Compton Background Research Articles

Borehole field calibration and measurement of low‐concentration manganese by decay gamma rays

The manganese concentration in the Arundel clay formation, Prince Georges County, Maryland, was determined from a borehole by using delayed neutron activation. The neutrons were produced by a [Formula: see text] source. The 847 keV gamma ray of manganese was detected continuously, and its counting rate was measured at intervals of 15 s as the measuring sonde was moved at a rate of 0.5 cm/s. The technique measured the concentration ratio of manganese to aluminum. This ratio, when combined with an estimate of the aluminum concentration of the clay, made it possible to determine the percentage concentration of manganese without using a test‐pit calibration facility. The measurements were made by using an NaI(Tl) scintillation detector and a Ge(HP) solid‐state detector cooled by solid propane. A two‐pass technique had to be used with the scintillation detector because Compton background from the 1 779 keV photopeak of aluminum masked the manganese line. The Compton background did not interfere when the solid‐state detector was used. The borehole measurements compared favorably with a chemical core analysis and were unaffected by water in the borehole.

Compton suppression gamma-counting: The effect of count rate

Past research has shown that anti-coincidence shielded Ge(Li) spectrometers enhanced the signal-to-background ratios for gamma-photopeaks, which are situated on high Compton backgrounds. Ordinarily, an anti- or non-coincidence spectrum (A) and a coincidence spectrum (C) are collected simultaneously with these systems. To be useful in neutron activation analysis (NAA), the fractions of the photopeak counts routed to the two spectra must be constant from sample to sample to variations must be corrected quantitatively. Most Compton suppression counting has been done at low count rate, but in NAA applications, count rates may be much higher. To operate over the wider dynamic range, the effect of count rate on the ratio of the photopeak counts in the two spectra (A/C) was studied. It was found that as the count rate increases, A/C decreases for gammas not coincident with other gammas from the same decay. For gammas coincident with other gammas, A/C increases to a maximum and then decreases. These results suggest that calibration curves are required to correct photopeak areas so quantitative data can be obtained at higher count rates.

Removal of sodium-24 by chromatographic extraction with a Kieselguhr column and a crown ether solution

Sodium-24 was readily removed from aqueous solutions by a chromatographic process based on an isotopic exchange reaction. The reaction was carried out with a granular Kieselguhr column and a chloroform solution of crown ether-sodium picrate. The process took about 1 h and can be utilized in neutron activation analysis of many elements, Cl, Br, Sc, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ru, In, Sn, Ce and W. It cannot be used, however, for alkali and alkaline earth elements. The amount of /sup 24/Na in a treated sample was 10/sup -2/ of the original amount. The Compton background was reduced in the range of ..gamma..-ray energy after the removal of sodium-24. 3 figures, 3 tables.

A Compton-suppression spectrometer for γ-γ coincidence measurements: Large solid angle and excellent suppression

For γ-γ coincidence measurements a Compton-suppression spectrometer with a large solid angle of 120 msr and excellent suppression has been designed. The dimensions of the NaI anticoincidence shield have been optimized by means of Monte Carlo calculations. The NaI shield has a length of 35 cm and a diameter of 30 cm. A 20% efficient HPGe crystal with a dead layer of 0.22 mm and a hollow core is used as central detector. For 60Co, the average suppression of the Compton background between 100 and 1100 keV amounts to 11.8 with a photopeak loss of 5.8%. The areas of the 1173 and 1332 keV peaks taken together amount to 60% of the total number of registered counts for the suppressed spectrum and to 15% for the non-suppressed spectrum. The spectrometer has been tested in a γ-γ coincidence experiment with the reaction 24Mg + (45 MeV) 16O.

