Plutonium-beryllium Source Research Articles

Retrieval and Characterization of a Plutonium-beryllium Source at the University of Utah.

A shielded neutron irradiation facility has been constructed to contain a 74 GBq plutonium-beryllium neutron source at the University of Utah. Due to lack of information and recent use, the GEANT4 Monte Carlo Toolkit was used to perform dose assessments and validation of the designed shield and beam port for storage and operational geometries where the source was to be placed. Borated polyethylene was used as the primary shielding material with a lead-lined beam port to collimate neutrons and reduce gamma rays within the active beam profile. The lead lining was found to reduce the gamma-to-neutron ratio within the profile to 0.259 ± 0.001 and maintain an average neutron flux of 4,633.7 ± 10.2 n cm-2 s-1. The measured dose rate of the source at 30 cm from its constructed storage configuration was found to be 22.3 ± 1.1 μSv h-1 and in good agreement with simulated values. This was also close to the target rate of 20 μSv h-1, the public limit for whole-body dose accumulation, imposed on the design. Measurements of the source during its retrieval and placement into the shield show good agreement with the simulated results and provide a strong validation for the future use of the source in experiments at the University of Utah.

Determination of Coal Ash Content by Neutron-Neutron Logging

The research is aimed at assessing the possibility of studying the ash content of coal seams using neutron-neutron logging in coal exploration wells drilled at the outcrops of coal seams under loose deposits using the materials of experimental work in the South Yakutsk coal basin. The prospects of using neutron-neutron logging to study coal well sections, on the one hand, is determined by the fact that hydrogen content in coal seams normally exceeds its content in the host rocks, and, on the other, by the small cross-sections of neutron capture by carbon. Within the same coal grade, an increase in its ash content both means a decrease in its hydrogen content and an increase in the content of elements with a higher capture cross section. Experimental studies were carried out at the Syllakh coal deposit. An IBN-8-1 type plutonium-beryllium source with an output of 5*104 neutrons/s was used as a fast neutron source, and a highly efficient SNM-17 type helium gas-discharge counter was used as a slow neutron detector. The logging depth provided by the equipment was 10 - 30 cm. During the processing of the obtained field data, a correlation was established between the count rate of neutron-neutron logging and coal ash content. It should be noted that the functional dependence of the count rate of neutron-neutron logging on ash content is not continuous – in the range of ash content of 45 - 55% a certain discontinuity point is observed, after which the functional dependence changes. To simplify the assessment of the dependence, the range of rock ash content above 45% is neglected since bituminous coals with an ash content of more than 45% are classified as carbonaceous rock and are not of industrial interest. A close correlation is established between the count rate of neutron-neutron logging and coal ash content. According to the results of statistical processing, the correlation coefficient is 0.97, which makes it possible to quantitatively determine the ash content according to neutron-neutron logging data. The absolute errors in ash content determination by neutron-neutron logging over the entire dataset are up to 3.625 %. The degree of analytical moisture influence on the data of neutron-neutron logging in determining coal ash content is estimated. No regular changes in the count rate of neutron-neutron logging due to a change in the analytical moisture index have been established. It is noteworthy that, with a sufficiently large dispersion value of the analytical moisture index, the trend line of this parameter regularly changes synchronously with the trend lines of ash content and count rate.

Express Assessment of the Quality of Fluorite-Containing Raw Materials

In the production of fluorspar (fluorite) of various grades, the rapid and accurate determination of fluorite is important. The chemical method is used as a marking method, and neutron activation analysis is used as an express method. Initially, the neutron-activation analysis method for fluorite was used by V. Ya. Bardovski for well logging. Its essence is reduced to the irradiation of rocks containing CaF2, a neutron flux from the polonium-beryllium source, followed by the measurement of induced activity on the short-lived isotopes 16N and 20F. This method has the following advantages in comparison with chemical: expressiveness and relatively simple analysis technique, the ability to determine very small amounts of individual elements in rocks and the possibility of element-by-element analysis of rock composition in natural occurrence. The results obtained from the studies indicate that a plutonium-beryllium source should be given preference. According to calculations by E M Filippov [10], 50% of oxygen using a polonium-beryllium source is equivalent to 0.025% fluorine, and for plutonium-beryllium it is 0.0085%.

