Photofission for the production of radioactive beams: Experimental data from an on-line measurement

A PARRNe 1 experiment (Production d'Atomes Radioactifs Riches en Neutrons) aimed at the production of neutron-rich radioactive noble gases produced by photofission has been performed at CERN. The LEP Pre-Injector (LPI) has been used to deliver a 50 MeV electron beam. The results obtained show clearly that the use of an electron beam to produce neutron-rich fission fragments for futur RNB facilities is an option that should not be neglected. Received: 20 July 2001 / Accepted: 5 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: ibrahim@ipno.in2p3.fr Communicated by D. Guerreau     

Physics with REX-ISOLDE and MINIBALL

REX-ISOLDEis an experiment atISOLDE/CERN with the aim to study the nuclear structure of neutron-rich nuclei using radioactive ion beams up to 2.2 MeV/u. The highly-efficient γ-ray detector set-up MINIBALL will be used to explore reactions induced by Coulomb excitation or neutron transfer.     

First $\gamma$-rays from radioactive beams at REX-ISOLDE

In order to demonstrate a novel scheme to accelerate radioactive ions and to provide radioactive ion beams for physics experiments, the radioactive beam experiment (REX) was installed at ISOLDE, CERN. One of the main experimental devices that will use these beams is the newly commissioned HPGe array MINIBALL featuring an excellent granularity, energy resolution, and rate capability. First experiments have been performed using beams of neutron-rich Na and Mg isotopes.Received: 8 November 2002, Published online: 24 February 2004PACS: 41.75.Lx Other advanced accelerator concepts - 29.30.Kv X- and -ray spectroscopy - 25.60.Je Transfer reactionsH. Scheit: For the REX-ISOLDE-MINIBALL Collaboration     

Coulomb excitation of neutron-rich 138,140,142Xe at REX-ISOLDE

We report on “safe” Coulomb excitation of neutron-rich ^138,140,142Xe nuclei. The radioactive nuclei have been produced by ISOLDE at CERN and post-accelerated by the REX-ISOLDE facility. The γ-rays emitted by the decay of excited states have been detected by the MINIBALL array. Recent results are presented.     

Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL

We report on “safe” Coulomb excitation of neutron-rich nuclei. The radioactive nuclei have been produced by ISOLDE at CERN and postaccelerated by the REX-ISOLDE facility. The γ rays emitted by the decay of excited states have been detected by the MINIBALL array. Recent results are presented and compared to theoretical models. on behalf of the MINIBALL and REX-ISOLDE Collaborations The text was submitted by the author in English.     

Independent yields of Kr and Xe isotopes in the photofission of heavy nuclei

The yields of Kr (A = 87–93) and Xe (A = 138–143) primary fission fragments produced in ²³²Th, ²³⁸U, and ²⁴⁴Pu photofission upon the scission of a target nucleus and neutron emission were measured in an experiment with bremsstrahlung from electrons accelerated to 25 MeV by a microtron, and the results of these measurements are presented. The experimental procedure used involved the transportation of fragments that escaped from the target by a gas flow through a capillary and the condensation of Kr and Xe inert gases in a cryostat at liquid-nitrogen temperature. The fragments of all other elements were retained with a filter at the capillary inlet. The isotopes of Kr and Xe were identified by the γ spectra of their daughter products. The mass-number distributions of the independent yields of Kr and Xe isotopes are obtained and compared with similar data on fission induced by thermal and fast neutrons; the shifts of the fragment charges with respect to the undistorted charge distribution are determined. Prospects for using photofission fragments in studying the structure of highly neutron-rich nuclei are discussed.     

Recent developments and on-line tests of uranium carbide targets for production of nuclides far from stability

The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. Yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are compared. The yields from ISOLDE original target are presented for comparison as well.     

Decay of neutron-rich Ga isotopes near N = 50 at PARRNe

The PARRNe facility has been used to produce neutron-rich isotopes ^83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in ⁸³Ge and the first excited level in ⁸⁴Ge have been measured for the first time.     

"Safe" Coulomb excitation of 30Mg

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."     

The beta-decay scheme of <Superscript>232</Superscript>Fr and the K = 0 ground-state band in <Superscript>232</Superscript>Ra

The beta-decay of ²³²Fr to excited states in ²³²Ra has been studied using gamma-gamma coincidence detection combined with the isotope separator on-line technique at the ISOLDE PSB facility at CERN. Earlier findings are confirmed and three new gamma lines are reported. In addition to the beta-decay characteristics of ²³²Fr, the K = 0 ground-state band in ²³²Ra is identified. A yield survey of neutron-rich Fr isotopes, important also for the EURISOL project, is incorporated.Received: 20 April 2004, Revised: 12 May 2004, Published online: 13 July 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 23.20.-g Electromagnetic transitions - 28.60. + s Isotope separation and enrichment - 29.25.Rm Sources of radioactive nuclei     

Role of thermal conduction in single-bubble cavitation

Effect of thermal conduction on radiation from a single cavitating bubble has been studied in a hydrochemical framework including variation of heat conductivity of noble gases up to 2500 K. Results of numerical simulation show that thermal conductivity plays an important role in determining ultimate cavitation temperature. Higher thermal conductivity of lighter noble gases causes to more thermal dissipation during the bubble collapse, leading to a lower peak temperature. Moreover, at the same driving conditions, radius of light emitting region is greater for heavier noble bubbles. Therefore, sonoluminescence radiation is more intensive from heavier noble gases. Phase diagrams of single-bubble sonoluminescence have also been calculated and in comparison with available experimental data, there is a relatively good agreement between the theory and experiment for noble gases.     

