Reaction mechanism studies using the CN/ER spin distribution

To study basic properties of the fusion reaction dynamics for heavy compound systems the partial-wave distribution can be employed as an alternative to the classically used fusion/fission excitation functions. A variety of reactions leading to compound nuclei (CN) in the Pb region can be used to investigate features like the fusion-fission competition, the role of deformation in the fusion of heavy systems and a possible effect of the Z = 82 shell on the enhancement of evaporation residue (ER) production.Received: 5 November 2002, Revised: 26 March 2003, Published online: 9 March 2004PACS: 24.75. + i General properties of fission - 25.70.Gh Compound nucleus - 25.70.Jj Fusion and fusion-fission reactions     

Fusion-fission of heavy and superheavy nuclei

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z=82–122 formed in the reactions with ⁴⁸Ca and ⁵⁸Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multidetector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments; fission, quasifission, and evaporation residue cross sections; and multiplicities of neutrons and γ-quanta and their dependences on the mechanism of formation and decay of compound systems have been studied.     

Search for new isotopes of element 112 by irradiation of 238U with 48Ca

The reaction ⁴⁸Ca+²³⁸U was investigated at the recoil separator VASSILISSA at the Flerov Laboratory of Nuclear Reactions, JINR Dubna, in attempts to synthesize new isotopes of element 112. The experiments were performed at two beam energies resulting in excitation energies of the compound nucleus of 33 and 39 MeV. The collected beam dose was 3.5 × 10¹⁸ and 2.2 × 10¹⁸, respectively. Two spontaneous fission events were observed at the lower beam energy, which tentatively were assigned to the new neutron rich isotope ²⁸³112 produced in the reaction ²³⁸U(⁴⁸Ca,3n)²⁸³112. The measured cross-section is (5.0^+6.3 _−3.2) pb and the half–life is (81⁺¹⁴⁷ ₋₃₂) s. No event was observed at the higher beam energy resulting in the upper cross–section limit of 7.3 pb. Received: 12 October 1998 / Revised version: 12 January 1999     

Gammasphere上裂变丰中子核核结构若干前沿领域的新进展(Ⅱ:第三和第四部分)(英文)

使用Gammasphere多探测器系统对252Cf裂变源瞬发γ射线进行γ-γ-γ和γ-γ(θ)符合测量,A～100(Z～40,N56)丰中子核区关于形状过渡、形状共存和形状突变的深入研究获得了新的进展。奇-Z核的系统研究揭示了从Z=39(Y)同位素的轴对称大四极形变到Z=43(Tc),44(Ru)和45(Rh)同位素中具有中等四极形变之大三轴形变的过渡。Nb(Z=41)同位素具有过渡核的特征。根据邻近同位素和同中素带交叉信息的系统性及推转壳模型(CSM)计算,Tc和Rh偶-N同位素中观察到的带交叉产生于一对h11/2中子的转动顺排。首次观察到100Nb(Z=41,N=59)的高自旋能级纲图和形变态,从而证实了100Nb中的形状共存,并确认,在Nb同位素链上,基态形状突变发生于N=58(球形)到N=59(大形变);而在Sr(Z=38),Y(Z=39)和Zr(Z=40)各同位素链上,基态形状突变均发生于N=59(球形)到N=60(大形变)。100Nb具有大形变基态,同现有理论预言相矛盾,其大形变的基态及转动带所具有的很大的和不规则的转动惯量具有重要的理论意义。对奇-质子Cs(Z=55)和La(Z=57)丰中子同位素八极激发的详细研究,发现了141,143,144Cs同位素链上电二极矩D0随中子数增加而减小的急剧变化,此前在145,147La中观察到的电二极矩D0的较缓和的减小似乎亦很陡地下延至148La。在Cs和La同位素中观察到的电二极矩D0的急剧下降很可能同偶-质子核146Ba和224Ra中观察到的电二极矩D0的急剧下降相类似,后者已获反射非对称平均场壳修正理论的成功解释。实验证明,141Cs具有很大电二极矩D0。141Cs和142Xe中观测到的很大的电二极矩D0和仅在141Cs中观察到的电二极矩D0的simplex量子数相关性需要进一步的理论研究。根据转动频率比值ω-(I)/ω+(I)的检定,同Xe同位素一样,认定Cs同位素中包括号143Cs的八极激发为八极振动,而在La同位素中存在八极形变。     

Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams

This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the synthesis of superheavy nuclei in reactions induced by ⁴⁸Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with stable beams are considered as a test for the suggested ideas. Received: 1 May 2001 / Accepted: 4 December 2001     

Multiplicity of prompt neutrons from spontaneous fission of the isotope 252102

The average number of prompt neutrons, $\text{v}$, emitted in the spontaneous fission of the isotope of element 102 with mass number 252 and a half-life of 2.4 s has been measured to be 4.15±0.30 relative to $\text{v}\text{= 2.69±0.01}$ for spontaneous fission of ²⁴⁴Cm.     

Production of high-purity26Al

²⁶Al is a positron emitting radioisotope of aluminium and has a half-life of 7.16×10⁵y. In addition to annihilation -rays of 511 keV, there are three high energy -rays 1129 (2.4%), 1809 (99.73%) and 2938 (0.27%) keV.²⁶Al is the only radioisotope of aluminium available for radiochemical applications, the half-lives of the other aluminium isotopes are seconds and minutes. The usage of²⁶Al is very important in the investigations of the metabolism of Al in human body (for example in Alzheimer disease studies) or as a tracer in radiochemical studies. But²⁶Al is such a long-lived isotope that the task of producing it in tangible amounts is a very difficult one.     

Investigation of uranium and thorium concentrations in the fluorite beds of Anatolia by using solid state nuclear track detectors

Uranium and thorium concentrations of fluorite samples taken from the main fluorite beds of Anatolia (Turkey) have been determined by fission fragment radiography using solid state nuclear track detectors (SSNTDs). The fissionable elements concentration of the fluorite samples were found to be 10^–4–10^–7 g/g. The Th/U ratio, obtained for all the fluorite samples, is found to be characteristic for the location of the samples. Some correlations between the concentration of Th and those of lanthanites and concentration of U and that of Mo or Zr are observed.