MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich

MLZ is a member of:

LENS> LENSERF-AISBL> ERF-AISBL

MLZ on social media:

The MLZ App – now available here! (Android)

MLZ App> MLZ App
Logo

MLZ (eng)

Lichtenbergstr.1
85748 Garching

PGAA

Prompt gamma activation analysis

approximate detection limits approximate detection limits The approximate detection limits of the chemical elements assuming a typical environmental sample under usual measuring conditions using PGAA © TUM

The approximate detection limits of the chemical elements assuming a typical environmental sample under usual measuring conditions using PGAA © TUM

PGAA as a method
Prompt Gamma Activation Analysis was recommended by Heinz Maier-Leibnitz in 1963. He immediately recognized the importance of low spectral background which is still the most important step in the instrument development. The first PGAA experiments were performed by Henkelmann and Born at FRM and ILL, Grenoble in 1968. FRM II also established a PGAA facility, it is located at the strongest neutron beam of the world opening possibilities to measure low-mass and/or low-cross-section materials.
Neutrons and gamma rays have a large penetration depth even in condensed matter, so samples with thicknesses up to a couple of centimeters can analyzed. The samples can be measured without any specific preparations, and the method yields the bulk composition of the irradiated volume. PGAA is non-destructive. The sample can be in any physical form: in proper containers liquids and gases can also be measured. Also the chemical form of the sample has no influence on the analysis. For each element, the result of the non-destructive analysis is an averaged concentration (mass fraction) over the irradiated sample volume, i.e. a bulk analysis.
In principle, all the chemical elements can be analyzed with PGAA. The analytical sensitivity of the method mainly depends on the neutron capture cross section of the elements which typically varies in the millibarn-kilobarn range. Certain elements can be determined only as major components (such as O, C, Be, Bi), some as trace elements (B, Cd, rare-earths) with detection limits down to nanograms, while most elements can be analyzed in the microgram range. The major advantage of the method is its capability in the analysis of light elements. It has a unique sensitivity for hydrogen or boron, which can be determined in the ppmw and ppbw level, respectively.

Dynamic range
Gamma spectra have an inherent dynamic range, i.e. the smallest detectable peaks have an area of 10–100 counts. However, the area of the same peaks have a practical upper limit, too, which is about six orders of magnitude higher, than the smallest detectable area. Hence, the elements detectable on the ng level can be determined up to mg level, i.e. as minor elements, and never major components, in much higher quantities than a milligram, because the peaks of the sensitive element alone will mask those from all other elements.

approximate detection limits NAA approximate detection limits NAA The approximate detection limits of the chemical elements assuming a typical environmental sample under usual measuring conditions using in-beam NAA. © TUM

The approximate detection limits of the chemical elements assuming a typical environmental sample under usual measuring conditions using in-beam NAA. © TUM

In-beam Neutron Activation Analysis (ibNAA)
The beam is so strong at PGAA (4–6×1010 cm–2 s–1) that its flux is comparable to those in small reactors fully dedicated to NAA. Activating in beam is more advantageous, because the neutron self-absorption can be corrected for in a much simpler way, than in an isotropic neutron field. Guided beams do not contain epithermal or fast neutrons, thus the activation process can also be described much simpler. Thanks to the high flux irradiation, many elements are activated, i.e. the induced radioactivity can be counted with much better sensitivities, than when using PGAA alone. Activity counting takes place in a low-background counting chamber with higher detector efficiencies. Even short-lived nuclides (with half-lives of a few seconds) can be detected here.

As in traditional NAA, the light elements are normally impossible to analyze based on their induced radioactivities. In the first two periods, the only exception is fluorine whose half-life is just 11 s, and its cross section is also low (9.6 mb), but right after the irradiation, it can be measured with a fair sensitivity. Cyclic irradiations/measurements can help in this context. The real strength of NAA is the analysis of elements in the fourth period of the Periodic Table and above, however, a few lighter ones are detectable with high sensitivities (like Na, Mn, Sc), too. The typical detection limit is around or even below the μg level.

