Alpha radiation detectors

The use of a low range Beta-Gamma or Alpha radiation detector... 

The alpha curve is higher than the beta curve from Region I to part of Region IV due to the larger number of ion pairs produced by the initial reaction of the incident radiation. Detector voltage principles are summarized below. 

Figure 11.7 X-ray diffraction equipment in capillary configuration showing from left to right Cu x-ray tube, monochromator to select Cu K-alpha radiation, sample mounted in capillary tube, beam tunnel, and X celerator position sensitive detector. The tube and the detector are scanned through a range of angles (theta) by the goniometer (the device in the background on which they are both mounted), and the XRPD is recorded and stored on a computer for subsequent analysis and processing.

Emitted by heavy atoms, such as uranium, radium, radon, and plutonium (to name a few), alpha particles are helium nuclei, making them the most massive kind of radiation. Alpha radiation can cause a great deal of damage to the living cells it encounters, but has such a short range in tissue (only a few microns) that external alpha radiation cannot penetrate the dead cells of the epidermis to irradiate the living cells beneath. If inhaled, swallowed, or introduced into open wounds, however, alpha radiation can be very damaging. In nature, alpha radiation is found in rocks and soils as part of the minerals, in air as radon gas, and dissolved in water as radium, uranium, or radon. Alpha emitters are also found in nuclear power plants, nuclear weapons, some luminous paints (radium may be used for this), smoke detectors, and some consumer products. Objects and patients exposed to alpha radiation may become contaminated, but they do not become radioactive. 

A solid-state nuclear track detector is a piece of special plastic which is exposed as the sensitive element in a radon monitor. The alpha radiation from Rn and RnD, which penetrates the surface of the plastic, causes radiation damage along the entrance path, as shown in the schematic in Fig. 9.26. Chemical etching of the plastic after exposure... 

Two types of track-etch monitor occur, open and closed types. In the open type, the SSNTD is not contained in a volume and is exposed to the air as a bare foil. This detector will register the alpha radiation from the Rn and RnD in the air, and the track density on the foil represents the sum of these activities. However, the Rn signal will be much larger than the signal from the RnD, except at very high levels of RnD (high F factor), and the track density has to be interpreted in terms of this ratio, which is typically unknown. In close monitors the SSNTD is enclosed in a closed container into which Rn diffuses through a filter. This prevents the entry of RnD and dust particles into the chamber, and the foil is then sensitive only to the alpha radiation from Rn and RnD formed in the container. There is a repeatable equilibrium between the isotopes in the container, and calibration provides the relationship between the Rn concentration and the track density on the foil. A typical track-etch radon monitor of the closed type is shown in Fig. 9.27. 

Table 32-1 lists the most important (from a chemist s viewpoint) types of radiation from radioactive decay. Four of these types — alpha particles, beta particles, gamma-ray photons, and X-ray photons —can be detected and recorded by the detector systems described in Section 12B-4. Most radittchcniical methods are based on counting the electronic signals produced when these decay particles or photons strike a radiation detector. 

The tracer and its radiation detector must be selected to avoid cross-talk between their radiations in measuring the two radionuclides. A tracer must be selected that emits different radiations than the radionuclide of interest, or emits the same type of radiation at an energy sufficiently different for resolution by spectral analysis. Use of radioactive tracer is common for actinides that are measured by alpha-particle spectral analysis. A correction factor may be applied if cross-talk cannot be entirely avoided but is small enough to maintain the reliability of the activity calculated for the radionuclide of interest. 

Radiation detectors are specially designed to provide information about the type (alpha, beta, gamma, etc.), energy (radiation spectrometry), and intensity (number of particles or quanta) of the radiation. Some detectors also provide information about the spatial distribution of the radiation (nuclear imaging detectors). 

Americium (the isotope Am) is the vital ingredient of household smoke detectors. The detector is a small chamber in which a low-level electrical voltage is appHed between two electrodes. In an ordinary situation, without smoke in the room, alpha particles from the isotope collide with the oxygen and nitrogen molecules in the detector and ions are produced. As a consequence a steady small electric current flows between the electrodes. When smoke enters the space between the electrodes, the alpha radiation from the isotope is absorbed by smoke particles. This causes the rate of ionization of the air to fall, the current is changed and this change sets off an alarm. The... 

The transuranium elements have a number of commercial uses. Plutonium-238 emits only alpha radiation, which is easily stopped by shielding. The isotope has been used as a power source for space sateUites, navigation buoys, and heart pacemakers. Americium-241 is both an alpha-ray and a gamma-ray emitter. The gamma rays are used in devices that measure the thickness of matmals such as metal sheets. Americium-241 is also used in home smoke detectors, in which the alpha radiation ionizes the air in a chamb within the detector and renders it electrically conducting. Smoke reduces the conductivity of the air, and this reduced conductivity is detected by an alarm drcuiL... 

X-ray diffraction (XRD) analysis of peak profiles was used to measure crystallite size and any orientation effects in the samples. Conventional XRD using copper K alpha radiation at settings of 35kv and 15ma, with a graphite monochromator and scintillation detector was used to create the peak profiles. 

Henshaw DL (1989) Application of sohd state nuclear track detectors to measurements of natural alpha-radioactivity in human body tissues. Nucl Tracks Radiat Meas 16(4) 253-270 Int J Radiat Appl lustrum Part D... 

Gas-filled detectors are used, for the most part, to measure alpha and beta particles, neutrons, and gamma rays. The detectors operate in the ionization, proportional, and G-M regions with an arrangement most sensitive to the type of radiation being measured. Neutron detectors utilize ionization chambers or proportional counters of appropriate design. Compensated ion chambers, BF3 counters, fission counters, and proton recoil counters are examples of neutron detectors. 

To a limited degree, the fill-gas will determine what type of radiation the proportional counter will be able to detect. Argon and helium are the most frequently used fill gases and allow for the detection of alpha, beta, and gamma radiation. When detection of neutrons is necessary, the detectors are usually filled with boron-triflouride gas. 

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