Nuclear Physics Group
Department of Physics & Astronomy
Equipment & Setups
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Nuclear Physics Group Department of Physics & Astronomy Equipment & Setups |
Here at UK we use inelastic neutron-scattering
reactions (n,n') to probe the nuclear structure of the isotopic sample in
question. These neutrons are produced through four main reactions involving
the accelerated ions on a gas or solid target. These reactions help produce
neutron energies which range between 60 keV and 23 MeV. These reactions
are as follows;
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| These energies allow comprehensive studies of the low-lying, low-spin, nuclear structure of isotopes. This is especially useful for studying weak-coupled states, one of the main areas for the group's studies. Three of the above reactions require either a source of tritium or deuterium. In the case of tritium, a beta-active source which can be very dangerous if inhaled or ingested, a number of safety procedures are enforced to minimize the possibility of accidents. When not in use, the tritium itself is placed in a 238U oven where the gas is absorbed by the uranium chips. When required, the oven is heated and the gas evolves from the uranium, and is placed in a specially designed cell. This cell is seperated from the vacuum of the beamline by a molybdenum foil. However, in this process the foil becomes heated due to the deposition of energy in the foil by the ions and must be replaced periodically. Fewer problems are associated with the handling of deuterium, although its weakly bound nature can cause technical difficulties with its use as both an incident ion and target. The photo to the right shows the deuterium cell, although the tritium cell looks very similar. |
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| Higher energy neutrons can be used to open higher order reaction channels such as (n,2n) and (n,3n) reactions. This allows an isotope with a low abundance to be investigated using a sample of the element's more abundant stable isotope. A recent example of this is the study of 180Ta, the least abundant isotope in the solar system, using a sample of 181Ta, through the (n,2n) reaction. |
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Once a nucleus has been excited by the incoming neutrons, it de-excites to a lower level by emitting a gamma-ray. It is these gamma rays which are detected, using HPGe (Hyper-Pure germanium) detectors. Over time, a spectrum of gamma rays is produced and recorded, which we then analyse using various methods to gain insight into the structure of the nucleus. The germanium crystal (effectively a PN junction) has an operating temperature below 100K, and must therefore be periodically filled with liquid nitrogen to maintain temperatures at this level. If they are allowed to warm, the crystals acquire surface contamination, and they must be repaired. The detectors are also damaged by neutrons, so they must be shielded from them (especially high energy neutrons) as much as possible. The efficiency of our detectors is around 51% - 53%.There are two detector arrangements, each used to obtain different information about the nucleus; singles setup and coincidence setup. A single HPGe detetctor can be seen to the left. |