1 / 58

Institute of Modern Physics, Lanzhou, China

Institute of Modern Physics, Lanzhou, China. 稀土区滴线附近  缓发质子衰变的实验研究. 徐树威和谢元祥. 中国物理学会 2008 年秋季学术会议 山东济南， 2008/09/19-21. Historical Review. Chart of the nuclides in neutron-deficient rare-earth region. Surface ionization Ion Source. 32 S. BEMS-2 (Dubna).

hunter
Télécharger la présentation

Institute of Modern Physics, Lanzhou, China

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Institute of Modern Physics, Lanzhou, China 稀土区滴线附近 缓发质子衰变的实验研究 徐树威和谢元祥 中国物理学会2008年秋季学术会议 山东济南，2008/09/19-21

  2. Historical Review

  3. Chart of the nuclides in neutron-deficient rare-earth region

  4. Surface ionization Ion Source 32S BEMS-2 (Dubna)

  5. Layout of the GSI mass separator facility FEBIAD ion source 58Ni

  6. Remarkable progress made by LBL Technical improvements High temperature ion source Cooling target Different heavy ions: 36Ar, 40Ca, 54,56Fe, 58,60Ni, 64Zn

  7. OASIS (LBL) Surface ionization ion source Working temperature >2800oC

  8. First studied by LBL in 1980s-early 1990s

  9. What is the difficulty for people to reach the odd-Z drip line ? One of the difficulties encountered in the study of βp near the drip line is caused by the isobaric contaminations.In order to identify a βp precursor near the drip line unambiguously, besides a mass separation, additional measurements, such as "x-p" coincidence, i.e., the coincidence between the characteristic x rays of the proton emitter and the βp, has to be carried out. However, due to the low branching ratio of the electron capture (EC), the "x-p" coincidence measurements will reduce the counting rate by one order of magnitude or two. This fact severely constrains the study of a βp channel with the production cross section as low as 100 nb.

  10. What we have done at IMP, Lanzhou, Chinaover the last ten years ?

  11. Production The studied nuclei were produced via heavy-ion induced fusion-evaporation reactions, such as 3n-, p3n- and 2p3n-evaporation reactions. The 32S, 36Ar and 40Ca were used as projectiles. For example 32S + 92Mo  3n + 121Ce 36Ar + 106Cd  3n + 135Gd 40Ca + 112Sn  3n + 149Yb 36Ar + 96Ru  p3n + 128Pm 40Ca + 112Sn  p3n + 142Ho 32S + 58Ni  2p3n + 85Mo 36Ar + 58Ni  3n + 89Ru 40Ca + 58Ni  2p3n + 93Pd

  12. Improvement of the identification In theEC/+ decay of an even(Z)-odd(N) p precursor, most of the excited-state decays in the even(Z-2)-even(N+1) daughter of each odd(Z-1)-even(N+1) proton “emitter” result in the transition between the lowest-energy 2+ state and 0+ ground state in the “daughter” nucleus. Therefore, instead of an ISOL facility, the coincidence between p and the 2+0+ -ray transition specific for a particular “daughter” nucleus, we call the “p-” coincidence, can be used to identify the mother, the p precursor. Similarly, this method can be also used for some of the odd(Z)-odd(N) precursors.

  13. The 185.8-keV -transition, i.e. the 2+-0+ transition in the “daughter” 120Ba, coincident with p can be used to identify the precursor 121Ce p Proposed partial decay scheme for p decay of 121Ce

  14. He-jet fast tape transport system (HJTTS) in combination with a “p-” coincidence

  15. He-jet tape transport system in combination with a multifold coincidence measurements

  16. (1)HJTTS with “p-”coincidence Transport efficiency of HJTTS  50% Sum of the proton branching ratios to the excited states followed by the 2+0+ transition in “daughter” nucleus  50% (2)ISOL with “x-p” coincidence Overall efficiency of ISOL 5-10% EC branching ratio resulting in the X-ray followed by p emission 5-10% Comparison of the efficiencies with two different methods for studying rare-earth or refractory nuclei As an estimation, using method (1) instead of method (2), the efficiency of measuring the p specific for a particular rare-earth or refractory precursor can be increased by a factor of 50.

