Thermal neutron flux density in a block of paraffin moderator was specified as part of the unpublished work .
The calculated value of the thermal neutron flux density was 1817.5 neutrons/[cm.sup.2]/s and the average value of kerma rate determined on this basis amounted to 244 [micro]Gy/h, and the dose equivalent rate stood at 610 [micro]Sv/h.
The Table 1 includes the calculated neutron flux density ([PHI]) as a function of the distance (L) from the edge of the paraffin block.
Calculated neutron flux density ([PHI]) as a function of the distance (L) from the edge of the paraffin block containing a [sup.239]Pu-Be source Neutron flux density [neutrons/[cm.sup.2]/s] Distance (M [+ or -] SD) [cm] calculated based on calculated based on registered tritons recorded [alpha] particles 39.7 1 597 [+ or -] 45 1 563 [+ or -] 27 33.6 1 285 [+ or -] 41 1 249 [+ or -] 24 27.6 933 [+ or -] 19 908 [+ or -] 28 21.6 641 [+ or -] 16 634 [+ or -] 11 15.6 415 [+ or -] 13 417 [+ or -] 12 10.3 285 [+ or -] 8 284 [+ or -] 9 [sup.239]Pu-Be--plutonium and beryllium.
In preliminary experiments an instantaneous value of 1.1 X [10.sup.18]/[cm.sup.2]s was obtained for the thermal neutron flux density. The experiment will be performed by the DIANNA Collaboration as International Science & Technology Center (ISTC) project No.
Therefore, the nn scattering intensity is proportional to the square of the neutron flux density, while the background intensity depends linearly on the flux density.
The situation is most favorable at pulsed neutron sources, where the thermal neutron flux density can be very high.
Then the detector counts [N.sub.nn] per pulse (integrated over the thermal part of the TOF spectrum) are related to the nn-scattering cross section [[sigma].sub.nn], the average neutron flux density [[PHI].sub.av], the effective pulse duration [DELTA]t, the effective nn-cavity volume V, and the most probable velocity [v.sub.0] by