Determination of selenium in environmental standard reference materials by a .gamma.-.gamma. coincidence method using lithium-drifted germanium detectors

A gamma-gamma coincidence technique is applied to the determination of low levels of selenium in NBS standard reference materials, using the /sup 75/Se (n,..gamma..) product. The method is shown to provide accurate determinations in a variety of materials. Removal of interfering ..gamma.. rays at 136 and 264 keV due to /sup 181/Hf and /sup 182/Ta and suppression of Compton background by three to four orders of magnitude are realized by the coincidence counting procedure. Selenium concentrations (..mu..g g/sup -1/) of 0.024, 0.065, 0.084, 0.053, 1.1, 2.6, and 8.8 were determined for SRMs 1570, 1571, 1573, 1575, 1577, 1632, and 1633, respectively. Two sigma Se detection limits were approximately 10 to 20 ng g/sup -1/ for biological reference materials, and 50 to 100 ng g/sup -1/ for fly ash and coal using the conditions reported. 2 tables.

Magnetic tape interfaces for a dual-parameter coincidence experiment

Two dual-parameter interfaces for nuclear coincidence experiments are described. One of them is used for interfacing the coincidence section to a magnetic tape transport. The other is used for reading the data from the magnetic tape into a multichannel analyzer. Options were provided to enable corrections of the undesired contributions from coincidence with the Compton background and also with the chance events. Tests on the systems have shown that both system are very efficient and reliable. The interfaces make use of integrated circuits and can therefore be built cheaply.

MÖSSBAUER EXPERIMENTS WITH HIGH ENERGY GAMMA RAYS : THE 158 keV TRANSITION IN 199Hg

The 158 keV Mossbauer resonance in 199Hg has been studied both in a transmission geometry by measuring the integral detector current and in backscattering experiments. From the isomer shifts observed between HgFz and sources of 199Au in Pt, V, Nb and Rh matrices one estimates A x + 1 x 10-3 fmz for the change mean square nuclear charge radius. 1, Introduction. - Mossbauer experiments with gammarays having energies above approximately 100 keV become increasingly difficult because of the small recoilfree fractions then encountered even in heavy elements. The 158 keV transition in lg9Hg presents particular difficulties, mainly due to the inherently low effective Debye temperatues of mercury in most of its compounds and alloys. To obtain Mossbauer spectra of the 158 keV gammarays within measuring times of the order of a few days, two approaches may be taken : One is to perform a standard transmission experiment with a very high gammaray intensity. In principle, in this way sufficient statistical accuracy can be obtained within a reasonable length of time, but even with fast counting electronics, one can hardly increase the countrate above several times lo6 s-I (I). Higher rates of events in a detector like a scintillator or a Ge(Li) crystal can, however, be handled if the integral detector current is measured rather than individual pulses (2, 31. Alternatively, one can use a backscattering geo- metry instead of the transmission arrangement. Again with sources of typically a few Curies, one then gets countrates that can easily be handled by a Ge(Li) detector, but the observed resonance effect can be 10'-lo3 times larger than in a transmission experiment (see, e. g. 141). Both the current integration and the backscattering technique are restricted to Mossbauer transitions that are fed by simple nuclear decay schemes, the former because of the inherent complete loss of energy resolution and the latter (*) Research performed under the auspices of the Bundes- ministerium fiir Forschung und Technologie and with financial support from the Gesellschaft fiir Kernforschung mbH, Karl- sruhe. because the strong Compton background produced by gammarays having higher energies than the Mossbauer line can easily swamp the elastic scattering peak.

Measurement of diffuse X-ray scattering between reciprocal-lattice points as a new experimental method in determining interstitial structures

For interstitials the scattering cross section between the Bragg reflections is very sensitive to the position of the defect atom and the displacements of the neighbouring lattice atoms. In contrast to this the scattering near the Bragg reflections (Huang scattering) is mainly governed by the displacement field at large distances from the defect and gives information about defect symmetry and strength [Trinkaus, H. (1972). Phys. Stat. Sol. (b) 51, 307–319]. For determining structures of point defects a measurement of scattering far from reciprocal-lattice points is therefore the best suited and most direct method. X-ray measurements of point-defect scattering in this region far from reciprocal-lattice points are difficult. With conventional X-ray set-ups it is not possible to separate the defect scattering from the thermal diffuse and Compton background scattering which is up to two orders of magnitude larger in the case of typical defect concentrations of some 10−4. Such measurements, however, become possible if large X-ray sources of high luminous density are used in connexion with multidetector arrangements. As an example an experimental arrangement [Haubold, H.-G. & Schilling, W. (1975). To be published; Haubold, H.-G. (1974). Rep. Kernforschungsanlage Jülich, JUL-1090-FF] is reviewed, in which the scattering cross-section of self-interstitials in aluminium was measured in samples containing an atomic density of interstitials up to 5 × 10−4.

