Héctor René Vega-Carrillo

Neutron and gamma-ray spectra of 239PuBe and 241AmBe.

Neutron and gamma-ray spectra of 239PuBe and 241AmBe were measured and their dosimetric features were calculated. Neutron spectra were measured using a multisphere neutron spectrometer with a 6LiI(Eu) scintillator. The 239PuBe neutron spectrum was measured in an open environment, while the 241AmBe neutron spectrum was measured in a closed environment. Gamma-ray spectra were measured using a NaI(Tl) scintillator using the same experimental conditions for both sources. The effect of measuring conditions for the 241AmBe neutron spectrum indicates the presence of epithermal and thermal neutrons. The low-resolution neutron spectra obtained with the multisphere spectrometer allows one to calculate the dosimetric features of neutron sources. At 100 cm both sources produce approximately the same count rate as that of the 4.4 MeV gamma-ray per unit of alpha emitter activity.

TLD pairs, as thermal neutron detectors in neutron multisphere spectrometry

Abstract Pairs of thermoluminescence dosimeters, TLD600 and TLD700, have been used as a thermal neutron detector in a multisphere neutron spectrometer. The neutron spectra from a bare 252Cf and a D2O moderated 252Cf sources were measured with the spectrometer with thermoluminescence dosimeters and with a 6LiI(Eu) scintillator. With the neutron spectra the total flux, average neutron energy, dose and equivalent dose were calculated. The neutron spectra and the calculated features are in agreement with the neutron sources characteristics.

Neutron and photon spectra in LINACs

A Monte Carlo calculation, using the MCNPX code, was carried out in order to estimate the photon and neutron spectra in two locations of two linacs operating at 15 and 18 MV. Detailed models of both linac heads were used in the calculations. Spectra were estimated below the flattening filter and at the isocenter. Neutron spectra show two components due to evaporation and knock-on neutrons. Lethargy spectra under the filter were compared to the spectra calculated from the function quoted by Tosi et al. that describes reasonably well neutron spectra beyond 1 MeV, though tends to underestimate the energy region between 10(-6) and 1 MeV. Neutron and the Bremsstrahlung spectra show the same features regardless of the linac voltage.

Multielement measurements in Mexican cigarette tobacco

The concentration of 21 elements in cigarette tobacco in nine different brands manufactured and commercially available in Mexico has been determined using neutron activation analysis. The concentration range of the measured elements (in μg g−1) were: As, (four brands) <0.55–3.24; Ba, 64–251; Br, (four brands) 49–136; Ce, <0.3–1.7; Co, 0.29–0.55; Cr, <0.8–2.4; Cs, 0.091–0.40; Eu, <0.03; Fe, 420–680; Hf, <0.03–0.13; K, (four brands) 18300–40300; La, (four brands) <0.2–0.66; Na, (four brands) 309–566; Rb, 19–50; Sb, <0.7; Sc, 0.13–0.22; Se, <0.7; Sm, (four brands) 0.07–0.14; Sr, 227–472; Th, <0.1–0.17 and Zn, 14–56. The results are compared with the literature values for the concentration of the above elements in cigarette tobacco from other countries.

Study of the neutron field in the vicinity of an unshielded PET cyclotron

The neutron field in the proximity of an unshielded PET cyclotron was investigated during 18F radioisotope production with an 18 MeV proton beam. Thermoluminescent detector (TLD) models TLD600 and TLD700 as well as Bonner moderating spheres were irradiated at different positions inside the vault room where the cyclotron is located to determine the thermal neutron flux, neutron spectrum and dose equivalent. Furthermore, from a combination of measurements and Monte Carlo simulations the neutron source intensity at the target was estimated. The resulting intensity is in good agreement with the IAEA recommendations. Neutron doses derived from the measured spectra were found to vary between 7 and 320 mSv per 1 microA h of proton-integrated current. Finally, gamma doses were determined from TLD700 readings and amounted to around 10% of the neutron doses.