  17. (X) spectrum gated on 2.5-6.0 MeV protons in the 32S + 92Mo reaction The 32S + 92Mo reaction was used to produce the studied nuclide 121Ce

  18. Triple Coincidence

  19. Decay curve of the 185.8-keV  line in coincidence with p

  20. Energy spectrum of p gated by the 185.8-keV  ray in the 32S + 92Mo reaction Fitted by a statistical model calculation [P. Hornshoj et al. Nucl. Phys. A187,609(1972) and J. C. Hardy, Phys. Lett.B109,242(1982)

  21. Comparison of the experimental relative branching ratios with the statistical-model calculations The ground-state spin of121Ce was assigned to be 5/2.

  22. With above method a progress has been made at IMP over the last 10 years First studied by IMP in 1996-2006improved by IMP Odd-Z drip line LBL 1980s-early 1990s Ho-142 Pm-128 142Ho and 128Pm are predicted proton drip-line nuclei

  23. Chart of the nuclides in the mass 90 regionnear the N = Z line By product 89Ru and 93Pd are waiting points in the rp-process, predicted by H. Schatz et al. Vol.294, 167 (1998) and Y. S. Chen, private communication(2003).

  24. Physical results and discussions • 1. Half-life • 2. Spin, parity and deformation • 3. Production-reaction cross section

  25. Half-lives of our studied nuclei in the rare-earth region [6] K.Takahashi et al. ADNDT, 12,101(1973);[7] T. Horiguchi et al. Chart of Nuclides, 1996 [8] M. Hirsch et al. ADNDT, 53, 165(1993) ; [9] P. Möller et al. ADNDT, 66,131(1997)

  26. Half-lives of our studied nuclei in mass 90 region [9] P. Möller et al., At. Data Nucl. Data Tables, 66, 131(1997) which was normally used as standard input data in astrophysics. [16] H. Herndl and B. A. Brown, Nncl. Phys. A627, 35 (1997)

  27. The mass abundances of the nuclei in the region strongly depends on the half-lives of the key nuclei in rp-process Nuclei 93Pd 92Rh 89Ru 85Mo 81Zr T1/2-Xu03(s) 1.3 3.0 1.2 3.2 5.3 T1/2-SCH98(s) 0.22 0.35 0.29 0.37 4.3 SCH98: H. Schatz et al., Phys. Reports, 294, 167(1998), originally from Möller et al.[9] When we use the experimental half-lives for the 5 nuclei instead of the predictions quoted by Schatz, originally from Möller et al, the mass abundances of the nuclei in the region will change considerably.

  28. Calculated abundances of 89Ru and 93Pd as functions of the processing time for rp-process at the typical conditions of the x-ray bursts, T = 1.5 and  = 1.5  106 g/cm3. 9 Network calculation by N.C. Shu and Y. S. Chen, CIAE, China The experimental half-lives of the 5 nuclides lead to about 4 times more products of these two waiting point nuclei around the peak abundances.

  29. The spins , parities and quadruple deformations(2) of studied rare-earth nuclei * * Except the odd(Z)-odd(N) nuclei 128Pm and 142Ho, most of the theoretical calculations for even (Z)-odd(N) nuclei [121Ce…]are consistent with our experimental results. The theoretical determination of the gs spin and parity for an e-o nucleus by means of the orbital occupied by the last neutron in the Nilsson diagram strongly depends on the nuclear deformation. Therefore, the consistency between the experimental spin-parity assignments and the predicted Nilsson diagrams is an indirect indication that the above 6 e-o nuclei are highly deformed with 2 ~ 0. 3 in the spherical-harmonic expansion.

  30. Using the Woods-Saxon-Strutinsky method,nuclear potential-energy surface (NPES)calculations for the o-o nuclei 128Pm and 142Ho were carried out by F.-R. Xu, Peking university, Beijing , China 142Ho: minimum at  = 0.251;  = 9.3o (7/2-[523] 7/2+[404])7- 128Pm: minimum at  = 0.319;  = -0.8o (5/2-[532] 7/2-[523])6+ 2 2 The calculated NPES results, 7- for 142Ho and 6+ for 128Pm, are consistent with our experimental assignment. Also, 142Ho and 128Pm both are highly deformed.

  31. The spins, parities, quadruple deformations and mass excesses of our studied nuclei in the mass 90 region The experimental assignment of 1/2+ to 85Mo is inconsistent with all theoretical calculations, possibly , because of the dramatic change of the deformation near the nucleus 85Mo. [12]T. Bengtsson et al. Table of isotopes, 8th ed. (1996); [13] G. Audi et al. Nucl. Phys. A624,1(1997)

  32. Fusion-evaporation reaction cross section • The reaction cross sections were overestimated 1 or 2 order of magnitudes by Alice code • The reaction cross sections were overestimated about 1 order of magnitude by K. Wang SINR, Shanghai, China, using a HIVAP code.

