Identification of New Isotope 238Th

Unreported heavy neutron-rich nuclide ²³⁸Th has been produced via a multinucleon transfer reaction by 60MeVIu ¹⁸0 ions bombardment of natural uranium.Thorium was radiochemically separated from the mixture of uranium and reaction products. ²³⁸Pa as a daughter nucleus of ²³⁸Th has been identified according to the growth and decay of ²³⁸Pa γ rays which has been observed. The half-life of ²³⁸Th was determined to be (9.4 + 2.0) min. At the same time, a new γ ray of (89.0 + 0.3) keV with T_1/2= (8.9 + 1.5)min was found in the γ spectrum gated with the K_α1, X ray of Pa and assigned to ²³⁸Th decay based on the measurements of its transition energy and the half-life.

     

新重丰中子同位素239Pa的合成

本文简述了新重丰中子同位素２３９Ｐａ的首次合成和鉴别,并测定其半衰期为１０６±３０ｍｉｎ． This paper reports that the new heavy neutron-rich isotope 239Pa has been observed for the first time and its half life has been determined to be 106±30min.     

新重丰中子同位素^238Th

利用兰州重离子加速器（ＨＩＲＦＬ）所提供的６０ＭｅＶ／ｕ的＾１８Ｏ离子束照射天然铀靶,通过多核子转移反应生成＾２３８Ｔｈ,由快速放射化学分离技术从铀及其反应产物的合物中分离出钍。使用２台高纯锗（ＨＰＧｅ）探测器对样品的γ（Ｘ）活性进行测量,观测到了＾２３８Ｔｈ的β－衰变子本＾２３８Ｐａ的６３５．０ｋｅＶ和１０６０．５ｋｅＶ２条γ射线峰的增长、衰变行为,利用分析递次衰变的计算机程序对其后一条进行了拟     

新丰中子核素208Hg的发现

新丰中子同位素208Hg,首次从30MeV/u的12C束轰击厚的天然铅靶反应产物中被鉴定出来,208Hg的鉴别基于二步化学分离及γ活性分析,第一步,借助于在本工作中所发展起来的熔化靶装置和一种特殊的热色谱技术,实现了Hg元素产物高效、高选择性的分离,第二步则是周期性的提取随着收集样品中的丰中子Hg同位素的β—衰变而生长起来的Tl元素,在提取的Tl样品中,观察到能量为2614.6keV、半衰期为191±10~4 50s的γ活性,它只能被指定为208Hg的β—衰变子体208Tl,将测得的208Hg半衰期42±23 12min与理论预言进行了比较。 The new neutron-rich isotope 208Hg was identified for the first time from the reactionproducts in a thick natPb target bombarded by a 30MeV/u 12C beam. The identification of 208Hg wasbased on two-step chemical separation and γ activity analysis. The first step was the release,separation and collection of Hg element products with a high efficiency and good selectivity bymeans of a melt target device and a special thermochromatographic technique developed in presentwork. The second step was..     

新同位素175Er

简介首次合成新核素１７5Ｅｒ及对其衰变纲图测定的实验方法和实验结果． the synthesis and γ decay scheme of new isotope175Er is reported for the first time.The related experimental process and main results are represented briefly also.     

New Neutron-Rich Isotope 208Hg

The new neutron-rich isotope ²⁰⁸Hg has been identified for the first time from the reaction products in fully-stopping thick ^nat.Pb target bombarded by 30MeV/u ¹²C beam provided by the Heavy Ion Research Facility in Lanzhou.Assignment of the nuclide ²⁰⁸Hg was based on the measurements of the deacy γ energy and halflife of its daughter ²⁰⁸Ti,which was grown up with ²⁰⁸Hg β-deacy.The half-life of ²⁰⁸Hg β-deacy was determined to be 42+23－12 min.The average production cross section of ²⁰⁸Hg over the incident energy region from Coulomb barrier to 30MeV/u is found to be 1.1±0.5μb.     

Subbarrier Complete Fusion-Fission Reactions of 16)O+232Th

We have succeeded in isolating the complete arising from complete fusion-fission in terms of the fragment folding angle technique,and measured complete fusion-fission cross sections and fragment angular distributions for the ¹⁶O+²³²Th system in the center-of-mass energies between 72.61 and 80.11 MeV.The observed fission excitation function is in quite good agreement with the expectation of the coupled-channels theory.However,the measured fragment angular distributions are more anisotropic than the predictions of both the saddle-point transition-state model and scission model.     

