Research

Superheavy Nuclei Research Group

Date:27-06-2012   |   【Print】 【close

How many elements exist? How electrons are arranged in the superheavy atoms? What are their chemical properties? How long is the life time of nuclides in the stability island? What determine the stability of these nuclides? The study for the superheavy elements (SHEs) could answer the above significant and meaningful questions in science.

In 1960s, the nuclear structure models including shell correction predicted the existence of a stability island of SHEs centered at Z=114, 120~126 and N=184, which is a region of the next doubly magic shell closure above 208Pb. Since then, great efforts have been devoted to the investigation of SHEs and remarkable successes have been achieved to explore the limits of the chart of nuclides toward its upper end both experimentally and theoretically.

With the construction of HIRFL-CSR (Heavy Ion Cooler-Storage-Ring Research Facility, Lanzhou) the research for heaviest nuclei has been one of the most important scientific missions. Over 15 years of research program, several new superheavy isotopes were synthesized and more promising programs are in planning.

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Achievement: 

In 2000, the new nuclide 259Db was produced in the complete-fusion reaction 241Am(22Ne, 4n)259Db. Evaporation residues were transported by the He-jet equipment and subsequently identified by genetic relationship to known nuclides. The α-decay energy and half-life value of 259Db were measured to be 9.47±0.03 MeV and 0.51±0.16 s, respectively.

Four years later, another new isotope 265Bh was unambiguously assigned via the reaction of a 243Am target with 26Mg ions (168 MeV). A total of eight correlated decay chains of 265Bh and four decay events of 264Bh were found using a set of rotating-wheels system. The measured α-decay energy (9.24±0.05 MeV) and half-life (0.94+0.70-0.31 s) were in agreement with theoretical predictions.

In 2012, the decay properties of 271Ds (Z = 110) were studied via the 208Pb(64Ni, n) reaction at a beam energy of 313.3MeV by means of the new commissioned gas-filled recoil separator. One correlated α-decay chain for 271Ds was established. The α-particles energy and decay time of the 271Ds nucleus were measured to be 10.644 MeV and 96.8 ms, which are consistent with the values reported in the literature.

This work indicates that the new apparatus has the basic ability for the study of superheavy nuclei with Z~110. And the -271Ds isotope is also the heaviest nuclei synthesized in the domestic experimental equipments so far.

Furthermore, to deeply understand the reaction mechanism of producing superheavy nuclides, we are also doing some relevant theoretical researches. The Di-Nuclear System model has been used to describe the fusion process for heavy ion reactions. Some published calculations are shown to be well in agreement with the measured data.

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Apparatus: 

A new gas-filled recoil separator was installed in the HIRFL (Heavy Ion Research Facility, Lanzhou) to separate the evaporation residues (EVRs) from other beam ions and unwanted reaction products. It is filled with helium gas at the pressure of about 0.8mbar. The focal plane detector system consisting a silicon box and a time-of-flight detector was improved.

 

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Research Staff: 

Gan Zaiguo

Leader, PhD. Supervisor

Email: zggan@impcas.ac.cn

Tel:+86-931-4969304

Huang Minhui

Email:hmh@impcas.ac.cn

Tel: +86-931-4969302

Huang tianheng

Email:huangth@impcas.ac.cn

Tel: +86-931-4969651

Ma Long

Email:mxl@impcas.ac.cn

Tel: +86-931-4969302

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List of Selected Publications: 

1) Z.G. Gan, Z. Qin, et al, A new alpha-particle–emitting isotope 259Db, Eur.Phy.J.A 10, 21–25 (2001)

2) Z.G. Gan, J.S. Guo, New isotope 265Bh, Eur.Phy.J.A 20, 385–387 (2004)

3)Z.Y.Zhang, Z.G. Gan, Ma Long, Observation of the Superheavy Nuclide 271Ds,Chin.Phys.Lett. Vol. 29, No. 1 (2012)

4)M.H Huang, Z.Y.Zhang, Z.G. Gan, Dynamical deformation in heavy ion collisions and formation of superheavy nuclei, Phys.Rev.C 84, 064619 (2011)