LiCaAlF6 scintillators in neutron and gamma radiation fields

Intentionally doped LiCaAlF6 (LiCAF) single crystals are prospective scintillators, especially for thermal neutron detection through the 6Li(n,t)4He nuclear reaction. Four different LiCAF scintillator samples were tested in various neutron and gamma fields. Two of the tested samples were LiCAF:Eu and LiCAF:Eu,Na single crystals, and another two samples were made of LiCAF:Eu micro crystals dispersed in transparent rubber, with different rubber dimensions. All LiCAF samples contain lithium enriched to[Formula: see text]Li. A plutonium–beryllium source was used as a neutron source. The neutron spectrum was modified by moderator and filter to get different ratios between thermal, epithermal and fast neutron fluence rates. The MCNP code was used for calculations of the fluence rates for different configurations. Radionuclides [Formula: see text]Cs and [Formula: see text]Co were applied as gamma radiation sources. The light signal from the scintillator was evaluated with a photomultiplier and a multichannel analyzer. The purpose of this work was to study the characteristics of LiCAF scintillators, especially the ability to discriminate signals from neutron and gamma radiation, which is the basic scintillator condition for neutron detection in mixed neutron-gamma radiation fields. Generally, the discrimination can be done by the pulse height and/or the pulse shape of the evaluated signals. Both methods can be used for a LiCAF scintillator. However, only the pulse height discrimination method is discussed in this paper. The possibility of fast neutron detection with LiCAF scintillators was also tested.

Characterization of Nuclear Recoils in High Pressure Xenon Gas: Towards a Simultaneous Search for WIMP Dark Matter and Neutrinoless Double Beta Decay

Xenon has recently been the medium of choice in several large scale detectors searching for WIMP dark matter and neutrinoless double beta decay. Though present-day large scale experiments use liquid xenon, the gas phase o_ers advantages favorable to both types of searches such as improved intrinsic energy resolution and fewer fluctuations in the partition of deposited energy between scintillation and ionization channels. We recently constructed a high pressure xenon gas TPC as a prototype for the NEXT (Neutrino Experiment with a Xenon TPC) neutrinoless double beta decay experiment and have demonstrated the feasibility of 0.5% FWHM energy resolution at the 136Xe double beta Q-value with 3-D tracking capabilities. We now present results from this prototype on the simultaneous observation of scintillation and ionization produced by nuclear recoils at approximately 14bar pressure. The recoils were produced by neutrons of approximately 2-6 MeV emitted from a radioisotope plutonium-beryllium source, and primary scintillation (S1) and electroluminescent photons produced by ionization (S2) were observed. We discuss the potential of gaseous xenon to distinguish between electron and nuclear recoils through the ratio of these two signals S2/S1. From these results combined with the possibility of using columnar recombination to sense nuclear recoil directionality at high pressures we envision a dual-purpose, ton-scale gaseous xenon detector capable of a combined search for WIMP dark matter and neutrinoless double beta decay. This work has been performed within the context of the NEXT collaboration.

