Clarification of the Three-Body Decay of 12C (12.71 MeV)

Using β decays of a clean source of 12 N produced at the IGISOL facility, we have measured the breakup of the 12 C (12.71 MeV) state into three α particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed

Study of β-delayed charged particle emission of 11Li: Evidence of new decay channels

5 pags., 3 figs. -- 9th International Conference on Clustering Aspects of Nuclear Structure and Dynamics (CLUSTERS'07) 3–7 September 2007, Stratford upon Avon, UKThe break-up of the 18.2 MeV state in 11Be was studied in a 11Li β-decay experiment. We report here on the study of the dominating breakup channels involving na6He or 3n2α in the final state, with special emphasis dedicated in this contribution to the three-particle channel. The two emitted charged particles were detected in coincidence using a highly segmented experimental set-up. The observed experimental energy-vs-energy scatter plot indicates a sequential breakup where nuclei of mass 4, alpha particles, and mass 7, 7He, are involved. A Monte-Carlo simulation of the sequential channel, 11Be* → α + 7He → nα6He was performed and compared to the experimental data and to a simulation of the direct break-up of the 18.2 MeV state nα6He by phase space energy distribution. The energy-versus-energy plot are explained by the sequential simulation but not by the phase space simulation. © 2008 IOP Publishing Ltd

A METHOD FOR SHARPENING FIM-SPECIMENS

A method is presented which makes it possible both to sharpen also extremely blunt specimens and to perform controlled back polishing without making the specimens blunter. The method seems to have quite general applications. It has been applied to such different materials as TiC-Ni-based and WC-Co-based cemented carbides, low alloyed and high alloyed steels, low alloyed zirconium and pure titanium

EVALUATION OF ATOM-PROBE SPECTRA FROM TITANIUM CARBONITRIDE

Four (Ti, W)(C, N)-Ni alloys with known composition have been used to investigate how the detected composition varies with crystallography, pulse ratio, nitrogen content and temperature. The interpretation of mass spectra is discussed and conditions of analysis with which correct results can be obtained are given

STATISTICAL CORRECTION FOR PILE-UP IN THE ATOM-PROBE DETECTOR SYSTEM

A procedure is described which can be used to correct atom-probe data for losses due to the detector dead time. The accuracy of the procedure is verified by comparing the experimental isotope distributions of Fe and C with tabulated values. It is also shown that a tilted detector can be used to increase the multi-hit detectivity

ATOM-PROBE ANALYSIS OF ZIRCALOY

Zirconium based alloys in the Zircaloy series have been analysed with atom-probe field-ion microscopy. During specimen preparation an anodic layer is formed, containing about 50% oxygen. In preliminary analyses of the matrix all the minor elements Fe, Ni, Cr and 0 were detected, and it appears possible to determine with the atom-probe whether any particular heat treatment causes matrix depletion

ON ATOM-PROBE ANALYSIS OF CUBIC MX-TYPE CARBIDES AND CARBONITRIDES

The field evaporation behaviour of cubic MX-type carbides and carbonitrides have been investigated using four (Ti,W)(C,N)-2 vol% Ni test alloys with well known compositions. Preferential field evaporation of titanium and nitrogen may occur when the analyses are done in certain crystallographic directions. The reproducibility of the analyses is not very good and this is mainly due to the very high tendency of the atoms to evaporate in pairs or small clusters. It is shown that as much as 14 % of the total C content and 9 % of the total Ti content is lost due to pair ion formation. Since there is no simple way to correct for these losses the instrument must be modified so that either the detector dead time or the mass resolution is decreased

MOLYBDENUM-NITROGEN AND MOLYBDENUM-CARBON COMPLEX FORMATION IN STEELS

The austenitic phase of four nitrogen containing duplex austenitic-ferritic stainless steels was studied by microhardness measurements and atom probe analysis. The hardness increased with nitrogen content, and atom probe analysis showed that a large fraction of the nitrogen atoms appeared as MoN molecular ions. It is argued that the observation of such molecular ions is due to the presence of Mo-N complexes in the austenite. Few CrN ions were observed, but the existence of Cr-N complexes cannot be ruled out. Comparison with earlier data from the martensitic and ferritic matrices of high speed steels suggest that also in these a complex formation may occur : ions of the type MoC were sometimes observed although to a much lesser extent than MoN in austenite. In the latter case, between 70 and 100% of the least abundant of Mo and N was observed as MoN