Heavy Water Target Research Articles

A reconsideration of photoneutron production through a 5 MeV electron LINAC using MCNP and FLUKA

In the present study, photoneutron production using a 5 MeV electron linear accelerator (LINAC) was investigated based on new photoneutron cross-sections (IAEA/PD-2019.2) from the International Atomic Energy Agency (IAEA). A detailed reconsideration of a past study has been done in order to make a photoneutron source based on a heavy water target. In this regard, new cross-sections of deuterium and beryllium were added to the library of the MCNP6.1 Monte Carlo code for the simulation of photoneutron production. In addition, the FLUKA4-3.0 Monte Carlo code was employed for comparison and data validation. Moreover, the obtained results from those two codes (MCNP and FLUKA) were compared and discussed with the theory and the previous study. Finally, it is concluded that the simulation of photoneutron production through an electron LINAC can have relatively different results based on the photoneutron cross-sections and even on the Monte Carlo code used. Therefore, a special attention should be paid to the difference between photoneutron cross-sections as well as the difference in Monte Carlo codes to maintain reliability.

The influence of target film material and coating on neutron yield and sputtering yield

The long-life, high yield deuterium-deuterium (D-D) neutron tube has become one of the research hotspots. Here, deuterated polyethylene target, heavy water target and titanium target were investigated by Stopping and Range of Ions in Matter (SRIM). The calculation showed that the deuterated polyethylene target, which was a potential target material, had the highest yield at an incident energy of 120 keV. Further, considering the unfavorable factors such as impurity ions and high temperature, the coating was used to protect the target material. Diamond, boron carbide, boron nitride, silicon carbide, and aluminum carbide were selected. The simulation results showed that the diamond composite deuterated polyethylene film had the best sputtering resistance, and the aluminum nitride composite heavy water target film had the lowest sputtering yield. The two coating materials shield the target, reduced the energy loss of incident ions, and provided a new method for the research of high yield and long life neutron tube.

Feasibility of using heavy water in order to design of a photoneutron source based on 5 MeV electron linear accelerator

Although electron energies higher than 5 MeV are generally required to produce an intense photoneutron flux, an optimized and compact photoneutron source based on a 5 MeV electron linear accelerator has been designed for boron neutron capture therapy (BNCT) and neutron activation applications using the MCNPX Monte Carlo code in this work. In fact, we investigated a heavy water target, which can be used as a coolant as well as a photoneutron target for the production of high neutron flux based on a 5 MeV electron linear accelerator and examined different neutron reflectors. Also, Be, BeO, BeD2, Graphite, ZrH2, and Pb have been studied as neutron reflector materials. In this study, after a comparison between beryllium and graphite it was obtained that beryllium increase neutron flux a factor of ∼130%, thus beryllium was chosen as the best neutron reflector. Finally, we concluded that the use of heavy water as a photoneutron target along with beryllium as a neutron reflector could increase the neutron flux in comparison to previous works that use beryllium and graphite as photoneutron target and neutron reflector, respectively. According to the optimum dimension photoneutron source, a neutron flux of 3.6× 108 ± 1.2% neutrons/cm2/mA/s is obtained at 50 cm away from the heavy water target. This results with an increase of ∼300% in comparison to the other works.

Neutrino Physics with SNO+

SNO+ is the successor to the Sudbury Neutrino Observatory (SNO) for which SNO's heavy water target is replaced by approximately 780 T of liquid scintillator (LAB). The combination of the 2 km underground location, the use of ultra-clean materials and the high light-yield of the liquid scintillator means that a low background level and a low energy threshold can be achieved. This creates a new multipurpose neutrino detector with the potential to address a diverse set of physics goals, including the detection of reactor, solar, geo- and supernova neutrinos. The main physics goal of SNO+ is the search for neutrinoless double beta decay. By loading the liquid scintillator with 0.3% of natural Tellurium, resulting in about 800 kg of 130Te (isotopic abundance is slightly over 34%), a competitive sensitivity to the effective neutrino mass can be reached.

Measurement of theνeand total8B solar neutrino fluxes with the Sudbury Neutrino Observatory phase-III data set

This paper details the solar neutrino analysis of the 385.17-day Phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of $^3$He proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active $^8$B solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be $5.54^{+0.33}_{-0.31}(stat.)^{+0.36}_{-0.34}(syst.)\times 10^{6}$ cm$^{-2}$ s$^{-1}$, consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of $\Delta m^2 = 7.59^{+0.19}_{-0.21}\times 10^{-5}{eV}^2$ and $\theta = 34.4^{+1.3}_{-1.2}$ degrees.

Neutron production by stopping 55 MeV deuterons in carbon and heavy water

Neutron production by stopping 55 MeV deuterons in thick carbon and heavy-water targets has been measured by the activation method. The geometry was close to the one defined for the SPIRAL2 uranium-carbide target in the initial phase. A comparative method for obtaining the neutron flux has been used and is presented in detail. The neutron flux generated by 55 MeV deuterons on carbon is 2.3 times the flux at the deuteron energy of 40 MeV. The flux further increases by a factor 1.4 when using a heavy-water target. These results are discussed in the context of an energy upgrade of the SPIRAL2 driver accelerator.

