Doppler Broadening of the 6.322-MeV γ-Ray from ¹⁵N Following μ^- Capture in ¹⁶O

Abstract

The very broad, 6.322-MeV ¹⁵N line observed¹ following µ⁻ capture in ¹⁶O can be fitted with a simple kinematic model by using the neutron energy spectra predicted in the resonance-capture calculation of Raphael, Uberall, and Werntz. If we assume complete isotropy in the reaction sequence

$$\begin{array}{l} \mu ^ - + ^{16} O \to ^{16} N^* + \nu \\ ^{16} N^* \to ^{15} N^* + n \\ ^{15} N^* \to ^{15} N + \gamma \\ \end{array}$$

and define $\vec \beta _1$ as the recoil velocity of the ¹⁶N* from ¹⁶O, $\vec \beta _2$ as the recoil velocity of the ¹⁵N* from ¹⁶N, and E₀ as the γ-ray energy in the ¹⁵N* rest frame, we can easily show that for monoenergetic neutron emission the γ ray will have the trapezoidal line shape shown in Fig. 1.