Prompt Gamma (PG) NAA:

In this methodology, first used in 1969, prompt gamma rays emitted during (n,γ) reaction as described in Figure are counted. An essential feature of this technique is in which detector system has to be placed in close vicinity of the irradiation facility so that γ rays are straight counted. It is often used for analysis and is especially suitable for the determination of lighter elements such as H, B, N, P, S, C and Si and components having high neutron absorption cross section e.g, Hg, Cd, Sm and Gd. A majority of PGNAA work is carried out using isotopic sources though counting facility can be setup at the reactor site as well. It is being increasingly used as a rapid instrumental, non-destructive and multielemental anal ysis technique. A further advancement of PGNAA is in-vivo PGNAA where the entire body or a segment of the patient/subject is irradiated with ²⁴¹Am-Be, ²⁵²Cf or an accelerator based neutron source followed by counting of prompt/delayed gamma rays. PGNAA has been widely used due to improved analytical sensitivity and detection limits especially by using low energy guided neutron beams.  It's most clinical use is the in vivo determination of ¹⁰B concentration needed to measure the radiation dose received through patients undergoing neutron capture therapy for tumours.

¹¹B(n, γ)¹²B(t_1/2 = 20.4 ms,E_γ =4.44 MeV);

⁴⁸Ca(n, γ)⁴⁹Ca(t_1/2 = 8.72 ms,E_γ =3.08 MeV);

¹⁴N(n, γ)¹⁵N STABLE,(E_γ =10.8 MeV);

¹¹³Cd(n, γ)¹¹⁴Cd STABLE,(E_γ =0.56 MeV);