Spectroscopy of No and its daughters

New high-statistics data have been obtained on the decay properties of ²⁵³No and its daughters using the reaction ²⁰⁷Pb(⁴⁸Ca, 2n)²⁵³No. This was made possible thanks to an improved transmission of fusion–evaporation residues through the VASSILISSA recoil separator and an increased efficiency of the GABRIELA detector setup. The decay schemes of ²⁵³No and ²⁴⁹Fm have been revisited. The known level scheme of ²⁴⁹Fm has been confirmed, including a new level at 669 keV excitation energy. The observation of L X-rays in coincidence with the α decay of ²⁴⁹Fm gives additional support to the ground-state configuration of 1/²⁺[631]$1/2^{+}[631]$ instead of 5/²⁺[622]$5/2^{+}[622]$ for ²⁴⁵Cf. In both ²⁴⁹Fm and ²⁴⁵Cf, the interpretation of the data has been checked by comparing experimental α-particle and γ-ray spectra with realistic simulations of the decay cascades and of the interaction of particles and photons in the detectors of GABRIELA. The population of a 0.7 ms isomeric state attributed to ²⁵³No is confirmed by an α-tagged calorimetric measurement and the corresponding γ and electron decay spectra are presented. Possible evidence for more than one isomer is given and a tentative partial decay scheme is discussed in the light of the available experimental data, systematics and theoretical expectations.     

Short-Lived Isotopes of Transfermium Elements: Studying Characteristics of Spontaneous Fissioning

series of experiments performed in 2014–2015 using the SHELS separator and a beam of multicharged ions from the U-400 accelerator at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research) in Dubna is described. In preparation for a large program of experiments with a beam of highly charged ions of ⁵⁰Ti, an experiment is performed to study the spontaneous fissioning (SF) of short-lived neutron-deficient isotope ²⁵⁶Rf formed in complete fusion reaction⁵⁰Ti + ²⁰⁸Pb = ²⁵⁶Rf + 2n. The half-life of ²⁵⁶Rf is measured along with the probability of its SF decay. The average number of neutrons per one event of ²⁵⁶Rf SF (\(\bar v\)= 4.47 ± 0.09) is obtained for the first time. The results from experiments to study the SF of short-lived neutron-deficient isotopes synthesized in complete fusion reaction ⁴⁸Ca + ²⁰⁴Pb → ²⁵²No* are presented as well. Two short-lived activities attributed to the SF of the ground and isomeric states of ²⁵⁰No are revealed. The half-life, total kinetic energies of fission fragments, and neutron multiplicities are measured for the obtained short-lived nuclei. The average numbers of neutrons per one SF event are \(\bar v\)= 4.38 ± 0.13 and \(\bar v\)= 3.90 ± 0.20, respectively, for SF activity with t_1/2 = 5.1 ± 0.3 and t_1/2 = 36 ± 3 μs.     

Spectroscopy of the Isotopes of Transfermium Elements in Dubna: Current Status and Prospects

Physics of Atomic Nuclei - A great many experimental studies devoted to exploring in detail the properties of radioactive decay of the isotopes of transfermium elements by means of alpha, beta, and...     

Neutron multiplicity at spontaneous fission of 246Fm

The neutron-deficient isotope ²⁴⁶Fm , produced in the complete fusion reaction ⁴⁰Ar$ + $²⁰⁸Pb , was investigated. The main goal of the experiment was to determine the neutron multiplicity at spontaneous fission of this isotope. For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 ³He -filled counters has been mounted around the focal-plane detector chamber. From the experimental data the average number of neutrons per spontaneous fission of ²⁴⁶Fm was determined ( $ \bar{{\nu}}$ = 3.55±0.5) .     

Spontaneous-fission decay properties and production cross-sections for the neutron-deficient nobelium isotopes formed in the 44, 48Ca + 204, 206, 208Pb reactions

Heavy-ion fusion reactions ⁴⁸Ca + ²⁰⁴Pb and ⁴⁴Ca + ²⁰⁸Pb leading to the same compound nucleus ²⁵²No^* were run in attempts to produce new neutron-deficient spontaneous-fission isotopes of ^249,250No using the electrostatic separator VASSILISSA. Production cross-sections for the spontaneous-fission activities with the half-lives 5.6 and 54 μs observed in these reactions are compared with the measured ones for the well-known isotopes of ^{251 - 255}No formed in the heavy-ion fusion reactions ⁴⁸Ca + ²⁰⁶Pb and ⁴⁸Ca + ²⁰⁸Pb. The obtained excitation functions for the reaction products formed after the evaporation of 1-4 neutrons from the corresponding compound No nuclei have been compared with similar data obtained earlier and results of statistical model calculations. Received: 26 July 2002 / Accepted: 5 November 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: eremin@sunvas.jinr.ru Communicated by J. ?yst?     

Isomeric states in 253No

Isomeric states in ²⁵³No have been investigated by conversion electron and γ -ray spectroscopy with the GABRIELA detection system. The 31μs isomer reported more than 30 years ago is found to decay to the ground state of ²⁵³No by the emission of a 167keV M2 transition. The spin and parity of this low-lying isomeric state are established to be 5/2⁺ . The presence of another longer-lived isomeric state is also discussed.