Cloud Chamber Detector

In a cloud chamber detector, ions at atmospheric pressure are electrically focused into a cloud chamber filled with cold water or octane vapors. The presence of the ion serves as the nucleus for the formation of small droplets that can scatter light from a laser beam passing through the cloud chamber. When mobility-separated ions entered the cloud chamber, perturbation in the laser light due to the formation of ion-nucleated particles was detected by a PMT. When the chamber was supersaturated with water, the scattered light intensity increased in the presence of ions, but when the chamber was supersaturated with octane, the intensity decreased in the presence of ions. Mobility spectra of difluorodibromomethane have been reported using cloud chamber detection.  

---

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

Some other detectors in common use either measure radiation in terms of exposure or by tracks. Among the former are ion chambers, dosimeters of various kinds, and photographic film. Tracks can be observed in other types of photographic film, cloud chambers, and track-etch films. 

Introductory remarks. Many of the detectors employed by cosmic ray physicists and low energy nuclear physics have proved useful in high energy nuclear physics. In that there are an abundant number of texts on most of these techniques the sections below deal with the problems involved in employing only a few of the most useful of these detectors, namely scintillation counters, Cerenkov counters, photographic plates, bubble chambers and cloud chambers. 

These results were important in establishing the validity of the assumption of the reaction being (50.3). In studying the stopping of cosmic ray -mesons they employed cloud chambers in some experiments, a large neutron detector in other experiments, and the combination of the two techniques in one case. 

Sampling Detectors. These consist of tubing distributed from the detector unit into the area(s) to be protected. An air pump draws air from the protected area back to the detector. A high-intensity strobe, laser particle counter, or cloud-chamber smoke detector may be used... 

In this technique, a liquid sample is nebulized in a cloud chamber and passed into a flame, where the element is dissociated by the heat from its chemical bonds and placed in an unexcited or ground state. Narrow wavelength light from a hollow cathode lamp is passed through the flame and some of the ground state atoms are excited by the radiation. This results in a net decrease in the intensity of the beam and this can be measured by a photoelectric detector. The process is therefore analagous to absorption spectrophotometry for the measurement of molecules. 

Alpha particles may be counted also by gaseous, liquid, plastic, and crystalline scintillation detectors. The resolution of these detectors is. In general, less, than Ionization chambers and their application more limited. Nuclear emulsions are used to record alpha activity. Such devices as cloud chambers are generally not used In the radloehemlatry laboratory. 

Simply, a quadrupole mass spcciromcier can be divided into three parts (I) the ionizer. (2 the mass tiller, and ( the detector, all of which are contained in a vacuum chamber maiillained at a low pressure. When a gaseous sample is inlroduced inio the system s ionizer, it is bombarded with a stream of electrons, producing positively charged parent ions (ions with the same molecular weight as the neutral molecule), and fragment ions. The ionizer lias a scries nl lenses lhal serve lo collimate the cloud of sample molecules toward the mass filter. 

Fig. 1.23. The electron diffraction apparatus developed by Parks and coworkers includes an rf-ion trap, Faraday cup, and microchaimel plate detector (MCP) and is structured to maintain a cylindrical symmetry around the electron beam axis [147]. The cluster aggregation source emits an ion beam that is injected into the trap through an aperture in the ring electrode. The electron beam passes through a trapped ion cloud producing diffracted electrons indicated by the dashed hues. The primary beam enters the Faraday cup and the diffracted electrons strike the MCP producing a ring pattern on the phosphor screen. This screen is imaged by a CCD camera mounted external to the UHV chamber. The distance from the trapped ion cloud to the MCP is approximately 10.5 cm in this experiment...

The tracks formed can be directly observed by the naked eye in cloud and bubble chambers, but the tracks remain only for a short time before they fade. For a permanent record we must use photography. On the other hand, in solid state nuclear track detectors (SSNTD), of which the photographic emulsion is the most common variant, the tracks have a much longer lifetime during which they can be made permanent and visible by a suitable chemical treatment. Because of the much higher density of the absorber, the tracks are also much shorter and oft therefore not visible for the naked eye. Thus the microscope is an essential tool for studying tracks in solids. 

The Si(Li) detector diode serves as a solid-state version of the gas-ionization chamber, which is the operating mode of the gas-flow proportional counter when the gas gain is unity (see Fig. 4.10). When an x-ray photon is stopped in the detector diode, a cloud of ionization is generated in the form of electron-hole pairs. The number of electron-hole pairs created, or in other words, the total electric charge released, is proportional to the energy of the detected photon. This charge is swept... 

With the normal operating reverse bias of approximately 1000 V, the diode is depleted of the remaining free charge carriers, and it becomes a solid-state ionization chamber. X-ray photons enter the detector through the front contact and interact primarily by the photoelectric process to produce a cloud of ionization in the form of electron-hole pairs. On the average the number of electron-hole pairs produced n is proportional to the photon energy E ... 

---