Lifetimes and Magnetic Moments of States of Nitrogen Sixteen and Sodium Twenty-Two the Recoil-Into Method
The lifetimes and magnetic moments of some of the low lying states of ('16)N and ('22)Na have been measured by means of the recoil-into-vacuum technique. The nuclear states under study are produced by a nuclear reaction, which causes the excited nucleus to recoil out of the target at velocities that are several percent of the speed of light. The nucleus is stopped by a stopper (plunger), which can be set at a variable distance from the target. The (gamma)-rays from a nucleus that decays in flight will be Doppler shifted, while those that come from a nucleus that has stopped in the plunger will be unshifted. By determining the ratio of the shifted to total number of (gamma)-rays as a function of distance (and thus time), the lifetime can be determined. When the nucleus is recoiling in vacuum, its spin also experiences a Larmor precession induced by the hyperfine field of the atomic electrons. For light nuclei the hyperfine field can be calculated exactly, since it is generally due to a single 1s electron. The Larmor precession can be measured by its effect on the (gamma)-ray angular distribution, and the g-factor can be extracted. The lifetime of the 657 keV, 0(,1)('+) state in ('22)Na was measured in a singles experiment with the reaction ('19)F((alpha),n)('22)Na at a beam energy of 4.3 MeV. Lifetime and moment measurements were made on the 297 keV, 3(,1)(' -) and 397 keV, 1(,1)('-) states in ('16)N, with the reaction d(('15)N, p)('16)N. Measurements detecting the outgoing coincidence proton were made at a beam energy of 34 MeV, while singles measurements were performed at 20 MeV. The results obtained are: (tau)(('22)Na, 657, 0('+)) = 28.8 (+OR-) 1.0 ps; (tau)(('16)N, 297, 3('-)) = 121.2 (+OR-) 3.0 ps; (tau)(('16)N, 397, 1('-)) = 6.46 (+OR-) 0.20 ps; (VBAR)g(('16)N, 297, 3('-))(VBAR) = (+OR-) 0.499 (+OR-) 0.025. The results are compared to other measurements and to values predicted by several recent theories.
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- Physics: Nuclear