Anticoincidence-Shielded Ge(Li) Gamma-Ray Spectrometer for Marine Environmental Radionuclide Analysis

An anti-Compton γ-ray spectrometer has been developed, which possesses a number of characteristics particularly adapted to direct measurement of low-level complex mixtures of radionuclides in marine environmental samples. The detector assembly consists of a 42.7 cm3 coaxial Ge(Li) detector and a well-type 6″diam. × 4″ Nal(Tl) detector for the anticoincidence shield. The sample to be measured is placed on the Ge(Li) detector inside the well of the Nal(Tl) crystal. Suppression of the Compton background is particularly marked at the Compton edge when the assembly is operated in anticoincidence mode. The anticoincidence shield reduces the 137Cs Compton edge by a factor of 6.6 to provide a peak-to-Compton edge ratio of 210: 1 without reducing the full-energy peak efficiency by more than 2%. Similarly, for the 1,332.5 keV 60Co γ-rays the Compton edge is reduced by a factor of 7 to give a peak-to-Compton ratio of 85:1, though in this case the peak efficiency is reduced by a factor of 1.8 due to the cascade decay. This spectrometer has permitted the detection of a few pCi of fallout nuclides such as 137Cs and 95Zr, contained in 30 g environmental wet samples counted at intervals of 1,000 min.

Anticoincidence-Shielded Ge(Li) Gamma-Ray Spectrometer for Marine Environmental Radionuclide Analysis

An anti-Compton γ-ray spectrometer has been developed, which possesses a number of characteristics particularly adapted to direct measurement of low-level complex mixtures of radionuclides in marine environmental samples.The detector assembly consists of a 42.7cm3 coaxial Ge(Li) detector and a well-type 6 diam. ×4 NaI(Tl) detector for the anticoincidence shield. The sample to be measured is placed on the Ge(Li) detector inside the well of the NaI(Tl) crystal.Suppression of the Compton background is particularly marked at the Compton edge when the assembly is operated in anticoincidence mode. The anticoincidence shield reduces the 137Cs Compton edge by a factor of 6.6 to provide a peak-to-Compton edge ratio of 210:1 without reducing the full-energy peak efficiency by more than 2%. Similarly, for the 1, 332.5keV 60Co γ-rays the Compton edge is reduced by a factor of 7 to give a peak-to-Compton ratio of 85:1, though in this case the peak efficiency is reduced by a factor of 1.8 due to the cascade decay.This spectrometer has permitted the detection of a few pCi of fallout nuclides such as 137Cs and 95Zr, contained in 30g environmenal wet samples counted at inervals of 1, 000min.

A Theoretical and Laboratory Evaluation of Carbon Logging - Laboratory Evaluation

