: Start: T1, RF Stop: T2, SD

37 Ca 的初步结果 GANIL results: T1/2 = 181.7(36) ms, E decay ~ 3.1 MeV

探测技术的发展

Layer 1 -- DSSD, T: 64 / 300  m, A: 64  64 mm 2, W: 0.96 mm, I: 0.04  m. D: 90 mm, H:  10 mm, W: 0.96mm, I: 0.04mm, 12 sectors Layer 2 – DSSD, T: 300  m / 1 mm, same type of layer 1. Layer 3 – CsI+PIN array, 4  4 (6  6)  50 mm 3 units. hodoscopes heavy particle & Light particle N early 4-  covered charged-particle detector array Under construction at CIAE

五、 RIBLL 合作的一些想法：  国际合作 VS 国内合作  RIBLL 设置的最佳化 － 沟通与协调  数据分析 － 成果共享  电子学（前放）与获取系统（ VME 获取）  大型实验设备的共建与共享 

谢 谢 ！