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We report the first successful extraction of accumulated ultracold neutrons (UCN) from a converter of superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. Windowless UCN extraction is performed in vertical direction through a mechanical cold valve. This prototype of a versatile UCN source is comprised of a novel cryostat designed to keep the source portable and to allow for rapid cooldown. We measured time constants for UCN storage and extraction into a detector at room temperature, with the converter held at various temperatures between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of extracted UCN is close to the theoretical expectation.

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Background: The 22 Ne(α, n) 25 Mg reaction is an important source of neutrons for the s-process. Direct measurement of this reaction and the competing 22 Ne(α, γ) 26 Mg reaction are challenging due to the gaseous nature of both reactants, the low cross section and the experimental challenges of detecting neutrons and high-energy γ rays. Detailed knowledge of the resonance properties enables the rates to be constrained for s-process models.Purpose: Previous experimental studies have demonstrated a lack of agreement in both the number and excitation energy of levels in 26 Mg. In order to try to resolve the disagreement between different experiments, proton and deuteron inelastic scattering from 26 Mg have been used to identify excited states.Method: Proton and deuteron beams from the tandem accelerator at the Maier-Leibnitz Laboratorium at Garching, Munich were incident upon enriched 26 MgO targets. Scattered particles were momentum-analysed in the Q3D magnetic spectrograph and detected at the focal plane.Results: Reassignments of states around Ex = 10.8 − 10.83 MeV in 26 Mg suggested in previous works have been confirmed. In addition, new states in 26 Mg have been observed, two below and two above the neutron threshold. Up to six additional states above the neutron threshold may have been observed compared to experimental studies of neutron reactions on 25 Mg but some or all of these states may be due to 24 Mg contamination in the target. Finally, inconsistencies between measured resonance strengths and some previously accepted J π assignments of excited 26 Mg states have been noted.Conclusion: There are still a large number of nuclear properties in 26 Mg which have yet to be determined and levels which are, at present, not included in calculations of the reaction rates. In addition, some inconsistencies between existing nuclear data exist which must be resolved in order for the reaction rates to be properly calculated. I. ASTROPHYSICAL BACKGROUND AND SUMMARY OF PREVIOUS EXPERIMENTAL STUDIESThe slow neutron-capture process (s-process) is one of the nucleosynthetic processes responsible for the production of elements heavier than iron [1]. The neutrons which contribute to the s-process result mainly from two reactions: 13 C(α, n) 16 O and 22 Ne(α, n) 25 Mg. The 13 C(α, n) 16 O reaction is active in thermally pulsing lowmass asymptotic giant branch stars. The 22 Ne(α, n) 25 Mg reaction is active during thermal pulses in low-and intermediate-mass asymptotic giant branch (AGB) stars and in the helium-burning and carbon-shell burning stages in massive stars (see Ref.[1] and references therein). The 22 Ne(α, n) 25 Mg reaction is slightly endothermic (Q = −478.29 keV, S n = 11.093 MeV) and does not strongly operate until slightly higher temperatures are reached during either the thermal pulse in AGB stars or, in massive stars, at the end of helium burning *

We report experiments on the production of ultracold neutrons (UCN) in a converter of superfluid helium coated with fluorinated grease (fomblin). We employed our special technique of window-free extraction of accumulated UCN from the superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. The fomblin-coating reduced the time constant for UCN passage through the extraction hole by a factor three compared to our previous experiment employing an uncoated stainless steel vessel. A time-of-flight measurement of the cold neutron spectrum incident on the converter, combined with a gold foil activation, allowed us to determine both the single-phonon and multi-phonon contributions to the UCN production. The UCN production rate is in reasonable agreement with the theoretical expectation.