Neutron Production by Cosmic Ray Muons at the Sudbury Neutrino Observatory

Neutrons produced by cosmic ray muon interactions can be a significant background in sensitive underground experiments. The Sudbury Neutrino Observatory (SNO) is an efficient and well-calibrated neutron detector capable of measuring the rate and characteristics of neutrons produced by muon interactions in its heavy water target, light water shielding and surrounding rock. The location of the detector, beneath a rock overburden of 2092 m (5890 ± 94 m water equivalent), means that the muon flux is particularly low in rate and high in energy. SNOʼs measurements, with unique target materials and high energy muons, are important for benchmarking Monte Carlo simulations. These simulations will be used to predict the muon-induced neutron fluxes in future low background experiments.

SNO+ Electronic Upgrades

The SNO+ experiment is designed to explore several topics in neutrino physics, including neutrinoless double beta decay and low energy solar neutrinos. SNO+ uses the existing Sudbury Neutrino Observatory (SNO), with the heavy water target replaced with liquid scintillator. Only a few additional modifications are needed to transition from SNO to SNO+, but one of these will be an upgrade to the electronics to handle the higher rates expected with scintillation light as compared to Cherenkov light. The front end electronics are being upgraded to autonomously push data to a central data acquisition computer by using a field programmable gate array (FPGA) with an embedded processor.

Determining the Low Energy Backgrounds at the Sudbury Neutrino Observatory

Naturally occurring radioisotopes can produce neutrons by photodisintegration and Cherenkov events via beta/gamma decays. The techniques used to measure the radioisotopes in the heavy water target and light water shield in the third phase of SNO is discussed.

Using a hall accelerator to investigate d(d, n)3He and d(p, γ)3He reactions in the astrophysical energy region

We present new results on astrophysical S-factors and cross sections for reactions dd → 3He + n(2.5MeV) and pd → 3He + γ (5.5MeV) in ultra-low energy ranges 2.3–6.2 keV and 8.3–10.1 keV, respectively. Experiments were performed with proton and neutron beams produced by a pulsed Hall accelerator (Nuclear Physics Institute, Tomsk) and deuterated polyethylene (CD2) and frozen heavy water (D2O) targets. Within measurement errors, our results are consistent with the literature’s experimental results on pd and dd reactions for the given energy ranges, where D2O or gaseous deuterium targets were used.

The calibration of the Sudbury Neutrino Observatory using uniformly distributed radioactive sources

The production and analysis of distributed sources of 24Na and 222Rn in the Sudbury Neutrino Observatory (SNO) are described. These unique sources provided accurate calibrations of the response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy betas and gammas. The application of these sources in determining the neutron detection efficiency and response of the 3He proportional counter array, and the characteristics of background Cherenkov light from trace amounts of natural radioactivity is described.

Neutron yield from carbon, light- and heavy-water thick targets irradiated by 40 MeV deuterons

Angular and energy distributions of neutrons produced by the interaction of deuterons of 40 MeV in carbon, light- and heavy-water targets, in which they are stopped, have been measured by the activation method. A discrepancy with a time-of-flight measurement for d + C has been found. The results are compared with a Monte-Carlo calculation and are discussed in the frame of building a deuteron-to-neutron converter for the SPIRAL2 radioactive ion-beam facility.

Study of the d (d, n)3He reaction in the astrophysical energy region with the use of the Hall accelerator

The results of the measurements of the astrophysical S -factor and cross-sections of the reaction dd → ^3He+ n in the deuteron energy collision range of 2.3-6.2keV are presented. The experiment was carried out at the high-current deuteron beam of the Hall pulsed accelerator (FSSI “Nuclear Physics Institute”, Tomsk). Deuterated polyethylene (CD2) targets and frozen heavy water (D2O) were used. Neutrons were detected by eight plastic scintillation counters ( 375×100×100 mm^3) located around the target. The results obtained in the present work substantially differ from the results of the experiments conducted with the use of deuterium saturated metal targets (TiD, TaD, ZrD, PtD). Within statistical errors of measurements there is no discrepancy between the present results and the results of the experiments performed with the heavy-water targets and filled with gaseous-deuterium targets.

Development of activation foils method for the IFMIF neutron flux characterization

This work proposes to use the activation foil method for the neutron spectrum determination in the IFMIF facility. Suitable elements were selected to this end with dosimetry reactions having thresholds and effective cross sections covering the whole IFMIF energy range up to 55 MeV. The available evaluated nuclear data libraries and experimental data were carefully screened to select appropriate dosimetry cross sections with uncertainties as low as possible. For the determination of the neutron spectra from the induced γ-activities the unfolding code SAND-II was applied after having it modified for the use of the selected dosimetry cross sections above 20 MeV. This approach was tested by measuring the white neutron spectrum at the cyclotron of Nuclear Physics Institute (Řež), where neutrons up to 35 MeV energy were generated by a 37 MeV proton beam impinging on a heavy water target. The paper concludes with recommendations for the procedure for determining the neutron energy differential flux in the IFMIF test cell with respect to the size of the dosimetry foils, the irradiation time and the expected induced activities.

