An innovative neutron spectrometer for soil moisture measurements

Soil moisture is a crucial variable in evaluating soil properties and its interaction with the atmosphere, yet none of the techniques currently employed is fully adequate for evaluating the water content in soil over an area of hectares and depth of tens of centimeters. In recent times, it has been shown how the water content over this volume can be accurately assessed measuring changes in the epithermal flux of cosmic neutrons, which is extremely sensitive to the moderation caused by hydrogen. The instruments employed for neutron flux measurements are usually neutron counters, covered with moderator coatings for enhancing their sensitivity in the epithermal energy range. On the other hand, the worldwide shortage of $${}^{3}$$ 3 He caused a considerable increase in the costs associated with the manufacturing of proportional counters based on this gas, which were widely employed for their great sensitivity and noise rejection capability. In this work, we developed a $${}^{3}$$ 3 He-free neutron spectrometer for performing these measurements, which detects neutrons in the energy range from 0.01 ev to 1 GeV. The reconstruction of the energy spectrum allows a more accurate evaluation of the epithermal neutron flux and provides other information which improves the quality of soil moisture measurements. Irradiations performed with neutron sources of $${}^{241}$$ 241 Am and AmBe allowed to evaluate the spectrometric capability of the instrument, whereas the measurements of cosmic neutrons were employed to assess its sensitivity to cosmic radiation. The sensitivity of the instrument is slightly less than the one of the neutron counters currently employed, yet the access to the spectrometric information should provide greater accuracy in the epithermal flux measurements.

Desain Beam Shaping Assembly (BSA) berbasis D-D Neutron Generator 2,45 MeV untuk Uji Fasilitas BNCT

<p>Boron Neutron Capture Therapy (BNCT) is one of the cancer treatments that are being developed in nowadays. In order to support BNCT treatment for cancer that exists in underneath skin like breast cancer, the facility needs a generator that is able to produce epithermal neutron. One of the generator that is able to produce neutron is D-D neutron generator with 2.45 MeV energy. Based on the calculation of this paper, we found that the total production of neutron per second (neutron yield) from Neutron Generator (NG) by PSTA-BATAN Yogyakarta is 2.55×10¹¹n/s. The energy and flux that we found is in the range of quick neutron. Thus, it needs to be moderated to the level of epithermal neutron which is located in the interval energy of 1 eV to 10 KeV with 10⁹ n/cm²s flux. This number is the recommendation standard from IAEA. Beam Shaping Assembly (BSA) is needed in order to moderate the quick neutron to the level of epithermal neutron. One part of BSA that has the responsibility in moderating the quick neutron to epithermal neutron is the moderator. The substance of moderator used in this paper is MgF₂ and A1F₃. The thickness of moderator has been set in in such a way by using MCNPX software in order to fulfill the standard of IAEA. As the result of optimizing BSA moderator, the data obtain epithermal flux with the total number of 4.64×10⁸n/cm²/s for both of moderators with the thickness of moderator up to 15 cm. At the end of this research, the number of epithermal flux does not follow the standard of IAEA. This is because the flux neutron that is being produced by NG is relatively small. In conclusion, the NG from PSTA-BATAN Yogyakarta is not ready to be used for the BNCT treatment facility for the underneath skin cancer like breast cancer.</p>