alpha radiometer

— alpha radiometer

— beta-gamma radiometer

— IR radiometer

— microwave radiometer

— roentgen radiometer

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SUBJECT AREA: Electricity

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Crookes entered the Royal College of Chemistry at the age of 15, and from 1850 to 1854 held the appointment of Assistant at the college. In 1854 he became Superintendent of the Meteorological Department at the Radcliffe Observatory in Oxford. He moved to a post at the College of Science in Chester the following year. Soon after this he inherited a large fortune and set up his own private laboratory in London. There he studied the nature of electrical discharges in gases at low pressure and discovered the dark space (later named after him) that surrounds the negative electrode, or cathode. He also established that the rays produced in the process (subsequently shown by J.J.Thompson to be a stream of electrons) not only travelled in straight lines, but were also capable of producing heat and/or light upon impact with suitable anode materials. Using a variety of new methods to investigate these "cathode" rays, he applied them to the spectral analysis of compounds of selenium and, as a result, in 1861 he discovered the element thallium, finally establishing its atomic weight in 1873. Following his discovery of thallium, he became involved in two main lines of research: the properties of rarified gases, and the investigation of the elements of the "rare earths". It was also during these experiments that he discovered the principle of the Crookes radiometer, a device in which light is converted into rotational motion and which used to be found frequently in the shop windows of English opticians. Also among the fruits of this work were the Crookes tubes and the development of spectacle lenses with differential ranges of radiational absorption. In the 1870s he became interested in spiritualism and acquired a reputation for his studies of psychic phenomena, but at the turn of the century he returned to traditional scientific investigations. In 1892 he wrote about the possibility of wireless telegraphy. His work in the field of radioactivity led to the invention of the spinthariscope, an early type of detector of alpha particles. In 1900 he undertook investigations into uranium which led to the study of scintillation, an important tool in the study of radioactivity.

While the theoretical basis of his work has not stood the test of time, his material discoveries, observations and investigations of new facts formed a basis on which others such as J.J. Thomson were to develop subatomic theory. His later involvement in the investigation of spiritualism led to much criticism, but could be justified on the basis of a belief in the duty to investigate all phenomena.

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