Activation of Eurofer in an IFMIF-like neutron field

An activation experiment on the Eurofer-97 low activation steel was performed to provide the database for validating activation cross-section data in the energy range relevant for the International Fusion Material Irradiation Facility (IFMIF). An IFMIF-like white neutron field extending up to energy of 32 MeV was produced at the isochronous cyclotron U-120M of the Nuclear Physics Institute (NPI) Řež, by bombarding a flowing heavy water target with a 37 MeV proton beam. The induced gamma radioactivity for 22 product radio-nuclides was determined by gamma ray spectrometry at different cooling time intervals using calibrated HPGe detectors. Activation calculations were performed with the ALARA inventory code using the activations cross-sections from the Intermediate Energy Activation File IEAF-2001. The neutron spectrum at sample sport was combined from one measured at large distance and calculated by MCNPX for energies below the detector threshold. The comparison of calculated and measured induced activities reveals reasonable agreement for half of the detected radio-nuclides and large discrepancies for the other ones. The analysis of the dominant reactions indicates the need for updating the relevant cross-sections in the IEAF-2001 data library.

Analysis of the Photoneutron Yield and Thermal Neutron Flux in an Unreflected Electron Accelerator-Driven Neutron Source

There are several potential uses for a high-flux thermal neutron source in both industrial and clinical applications. The viable commercial implementation of these applications requires a low-cost, high-flux thermal neutron generator suitable for installation in industrial and clinical environments. This paper describes the Monte Carlo for N-Particle modeling results of a high-flux thermal neutron source driven with an electron accelerator. An electron linear accelerator (linac), fitted with a standard X-ray converter, can produce high neutron yields in materials with low photonuclear threshold energies, such as D and 9Be. Results indicate that a 10-MeV, 10-kW electron linac can produce on the order of 1012 n/s in a heavy water photoneutron target. The thermal neutron flux in an unreflected heavy water target is calculated to be on the order of 1010 n·cm–2·s. The sensitivity of these answers to heavy water purity is also investigated, specifically the dilution of heavy water with light water. It is shown that the peak thermal neutron flux is not adversely effected by dilution up to a light water weight fraction of 35%.

Measurement of radium concentration in water with Mn-coated beads at the Sudbury Neutrino Observatory

We describe a method to measure the concentration of 224Ra and 226Ra in the heavy water target used to detect solar neutrinos at the Sudbury Neutrino Observatory and in the surrounding light water shielding. A water volume of (50-400) m^3 from the detector is passed through columns which contain beads coated with a compound of manganese oxide onto which the Ra dissolved in the water is adsorbed. The columns are removed, dried, and mounted below an electrostatic chamber into which the Rn from the decay of trapped Ra is continuously flowed by a stream of nitrogen gas. The subsequent decay of Rn gives charged Po ions which are swept by the electric field onto a solid-state alpha counter. The content of Ra in the water is inferred from the measured decay rates of 212Po, 214Po, 216Po, and 218Po. The Ra extraction efficiency is >95%, the counting efficiency is 24% for 214Po and 6% for 216Po, and the method can detect a few atoms of 224Ra per m^3 and a few tens of thousands of atoms of 226Ra per m^3. Converted to equivalent equilibrium values of the topmost elements of the natural radioactive chains, the detection limit in a single assay is a few times 10^(-16) g Th or U/cm^3. The results of some typical assays are presented and the contributions to the systematic error are discussed.

New limit on the proton lifetime from neutrino experiments with heavy water

Experimental data on the number of neutrons born in the heavy water targets of large neutrino detectors are used to set the limit on the proton lifetime independently of the decay mode through the reaction d → n+? The best up-to-date limit τ p >4×1023 yr with 95% C.L. is derived from measurements with the D2O target (mass of 267 kg) installed near the Bugey reactor. This value can be improved by six orders of magnitude with future data accumulated with the SNO detector containing 1000 t of D2O.

New limit on the proton life-time independent on channel from the neutrino experiments with heavy water

Experimental data on the number of neutrons born in the heavy water targets of the large neutrino detectors are used to set the limit on the proton life-time independently on decay mode through the reaction d → n + ?. The best up-to-date limit τ p > 4×10 23 yr with 95% C.L. is derived from the measurements with D 2O target (mass 267 kg) installed near the Bugey reactor. This value can be improved by six orders of magnitude with future data accumulated with the SNO detector containing 1000 t of D 2O.

Experimental limits on the proton life-time from the neutrino experiments with heavy water

Experimental data on the number of neutrons born in the heavy water targets of the large neutrino detectors are used to set the limit on the proton life-time independently on decay mode through the reaction d→n + ? . The best up-to-date limit τ p >4×10 23 yr with 95% C.L. is derived from the measurements with D 2O target (mass 267 kg) installed near the Bugey reactor. This value can be improved by six orders of magnitude with future data accumulated with the SNO detector containing 1000 t of D 2O.