Classic NAA, without chemical treatment also called instrumental NAA (INAA), can also be performed at FRM II. The activation takes place in the irradiation channels of the reactor in a much higher flux (>1013 ~1014/cm²s) . The highly thermalized neutron field of FRM II reactor offers unique possibilities for the classical instrumental NAA, too.

PGAA and NAA complement each-other. PGAA is best used for the determination the major components of the samples, while NAA analyses the (minor and) trace elements.

Selected Applications
  • Archaeology – restauration / conservation, provenance, check of authenticity (ceramics, glass, building material, coins and other metal objects)
  • Cosmochemistry (mainly meteorites)
  • Geology / Petrology (maceral sediments, iron ore)
  • Environmental Research (air pollution, alluvial sediments)
  • Medicine (B, Li, Cd, Mn in tissue, nano particles for cancer therapy, irradiation damages of DNA)
  • Semiconductor and Superconductor Materials (e.g. H, B, P in Si for solar cells)
  • Analysis of new Materials (catalysts, clathrates, crystals, superalloys)
  • Reactor Physics (shielding, new materials)
  • Irradiations (test of radiation hardness of chips, scintillators)
  • Basic Research (nuclear data, low-spin excited states in nuclei, partial and total cross sections for neutron capture)
Sample environment

The samples are located in the beam in aluminum frames among Teflon strings. Their typical diameter is a few centimeters with thicknesses in the millimeter range. 16 such samples can be placed in the automatic sample changer. The sample chamber can be evacuated to exclude the possibly interfering prompt gamma lines of nitrogen (and argon).

Technical Data

Neutron beam
The PGAA facility is located in the neutron guide hall at the end of the curved neutron guide 4B with the length of 55 m. The last 6.9 m of the guide is elliptically tapered. The thermal equivalent flux (or the capture flux) of the focused neutron beam in the focal point is 6×1010 cm–2 s–1, the highest beam flux recorded. The last 1.1 m of the elliptical guide can be replaced by a set of collimators keeping the beam uniform and parallel.
Using a set of beam attenuators, the flux can be adjusted between 3×107 cm–2 s–1 and 4×1010 cm–2 s–1 (the maximum value at sample position is somewhat lower than that in the sample position) to find the best irradiation conditions matching the sample.

Cold neutron spectrum of guide NL4b (last 5.8 m elliptically focused) with a mean energy of 1.83 meV (6.7 Å).
Two different beam conditions:

For bigger samples with collimation:

  • Beam size: 20×30 mm2
  • Neutron beam flux max.: 2 × 109 n cm-2 s-1 therm. n. equ.

For smaller samples with 1.1 m elliptical neutron guide:

  • Beam size: 11 × 16 mm2
  • Neutron beam flux max.: 6 × 1010 n cm-2 s-1 therm. n. equ.

*Measuring conditions *

  • Vacuum down to 0.05 mbar
  • Standard sample masses: 0.1 mg – 10 g
  • max. standard sample size: ca. 40 × 40 × 40 mm3
  • larger samples can be measured in a special arrangement
  • automatic measurement: up to 16 samples per batch (a carousel with pneumatic lift)
  • Powder samples (and certain condensed samples) are sealed in FEP bags or other suitable foils

Detector system

  • Standard PGAA with Compton supression (60-% HPGe detector surrounded by BGO scintillator in anti-coincinence mode). LEGe detektor available for high resolution measurements in the low-energy reagion.
  • Separate low-background chamber with 30-% HPGe detector and DSpec-50 unit for recording of decay spectra after in-beam sample activation
  • Energy range: 30 keV – 12,000 keV

  • Detector #1: n-type high-purity germanium (HPGe) detector (manufactured by Ortec) with a relative efficiency of 60% surrounded by bismuth germanate (BGO) scintillator annulus for Compton suppression.
  • Detector #2: n-type low-energy HPGe (LEGe) detector (manufactured by Canberra) for the detection of low-energy gamma ray (typically <1MeV) surrounded by bismuth germanate (BGO) scintillator annulus for Compton suppression.
  • Detector #3: n-type high-purity germanium (HPGe) detector (manufactured by Ortec) with a relative efficiency of 30% surrounded by sodium iodide scintillator annulus for Compton suppression.

