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The absolute measurement of neutron emission rate from the whole plasma is a very important diagnostics as a fusion power monitor in fusion experimental devices with D-T or D-T operations. Here measurement techniques of time-resolved and time-integrated absolute neutron emission on the present tokamaks and ITER are reviewed. In the present tokamaks, fission chamber installed outside the vacuum vessel are very popular in the absolute neutron emission rate measurement. As well as conventional neutron monitors installed outside the vacuum vessel, in-vessel neutron monitors using micro fission chamber are proposed for the absolute neutron emission rate measurement in ITER. The neutron activation system provides time-integrated measurements of the total neutron yield with high accuracy by using well known neutron reaction cross sections, which is useful to maintain a robust measure of fusion energy production with stability and wide dynamic range. The calibration of the relation between the neutron emission rate in the whole plasma and the output of neutron monitor is the most important issue in the absolute neutron emission rate measurements. The calibration of the neutron detectors has been performed by moving a neutron source such as a 252Cf neutron or a small accelerator-based neutron generator. For the calibration in ITER, the neutron generator with neutron emission rate of 1011 s-1 or stronger is required to obtain high accuracy. [ABSTRACT FROM AUTHOR]

Last year the worldwide network of neutron monitors recorded a new ground level enhancement (GLE) of cosmic my intensity (CR) on 20th of January 2005, during the recovery phase of a series of Forbush effects taking place at a time-period very close to the minimum of the current cycle of solar activity. This enhancement seems to be the greatest GLE of the current solar cycle, reaching almost 5000% in some polar stations. A joint analysis of data from ground level stations (neutron monitors) and satellite measurements has been performed in order to calculate the amplitude and the anisotropy of the event as well as the energy of the more fast particles arriving at the Earth. A new GLE — model has been created in order to couple the primary solar cosmic ray flux on the top of the magnetosphere with the flux recorded by neutron monitors and define this way the primary solar cosmic ray spectrum during the event. Moreover, the absorption length of solar energetic particles propagating through the Earth’s atmosphere has been calculated applying the Wilson et al. method (1967). These results have been compared with the respective results calculated for other ground level enhancements. Finally, a comparison between this enhancement and the big GLE of 1956 has been performed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]