Abstract Results we presented from a laboratory experimental evaluation of a carbon well-logging tool based on the detection of the 4.43-MeV gamma rays produced by the inelastic scattering of 14-MeV neutrons. The success of a carbon logging tool is dependent primarily upon the gamma-ray detection scheme used, which in this investigation is a two-crystal pair spectrometer. Using such a device in a simulated reservoir with and without casing and a cement annulus, semiquantitative detection of carbon was accomplished for a fluid-filled packed sand of 35-percent porosity. Analysis of the spectral results show that the log would be sensitive to lithology, saturation and porosity as well as carbon. With the resolution of this particular gamma-ray detector scheme, the presence of the casing using seen, but did not interfere with the carbon signal. Likewise the 1-in. annulus of concrete had no effect on the carbon detection. Comparison of our results with those previously published show that the oxygen and silicon interference encountered i, other proposed logging schemes is eliminated by the two-crystal pair spectrometer. As presently envisaged, between 5 to 10 minutes per pay zone to be evaluated is required to per pay zone to be evaluated is required to accumulate raw data. However, the growth potential offered by the new Ge(Li) gamma-ray counters may well remove this restriction. Introduction Theoretical results presented in Ref. 1 have indicated that liquid hydrocarbons should be detectable in noncarbonaceous reservoirs. Although the interference problem posed by energy degraded gamma rays from omnipresent oxygen is severe, it is not severe enough to prohibit detection of hydrocarbons by nuclear means. The theoretical data also showed thermal neutron effects caused by energy degradation of gamma rays from thermal capture in silicon, chlorine and iron could be eliminated by proper choice of a neutron source gamma detector gating scheme. Indeed, this has been demonstrated experimentally. The crux of the hydrocarbon detection problem lies with finding a gamma detector system with sufficient resolution to pick out 4.43-MeV gamma rays (carbon) from the background provided by oxygen. Previous investigations have shown that single NaI(T1) crystal detectors did not have sufficient energy resolution to accomplish the task. However, energy resolution is not the whole answer when it comes to extracting a monoenergetic signal from a continuum background. In addition to the interfering gamma rays produced through Compton collisions external to the detector system, there is an in-crystal Compton background in single-crystal spectrometry. The second source of interference arises because gamma rays entering the crystal at energies higher than the discrete energy of interest will produce Compton collisions within the crystal generating electrons that have precisely the same energy as that of the "desired signal". This second source of interference significantly reduces the carbon sensitivity of a single-crystal detector. Hence, elimination of the in-crystal background from oxygen produced gamma rays would go far in improving the in-situ carbon detection picture. In searching for an acceptable detector system, this point was kept foremost in mind. It was known a three-crystal pair spectrometer would virtually eliminate the in-crystal Compton background, but limitations imposed by borehole tool size ruled out its use. However, from studying the working principle of this device the concept of the principle of this device the concept of the two-crystal pair spectrometer emerged. A description of such a device was later found in Ref. 4 although no evidence has been found that such a device has been used to record spectra in a borehole or simulated borehole environment. This report presents experimental results obtained with such a presents experimental results obtained with such a two-crystal spectrometer in various simulated reservoir conditions.

Ge(Li)Ge(Li) sum coincidence: A bonus from Ge(Li)Ge(Li) megachannel coincidence experiments

The sum-coincidence technique in Ge(Li)Ge(Li) γ-ray spectroscopy is shown to be a viable and useful method for reducing Compton backgrounds and the resulting confusion they can cause. When used in conjunction with the digital readout from a two-dimensional “megachannel” coincidence experiment, many of the disadvantages and much of the tedium associated with the technique can be eliminated. It thus becomes a valuable, complementary technique to be used as needed in processing the data from a γ-γ coincidence experiment, requiring little or no additional experimental preparation. We present examples of its use in a relatively simple ( 63Zn) and a very complex ( 205Bi) spectrum.

Evaluation of X-ray fluorescence and mass spectrometric analyses of Rb and Sr in some silicate standards

X-ray fluorescence analysis of Rb and Sr in five rock standards, using computed mass absorption corrections, agrees satisfactorily with mass spectrometer results. Comparable agreement is found by averaging Rb and Sr values obtained with matrix corrections based on the reciprocals of Compton scatter and background intensity.

21. 非破壊法による使用済み燃料の燃焼度測定

This report describes a nondestructive measurement on average burnup of irradiated fuel rods with use of a Ge(Li) detector. In order to obtain the average burnup directly and to simplify measurement and analysis, the γ-ray spectrum from the irradiated fuel rod was measured by scanning along the whole length of the rod. The total absorption peaks for the 0.662MeV (137Cs) and the 2.18MeV (144Pr) γ-rays were used in the analysis, and the peak areas were estimated by Covell's method. The absolute value of overqge burnup was determined by comparison of the peak area with that of a standard fuel rod.The accuracy of the nondestructive measurement is discussed on the basis of an accurate value from destructive analysis. The result shows that it is possible to give the average burnup with good accuracy when the ratio of the peak height for 137Cs to the Compton background is larger than about 1.5, that is, after about 1 year of cooling.