Detectors #1 and #2 are on the two opposite sides of the PGAA sample chamber to detect the prompt gamma rays from the irradiated samples. Detector #3 is located outside the concrete bunker of the facility in a low-background chamber dedicated to counting the activated nuclides for iBNAA.

Shielding
The shielding is made of mainly lead against the high-energy gamma rays, lined with boron- and lithium-containing layers to shield against neutrons. The components can be easily moved or modified, so that the shielding accommodates other setups (NDP, Prompt Gamma Activation Imaging + Neutron Tomography (PGAI-NT) or gamma-gamma coincidence system).

Data recording system
The spectra are evaluated using the Hypermet code5, the list of the peaks are then compared to the spectroscopic data library6, finally the qualitative and quantitative analysis is performed based on statistical methods.7

  • Software with NICOS-GUI for automatic control for up to 16 samples per batch
  • automatic data acquisition with DSPEC-50 digital spectrometers
  • Calibration of the system (efficiency function and non-linearity) and unfolding of spektra with Hypermet-PC Software (developed in Budapest)
  • Data evaluation including calculation of the elemental composition with Excel macrosheet pakage ProSpeRo
References

[1] Zs. Révay, T. Belgya, in: Handbook of Prompt Gamma Activation Analysis with Neutron Beams (Ed. G.L. Molnár) Kluwer, Dordrecht, 2004, p 1.
[2] M. Crittin, J. Kern, J.-L. Schenker, Nucl. Instrum. and Meth. A449 (2000) 221.
[3] P. Kudejova et al, J Radioanal Nucl Chem 265 (2005) 221.
[4] Zs. Révay, P. Kudějová, K. Kleszcz, S. Söllradl, Christoph Genreith: In-beam activation analysis facility at MLZ, Garching, Nucl Instrum Meth A799114–123.
[5] B. Fazekas, J. Östör, Z. Kis, G. L. Molnár, A. Simonits: The new features of Hypermet-PC, in: Proceedings of the 9th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics, Budapest, Hungary, October 8-12, (Eds. G. Molnár, T. Belgya, Zs. Révay) Springer Verlag, Budapest/Berlin/Heidelberg, 1997, p. 774.
[6] Zs. Révay, R.B. Firestone, G.L. Monár, T. Belgya, in: Handbook of Prompt Gamma Activation Analysis with Neutron Beams (Ed. G.L. Molnár) Kluwer, Dordrecht, 2004, p. 173.
[7] Zs. Revay, Anal. Chem. 81 (2009) 6851.

Instrument Scientists

Dr. Zsolt Revay
Phone: +49 (0)89 289-12694
E-Mail: zsolt.revay@frm2.tum.de

Dr. Christian Stieghorst
Phone: +49 (0)89 289-54871
E-Mail: christian.stieghorst@frm2.tum.de

Dr. Xiaosong Li
Phone: +49 (0)89 289-12130
E-Mail: xiaosong.li@frm2.tum.de

PGAA
Phone: +49 (0)89 289-14906

Operated by

TUM

TUM Logo © TUM

Publications

Find the latest publications regarding PGAA in our publication database iMPULSE:

impulse.mlz-garching.de

Citation of the instrument

Heinz Maier-Leibnitz Zentrum. (2015). PGAA: Prompt gamma and in-beam neutron activation analysis facility. Journal of large-scale research facilities, 1, A20. http://dx.doi.org/10.17815/jlsrf-1-46

Zs Revay, P Kudejova, K Kleszczm S Sölradl, Ch Genreith, In-beam activation analysis at Heinz Maier-Leibnitz Zentrum, Garching. (2015). Nucl Instrum Meth A799, 114-123. http://dx.doi.org/10.1016/j.nima.2015.07.063

For citation please always include the DOI.

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich

MLZ is a member of:

LENS> LENSERF-AISBL> ERF-AISBL

MLZ on social media:

The MLZ App – now available here! (Android)

MLZ App> MLZ App