Precise branching ratios to unbound 12C states from ¹²N and ¹²B β-decays

Two complementary experimental techniques have been used to extract precise branching ratios to unbound states in 12C from 12N and 12B β-decays. In the first the three α-particles emitted after β-decay are measured in coincidence in separate detectors, while in the second method 12N and 12B are implanted in a detector and the summed energy of the three α-particles is measured directly. For the narrow states at 7.654 MeV (0+) and 12.71 MeV (1+) the resulting branching ratios are both smaller than previous measurements by a factor of ~2. The experimental results are compared to no-core shell model calculations with realistic interactions from chiral perturbation theory, and inclusion of three-nucleon forces is found to give improved agreement.status: publishe

Precise branching ratios to unbound 12 C states from 12 N and 12 B β-decays

Two complementary experimental techniques have been used to extract precise branching ratios to unbound states in 12C from 12N and 12B β-decays. In the first the three α-particles emitted after β-decay are measured in coincidence in separate detectors

Precise branching ratios to unbound 12C states from 12N and 12B β-decays

6 pages, 2 tables, 4 figures.--PACS nrs.: 21.45.-v; 23.40.-s; 27.20.+n; 21.60.De.--Printed version published Aug 3, 2009Two complementary experimental techniques have been used to extract precise branching ratios to unbound states in 12C from 12N and 12B β-decays. In the first the three α-particles emitted after β-decay are measured in coincidence in separate detectors, while in the second method 12N and 12B are implanted in a detector and the summed energy of the three α-particles is measured directly. For the narrow states at 7.654 MeV (0+) and 12.71 MeV (1+) the resulting branching ratios are both smaller than previous measurements by a factor of 2. The experimental results are compared to no-core shell model calculations with realistic interactions from chiral perturbation theory, and inclusion of three-nucleon forces is found to give improved agreement.This research was supported by the Academy of Finland (No.project 44875), by the Spanish Agency CICYT (No. FPA2005-02379) and the MEC Consolider project CSD2007-00042, by the Belgian IAP P6/23 project and FWO-Vlaanderen, by the European Union sixth Framework Programme “EURONS” (No. 506065), by the Swedish Research Council and the Knut and Alice Wallenberg foundation, by LLNL (Contract DE-AC52-07NA27344 and DE-FC02-07ER41457) and by DE-FG02-87ER40371.Peer reviewe