Design, Development and Installation of Jordan Subcritical Assembly

Following its announcement in 2007 to pursue a nuclear power program and in the absence of any nuclear facility essential for the education, training, and research, Jordan decided to build a subcritical reactor as its first nuclear facility. Jordan Subcritical Assembly (JSA) is uranium fueled light water moderated and reflected subcritical reactor driven by a plutonium-beryllium source, and the core consists of 313 LEU fuel rods, loaded into a water-filled vessel in a square lattice of 19.11&#x2009;mm pitch. The fuel rods are based on PWR fuel structural pattern type, made of uranium oxide (UO<sub >2</sub>) with 3.4&#x2009;wt&#x25; <sup >235</sup>U enrichment in zirconium alloy (Zr-4) cladding. Design, optimization, and verification were performed using MCNP5 nuclear code; the computed effective multiplication factor <svg style="vertical-align:-3.39069pt;width:37.962502px;" id="M1" height="16.4125" version="1.1" viewBox="0 0 37.962502 16.4125" width="37.962502" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,12.138)"><path id="x28" d="M300 -147l-18 -23q-106 71 -159 185.5t-53 254.5v1q0 139 53 252.5t159 186.5l18 -24q-74 -62 -115.5 -173.5t-41.5 -242.5q0 -130 41.5 -242.5t115.5 -174.5z" /></g><g transform="matrix(.017,-0,0,-.017,5.944,12.138)"><path id="x1D43E" d="M764 650l-7 -26q-61 -10 -91.5 -22.5t-76.5 -48.5l-235 -184q104 -152 208 -276q31 -37 54.5 -48.5t68.5 -16.5l-7 -28h-156q-138 170 -213 284q-19 29 -33.5 35t-33.5 -7l-29 -173q-15 -75 -5.5 -90.5t74.5 -20.5l-5 -28h-260l7 28q58 5 74 21.5t30 89.5l70 378&#xA;q12 68 2 83t-72 22l6 28h257l-7 -28q-62 -7 -76 -21.5t-27 -83.5l-32 -172q29 11 78 46q112 84 217 179q18 16 23.5 25.5t-1 14.5t-26.5 8l-30 4l5 28h249z" /></g> <g transform="matrix(.012,-0,0,-.012,19.138,16.212)"><path id="x65" d="M380 106l15 -22q-42 -52 -87 -74t-76 -22q-89 0 -142 62t-53 151q0 103 66 175q67 73 146 73h1q61 0 105.5 -46.5t44.5 -105.5q0 -16 -4.5 -22.5t-18.5 -9.5q-54 -10 -262 -17q1 -95 46 -143.5t104 -48.5q61 0 115 50zM225 412q-35 0 -64.5 -32.5t-40.5 -90.5q83 0 170 3&#xA;q14 0 19 4.5t5 15.5q1 41 -23.5 70.5t-65.5 29.5z" /></g><g transform="matrix(.012,-0,0,-.012,24.194,16.212)"><path id="xFB00" d="M187 566v-116h189c1.33478 44.0001 4.00146 75.3334 8 94c5.33411 24.0005 14.0008 46.3339 26 67c28 48 75 72 141 72c30.0005 0 54.8339 -5.83331 74.5 -17.5c19.6691 -11.6667 29.5024 -26.5 29.5 -44.5c0 -11.3368 -4 -21.0035 -12 -29c-8 -8 -18 -12 -30 -12&#xA;c-16 0 -31 12 -45 36c-16.0016 26 -33.6682 39 -53 39c-37.3333 -0.000915527 -56 -29.6676 -56 -89v-116h115v-32h-115v-315c0 -37.3333 5 -61 15 -71c11.3333 -10.6667 37.3333 -16.3333 78 -17v-15h-245v15c28.6667 2 47 8.33333 55 19c8.66666 10.6667 13 34 13 70v314&#xA;h-188v-314c0 -38 3.66667 -61.6667 11 -71c6.66667 -8.66667 25.6667 -14.6667 57 -18v-15h-235v15c36.6667 2 59.3333 8 68 18c10 11.3333 15 35 15 71v314h-82v32h82c1.33344 43.3338 4.0001 74.3338 8 93c4.66666 22 13.6667 44.6667 27 68c28 48 75 72 141 72&#xA;c29.3333 0 52.8333 -5.83331 70.5 -17.5s26.5 -26.5 26.5 -44.5c0 -11.3368 -4 -21.0035 -12 -29c-8 -8 -18 -12 -30 -12c-8 0 -14.1667 2.16669 -18.5 6.5s-10.8333 14.1667 -19.5 29.5c-16 26 -33.6667 39 -53 39c-37.3335 -0.000915527 -56.0001 -29.6676 -56 -89z" /></g> <g transform="matrix(.017,-0,0,-.017,32.012,12.138)"><path id="x29" d="M275 270q0 -296 -211 -440l-19 23q75 62 116.5 174t41.5 243t-42 243t-116 173l19 24q211 -144 211 -440z" /></g> </svg> is 0.95923. The JSA is designed to fulfill the training needs of students and is equipped to perform all of the fundamental experiments required for a typical nuclear engineering university program. This paper presents the design, development, modeling, core analysis, and utilization of Jordan&#x2019;s first nuclear facility and why this simplified low cost reactor presents an attractive choice to fulfill the preliminary experimental needs of nuclear engineering education in developing countries.

Characterization of a plutonium beryllium source for use in neutron damage studies

Standard lead loaded Hypalon gloves deteriorate at an accelerated pace in the glovebox environments of Los Alamos National Laboratory. In an effort to minimize glovebox breaches, a project was undertaken to characterize polymer damage due to various environments. For one such study, experimental techniques were used to facilitate the use of a neutron source in damage studies involving glovebox gloves. In order to identify the radiation field experienced by the polymer samples, a characterization of the neutron source in the experimental setup was needed. The plutoniumberyllium source used was chosen to mimic an average neutron flux in a typical LANL glovebox. However, it was surmised that a more exact experimental flux should be found rather then using merely numerical analysis. Subsequent to ascertaining the impending neutron flux, polyurethane gloves show superior properties when compared against standard leaded Hypalon gloves; however, polyurethane is shown to degrade faster following neutron irradiation.