Low-intensity gamma rays in 90Nb decay

Gamma rays de-exciting levels in 90Zr populated in the decay of 90Nb have been analysed with a Ge(Li) spectrometer. To enhance photopeaks from the weak transitions observed in recently reported conversion electron studies, the Compton background from the strong high-energy lines in the spectrum was suppressed by partially surrounding the Ge(Li) detector with a NaI(Tl) scintillator operated in anticoincidence. Energies, intensities, K-conversion coefficients, and probable multipolarities have been determined for 13 transitions. These transitions are placed in a decay scheme which includes 10 excited states in 90Zr.

Decay of 95Ru

Ge(Li) detectors have been used singly and in coincidence to study γ-rays in the decay of 95Ru to 95Tc. A NaI(Tl) anticoincidence shield was used to suppress the Compton background in the singles spectrum, increasing sensitivity to low-intensity gammas. Energies and intensities have been determined for 36 transitions. A decay scheme is proposed which accommodates 33 of these transitions. Spins and parities for these levels are assigned from calculated log ƒt values and measured γ-ray branching ratios.

Determination of rare-earth eleemnts in rock samples by neutron activation analysis

A Ge(Li) detector combined with cation exchange separation has been used for the determination of 12 rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb, and Lu) in rock samples by neutron activation analysis. After purification by the conventional hydroxide-fluoride precipitation, the rare-earth elements are separated into two fractions, light (La-Tb) and heavy (Ho-Lu), by EDTA cation exchange, and the γ-activities of the two fractions are measured by a Ge(Li) detector. The heavy rare-earths, such as Ho, Er, and Tm, can be easily γ-counted without serious interference from the intense Compton background and photopeaks due to the light rare-earths such as140La,153Sm,152Eu, and160Tb. The chemical yields (60%) for the individual rare-earths are determined by a reactivation technique. The results obtained for the U.S. Geological Survey standard rocks G-1 and W-1 are compared with the previously reported data.

Further Test ofM1Admixtures in the Decay of2+′ Beta Vibrational States

The $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ directional correlation of the 692-123 keV, ${2}^{+}$\ensuremath{'} \ensuremath{\rightarrow} ${2}^{+}$ \ensuremath{\rightarrow} ${0}^{+}$ cascade in $^{154}\mathrm{Gd}$ was remeasured with an improved Ge(Li)-NaI system. The spectra in coincidence with the Compton background and the 123-keV photopeak were simultaneously recorded at each angle. The new results averaged with our earlier work yield ${A}_{2}=\ensuremath{-}0.141\ifmmode\pm\else\textpm\fi{}0.022$ and ${A}_{4}=0.311\ifmmode\pm\else\textpm\fi{}0.040$. These values are consistent only with the 692-keV transition being essentially pure $E2$.

A high-resolution Ge(Li) anti-compton spectrometer for radiative neutron capture spectroscopy

A Ge(Li) anti-Compton spectrometer for the energy range up to 3 MeV is described which allows for the special conditions of (n,γ) spectroscopy and which gives improved performance compared to previously reported devices. The system consists of a planar 4.9 cm 3 Ge(Li)diode, a 50 cm dia. × 40 cm plastic scintillator and a 4“ dia. × 6” NaI(Tl) detector at scattering angle 0°. The anti-coincidence method together with a pulse-shape discrimination technique very effectively suppress the Compton background under the peaks. The energy resolution is 2.15 keV fwhm at 0.662 MeV. Typical capture spectra are presented to illustrate the performance of the system.

A single crystal Ge(Li) Compton spectrometer

A single crystal Ge(Li) Compton spectrometer has been tested showing considerable promise as a device for detecting γ-rays in the presence of strong Compton and neutron backgrounds.