Application of time-dependent processes in the prompt-gamma activation analysis
Ph.D. thesis by László SzentmiklósiDownloads
The complete
text of the dissertation, the abstracts and the collection of the
related papers as an appendix.
- File: Phd_SzL.pdf (in Hungarian, File size: 12.3 MB, date: 22 Nov 2006)
- File: Tezisfuzet_SzL.pdf (in Hungarian, File size: 1.6 MB, date: 22 Nov 2006)
- File:
Tezisfuzet_SzL_angol.pdf
(in English, File size: 730 kB, date: 22 Nov 2006)
Abstract
Prompt-gamma
activation analysis (PGAA, or PGNAA) is a nuclear analytical technique
for non-destructive determination of elemental and isotopic
compositions. In the present work the time-dependent processes of PGAA
were investigated and utilized to attain better precision and more
reliable analysis. The characteristic times of these vary between
picoseconds and several hours; hence different methods have to be
involved.
My
first task was to test the capabilities of three digital signal
processors when used for PGAA, and to compare their performance to our
existing analog electronics. The energy resolution at different gains,
as well as the time stability and noise sensitivity were examined. It
was concluded that the digital spectrometers have worse resolution than
the analog system, and seem to be incompatible with detectors having
non-ideal preamplifiers. However, I managed to utilize many existing
advantages of the digital spectrometry. The principle of the list-mode
data acquisition, as implemented in a digital spectrometer of XIA
(X-Ray Instrumentation Associates), was used with success in
investigation of radioactive decays. It was shown that this kind of
acquisition preserves very detailed time and energy information which
can be utilized with great flexibility at the evaluation stage. A
computer program was prepared to process the raw data, by sorting the
events into energy-spectra, time spectra or two-dimensional histograms.
A dead-time correction model was worked out, and was validated with
measurements. Methods for background correction of decay spectra and a
fitting procedure for 3D regions were invented. I proved that the
method gives correct half-life data for various medium-lived
radionuclides. I compared the precision of the off-line processing
techniques and demonstrated that they give more accurate results than
the conventional multichannel scaler (MCS) technique on the same
dataset. I demonstrated that by simultaneous use of energy and time
information, peaks overlapping in the energy spectrum can be
decomposed. The elemental compositions of halogenide samples were
determined with combined use of PGAA and post-irradiation counting. The
latter method was able to reduce the limit of detection for Th.
A
new beam-chopper was also installed at the PGAA facility. This is an
effective tool to investigate short-lived nuclides, to reduce the
limits of detection and improve the selectivity for a group of
elements. I set up new controller and data acquisition electronics, to
acquire the beam-on and beam-off spectra concurrently. I derived
simplified formulas for use in chopped-beam PGAA and calculated the
in-beam saturation factor for the case of branching activation. Partial
gamma-ray production cross-sectionsand k 0-factors
of 16 short-lived nuclides were determined with this technique. The
experimental results were compared to the k0-NAA
literature. A thorough estimation of uncertainties was also done,
following the guidelines of ISO. I proved that the technique can offer
better selectivity and lower detection limits for many elements than
conventional PGAA.
Finally,
a new fitting procedure for the Doppler-broadened peak of Boron was
worked out and validated. I used a more sophisticated peak-shape
function and a modified background-shape in the model function. I also
paid attention to the energy-dependent efficiency. The sample method
was extensively checked on model samples, representing typical peak
shapes. The effect of the matrix on the peak shape was also studied.
Peaks of Boron and interfering elements were successfully decomposed in
geological and dosimetrical samples.
Related publications
1.
L. Szentmiklósi, T. Belgya , Zs. Révay, G. L. Molnár: Digital signal
processing in prompt-gamma activation analysis, J. Radioanal. Nucl.
Chem. 264
(1) (2005) 229-234.
2.
Zs. Révay, T. Belgya, L. Szentmiklósi, G. L. Molnár: Prompt gamma
activation analysis using a chopped neutron beam, J. Radioanal. Nucl.
Chem. 264
(2) (2005) 277-281
3.
G. L. Molnár, Zs. Révay, L. Szentmiklósi: New perspectives for very
short-lived neutron activation analysis, J. Radioanal. Nucl.
Chem. 262
(1) (2004) 157-163
4. L. Szentmiklósi, T. Belgya, G. L. Molnár,
Zs. Révay: Time resolved gamma-ray spectrometry, J. Radioanal. Nucl.
Chem. 271
(2) (2007) 439-445
5.
L. Szentmiklósi, K. Gméling, Zs. Révay: Fitting the boron peak and
resolving interferences in the 450-490 keV region of PGAA spectra, J.
Radioanal. Nucl. Chem. 271
(2) (2007) 447-453
6.
L. Szentmiklósi, Zs. Révay, G. L. Molnár: Three-dimensional data
processing for the time resolved gamma-ray spectrometry, J. Radioanal.
Nucl. Chem. 265
(2) (2005) 213-219.
7. L. Szentmiklósi, Zs. Révay, R. Chobola, P.
Mell, S. Szakács, I. Kása: Characterization of CaSO4-based
dosimeter materials with PGAA and thermoluminescent methods, J.
Radioanal. Nucl. Chem, 267
(2) (2006) 415-420
8.
L. Szentmiklósi, Zs. Révay, T. Belgya: An improved beam chopper setup
at the Budapest PGNAA-NIPS facility (accepted for publication, IRRMA-6
proceedings of Nucl. Instr. Meth. B.)
9.
L. Szentmiklósi, Zs. Révay, T. Belgya: Investigation of nuclides
activated in-beam with chopped-beam PGAA, Nucl. Instr. Meth. A 564 (2006) 655-661