136 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 5 



Table 20. Thermal Neutron Activation Cross Sections 

 The following table is a list of thermal neutron activation cross sections measured and 

 reported by L. Sercn, II. N. Friedlander, and S. H. Turkel, Phys. Rev., 72, 888 (1947). 

 Cross sections were determined by measuring the absolute beta emission (or positron and 

 K capture) from thin foils irradiated with thermal neutrons. Assuming that one beta 

 particle is emitted per neutron captured, the thermal neutron cross section a was calculated 

 from u = nva-N, where u = number of neutrons captured per unit time, nv = thermal neu- 

 tron flux, and N = number of atoms of detector. The probable error of most values is 

 20 per cent; those with a probable error of 10 per cent are indicated by * and those with a 

 probable error of 40 per cent by ]. 