Identification of New Isotope 238Th

利用60MeV／u的     

Temporal variation of fundamental constants in 229Th transition

If is there enhanced sensitivity to variations of fine structure constant, nucleon mass and meson masses in the transition between the low energy and long-lived nuclear isomer and ground states? To answer this open problem, we investigate the transition between the long-lived 7.6±0.5 eV isomer and ground states in ²²⁹Th based on the formulae derived from both the Nilsson model and Feynman-Hellmann theorem. Consistent conclusions are drawn by these two method. The sensitivity to relative variation of fine structure constant could be enhanced by 3—4 orders of magnitude, and to variations of nucleon mass and meson masses are enhanced by about 5—6 orders of magnitude in the ²²⁹Th transition.     

232Th 中子诱发裂变产额数据比对评价

232Th 中子诱发裂变产额在Th/U 燃料循环的核能开发中具有重要的意义,在现有国际评价产额数据库基础上,结合最新的实验数据,对产物核的质量分布和反应堆计算所需的重点产物核进行了比对。这些产物核包括95Mo,99Tc,101Ru,103Rh,109Ag,133Cs,147Sm,149Sm,150Sm,151Sm,152Sm,143Nd,145Nd 和153Eu 等,对有分歧的133Cs,152Sm 和153Eu 累积产额数据进行了评价调整。最后推荐给出了n+232Th 裂变的产额数据库,作为CENDL 库的组成部分。The yields of n+232Th fission are important in study of the Th/U fuel cycle. Based upon the evaluated nuclear data libraries and recent experimental data,comparison and evaluation for yield mass distribution and cumulativeyield were performed for those products are needed and important in reactor calculations,including 95Mo,99Tc,101Ru,103Rh,109Ag,133Cs,147Sm,149Sm,150Sm,151Sm,152Sm,143Nd,145Nd adn 153Eu etc. Adjustments were made for 133Cs, 152Sm and 153En which have discrepancies among the libraries. Database for n+233Th fission yield is recommended as a part of CENDL update.     

新同位素235Am的产生与鉴别

一种缺中子新同位素２３５Ａｍ通过２３８Ｐｕ（ｐ,４ｎ）２３５Ａｍ反应而产生．产物借助Ｈｅ－ｊｅｔ系统的传输,快化学分离以及γ、Ｘ射线和γ－Ｘ（γ）符合测量等得到鉴别,测得其半衰期为１５±５ｍｉｎ． A new neutron deficient isotope 235 Am was produced via 238 Pu(p,4n) 235 Am reaction. The products were identified by means of the transporting of He jet system, separating of rapid radiochemical method and measuring of γ and X rays as well as X γ coincidence. The measured half life of 235 Am is 15±5min.     

RADIOCHEMICAL INVESTIGATION OF MASS DISTRIBUTIONS IN 12C-INDUCED FISSION OF 209Bi AND 238U

The yields of 15 and 17 fission, products have been obtained by radiochemical determinations in ¹²C-induced fission of ²⁰⁹Bi and ²³⁸U respectively. From these data, the mass distributions of fission fragments are calculated based on three different hypotheses for the charge distribution. The results seem to indicate that the hypothesis of equal charge displacement gives the best fit to the Gaussian distribution for the masses of the fission fragments. By comparison with the mass distributions for ²⁰⁹Bi (¹²C, f), ²³⁸U(¹²C, f) and ¹⁹⁷Au(¹²C, f) in our early measurement, we find that for fission parameter Z²/A>37, the width of the mass distributions increases with Z²/A rapidly.     

CHARGE DISTRIBUTION IN THE FISSION OF 232Th BY 14MeV NEUTRON

Independent yields of ⁸²Br, ⁹⁶Nb, ¹¹²Ag, ¹³⁰I,¹³²I, ¹³⁴I, ^134mCs, ^135mCs, ¹³⁶Cs and upper limitof independent yield for ¹⁴⁰La in the fission of ²³²Th induced by neutrons of 14 MeVwere determined with nuclear chemistry techniques. The correlation of the fractionalindependent yields in the high yield mass chains with a Gaussian curve of charge dis-tribution has been investigated using various mass formulae and charge distributionhypotheses. The results indicate that the hrpothesis of minimum potential energy witha shell-effected mass equation gives the best fit to the data. The width parameter Cof the charge distribution is found to be 0.80. The large deviations of ³²Br and ¹¹²Ag from the Gaussian curve seem to show that the low yield in very asymmetric fissioncan be attributed to a narrower width of charge distribution, whereas the high yield insymmetric fission may correlate with a wider width. The trends have been explainedqualitatively in terms of a liquid drop model. There is no evidence for 40-proton subshell effect on the fission yield.     

