At your request, I looked into the feasibility of using a Sb-Be neutron source in the reactor. The purported advantage of such a unit is that it would be continually activated by the thermal neutrons from the reactor by the reaction. 51Sb123 + on1 -> 52Sb124

The cross-section for neutron absorption in the Sb123 isotope, abundance 42.75% is 2.5 barns.

The Sb124 isotope (60 day half-life) yields a variety of gamma rays of the order of an Mev energy. These will cause photodisintegration of Beryllium to give neutrons. These reactions are: 52sb124 -> 53Te124 + -1eo + γ 4Be9 + γ -> on1 + 4Be8

The Sb-Be sources supplied by Oak Ridge of a 3/4" x 3/4" Sb cylinder, surrounded by 11/64" of Be, and inserted in an Al can of 1/32" wall thickness. The over-all diameter is 1.15 inches, the antimony weight is 35 grains. The activity quoted for 120 day irradiation is 2.6 curies, in comparison with the saturation activity of 3.5 curies. The number of neutrons per second of the freshly-prepared source is given as 106/sec., which is marginal for reactor start up. Assuming, however, that this number might be sufficient, the question to be answered is whether irradiation in our flux would keep it at this strength. An estimate of this follows.

Let the saturation activity be identical to g, the generation rate in the ORNL reactor flux φ. If the macroscopic absorption cross-section of Sb123 is Σ, and the source volume is V, then g=Σ φ V

From the density of Sb (6.691 gm/cm3) the atomic weight (121.76 grams) and the abundance, we find the number of Sb123 nuclei per cm3 to be 0.0142 x 10-4. Thus Σ = 0.0355. Taking g = 3.5 curries (1.3 x 1011 d/sec), we find φ = 6.9 x 1011 n/cm2 sec.

A source irradiated at the center of the Raleigh Reactor at full power for an average of 6 hours per day would experience an effective flux of about 1.25 x 1011 n/cm2 sec. (The peak central flux is 5 x 1011).