Photoneutron spectrum measured with a Bonner sphere spectrometer in planetary method mode

The spectrum of photoneutrons produced by a 15 MV VARIAN iX linac working in Bremsstrahlung mode was measured a 100 cm from the IC located 5 cm-depth of a solid water phantom. The spectrum was measured with a Bonner spheres spectrometer with pairs of TLDs as thermal neutron detector. The measurements were carried out using the spectrometer in planetary method mode where a single shoot of the LINAC was required.

NSDUAZ unfolding package for neutron spectrometry and dosimetry with Bonner spheres

NSDUAZ (Neutron Spectrometry and Dosimetry from the Universidad Autónoma de Zacatecas) is a user friendly neutron unfolding package for Bonner sphere spectrometer with (6)LiI(Eu) developed under LabView(®) environment. Unfolding is carried out using a recursive iterative procedure with the SPUNIT algorithm, where the starting spectrum is obtained from a library initial guess spectra to start the iterations. The NSDUAZ performance was evaluated using (252)Cf, (252)Cf/D(2)O, (241)AmBe neutron sources and the neutrons outside the radial beam port of a TRIGA Mark III nuclear reactor running to 10 W.

Testing of a High-Density Concrete as Neutron Shielding Material

Abstract We present the testing of a high-density magnetite concrete [commercially available under the name Hormirad™, developed by the Spanish company Construcciones Tecnicas de Radioterapia, S.L. (CT-RAD)] as neutron shielding material. The purpose of this work was to characterize the material behavior against neutrons, as well as to test different mixings including boron compounds in an effort to improve neutron shielding efficiency. Hormirad™ slabs of different thicknesses were exposed to a 241Am-Be neutron source under controlled conditions. The original mix, which includes a high fraction of magnetite, was then modified by adding different proportions of anhydrous borax (Na2B4O7). Looking for a comparison, the same experiment was repeated with slabs of ordinary concrete (HA-25) used to shield medical accelerator facilities. In parallel to the experiments, Monte Carlo calculations were performed with MCNP5, with some differences found with regard to the experiments, attributable to uncertainties in the elemental composition of the samples tested. Tenth-value layers have been determined for the different types of concrete tested for the 241Am-Be neutron source. The results show an advantageous behavior of the Hormirad™ when comparing it with ordinary concrete. Although borated concretes show a small improvement in neutron attenuation when they are compared with Hormirad™ alone, the resulting reduction in density and structural properties makes them less practical.

Elemental content in ground and soluble/instant coffee

The concentration of thirty-four elements in twelve coffee brands has been measured using instrumental neutron activation analysis. The samples investigated included four brands of commercially available ground coffee and eight brands of soluble/instant coffee. The elements measured were Al, As, Ba, Ca, Ce, Co, Cr, Cs, Dy, Eu, Fe, Gd, Hf, K, La, Lu, Mg, Mn, Na, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, Ti, Tm, U, V, Yb and Zn. Twenty four elements were found to be below the detection limit in one or more samples. These elements were Ce, Cr, Fe, V, As, Eu, Ba, Dy, Gd, Hf, La, Lu, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, Ti, Yb, Tm, and U.

Determination of mercury and other elements in La Zacatecana Dam sediment in Mexico

Abstract Sediment samples from the La Zacatecana Dam together with samples from two sites, at 7 and 180 km N.W. of the dam, were analyzed by instrumental neutron activation analysis and the concentration of mercury and 28 elements; As, Au, Ba, Br, Ce, Co, Cr, Cs, Eu, Fe, Ga, Hf, K, La, Na, Nd, Ni, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, U and Zn are reported. The ratio between the concentration of an element in the dam sediment and the average concentration at the other two sites (i.e. enrichment factor (EF) of the element) was calculated. Mercury showed an EF of 194. As, Au, Sb, Sm and Zn showed EFs of between 4–11. The EF for the rest of the measured elements was ∼ 1.