New Gamma Rays from the Neutron-Rich Isotope 189W Decay

The natural Osmium powder was irradiated with fast neutrons.After the chemical separation,the characteristic gamma ray spectra and the time-sequential spectra in the W fraction were measured.11 new gamma lines os ¹⁸⁹W unknown previously were found.     

Measurement of L X-Ray Intensity Ratios for^92U and ^90Th Elements Using Photoionization in an External Magnetic Field

L x-ray intensity ratios Le/Lγ, Lα/L7 and Lβ/Lγ for ^92U and ^90Th are measured by using 59.5keV incident photon energy at 110° and 125° scattering angles. The samples are located in the external magnetic field of intensities ±0.15T, ±0.30T, ±0.45T, ±0.60T and ±0.75T. The experimental results obtained for B = 0 are compared with the theoretical values calculated using Scofield＇s tables based on the Hartree Slater theory. The contribution to the alignment of the external magnetic field is discussed. It is observed that the L x-ray intensity ratios decrease with the increasing magnetic field intensity.     

Production cross-section of 230Ra in the reaction of 60 MeV/u 18O ions with 238U

A thick natural uranium target was bombarded with a 60 MeV/u ¹⁸O beam. The neutron-rich isotope ²³⁰Ra as the target residue was produced through the multinucleon transfer reaction(²³⁸U-4p-4n). The barium and radium fraction as BaCl₂ precipitate were radiochemically separated first from the mixture of uranium and reaction products. Then, the radium fraction was separated from BaCl₂ precipitate by using cation exchange technique. The γ-ray spectra of the Ra fraction were measured using an HPGe detector. The production cross sections of ²³⁰Ra were obtained by a combination of the radiochemical separation technique and off-line γ-ray spectroscopy. The cross section of ²³⁰Ra has been determined to be 66±20 μb.     

Fission Fragment Angular Correlation in the Reaction Induced by 84.0MeV 16O Bombarded 238U

Fission fragment angular distribution and angular correlation in the reaction induced by 84.0MeV ¹⁶O bombarded ²³⁸U have been measured by using two position-sensitive PPAC with large area.Transfer fission has been removed from total fission using fission fragment angular correlation technique.The contribution to the total fission cross section arising from transfer is about 10%.The anisotropy of fission fragment for transfer-fission is rather small,thus the removal of the transfer fission has little effect on the total fragment angular distribution.Indeed the anisotropy becomes larger by about 5% and anomalously anisotropies still persist.     

Monte-Carlo Simulation and Study of Sideward Flow for 238U238U Collisions at CSR Energy Area

The ART(a Relativistic Transport) Model is applied for studying the UU collisions at a beam kinetic energy about 0.52GeV/nucleon. We discuss the time evolution and the centrality dependence for sideward flow of nucleons and pions at two extreme orientation UU collisions. It is found that the collective (side) flow is developed in the high density region and has a saturation in the expansion phase, so it is a sensitive probe for the reaction dynamics in the high density region. A distinct transition from pion flow to antiflow, which is relative to nucleons flow, occurs at the impact parameters of about 8fm and 2fm in tip-tip and body-body UU collisions, respectively. The pion flow is a result of the competition between the collective flow of baryon resonances and the shadowing of spectators through rescatterings and reabsorptions.     

A New Level Scheme of 127I

Study of in beam γ ray spectroscopy of ¹²⁷I has been performed using ¹²⁴Sn(⁷Li, 4n)¹²⁷I reaction at 32 MeV beam energy. A new level scheme of ¹²⁷I has been established including 25 new levels and 52 new γ transitions. Negative parity levels based on 11/2^－ π h_11/2 particle state have been observed up to (35/2^－) extending our knowledge of decoupled structures to the heavier iodine isotope. Two ΔI=2 yrast positive-parity levels have been proposed to be associated mainly with the πg_7/2 configuration due to observations of several strong inter band transitions. Two weakly populated ΔI=2 positive parity levels and a high-lying ΔI=1 cascade have been newly identified and tentatively assigned as πd_5/2 one-quasiparticle and three quasiparticle bands, respectively.     

A Three-Body Model of 11Li,14Be and 17B

The nuclei ¹¹Li,¹⁴Be and ¹⁷B are considered as three-body systems composed of the N=2Z core and two outside neutrons.The core-neutron and neutronneutron interactions are assumed to be the attractive exponential potentials.It has been shown that the three-body system can have a bound state although any two constituents of the system cannot have a bound state. The experimental data of the binding energy and extraordinarily large matter root-mean-square radius can be explained in the frame of the three-body model.