S. S. Belyshev

Measuring nuclear reaction yields in a procedure based on decay chain analysis

The problem of finding nuclear reaction yields in activation experiments is analyzed. It was shown that in the presence of complex decay chains the activity of gamma-spectrum lines of the nuclei can be described with a linear statistical model. Since the covariance matrix is unavailable the iteratively reweighted general least squares method is an appropriate means of obtaining a maximum-likelihood estimation. The relationship between the variances of estimated yields and the duration of spectrum measurements is discussed.

Photodisintegration of cadmium isotopes

The yields of photonucleon reactions having various multiplicities and occurring on a natural mixture of cadmium isotopes were measured. Bremsstrahlung whose spectrum had an endpoint energy of 55 MeV was used as a gamma-ray source. The reaction yields were determined with the aid of the induced-activity method. The yields of photonuclear reactions for several channels of decay of excited states of cadmium isotopes in the energy region extending up to 55MeV were obtained for the first time. A comparison of the results obtained experimentallywith the results of theoretical calculations reveals that, in the case of heavy cadmium isotopes, it is possible to obtain a reasonably good description of experimental data. In the case of the light isotope 106Cd, however, the results of the theoretical calculations are at odds with experimental data, and this is likely to be due to special features of the shell structure of the isotope 106Cd, which lies near the beta-stability boundary.

Production of the isotope 18F in the reaction 23Na(γ,αn)18F at E b = 55 MeV

The activity of 18F that was produced in the 23Na(γ,αn)18F reaction with the maximum bremsstrahlung energy Eb = 55 MeV was measured.

Photonuclear reactions on the cadmium isotopes 106,108Cd at the bremsstrahlung endpoint energy of 55.5 MeV

The gamma-activation technique was used to measure the absolute yields of photonuclear reactions on the cadmium isotopes 106,108Cd. The results obtained in this way were compared with the results of the calculations based on the statistical model. For reactions on the isotope 108Cd, agreement between these theoretical and experimental results is good, but the experimental ratio of the yields of photoproton and photoneutron reactions on the isotope 106Cd differs substantially from its theoretical counterpart. The results of our present study are discussed from the point of view of the production of bypassed nuclei in the p-process of nucleosynthesis.

Automatic data acquisition and analysis in activation experiments

A system for the automatic acquisition and analysis of gamma-ray spectra that is used in the studies of photonuclear reactions with the activation technique in described. The system is comprised of a database, which is used to access data over a network, and of a spectrum analysis program. Experimental procedures and data analysis are greatly simplified with the use of the described system.

18F production in the 19F(γ, n) reaction

A race-track microtron is used to measure the yield of 18F in the reaction 19F(γ, n) at an energy of the electron beam of 55 MeV. 18F is widely used in positron emission tomography for high-sensitivity diagnostics. The currently available data are not sufficient to make accurate estimates of the yield of 18F in isotope production experiments using the reaction (γ, n). The value of σ−1 estimated in this work is (1.7 ± 0.1) mb.

Cross sections of the reactions 14N(γ, 2n)12N, 14N(γ, 2p)12B, and 13C(γ, p)12B

Known experimental and model-calculated data, along with independent calculations using the TALYS- and EMPIRE-codes, are compiled for the cross sections of reactions 14N(γ, 2n)12N, 14N(γ, 2p)12B, and 13C(γ, p)12B used in the photonuclear technique under development for the detection of hidden explosives. Indications of a substantial underestimate of model-calculated values, compared to the available measured results, are obtained.

Isomeric ratios for products of photonuclear reactions on a natural mixture of silver isotopes

Photonuclear reactions on a naturalmixture of silver isotopes at the electron-accelerator energy of 55 MeV are studied by the gamma-activation method. The yields of photonuclear reactions involving the emission of up to four neutrons are determined. The isomeric ratios are obtained for 104Ag and 106Ag. The values found for these isomeric ratios are compared with the results of other studies and with the results of calculations based on the cascade–evaporation model.

Photodisintegration of the isotope 116Cd

The results obtained by measuring the yields of photodisintegration of the isotope 116Cd irradiated with bremsstrahlung photons whose spectrum had an endpoint energy of 55 MeV are presented and compared with the results of theoretical calculations.

Emission of γ-quanta, electrons, and positrons upon the decay of 12N and 12B produced in characteristic targets

The emission of γ-quanta, electrons, and positrons upon the decay of 12N and 12B produced in characteristic targets is calculated within radiation–matter interaction models generated using the GEANT and MCNP simulation software.