The direct 3α decay branch from the 02+ state at Ex=7.65  MeV in 12C, which is known as the Hoyle state, is considered to affect the triple-α reaction rate strongly and to give crucial information on its structure. We have performed a high-precision measurement of the 3α decay from this state using the 12C(12C,3α)12C reaction at E12C=110  MeV. The branching ratio of the direct 3α decay was under the detection limit in the present experiment. By comparing with Monte Carlo simulations for three decay mechanisms as the sequential decay through the ground state of ^{8}Be, the direct decay with equal energies of three α particles, and the direct decay to the phase space uniformly, we have obtained the upper limit of 0.2% on the direct 3α decay.

Background-free" spectra of inelastic α-particle scattering have been measured at a beam energy of 385 MeV in 90,92 Zr and 92 Mo at extremely forward angles, including 0 • . The ISGMR strength distributions for the three nuclei coincide with each other, establishing clearly that nuclear incompressibility is not influenced by nuclear shell structure near A ∼90 as was claimed in recent measurements. PACS numbers: 24.30.Cz, 21.65.+f, 25.55.Ci, 27.60.+j Nuclear incompressibility is a fundamental quantity characterizing the equation of state (EOS) of nuclear matter [1]. A number of important phenomena such as the radii of neutron stars, the strength of supernova explosions, transverse flow in relativistic heavy-ion collisions, the nuclear skin thickness, etc. require a good understanding of the EOS of nuclear matter [2,3]. The nuclear incompressibility for infinite nuclear matter, K ∞ , may be determined experimentally from the compressional "breathing mode" of nuclear density oscillation, the isoscalar giant monopole resonance (ISGMR), in finite nuclei [4,5]. In the scaling model, the energy of the ISGMR is directly related to the nuclear incompressibility of the nucleus and is given by [4]:where K A is the incompressibility of a nucleus with mass number A, r 2 0 is the ground state mean square radius, and m is the nucleon mass. The determination of K ∞ from K A is achieved within a framework of self-consistent RPA calculations, using the widely accepted method described by Blaizot et al. [2,6]. The presently accepted value of K ∞ , determined from ISGMR in "standard" nuclei such as 90 Zr and 208 Pb, is 240 ± 20 MeV [7-10]. Because the compressional modes are collective phenomena, the determination of K ∞ should be independent of the choice of the nucleus, provided that approximately 100% of the energy weighted sum rule (EWSR) fraction is exhausted in the ISGMR peak; this condition is satisfied for sufficiently heavy nuclei (A ≥ 90) [2]. The use of the aforementioned "standard nuclei" stems primarily from the relative ease in doing theoretical calculations for the doubly-magic nuclei.In recent work by the Texas A & M group [11][12][13], it has been claimed that the ISGMR strength distributions vary in a rather dramatic manner in nuclei in the A ∼ 90 region. In particular, the A=92 nuclei, 92 Zr and 92 Mo, emerged quite disparate from the others: The ISGMR energies (E ISGMR ) for 92 Zr and 92 Mo were observed to be, respectively, 1.22 and 2.80 MeV higher than that of 90 Zr. Consequently, the K A values determined for 92 Zr and 92 Mo were ∼27 MeV and ∼56 MeV, respectively, higher than that of 90 Zr. These results, if correct, imply significant nuclear structure contribution to the nuclear incompressibility in this mass region. Such nuclear structure effects have not been observed in any of the investigations of ISGMR going back to its first identification in the late 1970's [14,15] and, indeed, would be contrary to the standard hydrodynamical picture associated with this mode of collective oscillation [16]. Further...

We report on the operation of co-located 129 Xe and 131 Xe nuclear spin masers with an external feedback scheme, and discuss the use of 131 Xe as a comagnetometer in measurements of the 129 Xe spin precession frequency. By applying a correction based on the observed change in the 131 Xe frequency, the frequency instability due to magnetic field and cell temperature drifts are eliminated by two orders of magnitude. The frequency precision of 6.2 µHz is obtained for a 10 4 s averaging time, suggesting the possibility of future improvement to ≈ 1 nHz by improving the signal-to-noise ratio of the observation.