Gamma-ray measurement

To summarize, the total gamma ray measurements are used for real-time correlation, lithology identification, depth marker and kick-off point selection. 

Short Normal Resistivity (after Anadriii). The short normal (SN) resistivity sub provides a real-time measurement of formation resistivity using a 16-in. electrode device suitable for formations drilled with water-base muds having a moderate salinity. A total gamma ray measurement is included with the resistivity measurement an annular bottomhole mud temperature sensor is optional. The short normal resistivity sub schematically shown in Figure 4-273 must be attached to the MWD telemetry tools and operates in the same conditions as the other sensors. 

Palmer HE, Spitz HB, Rieksts GA. 1985. Part III Gamma-ray measurements. Health Phys 49(4) 577-586. 

Tossing a mental coin, the decision was to analyze the case of noise proportional to the square root of the signal. This, as you will recall, is Poisson-distributed noise, characteristic of the noise encountered when the limiting noise source is the shot noise that occurs when individual photons are detected and represent the ultimate sensitivity of the measurement. This is a situation that is fairly commonly encountered, since it occurs, as mentioned previously, in UV-Vis instrumentation as well as in X-ray and gamma-ray measurements. This noise source may also enter into readings made in mass spectrometers, if the detection method includes counting individual ions. We have, in... 

Fig. 3. Angular distribution of the 1107-keV gamma ray measured at 3.4-MeV neutron energy. The solid line represents the angular distribution calculated with the Hauser-Feshbach theory for a streched 4+->2+ transition.

Compared to the simplicity of the relative method, with its simple measurement equation, there is a hidden complexity in the k0 method complex algorithms, dedicated software for reactor neutron fluxes and gamma ray measurement efficiency and many problems associated with spectrum deconvolution. The method relies on a complex set of written standards which are not always fully understood by the average user. It uses non-transparent instrumentation and measurement processes. In short the method becomes, forgive the terminology, non-traceable to the user and this is, I believe, worse than non-traceable to SI units. 

Analysis. The analytical system used for gamma-ray measurements consisted of a lithium drifted germanium (GeLi) crystal detector, a 4096 multi-channel analyzer, a PDP 11 computer, and a cassette magnetic tape storage. The germanium detector crystal has a volume of 55 cm with FWHM resolution of 2.3 keV at 1.33 MeV. The computer was used to analyze the gamma ray spectra, to identify the radio isotopes, and to calculate the concentration (Table III). 

Tables 2-4 show the results of the gamma-ray measurements of soil, wheat root and wheat stem from the two agricultural systems.

Semiconductor detectors, made from single crystals of very pure germanium or silicon, are the highest performance detector type. The superior resolution of these detectors has revolutionized data-gathering for X-ray and gamma-ray measurements. The comparison of the pulse resolving ability of the three types of X-ray detectors scintillator, gas proportional and Si(Li) is shown in Fig. 5.18. 

PGNAA Prompt gamma-ray measurements are used for elements producing either very short or very long lived radionuclides, commonly H, C, N, Si, P and S. Enhanced sensitivities are obtained by direct measurement of prompt gamma-rays emitted by the transient compound nucleus instead of the radioactive reaction product. 

One effective medium in common use for gamma-ray measurements is thallium-activated sodium iodide [Nal(Tl)]. The relatively high-Z iodine atom provides a high attenuation coefficient for interacting with energetic gamma radiation. It... 

Most of the radioisotopes used as isotopic labels in activation analysis decay with beta (positron and negatron) radiations and/or gamma rays. By convention, beta-emitting radionuclides are usually measured by gas-filled or gas-flow proportional counters or Geiger counters. Sometimes, liquid scintillation counters are used to complete a beta-ray measurement. The more conventional method for gamma-ray measurements involves the use of a gamma-ray spectrometer equipped with either a scintillation or solid-state detector. Stevenson (918) discusses the characteristics of radioactive decay and gives details on the methods and instruments used to detect emitted radiations. 

In the context of neutron and gamma-ray measurements, NDA techniques used by the inspectorate can be categorized as passive NDA or active NDA. Passive NDA refers to techniques that measure radiation emitted spontaneously from nuclear material. This method is often applied to Pu samples, because of the large spontaneous fission rate of the even-even Pu isotopes. Active NDA, on the other hand, refers to techniques that measure induced radiation responses from a sample, often using an external neutron source. These active methods are usually applied to perform uranium measurements where the spontaneous fission rate is low. 

Figure 2.4, a photoelectric absorption can be followed by the emission of a characteristic X-ray of the absorbing medium. There is a significant possibility that this fluorescent X-ray may escape the shielding and that it will be detected by the detector, as indicated in Figure 2.13. The result will be a number of X-ray peaks in the gamma spectrum in the region 70-85 keV. This may or may not be a problem in practice, depending upon the type of gamma-ray spectrum measured. However, if low-energy gamma-ray measurements are contemplated, fluorescent X-rays are an unnecessary complication.

Figure 5.4 Portions of the spectrum of Co gamma-rays measured on (a) Nal(TI) scintillation, and (b) Ge semiconductor detectors (the dotted lines represent the underlying Gaussian distribution of counts)...

Scintillation detection has been used since the earliest days of radioactivity and is still today employed to measure the whole range of radioactive emissions — alpha-and beta-particles, gamma-rays, neutrons and the more exotic leptons and mesons. In this chapter, I will restrict myself exclusively to scintillation as apphed to gamma-ray measurements. 

The materials that have found particular application for gamma-ray measurements are all inorganic crystals sodium iodide (Nal), caesium iodide (Csl), calcium fluoride (CaF2), bismuth germanate (BGO) and, recently, lanthanum halides. Of these, the first is the most important and the last are materials rapidly gaining in importance. 

The relevant physical parameters for a number of materials in use for gamma-ray measurement are listed in Table 10.1. A word of explanation is needed about the measures of light emission quoted in the literature. In... 

The design of photomultipliers varies depending upon what they are to measure. For scintillation gamma-ray measurements, they are always of an end-window design with the photocathode deposited on the inside of the face of the tube. The whole structure is enclosed within an evacuated glass envelope and connections made via a multipin plug at the anode end. 

An experimental result can only be as good as the data used in its production. Sources of nuclear data are many and it is not always clear which are reliable. With gamma-ray measurements, there are four pieces of nuclear information required for each nuclide to be measured ... 

The International Atomic Energy Authority (IAEA) maintains a very detailed list of nuclear databases of all kinds at http //www-nds.iaea.org/, including those of value to persons engaged in prompt gamma-ray measurements at http //www-nds.iaea.org/pgaa/. 

HRGS High Resolution Gamma Spectrometry Usually used to describe gamma-ray measurement techniques involving germanium detectors as opposed to detectors made of other materials. 

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