In positron-emission tomography (PET) used in medical research and diagnosis, compounds containing unstable nuclei that emit positrons are introduced into the brain, destined for a site of interest in the brain. When a positron is emitted, it goes only a short distance before coming nearly to rest. It forms a bound state with an electron, called "positronium", which is rather similar to a hydrogen atom. The binding energy of positronium is very small compared to the rest energy of an electron. After a short time the positron and electron annihilate. In the annihilation, the positron and the electron disappear, and all of their rest energy goes into two photons (particles of light) which have zero mass; all their energy is kinetic energy. These high energy photons, called "gamma rays", are emitted at nearly 180° to each other. What energy of gamma ray (in MeV, million electron volts) should each of the detectors be made sensitive to? (The mass of an electron or positron is 9 × 10-31 kg. 1 eV = 1.6 × 10-19 joules.
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Physics, 23.06.2019 13:00
After identifying which method the theory relates better to, use the example of feyerabend to discuss why you think philosophy and science (and, philosophers and scientists) have theories and ideas that blend into one another. how are these two disciplines related?
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Physics, 23.06.2019 15:30
The volume of a right circular cylinder can be approximated as follows: volume = ? r2h; where r is the radius of the cylinder and h is the height of the cylinder; ? is a constant that is roughly equal to 3. using the simple approximation above, calculate the volume of a right circular cylinder with a radius of 2 meters and a height of 7 meters
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In positron-emission tomography (PET) used in medical research and diagnosis, compounds containing u...
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