One cannot expect measurements alone to supply all of the neutron-induced activation cross-section data required by the fission reactor, fusion reactor, and nuclear weapons development communities, given the wide ranges of incident neutron energies, the great variety of possible reaction types leading to activation, and targets both stable and unstable. Therefore, the evaluator must look to nuclear model calculations and systematics to aid in fulfilling these cross-section data needs. This review presents some of the recent developments and improvements in the prediction of neutron activation cross sections, with specific emphasis on the use of empirical and semiempirical methods. Since such systematics require much less nuclear informaion as input and much less computational time than do the multistep Hauser-Feshbach codes, they can often provide certain cross-section data at a sufficient level of accuracy within a minimum amount of time. The cross-section information that these systematics can and cannot provide and those cases in which they can be used most reliably are discussed.

Results of new activation cross section measurements are presented for the following neutron-induced reactions: 58Ni(n,p)58m+gCo, 58Ni(n,p)58mCo, 58Ni(n,x)57Co, 58Ni(n,2n)57Ni, 60Ni(n,p )60m+gCo, 60Ni(n,p)60mCo, 61Ni(n,p)61Co, 61Ni(n,x)60mCo, 62Ni(n,x)61Co, 59Co(n,2)58m+gCo, 63Cu(n ,a)60m+gCo, 90Zr(n,a)87mSr, 90Zr(n,p)90mY, 91Zr(n,x)90mY, 91Zr(n,p)91mY, 92Zr(n,x)91mY, 92Zr(n,p)92Y, 204Pb(h,n')204Pb, 204(n,2n)203m1+m2Pb, and 207Pb(n,p)207 TI with emphasis on incident energies between 14 and 20 MeV. ln addition, new results have been obtained for the isomeric cross section ratios of the 58Ni(n,p )58m,gCo, the 60Ni(n ,p )60m,gCo and 59Co(n,2n)58m,gCo reactions. The irradiations were carried out at the 7 MV Van de Graaff accelerator at IRMM, Geel. Quasi mono-energetic neutrons with energies between 13.3 and 20,5 MeV were produced via the 3H(d,n)4He reaction, and for the production of neutrons with energies between 1 and 3.4 MeV the 3H(p,n)3He reaction was used. In some cases isotopically enriched materials were used to enhance the reaction yield or to facilitate correction for interfering reactions leading to the same product. The half lives for the reaction products range from 6.3 s to 5.3 years. A pneumatic sample transport system was used for the measurements of short-lived reaction cross sections. All reaction cross sections measured in the present work are referenced to the 27Al(n,a)24Na standard reaction cross section. The neutron flux spectra were determined using neutron-spectrum information obtained by the time-of-flight method and the spectral index method that involves 115In(n,n')115mIn, 58Ni(n,p)58m+gCo, 27Al(n,p)27Mg, 56Fe(n,p)56Mn, 27Al(n,a)24Na and 93 Nb(n,2n)92mNb monitor reactions with distinct energy thresholds. Standard y-ray spectrometry was employed for the measurement of radioactivity. Three lead-shielded HPGe detectors and one planar HPGe detector with carbon fibre window were used depending on the energy of the measured y-line. Isomeric cross section ratios of the two investigated reactions leading to the production of 58Co were determined by measurement of the complex decay curve of 58gCo. Corrections have been applied for sample irradiation and counting geometry, beam intensity variations during irradiation, background neutrons, neutron absorption and scattering, y-ray absorption and y-ray sum coincidences. The present results are compared with other measurements, and evaluated data. The experimental data are compared with STARPE-H code calculations. In some cases a comparison with TALYS code calculations is included as well.

A library of evaluated neutron-induced activation cross sections (ACTL) was compiled. The library covers incident neutron energies from 10−1° to 20 MeV. General descriptions of the evaluation methods and an index to the evaluated cross sections are presented. 21 references.