Study On The α-decay Properties Of N=128-131 Short-lived Actinides

Isotopes with Z>83,N=128-130 are among the shortest-livedαemitters in the chart of nuclides.For isotopes with Z>90,their production cross sections via fusion evaporation reactions are very low,in the order of nano-barn.So their experimental data is scarce.Located in the transitional region between the spherical N¹26 nuclei and quadrupole-octupole deformed N¹34 ones,shape coexistence was predicted in this region.In the present thesis work,some light short-lived actinides were produced via the fusion-evaporation reactions ⁴⁰Ar+¹⁸⁷Re/¹⁸⁶W,separated using the gas-filled recoil separator SHANS and implanted in a double sided silicon strip detector,where the implantation and subsequentαdecay were recorded.Short-livedαradioactivities with half-lives down to tens of nanoseconds were resolved by using the fast digitial pulse processing technique.The preamplifier signal has fast rise time⁴0 ns and slow exponential decay time with decay constant⁵00 ms.Fast digitial pulse processing technique was used to register the waveforms of the preamplifier signals.Algorithms for extracting amplitudes and times of overlapping pulses from the pileup waveforms were developed.For overlapping pulses with time difference 500 ns<?T<15μs,the trapezoidal algorithm and RC-CR² filter were used to extract the amplitude and time,respectively,the energy resolution obtained was 55 keV.For pileup pulses with time difference 200 ns<?T<500 ns,average difference algorithm and exponential fitting method were used to extract the amplitude and time,respectively,the energy resolution obtained was70 keV.Two new short-lived isotopes ^223,224Np were identified,and theα-decay chains of their short-lived daughters ^219,220Pa were established for the first time.The absence of the Z=92subshell closure near N=126 is supported by the trend in the proton separation energy of N=130 isotones up to Z=93.Fine structure in theαdecay of ²²³U was observed and theα-particle energy for the ground-state to ground-state transition was revised.Based on the systematics of reducedα-decay width,shape/structure evolutions along the N=129 and 131isotonic chains are found asynchronous.Onset of octuople deformation was revealed to start in N=131 istones from Z=88 and shape co-exsitence was proposed in the N=129 isotones215Rn and ²¹⁷Ra.