Lifetimes of levels inF20,21,Ne22, andN16

The recoil distance method has been used to measure the mean lifetime of the

J^{π} = {\frac{9}{2}}^{+}

1755-keV level of

{}^{21}F

, formed (predominantly) via the

{}^{7}{Li} ({}^{18}O, α) {}^{21}F

fusion-evaporation reaction. The lifetimes of the 984- and 1309-keV levels of

{}^{20}F

and the 1275-keV level of

{}^{22}{Ne}

were obtained coincidentally. Similar measurements in the

{}^{7}{Li} ({}^{11}B, p n) {}^{16}N

reaction determine the lifetimes of the 298- and 397-keV levels of

{}^{16}N

. Data were acquired at

θ_{γ} = 0 °

using an escape suppression spectrometer, with

{}^{18}O

and

{}^{11}B

incident energies of 28.5 and 15.3 MeV, respectively. The experimental results are the following:

{}^{16}N

(298,

3^{-}

τ = 133 \pm 4

ps;

{}^{16}N

(397,

1^{-}

τ = 6.60 \pm 0.48

ps;

{}^{20}F

(984,

1^{-}

τ = 1.8 \pm 0.3

ps;

{}^{20}F

(1309,

2^{-}

τ = 1.9 \pm 0.3

ps;

{}^{21}F (1755, {\frac{9}{2}}^{+})

τ = 3.5 \pm 0.5

ps;

{}^{22}{Ne}

(1275,

2^{+}

τ = 5.1 \pm 0.2

ps. Shell-model calculations for

{}^{16}N

and

{}^{20, 21}F

have been performed and are compared to experimental results.

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