  33. Recent results 同时观测EC/β+衰变的β缓发和 β p 分别建立了143Dy和133Sm的基态和同质异能态的衰变纲图 The βp decay, in particular , the branching ratios to low-lying states in daughter nuclei are very sensitive to the spin and parity of the precursor. The “p-” coincidence can provide the information of the branching ratios, therefore, sometimes we are able to separate the component of βp decay of an isomeric state from that of the ground state.

  34. Example (1) The first observation of the β-delayed proton decay of ¹⁴³Dy with proton energies of 2.0 MeV to 6.4 MeV was reported by Nitschke et al , LBL in 1983. However, three different values for its half-life, 4.1(3)s, 3.2(6)s and 3.8(6)s , were given by the same group. Now we found two components, one from the 1/2+ ground state with the half-life of 5.3(6) s , another from a 11/2- isomeric state with half-life of 3.0(2) s. This result was supported by beta-delayed  decay and nuclear potential energy surface calculations.

  35. NPES calculated by W-S-S method β2 = 0.202  = -26o 1/2+[400] β2= 0.198  = 47o 11/2-[505]

  36. Simple decay scheme of11/2-isomeric state in143Dy

  37. Simpledecay scheme of 1/2+ ground statein 143Dy

  38. Example (2) The first observation of the β-delayed proton decay of 133Sm was made by Dubna in 1977, with a half-live of 3.2(4) s, and the spin and parity of 5/2+ suggested. However, J  = 5/2+ was questioned by LBL people in 1983. Recently, we found two components, 1/2- ground state with half-life of 3.4(5) s and a 5/2+ isomeric state with half-life of 2.8(5) s. This result was also supported by beta-delayed  decay and nuclear potential energy surface calculations.

  39. NPES calculated by W-S-S method β2 = 0.327  = -0.025o 1/2[541] β2 = 0.291  = 0.000o 5/2[402]

  40. Simple decay schemes of 1/2- ground state and 5/2+ isomeric state in133Sm

  41. 上述工作,特别是合成和研究新核素的成 果, 得到了国外同行的认可与好评。 作为工具手册的日、美、法、德等新版 核素图都采用了我们发现的新核素数据。

  42. Our synthesized 11 new nuclides, including 9 β–delayed proton precursors, are cited in Japanese Chart of the Nuclides - 2004 引用了我们11种新核素版核素图引用了我们11种新核素 Speculated odd-Z proton drip line by S. Hofmann Synthesized new nuclides

  43. 美国能源部－2002年新版核素图引用了我们10种新核素美国能源部－2002年新版核素图引用了我们10种新核素

  44. 法国－2002 版核素图引用了我们10种新核素

  45. Our synthesized 10 new nuclides, including 9 β–delayed proton precursors, are cited in German Chart of the Nuclides - 2006

  46. Reports on progress in Physics, 2004 “Lightest observed isotopes, at present, for 50<Z≤82” are listed together with the production reaction, observed decay, laboratory and reference of the first observation . M. Thoennessen Among the listed 32 isotopes, (8) isotopes were first observed by our group in Lanzhou, China, as well as (7) by ANL USA; (6) by GSI Germany; (4)by Daresbury UK; (3) by ORNL USA; (1) by Dubna Russia; (1) by GANIL France; (1) by LBL USA; (1) by Legnaro; Italy. Rare earth

  47. Perspective in near future Now we are working in the region along the odd-Z proton drip line. The even-Z proton drip line around the rare-earth region is about 4-5 neutrons less than the odd-Z proton drip line. One of major decay mode for the nuclei between these two lines is βp decay. Using the “p-” coincidence, we are able to study the βp decays in this uncultivated, weak bound area, starting from the odd-Z proton drip line, and gradually reaching the even-Z proton drip line.

  48. The present margin of known isotopes consists of The proton radioactivities first studied in different foreign Labs. The βp precursors first studied in IMP, Lanzhou The βp precursors could be studiedat Lanzhou in near future 区域特点是：缓发质子衰变是主要衰变方式，而不存在直接质子衰变

  49. Search for following 15 b-delayed proton precursors • *Predicted • half-lives: • 100－500ms • Estimated • partial cross • section of bp: •  50nb • -3n evap. •  2nb • -5nevap.

More Related