Nguyen Van Do

Nuclear reactions with 14 MeV neutrons and bremsstrahlungs in giant dipole resonance (GDR) region using small accelerators

Abstract In 1974 an accelerator of deterium, namely neutron generator NA-3-C was put into operation and in 1982 another accelerator of electron Microtron MT-17 started its work in the Institute of Physics. Though very modest these accelerators are useful for developing countries as Vietnam in both Nuclear Physics Research and Training. In this report we present some results obtained in studies on Nuclear Data, Nuclear Reactions as well as nuclear activation analysis methods. We also would like to discuss about the possibilities of collaboration in the future.

Method for detector calibration in radiation measurement of large samples

A method for detector calibration in radiation measurements of large samples by Monte-Carlo calculation is presented. This method is useful in the absolute radioactivity measurements when the relative method cannot be applied as suitable large standard samples are not available.

STUDIES OF PHOTONUCLEAR REACTIONS AND PHOTON ACTIVATION ANALYSIS IN THE GIANT DIPOLE RESONANCE REGION USING MICROTRONS

Mictrorons are accelerators of electrons and are simultaneous sources of bremsstrahlung photon flux and fission neutrons. In 1982, a microtron of seventeen trajectories Microtron MT - 17 was put into operation at the National Institute of Physics of Vietnam. Though very modest, microtons are very useful for developing countries such as Vietnam in both fundamental and applied physics research. During the recent years by using the above mentioned MT - 17 and microtrons from other institutes we have carried out different investigations. In this report we present some results obtained in the studies of photonuclear reactions and photon activation analysis in the giant dipole resonance region.

Measurement of isomeric yield ratios of 99m,g;101m,g;102m,gRh in the natPd(γ,pxn) reactions with the bremsstrahlung end-point energies of 50–70 MeV

The isomeric yield ratios of 99m,gRh, 101m,ggRh, and 102m,gRh isomeric pairs produced from the natPd(γ,pxn) reactions were measured with the bremsstrahlung end-point energies of 50-, 55-, 60-, 65-, and 70-MeV at the 100MeV electron linac of the Pohang Accelerator Laboratory, Korea. The measurements were carried out with the activation method in combination with off-line γ-ray spectrometry. In order to improve the accuracy of the activity measurements, the separation of the overlapping γ-rays and the necessary corrections for the counting losses were made. The new experimental results are compared with the theoretical values of the TALYS-1.6 code.

Fast determination of the tin content in cassiterite ores by photon activation method

Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores based on the 159.7 keV gamma line of123mSn produced in the124Sn/γ, n/123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and 10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin in geological samples.

An internal standard method for the determination of tin and tungstein in cassiterite by photon activation analysis

A method is described for the simultaneous determination of tin and tungsten in cassiterite ores by photon activation analysis using both elements and zirconium and zinc as internal standards. By using a 15-MeV photon beam, some interfering reactions with higher threshold energies can be eliminated. Thus the data processing becomes simpler and more accurate. The proposed procedure can be used for the routine analysis of tin and tungsten in cassiterite samples.

Study of the \(^{nat}\)Sm\((\gamma ,xn)^{143m,g}\)Sm Reactions Induced by Bremsstrahlung with End-point Energies Just above GDR Region

We investigate the energy dependence of the isomeric yield ratios for the natSm(γ,xn)143m,gSm reactions with bremsstrahlung energies of 40-, 45-, and 50-MeV, just above the giant dipole resonance (GDR) region by the off-line γ-ray spectrometric method. The bremsstrahlung photons were produced from the 100 MeV electron linear accelerator (linac) at the Pohang accelerator laboratory (PAL), Pohang, Korea. In order to improve the accuracy of the experimental results the necessary corrections were made. The present results are compared with similar literature data of the natSm(γ ,xn)143m,gSm reactions measured at various photon energies and of the natSm(n,2n)143m,gSm reaction induced by 14 MeV neutrons in order to examine the effects of an excitation energy and an input angular momentum.

Study of Multiple Photoneutron Reactions on 197Au Induced by 2.5 GeV Bremsstrahlung

We identified eight radionuclides Au, Au, Au, Au, Au, Au, Au, Au formed via the multiple photoneutron reactions Au(γ, kn)197−kAu with 2.5 GeV bremsstrahlung. The yields of radionuclides that decay by emitting γ-ray were measured using high purity germanium (HPGe) detector coupled to a PC-based multichannel analyzer. In order to improve the accuracy of the experimental results the necessary corrections were made. The obtained results are compared with reference data and the variations of the 197Au(γ,kn)197−kAu reaction yields according to incident bremsstrahlung energy and neutron multiplicity are also discussed.

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral for the \(^{45}\)Sc\((n,\gamma)^{46}\)Sc Reaction with Pulsed Neutrons

Thermal neutron capture cross section and resonance integral for the 45Sc(n,γ)46Sc reaction were measured by the activation method using the 197Au(n,γ)198Au reaction as a single comparator. The high-purity scandium and gold samples with and without Cd cover with the thickness of 0.5 mm were irradiated in a pulsed neutron field of the 100 MeV electron linac of the Pohang Accelerator Laboratory (PAL). The induced activities in the activated foils were measured with a well calibrated HPGe detector. In order to improve the accuracy of the experimental results the effect of the non-ideal epithermal spectrum was taken in to account by determining the neutron spectrum shape factor (α), and the corrections for the thermal (Gth) and the resonance (Gepi) neutron self-shielding effects, the γ-ray attenuation (Fg) and the γ-ray coincidence summing effect were made. The thermal neutron cross-section for the 45Sc(n,γ)46Sc reaction has been determined to be σo = 27.6 ± 0.8 barn. By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the 45Sc(n,γ)46Sc reaction has been determined to be Io = 12.7±0.7 barn. The present results are compared with the reference data and discussed.

An empirical formula for (n, 2n) reaction cross sections in the neutron energy range of about 14.5 MeV

The (n,2n) threshold reaction cross-sections, available in the literature are analysed for nuclei with 20≤Z≤92 in the neutron energy range of about 14.5 MeV. An empirical formula based on multiple regression technique is proposed for quick estimation of the (n,2n) reaction cross sections. The results obtained are compared with experimental data and those from other empirical formulae as long as byN-Z systematic. The validity of this formula is discussed.