As the uncharged member of the nucleon pair, the neutron plays a fundamental

Photoneutron Sources In a process similar to the (α,n) sources discussed above, we can use the (γ, n) reaction to produce neutrons. The advantage of photoneutron production is that we can make the neutrons more nearly monoenergetic, particularly if the photon source is nearly monoenergetic. For example, ²⁴Na emits a y of 2.76 MeV, absorption of which would be sufficient to overcome the neutron binding energy of ⁹Be:

y +⁹Be +⁸Be + n

The yield is acceptable (2 ∙ 10⁶ neutrons/s per Ci of ²⁴Na),but the half-life is short (15 h). The neutron energy is about 0.8 MeV. A longer-lived isotope ¹²⁴Sb (60 d) emits a strong γ whose energy just exceeds the ⁹Be neutron binding energy; the emitted neutron has a much lower energy, about 24 keV.