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Recent Progress for Lanzhou Gas-Filled Recoil Separator

Recent Progress for Lanzhou Gas-Filled Recoil Separator. 报告人：张志远 中科院近代物理研究所. 2012 超重核合成机制与性质研讨会. Outline. Introduction of the Lanzhou gas-filled recoil separator First fusion reaction experiment: 175 Lu( 40 Ar,n) 215-x Ac First superheavy nuclei experiment: 208 Pb( 64 Ni,n) 271 Ds

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Recent Progress for Lanzhou Gas-Filled Recoil Separator

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  1. Recent Progress for Lanzhou Gas-Filled Recoil Separator 报告人：张志远 中科院近代物理研究所 2012超重核合成机制与性质研讨会

  2. Outline Introduction of the Lanzhou gas-filled recoil separator First fusion reaction experiment: 175Lu(40Ar,n)215-xAc First superheavy nuclei experiment: 208Pb(64Ni,n)271Ds New detector system and the performance in the 40Ca+175Lu and 40Ca+169Tm experiments Summary

  3. Introduction Location GFSL Gas-filled recoil separator in Lanzhou HIRFL-CSR

  4. Schematic View Dh : the dipole magnet with horizontally focusing ability Qv and Qh : the vertically and horizontally focusing quadrupole magnets, respectively

  5. Technical Parameters

  6. Comparison Table 2 Comparison of the gas-filled separators The subscripts h and v stand for horizontally and vertically focusing, respectively. * HTM : High Transmission Mode * SIM : Small Image-size Mode

  7. Position Sensitive Silicon Detector Active area：58 mm * 58 mm Strip Number：16 (vertical) Width of one strip：3.6 mm Thickness：300 m Manufacture: CANBERRA • Energy resolution(FWMH)： ~50 keV(212Po-8.785MeV) • Position resolution (FWMH)： ~1.5 mm(ER-)

  8. First fusion reaction experiment : 175Lu(40Ar, xn)215-xAc 175Lu(40Ar, xn)215-xAc • 实验目的： • 探索谱仪运行最佳条件，为超重核实验做准备 • 反冲余核在焦平面探测器上的分布 • 充气气压对余核平衡电荷态的影响 • 余核211,210Ac传输效率 • 实验条件： • 175Lu靶厚 0.53 mg/cm2 • 40Ar束流能量 177 MeV，靶中心能量175 MeV • 流强 2.8×1011 s-1 • 氦气气压 0.7~1.0 mbar • 磁刚度 ~1.7 Tm

  9. First fusion reaction experiment: 40Ar + 175Lu -> 215Ac* 4n-5n p2n-p3n a2n-a3n 2n-3n 211,210Ac 215Ac* 7.5 MeV, 0.25~0.35 s α1 207,206Fr 6.8 MeV, 15~16 s α2 203,202At 203At 6.1 MeV, 7.4 min 202At 6.2 MeV, 184 s α3

  10. On-line spectra 210,211Ac T1/2=0.24±0.01 s P=0.84 mbar B=1.73 Tm

  11. Equilibrium charge state • 余核平衡电荷态受以下几方面因素的影响： • 余核核电荷数 (Z) • 余核飞行速度 (v) • 余核核外电子排布 (4f, 5f) • 气体种类 (He, H2) • 气体压强 (Pressure) LBNL Exp. Data

  12. Equilibrium charge state “density effect”

  13. Transmission Efficiency 175Lu(40Ar, xn)215-xAc • Beam intensity：1 eA • Helium gas pressure：0.84 mbar • Magnetic rigidity：1.73 Tm • Counting rate of the decay of 211,210Ac：300 counts/min • Detection efficiency：50% • Abundance of 175Lu：97% • Production cross section of 211,210Ac：68.8 b • Transmission efficiency：14% Vermeulen D, et al. Z. Phys. A, 1984, 318(157).

  14. First superheavy nuclei experiment: 208Pb(64Ni, n)271Ds • Beam：64Ni19+ (HIRFL-SFC) • Energy：317.1 MeV Intensity：~100 pnA(6.6×1011 ions/s) • Beam time: 01/15/2011 ~ 01/21/2011 7days • 03/15/2011 ~ 03/26/2011 12days • Total dose：6.4×1017 ions • Beam energy at the centre of target: 313.3 MeV • Excitation energy of the compound nucleus: 14.4 MeV 指导合作： 张焕乔（中国原子能科学研究院） 任中洲（南京大学） 周善贵（中科院理论物理研究所） …… Br=2.01 Tm Helium gas P=0.8 mbar

  15. Rotating Target System • To avoid the melting of 208Pb target, the rotating target system and sandwiched target were prepared in the experiment. • During the irradiation, the target wheel rotated at the speed of 600 rpm.

