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Neutron Emission from Nuclei Excited by High Energy Protons
| Content Provider | Semantic Scholar |
|---|---|
| Author | Williams, Wesley C. |
| Copyright Year | 2007 |
| Abstract | NUCLEAR reactions induced by high energy protons are thought to take place in two stages (Serber 1947). In the first stage the incoming particle makes collisions with individual nucleons in the target nucleus, and some of the products of these collisions pass directly out of the nuclear field. These " prompt " particles have high kinetic energy and they are emitted predominantly in the direction of motion of the incoming particle. After their departure the residual nucleus is left highly excited, and in the second stage of the reaction the excitation energy is dissipated by the emission of neutrons, charged particles and eventually y-rays. These " evaporation " particles have relatively low energies, and they are emitted isotropically because of the comparatively long lifetime of the intermediate nuclei. Evaporation protons have often been studied before (e. g. Harding, Lattimore and Perkins 1949), but there has been little investigation of the neutrons following high energy reactions. This letter reports preliminary results of an investigation of evaporation neutrons from carbon and tungsten targets bombarded in the Harwell cyclotron. Values have been obtained for the differential cross-section for neutron evaporation as a function of the kinetic energy of the emitted neutron. I f some assumptions are made as to the value of the proton inelastic cross-section of the target nuclei, the average number of neutrons emitted per excited nucleus can be determined also. The two targets were exposed in turn to the internal proton beam, whose maximum energy was calculated to be 171 MeV. Slowing down in the targets reduces t h e effective primary proton energy to about 157 MeV. in both cases. Neutrons emitted backwards (i. e. at 180 ° to the direction of the ingoing proton beam) were collimated by 2 in. diameter holes in concrete blocks and entered photographic plates 18.9 metres from the target. The distributions in energy of these neutrons were determined by means of the tracks of recoil protons produced in the photographic emulsions (Champion and Powell 1944). The numbers of primary protons striking the targets in the two runs were determined measuring the amount of 7Be produced by the leC(p, 3p3n)TBe reaction, whose cross-section is known with an accuracy of 10 per cent (Dickson and Randle 1951). Several thin plates of carbon were incorporated in the tungsten target, for this purpose. Two subsidiary experiments were carried out to check that the neutrons did, in fact, come directly from the target. Negligible numbers of recoil proton tracks were observed |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.hep.princeton.edu/~mcdonald/examples/EP/skyrme_pm_42_1187_51.pdf |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | C-slowing Cell Nucleus Charge (electrical) Cyclotrons Diameter (qualifier value) Energy, Physics Excitation Experiment Harwell computer Ions Kinetics Neutrons Nucleons Occur (action) Photographic plate Powell's method Proton-Translocating ATPases Protons Radiation Stage level 1 Stage level 2 Thin-film transistor Track (course) collision evaporation proton beam subsidiary tungsten |
| Content Type | Text |
| Resource Type | Article |
