Measurement Of The ～7Be Electron-capture Decay Rate Variation In Metallic Environments And Production Of ～(15)O Secondary Beam

This dissertation contains two pieces of experimental work. One is themeasurement of ⁷Be halflife in metallic environments; the other is the production ofan ¹⁵O secondary beam for measurements of reactions of nuclear astrophysicalinterests.Investigations of decay rate variations of some nuclei in different environmentswere performed intensively since it can provide valuable information in nuclearphysics, condensed matter physics, and astrophysics.In recent years, Rolfs et al. and other researchers systemically measured Up(electron screening potential energy) of a series of reactions, such as D(d, p)T, ⁷Li(p,α)⁴He, ¹⁷⁶Lu(p, n)¹⁷⁶Hf etc., in metallic environments. As compared to measurementsperformed with semiconductor and insulator, a large effect has been observed in mostmetals. After analyzing systemically these experimental results, we can see that U_Dcan be scaled with the nuclear charge Z_t of target atoms and the charge Z_i of theincident ions, U_D∝Z_t Z_i. Furthermore, the enhanced electron screening potentialenergy decreases with increasing temperature, U_D∝T^-1/2. A reasonable explanation ofrelation of U_D and Z_t, Z_i, T^-1/2 in metals is provided by the classical plasma screeningof Debye applied to the quasi-free metallic electrons.The Debye model is probably suitable for radioactive decay of nuclides in ametallic environment. In general, for the electron-capture process one expects alonger halflife due to the screening effect of the Debye electron clouds for negativelycharged particles. Being the lightest radioactive nuclei that decay by electron capturewith a half-life of～53 days, ⁷Be is a good candidate for studying the change ofnuclear decay rate.In order to prove the prediction, we carried out the measurements of ⁷Be in themetallic environments Pd, In and in the insulator Li₂O at low temperature (all samplescooled to T=12 K). We alternatively measured the characteristic 478 keV Gammarays of ⁷Be decay, and then analyzed the radioactivity to deduce the changes of ⁷Behalflife. For the electron capture of ⁷Be in Pd and In, the ⁷Be halflife was observed toincrease by 0.5±0.2 and 0.7±0.2%, respectively, while in the insulator it wasunchanged within experimental error. For the sample of ⁷Be in Pd, we performedmeasurement in a new geometrical setup and the ⁷Be halflife was observed to increaseby 1.2±0.2%. These results are qualitatively consistent with-but lower than-theexpectations from the Debye plasma model; however, they demonstrate that there is atemperature dependence of the ⁷Be lifetime down to T=12 K.Hot CNO cycle is a part of process of explosive hydrogen burning. The ¹⁵O(α,γ)¹⁹Ne reaction is one of key reactions of reaction pathways of rp-process. The reactionis dominated by resonance capture process. We may obtain some valuable informationof resonance states in ¹⁹Ne by using the resonance elastic scattering of ¹⁵O+αwith aradioactive ion beam of ¹⁵O and a thick ⁴He gas target.An ¹⁵O secondary beam is produced via ²H(¹⁴N, ¹⁵O^*)n reaction in inversekinematics on the secondary beam facility at the HI-13 tandem accelerator. Theenergy of the ¹⁵O secondary beam is 74.3±0.7 MeV, with a purity of 50 %. With theintensity of primary beam of 10 pnA, the intensity of the ¹⁵O secondary beam is about800 s^-1. Some discussions on how to increase the intensity of the ¹⁵O secondary beamis provided.