  16. Schematic Diagram of Data Acquisition N568B Amplifier 1~20 MeV 5~200 MeV Scaler ADC Accelerator Beam Chopper CAMAC

  17. Kinematics 焦平面探测器 充气反冲谱仪 蒸发余核 He 靶 束流 PSD Veto • 64Ni束流在靶中心能量313.3 MeV，在靶中能量损失 ~6.5 MeV • 复合核272Ds*激发能 14.4 MeV • 蒸发余核271Ds反冲能 70.7 MeV，速度 7.1×106 m/s，平衡电荷态qave=9.6~9.7 (经验公式计算) • 蒸发余核271Ds在硅探测器注入能量 ~65 MeV，考虑脉冲幅度亏损(PHD)后的注入能量 ~35 MeV，注入深度 ~10 m • 271Ds衰变产生的a粒子在探测器中射程 ~65 m

  18. One -decay chain assigned to 271Ds 208Pb(64Ni, n)271Ds (Z=110) Known data

  19. Comparison with other laboratory data Decay energy Decay time

  20. Probability of Accidental Coincidence 208Pb(64Ni, n)271Ds (Z=110) • Counting rate: • 25 s-1 in the focal plane detector • 3.5 s-1 in the -decay energy range (7-11 MeV) • Probability of accidental coincidence • 3 mmposition window，309 pixels • EVR-a1: 1.1×10-3 • EVR-a4: 7.1×10-2 • EVR-a5: 2.7×10-1 • EVR-a1-a4-a5: 2.1×10-5

  21. New Detector System Si-box detector stop detectors TOF detector veto detector side detector Recoil flight path Si-box: Stop detector: 50mm×50mm×3 (active area), position-sensitive detectors (each has 16 vertical strips), 300m (thickness) Side detector: 50mm×50mm×8 (active area), non-position-sensitive detectors, Veto detector: 50mm×50mm×3 (active area), non-position-sensitive detectors TOF detector (Multi Wire Proportional Counter): 80mm×180mm (active area), 0.5m mylar window, isobutane gas (2 mbar)

  22. Photos Focal plane detector Silicon-box detector Time-of-flight detector Micro-Channel Plate detector Multi-Wire Proportional Counter

  23. 40Ca+175Lu->215Pa* • Observed in the bombardment 40Ca+175Lu with an energy of 4.83 MeV/u • Without the veto detector • With old beam dump, the total counting rate of stop detector was up to 300 events/s 209,210Ra 206,207Fr 205,206Rn 211,212Ra 207,208Rn, 203At 208,209Fr 210,211Ac 210,211Fr Signals obtained from both MWPCand Si-box Total spectrum of silicon detector -decay spectrum

  24. 40Ca+169Tm->209Ac* • Observed in the bombardment 40Ca+169Tm with an energy of 4.84 MeV/u • Three veto detectors mounted downstream of the stop detector • With the improvement of beam dump, the total counting rate decreased to 120 events/s

  25. 40Ca+169Tm->209Ac* Energy spectrum from the stop detector All E<10 MeV signals E<10 MeV signals obtained from both stop detector and TOF E<10 MeV signals anti-coincident with TOF signals E<10 MeV signals obtained from both stop detector and veto detector with no TOF signals E<10 MeV signals anti-coincident with TOF and veto signals E<10 MeV signals obtained from both stop detector and side detector with no TOF and veto signals

  26. 40Ca+169Tm->209Ac* 204Rn 201At 204Fr 205Fr 205,206Rn 200Po 203mRn 206Fr -decay spectrum The data for Ca+Lu and Ca+Tm experiments are analyzed in progress.

  27. Summary 兰州充气谱仪已成功投入运行，初步具备进行重核和超重核实验研究的能力。 谱仪上首次开展了熔合反应175Lu(40Ar, xn)215-xAc的实验研究，探索了谱仪正常运行的最佳条件，为谱仪上进行超重核实验做准备。 利用兰州充气反冲谱仪首次开展了超重核271Ds(Z=110)的实验研究。采用的反应道为208Pb(64Ni, n)271Ds ，观察到一条271Ds的衰变链，验证了超重核271Ds的衰变性质。 完成了谱仪新焦平面探测系统的研制，并将其成功应用于40Ca+175Lu、 40Ca+169Tm的在线实验中，达到了预期目标。

  28. 下一步工作展望 • 实验技术方面 • 优化谱仪传输光学，提高余核传输效率 • 利用两块TOF探测器，提高时间分辨，得到穿透粒子的质量信息 • 在焦平面探测器周围添加探测器，或进行“反冲衰变标记(RDT)”实验研究，获取余核衰变的谱学信息 • 物理实验方面 • 继续开展Z~110超重核区核素的合成和性质研究 • 开展对重核区质子滴线附近核素的合成和性质研究 • 开展重核区核素衰变谱学研究，得到相关核结构信息

  29. 研究组成员 近代物理研究所超重核研究组 小组成员： 研究员: 甘再国、李君清 黄天衡、黄明辉、马龙、张志远、郁琳、杨华彬

  30. Thank You !

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