Neutron capture prompt gamma activation analysis (PGAA) is a rapid, nondestructive, instrumental, nuclear technique which is used for trace and major component analysis of various elements.
A dedicated facility for performing PGAA has been developed at the Nuclear Engineering Teaching Laboratory (NETL) research reactor. In association with Neutron Activation Analysis (NAA), we have the capability of measuring the concentration of almost all elements.
Schematic of Texas PGAA facility.
PGAA has a high degree of sensitivity for many elements including H, B, Cl, Na, K, B, Ca, P, and N.
PGAA is based on detection of capture gamma rays emitted by a target material while it is being irradiated with neutrons. Nuclei formed in capture have excitation energies equal to the binding energy of the added neutron. The excitation energy is released by emission of gamma rays. The gamma-ray energies range from 100 keV to 10 MeV.
Nearly every neutron capture yields gamma rays that are potentially usable for analysis of the capturing element. However, the energy spectrum of capture gamma rays of most nuclides is fairly complex. The capture gamma rays emitted by shielding material, etc., also complicates the analysis. Therefore, the relative merit of this technique for analysis of a particular element must be reviewed on a case by case basis.
PGAA is a nondestructive technique. The analysis can be done in a relatively short time. PGAA is complementary to NAA. The advantages over NAA are as follows:
- PGAA is suitable for elements like B, H, and S that are difficult to measure via classic NAA.
- PGAA can often outperform NAA on biological samples due to the reduction of matrix interferences from Na, K, and Cl.
- Since PGAA irradiation is performed in beam lines external to the reactor core, this technique is more suitable for large samples in comparison to NAA.
The bulk of the applications of PGAA is the nondestructive multielement analysis. Some examples of these applications are:
- Analysis of H in various H storage materials.
- Analysis of B and H in battery materials.
- Determination of the elements B, Cd, In, Hg, Mn, Fe, Co, Ni, S, and Cu in geological samples and environmental materials.
- Determination of the elements H, Cl, Na, K, B, Ca, P, and N in biological samples.
- Analysis of Fe, Cr, Ni, Mn, and B in stainless steel and iron ore samples.
The PGAA facility at UT, in operation since 1995, can run in parallel with the Texas Cold Neutron Source (TCNS) and is equipped with a 6-m long curved neutron guide for the preferential transmission of slow velocity neutrons. The thermal equivalent neutron fluxes at the sample position are:
9 ×107 n cm-2 s-1 (Texas Cold Neutron Source OFF)
1.5×107 n cm-2 s-1 (Texas Cold Neutron Source ON)
The effective neutron beam temperature was measured to be 39 ± 6 K.
Top view of Texas PGAA facility on Beam Port 3.