Measurement of fusion excitation functions of 27, 29, 31Al + 197Au

A systematic study of the sub-barrier fusion reactions with neutron-rich projectiles has been carried out for three isotopes ^27,29,31Al bombarding a ¹⁹⁷Au target. A target chamber equipped with a target stack and sets of MWPC was employed in order to enhance the efficiency of the radioactive beam experiment. Coupled-channel calculations including the quadrupole excitations do not well fit the measured fusion excitation functions, whereas flat barrier distributions to represent the coupling to the neutron transfer largely account for the observed enhancement of the sub-barrier fusion cross-sections. Received: 13 March 2001 / Accepted: 27 April 2001     

Influence of noble gases on electron cyclotron heated hydrogen plasma

A quartz-chamber 2.45-GHz electron cyclotron resonance ion source (ECRIS) is designed at Peking University for the diagnostic purpose. Experimental results show that the added noble gases in hydrogen could cause a decrease of electron temperature and an increase of electron density. In this work, a numerical model is upgraded for ECR plasma generated by mixed gases. On this basis, the model is applied for the composed hydrogen plasma with additional noble gases. And dependences of neutral gas density and electron density on electron temperature are presented for individual gas (He, Ar, and H₂) and gas mixture, respectively. The calculated results are basically in accordance with the diagnostic results of ECRIS.     

600MeV ~(18)O+~(nat)Pb(厚靶)系统生成Hg同位素独立产额测量(Ⅱ)结果与分析

报道了600MeV（18）O轰击（nat）Ph（厚靶）生成的质量数在180—209之间的Hg同位素产物独立截面的测量结果．通过与600MeV质子轰击天然铅靶生成Hg同位素产额分布的比较，讨论了几个质量区段Hg同位素的生成机制．测量结果也与相对论重离子碎裂反应双质子移出道的产额分布进行了比较．结果表明，中能重离子与中子较富集靶核组成的反应系统对生成丰中子类靶余核具有较明显的优势．     

New information on β-delayed neutron emission from 12,14Be

The β-delayed neutron branches from neutron-rich Be-isotopes have been measured with a setup sensitive down to thermal energies. For ¹⁴Be a new value of P_n = 101 ± 4% has been found for the total neutron-emission probability and an upper limit of 2.4% (95% confidence level) is imposed on the combination P_2n + 3P_3n of multi-neutron emission probabilities. Moreover, an improved value of P_n = 0.50 ± 0.03% has been obtained for ¹²Be. A time-correlation method, previously developed for a continuous radioactive beam to determine neutron branching ratios, has been revised and adapted to the pulsed secondary beam at ISOLDE, CERN.     

中能区丰中子核11Li的反应总截面的测量

利用HIRFL提供的50MeV/u的¹³C束流轰击Be靶, 通过RIBLL选择出放射性核素¹¹Li. 实验采用透射法测量了25—45MeV/u的¹¹Li在²⁸Si靶上的反应总截面. 采用双参数Gauss密度分布形式, 利用Glauber模型很好地拟合了高能和中能区的¹¹Li实验数据, 并从密度分布中提取了核的物质均方根半径.     

Total Photoabsorption Cross Section and Excitation Function in the Quasi-Deuteron Energy Region

In photofission a lot of studies have been made to analyze the energy of the nuclei to understand their inner structure. The relevance of the excitation function has been pointed out. The Rami J tonian of interaction for the photofission was deduced and connected to the excitation function.     

Segregation of vapor and gas in a sonoluminescing bubble

Computer simulations of bubble oscillations in water are performed for various noble gases taking into account the segregation of water vapor and noble gas inside a collapsing bubble, which was predicted by Storey and Szeri [J. Fluid Mech. 396 (1999) 203]. It is clarified that the number of water vapor molecules dissociated inside a collapsing bubble is larger for heavier noble gases because of the lower thermal conductivity and the segregation of vapor and noble gas. It is also clarified that the temperature inside a helium bubble at the collapse increases considerably by the mixture segregation because a lesser amount of vapor is trapped inside a collapsing bubble. It is also clarified that multibubble sonoluminescence (MBSL) from heavier noble gases is brighter because of the lower ionization potential which results in the higher electron density and stronger plasma emissions.     

放射性核束的库仑激发

综述了利用中、高能放射性核束的库仑激发方法研究位于N＝20和28主壳隙附近的丰中子核结构所取得的进展．系统的实验结果清晰地表明,在离开β稳定线区域时N＝20兰壳隙突然消失和N＝28主壳隙的减弱过程．提出了利用兰州放射性束流线开展双幻核Ni50附近核素的低位能级核结构研究的构想． The study of coulomb excitation of the neutron-rich nuclei around N=20 and 28 shell closure with radioactive ion beam at intermediate energy is reviewed. The systematics of the measured energy of the 2+1 state shows that the N=20 shell closure in neutron-rich isotopes with Z≤12 disappears suddenly and N=28 shell elosure appears to be weak for 44S.The coulomb excitation studies of the exotic nuclei around the double magic 7828Ni50 at RIBLL are proposed.     

Measurement of hadron shower punchthrough in iron

The total punchthrough probability of showers produced by negatively charged pions of momenta 30, 40, 50, 75, 100, 200 and 300 GeV/c, has been measured in the RD5 experiment at CERN using a toroidal spectrometer. The range of the measurement extends to 5.3 m of equivalent iron. Our results have been obtained by two different analysis methods and are compared with the resutls of a previous experiment.partially supported by Hungarian grant OTKA-4089