ENSDF evaluation for A=260-265

1. ENSDF evaluation forA=260-265 M. Gupta Manipal University, Manipal, India T. W. Burrows National Nuclear Data Center, Brookhaven National Laboratory, USA

2. Motivation for evaluation • α-decay mass chains from some heavier nuclei (A≥266) end in this region • update of this region is due Earlier evaluations of these nuclides in : 1999Ar21, 1999Ak02 and 2001Ak11 265Rf : 2000Fi12 • the same evaluation methodology adopted for (distant) ancestors could be usefully extended to descendents within an α-decay chain for consistency and uniformity of treatment • New results / chemistry

3. Chart of Nuclides showing A=260-265 region Cold fusion Hot fusion Physics interest: Deformed shell region N ~162-164 A=265 A=260

4. Guidelines for evaluation: As established in 2005Gu33: International Union of Pure and Applied Chemistry, Trans-fermium Working Group (IUPAC-TWG-JWP): R. C. Barber et. al.,Prog. Part. Nucl. Phys., v29, p453-530, 1992 • IUPAC/IUPAP - TWG is concerned with thediscovery of a new element • ENSDF evaluations seek primarily to adopt thebest set of data for a givenisotope Priority of discovery for elements in the A=260-265 region already established by IUPAC/IUPAP-TWG/JWP Guidelines serve well to re-visit older data and evaluate new data within a consistent framework

5. Data checked for: • Measurement of excitation functions • Cross-bombardments: • changing the relative yields of xn-evaporation channels by • varying mass number of Projectile or Target (useful in “hot • fusion”) • Independent verification by another laboratory • Redundancy and internal consistency of data • Estimates of randomness • Consistency of assignments of daughters: • secured connection to known descendents; (“cold-fusion”) • presence of elemental signatures such as x-rays (in the • absence of mass measurements); • direct measurements of nuclei in the decay chain by • independent chemical studies  determination of Z • T1/2 : larger statistics, better value(results can be ‘combined’)

6. Statistical determination of uncertainties Where not quoted or for combining /including new data Method of K.-H. Schmidt et. al., Z. Phys. A316, 19, 1984 τu = Upper limit (estimate); τl = lower limit (estimate) tm = average mean time; z = 1 for 68% confidence level; n = # of events Expected accuracy of approximation: within 10%

7. “Viola-Seaborg” Phenomenology ‘Dubna’ parameter set, obtained by a fit to 65 even-even nuclei: V. E. Viola and G. T. Seaborg, J. Inorg. Nucl. Chem., v28, p741, 1966

8. A=260-265 • Available data for 31 observed nuclides considered • A = 265 (4); 264 (3); 263 (6); 262 (5); 261 (6); 260 (7) • Experimental details include: • Differences in interpretation of observations for parents and daughters • e.g. 265/266Sg  261/262Rf • Cross-sections • including revisions in cross-sections following re-interpretation of data (e.g. 262/263Db) • Reassignments --- existing data • noted in both original and “re-assigned” data sets • SF: TKE, mass distributions, n-multiplicity • Chemical properties

9. Chemical studies: A=260-265 region • ~40% nuclides studied using chemistry • Reporting of experimental uncertainties in chemical studies varies with: • Specific chemical techniques used (e.g. parent half-life not measured in some cases) • Motivation for experiment (e.g. measurement for presence or absence of nuclide rather than accurate half-life) • Interpretation of half-lives (e.g. upper or lower limits?) • Properties derived from chemical studies supported if same nuclides are also studied by “physical” techniques • Re-assignments possible due to ambiguities in data

10. Conclusions • Uniform criteria used to evaluate A=260 – 294 region • Evaluation methodology is internally consistent • Re-visiting ‘old’ data yields useful information • Reveals important experimental parameters vital to adopting the bestdata set in the absence of mass measurements • e.g. cross-sections / excitation function measurements • Atomic properties revealed by chemistry • Chemical methods: • Increased statistics • Independent verification