Radiation source, electron-capture detector

With all electron capture detectors which use tritium as the source of beta radiation, alcohols and water should be rigorously avoided as solvents for the sample and oxygen or air as a matrix for a gas sample should similarly be avoided if possible. These precautions are mentioned because each of these materials can exchange or react with the tritium in the cell resulting in decreased sensitivity or decreased detector life. 

The electron capture detector has a layer of Ni63 as a (3-radiation source. The radioactivity of the radiation source amounts from 10 up to 15 mC (370 to 550 MBq). 

Radioactive heavy elements such as uranium, thorium, or plutonium are used as nuclear fuel radium is used in the radiography of metals and radon is used as a surface label to study surface reactions, as well, in the determination of radium or thorium. Among the lighter isotopes, Ni is used in electron capture detectors for GC analysis, in radiocarbon dating and as a tracer, and tritium in nuclear fusion and as a tracer in the studies of reactions. Many radioactive elements are used as a source of radiation, in medicine to diagnose disease, and for treatment. 

It is important to place in perspective the relative ionizing radiation dose acquired in common laboratory settings. The most commonly encountered source is a Ni source used in gas chromatographic electron capture detectors and in ion mobility spectrometers (Ref. 1). In both instruments, the source is sealed and has a radioactivity of 15 mCi. The exposures cited refer only to normal operation it does not consider exposures if the device is dismantled or allowed to overheat. 

The emission spectmm of Co, as recorded with an ideal detector with energy-independent efficiency and constant resolution (line width), is shown in Fig. 3.6b. In addition to the expected three y-lines of Fe at 14.4, 122, and 136 keV, there is also a strong X-ray line at 6.4 keV. This is due to an after-effect of K-capture, arising from electron-hole recombination in the K-shell of the atom. The spontaneous transition of an L-electron filling up the hole in the K-shell yields Fe-X X-radiation. However, in a practical Mossbauer experiment, this and other soft X-rays rarely reach the y-detector because of the strong mass absorption in the Mossbauer sample. On the other hand, the sample itself may also emit substantial X-ray fluorescence (XRF) radiation, resulting from photo absorption of y-rays (not shown here). Another X-ray line is expected to appear in the y-spectrum due to XRF of the carrier material of the source. For rhodium metal, which is commonly used as the source matrix for Co, the corresponding line is found at 22 keV. 

Ar. Ns This detector employs a source of P radiation (usually 6JNi-cf. helium ionisation detector). The 1000-10.000 velocities of the high energy electrons are reduced to thermal velocities by coOisioo with atoms of inert gas with which the detector chamber is purged. When a sample of a gas with a greater election affinity than the inert gas is introduced into the ccC some of the electrons are captured and form negative ioas. 

Compton scatter telescopes utilize two detector planes designed to scatter the incident radiation in the top plane and capture the scattered photon in the lower plane. Measurements of the energy losses and positions of the interactions in the two detector planes permits the reconstruction of the incident photon direction, hi telescopes such as this and COMPTEL on GRO [4], it is not possible to measure the direction of the Compton electron in the top detector and the possible directions, when projected onto the sky, produce a small circle of the half-angle specified by the scatter angle and centered on the direction of the scattered photon. A point source of gamma... 

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