12/16/95-3/15/96 PERIOD MULTI-PARAMETER ON-LINE COAL BULK ANALYSIS. 2, 1. Thermal Neutron Flux in Coal: New Coal Container Geometry

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1 DDG/Pc/q+wl TECHNCAL PROGRESS REPORT 2/6/95-3/5/96 PEROD GRANT DE-FG22-93PC932 MULT-PARAMETER ON-LNE COAL BULK ANALYSS Scientific work VD 0 % s g; e 0% 2% -2- G? 2,. Thermal Neutron Flux in Coal: New Coal Container Geometry F> cn CJ r*; We have performed extensive calculations with the MCNP computer code in order the optimum geometry of the coal container. Based on these calculations, a new coal container was designed. This new configuration resulted in an increase of the gamma-ray yield. This can be seen in Figure, where the new gamma-ray yield is compared with the yield with the previous container geometry. Consider the gamma-ray peak at 2223 kev resulting from prompt-neutron capture by hydrogen. The net counts in this peak for the new sample container geometry is 650% larger than coal in our old container. This improvement is a result of having higher thermal neutron flux in the new container geometry. The impact of this improvement on the PFTNA performance is illustrated in Figures 2 to 4. Figure 2 shows the gamma-ray spectm of two coal samples having 0.65% and 2% w/w sulfur content. n the 5420 kev sulfur peak done, a coal sample with 2% w/w sulfur shows over 27,000 net counts. Figures 3 and 4 show the high energy part of a gamma-ray spectrum of a coal sample. With the improved neutron fluxes, important elements such as Fe and N can be easily seen. t is noteworthy to mention that we had not seen Fe or N in the previous sample container geometry. The Monte Carlo method for the transport of neutrons and gamma-rays is a powerful technique for improving the performance of a nuclear analyzer. This method is not only economical but also helps us understand the underline physics that are responsible for these improvements. The information obtained from MCNP-based numerical calculations for designing our coal analyzer made a 650% improvement in system performances... 3 Determination of the Sulfur Content in Coal We use the least-squares gamma-ray spectrum deconvolution technique to determine the sulfur content of coal. We prepared a series of 32 kg coal samples, having sulfur contents from % to 5 % w/w. These samples were prepared by adding various amounts of sulfur to #9500 coal, which has 0.65% w/w of sulfur. After the sulfur addition, the sample was thoroughly blended in a V-blender. The sample preparation method is described in detail in section 5. Measuring time of a sample, Le., neutron irradiation and simultaneous recording of the gamma-rays, was 20 minutes. v DSTRBUTON OF THS DOCUMENT S UNLMTED

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4 Figure 5 -Curve shows the results of these measurements. The calibration curve shows a linear dependence of the S count rates to the % S in the sample. Figure 5-Curve 2 shows the expected S count rate dependence on the absolute S concentration. The decrease in the slope of the curve indicates a change in the thermal neutron flux in coal. At higher concentrations, the slope of the cuwe decreases indicating a change in the thermal neutron flux in coal. Figure 6 shows the S count rate normalized to thermal neutron flux. Here, the thermal neutron flux is assumed to be proportional to the net counts in the 2223 kev hydrogen peak divided by the number density of hydrogen in coal. The net area of the 2223 kev peak is determined using the computer program SAM (Table ). The linearity is retained up to 4% w/w S content. However, the 5% w/w sulfur sample deviates from this line. This sample was measured in a different day and showed a high H count rate (SAM fit gave 3644,596 net count) indicating neutron output variation in the generator. The uncertainty of sulfur measurement in this set of measurements is 0.% w/w. However, the uncertainty determined from counting statistics is 0.05% w/w ( For the 0.65% w/w sulfur sample, the sulfur count rate is 3 cps.) We believe, with improvements in spectrum deconvolution methods, sample preparation methods, and incorporating the neutron detector for monitoring neutron fluence, the uncertainty of sulfur measurement can be improved to 0.05% w/w. * 3. G a m m a - R a y! Measurements At present, we have two set-ups to acquire gamma-ray spectra from fast neutron interactions and thermal neutron interactions. The generator to detector distance for acquiring the two spectra are 00 and 50 cm, respectively. These set-ups were designed for obtaining high quality spectra without distortions from gamma-ray pile-up events. The maximum allowable count rate in the TN 244 amplifier with Pile-Up Rejector (PUR) is 00,000 cps. For these two set-ups, we have measured the gamma-ray count rate at the amplifier output using a SCA and a scaler (Figures 7). For these measurements, the single channel analyzer s lower level discrimination was set at 80 kev. Count rates have been normalized to the duty factors. These measurements led us to the following conclusions:. At 00% output, thermal count rate at 00 cm is a factor of 3 lower than at 50 cm. 2. To obtain a high quality fast spectrum at 50 cm, the generator output cannot exceed 20%. 3. The TN 244 amplifier with the Pile Up Reject ON,functions according to its specifications. 4. Least-SaucgesGamma-Rav Spectrum Deconvolution Proaram -Windows Versim With the present improvements in the precision of the measurements, we are critically evaluating the underline assumptions in this numerical method for the analysis of the gamma-ray spectra. We are re-considering the ambiguities in the calculated count rate of an element that has only one prominent gamma-ray peak with an energy equal to a peak from another element. For example, the 4950 kev peak in the thermal spectrum can be from C, Si, and from the S single escape of 5420 kev. We are planning to incorporate constraints such as the expected count rate from C (determined from the fast spectrum) for improving the accuracy of the method. Such improvements in the data analysis are important for the PFTNA method to be an absolute method of elemental analysis. 2

5 Preset-L 200,000 Stopped True Time Live T i m e s "? N nl N zoo.000 % Dead ross Counl Counts/sec Start Time Mar/5/996 0:42:05AM Stop T i m e Mar/5/996 ll:05:02am U s e r D

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7 in Preset-L L i v e Time 6..8 Gross Count CountsJsec Start Time Mar/25/996 2 :54 :3 8PM Stop Time Mar/25/99E 3 :7 : 9PM User D % Dead r---

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9 . Sulfur in coal w/w % of sulfur in coal

10 .... \ 4.5e-5 4.0e-5 3.5e-5 3.0e-5 2.5e-5 i 2.0e-5.5e-5.Oe-5 5.0e S Concentration (w/w%) 5 6

11 P Count Rate (After Amplifier, Coal #9500, Natural, 32 kg) 90 Degree 50 cm.oe+5.oe Generator Out (YO)