. Written in Pascal, and operating in windows and menus data manipulation mode, ANGLE yields the efficiencies for: (1) HPGe true- and closed-end coaxial (bothn- andp-types), (2) Ge(Li) open- and closed-end, (3) planar LEPD and (4) well-type detectors. Supposing coaxial positioning, cylindrical or Marinelli sources can be treated, regardless of their dimensions (this includes point, disk and ring sources, bulky samples and infinite geometrics). Possible displacement between source and detector axes is treated in our another work, relative to this one. ANGLE input parameters are: (1) reference efficiency curve for the detector used (i.e., efficiency vs. -energy for calibrated point sources at a reference distance), (2) detector type and configuration (active body and inactive layers, end cap, windows, housing, shielding, (3) source data (dimension and composition of both container and active material), (4) source-detector geometry (distance, intercepting layers and their composition) and (5) some computational data (Gauss integration coefficients). Gamma-attenuation is calculated upon an extensive (per element and per energy) data file. In the output, efficiency vs. -energy is found, both in forms of tables and graphs. In routine applications accuracies of 3–4% are achieved (not worse than 7% for the most unfavourable geometries). Computation times when using recent PC models are of the order of minutes. ANGLE frame is also easily adjustable to other semiempirical or Monte Carlo models for efficiency calculations.
Positron emission tomography (PET) is rapidly becoming the main nuclear imaging modality of the present century. The future
of PET instrumentation relies on semiconductor detectors because of their excellent characteristics. Three-photon positron
annihilation has been recently investigated as a novel imaging modality, which demands the crucial high energy resolution
of semiconductor detector. In this work the evaluation of the NaI(Tl) scintillator and HPGe and CdZTe semiconductor detectors,
to construct a simple three-photon positron annihilation scanner has been explored. The effect of detector and scanner size
on spatial resolution (FWHM) is discussed. The characteristics: energy resolution versus count rate and point-spread function
of the three-photon positron annihilation image profile from triple coincidence measurements were investigated.
Authors:M. Toribio, J. García, A. Izquierdo-Ridorsa, G. Rauret, A. Coll, I. Vallés, and X. Ortega
The activity of -emitting radionuclides is usually measured by semiconductor detectors (surface barrier or ion implanted). Overlapping and composite bands are quite common problems depending on energy differences of the radionuclides and counting source preparation. The classical approach to activity quantification is based on peak integration and, when it is used, overlapping may be overcome by a detailed study of each case, whereas composite bands can not be completely resolved. Here, spectra of the -emitting plutonium isotopes, obtained by ion implanted semiconductor detectors, have been used to compare the classical approach with a multivariate calibration method (MVC-PLS). The study is performed at environmental activity levels (0–52 dpm). The relative errors obtained for239+240Pu activity determination, using either the classical or the MVC-PLS approach with replicates, are good enough to quantify isotopes at low level activities. The distribution of relative errors is asymmetric, with a positive component for 0–10.5 dpm subset, in the classical approach whereas it is more symmetric in the MVC-PLS method. The results show that the classical approach depends on peak overlap, whereas the MVC does not. As a whole, MVC is a more robust method than the classical approach. Composite bands were studied using the239Pu–240Pu mixture; the MVC approach did not allow individual quantification due to the lack of signal reproducibility. This instability does not affect the regular integration procedures but it is important in the deconvolution processes. The lack of reproducibility is related to the source preparation process.
Authors:E. Abuelhia, K. Alzimami, M. Alkhorayef, Z. Podolyák, and N. Spyrou
The coincidence timing resolution is a critical parameter for triple coincidence to measure the three photon positron annihilation
yield. The yield is inversely proportional to the concentration of oxygen which acts as a quenching agent within the tissue
and, therefore, provides important information about the state of the cancerous tumor. A comparison between scintillation
and semiconductor detectors with respect to their timing properties for triple coincidence measurements and imaging was carried
out. The coincidence timing resolution for example for HPGe detectors was found to vary between 35.4±0.02 and 42.8±0.02 ns.
A comparison of all detector characteristics with respect to HPGe is presented.
Authors:H. Sakai, A. Uritani, K. Inoue, Y. Takenaka, and C. Mori
We have studied the improvement of energy spectra of a cadmium telluride (CdTe) semiconductor detector by means of a neural network algorithm. The neural network recognized pulse shapes and determined the corrective magnification factors of digitally shaped pulse heights. That is to say, the neural network recognized the difference in the pulse shapes due to the incomplete charge collection and made up for the ballistic deficit of each pulse. We obtained the energy spectra of several gamma ray sources. After the processing, the energy spectra became more ideal profile and the energy resolution (FWHM) changed for the better.
The problem of gamma-ray spectrum analysis is treated by combination of peak-searching, choosing the fitting intervals and
fitting the line shape by a shape function. The performance of the program is examined by analysis of a test spectrum,177mLu.
The total efficiency of γ-ray detection by Ge(Li) semiconductors is calculated for the energy range 0.1 to 10 MeV, for cylindrical
detectors with radii from 0.25 cm to 2.5 cm and thicknesses from 0.1 cm to 1 cm, at distances between the source and detector
ranging from 2 cm to 20 cm.
Authors:J. Lund, N. Hilton, J. McKisson, J. Van Scyoc, B. Brunett, H. Hermon, and R. James
We report on the design, construction, and testing of a gamma-ray imaging system with spectroscopic capabilities. The imaging
system consists of an orthogonal strip detector made from either HgI2 or CdZnTe crystals. The detectors utilize an 8×8 orthogonal strip configuration with 64 effective pixels. Both HgI2 or CdZnTe detectors are 1 cm2 devices with a strip pitch of approximately 1.2 mm (producing pixels of 1.2 mm × 1.2 mm). The readout electronics consist
of parallel channels of preamplifier, shaping amplifier, discriminators, and peak sensing ADC. The preamplifiers are configured
in hybrid technology, and the rest of the electronics are implemented in NIM and CAMAC with control via a Power Macintosh
computer. The software used to readout the instrument is capable of performing intensity measurements as well as spectroscopy
on all 64 pixels of the device. We report on the performance of the system imaging gamma-rays in the 20–500 keV energy range
and using a pin-hole collimator to form the image.
Authors:A. Yakubovich, S. Prizhiyalgovsky, G. Tsamerian, and I. Roschina
This paper deals with the evaluation methods of matrix effect in multicomponent X-ray radiometry using a semiconductor spectrometer.
These methods consist in measuring the radiation incoherently scattered by a sample. Relationships for the calculation of
the element content of interest are given with the use of the predetermined content of an element without considering the
matrix effect determined from calibration curves, as well as analytic expressions enabling the automation of the processing
of measured results by an electronic computer. Experimental verification of these methods, carried out in this case on the
analysis of complex ores (determination of copper, zinc and lead), has shown that analysis errors do not exceed 5% rel.