The All Boron Carbide Diode Neutron Detector: Experiment and Modeling Approach

AbstractBoron carbide diode detectors, fabricated from two different polytypes of semiconducting boron carbide, will detect neutrons in reasonable agreement with theoretical expectations. The performance of the all boron carbide neutron detector differs, as expected, from devices where a boron rich neutron capture layer is distinct from the diode charge collection region (i.e. a conversion layer solid state detector).Diodes were fabricated from natural abundance boron (20% 10B and 80% 11B.) directly on the metal substrates and metal contacts applied to the films as grown. The total boron depth was on the order of 2 microns. This is clearly not a conversion-layer configuration. The diodes were exposed to thermal neutrons generated from a paraffin moderated plutonium-beryllium source in moderated and unmoderated, as well as shielded and unshielded experimental configurations, where the expected energy peaks at at 2.31 MeV and 2.8 MeV were clearly observed, albeit with some incomplete charge collection typical of thinner diode structures. The results are compared with other boron based thin film detectors and literature models.

Effects of negative pions and neutrons on the growth of Vicia faba bean roots.

Vicia faba bean roots have been irratiated with neutrons of various energies and with negative pi-mesons, and the effect on the ten-day growth of the roots has been determened. The neutron irratiations were made in beams of 400 and 600 MeV maximum energy, as well as with neutrons from a plutonium-beryllium source (mean energy 4.4 MeV) and from a 14 MeV neutron generator. The bean roots have also been irradiated at various points along the depth-dose curve of negative pi-mesons, including the gegion where the pions annihilate on coming to rest. The results show a maximum relative biological effectiveness (RBE) of 3.7 for 50% reduction in ten days growth for stopped negative pions and values up to 3.3 for high-energy neutrons, compared to 5.5 for 14 MeV neutrons. The biological effectiveness of high-energy neutrons and stopped pions shows a more pronounced dependence on dose than does the effect with lower-energy neutrons.

Chromosome rearrangements from spermatogonial chronic neutron irradiation in mice

Adult male mice were given a range of neutron doses at 80 ± 20 mrad/h from a plutonium-beryllium source. Cytogenetic analysis indicated that chronic spermatogonial exposure to a mean total dose of 10, 30, 52, 98 or 150 rad produced translocations, sampled in spermatocytes four months later, amounting to 0.32, 0.99. 1.69, 1.91 and 1.65%, respectively. The dose response for the 0–52 rad range was linear. For higher doses, a better fit to the data was an expression with dose exponent above unity.

Deterioration of large Ge(Li) diodes caused by fast neutrons

The large Ge(Li) gamma-ray detector has become a powerful tool for the investigation of nuclear reactions. Unfortunately these detectors are quite susceptible to fast neutron damage and this makes it difficult to decide whether or not to risk using a detector to study reactions at accelerators where fast neutrons are inevitably present. After ruining several detectors we decided to study the problem in a controlled way. A 30 cm 3 true coaxial diode was systematically irradiated by neutrons from a plutonium-beryllium source. An increase in the width of the 2.614 MeV gamma-ray from 208Tl was first detected after an irradiation of 5 × 10 7 n/cm 2. When the total irradiation had reached 6 × 10 8 n/cm 2, the peak width had increased by more than 50 percent. The irradiated detector was then reprocessed to remove the damage. The diode was again subjected to neutron irradiation. The second curve of resolution deterioration as a function of neutron flux was quite similar to the first one. The procedure was repeated a third time with similar results. Thus, reprocessing a detector effectively removes the neutron damage at a cost of only about 10 to 15 percent of the original price. A method was also developed for using the gamma-ray spectrum to evaluate the amount of neutron flux incident on the detector. The number of counts in the 693 keV peak [from (n,n′) reaction with the 72Ge in the detector] can be multiplied by 20 to get a rough measure of the neutron flux in n/cm 2.

Yield of the Fricke Dosimeter to 14.6 Mev Neutrons

Cheap, relatively copious supplies of fast neutrons are now available from small laboratory accelerators that utilize the H3(d, n)He4 reaction. Such sources make possible a variety of experiments, including studies of radiation chemistry and radiation damage, in an essentially 7-free environment. Whereas the dosimetry of fast neutrons from nuclear reactors is difficult and inexact, the dosimetry of fast, monoenergetic neutrons is amenable to straightforward attack. A previous paper (1) reported a study of the radiation chemistry of fast neutrons impinging on mixtures of liquid N2 and 02. For dosimetry the neutron flux was measured with a counter-a boron trifluoride proportional counter with a thick paraffin shield that provides a uniform response to 14-Mev neutrons and to neutrons from a calibrating plutonium-beryllium source. The flux measurement was then combined with cross-section and nuclear reaction data, as well as a geometrical analysis, to give the dose. The method required constant monitoring of the neutron flux during irradiations and frequent instrumental checks and calibrations. Because such studies often involve long irradiations during which the neutron flux varies appreciably, it would be most convenient to have a reliable chemical dosimeter. The Fricke dosimeter (an air-saturated dilute solution of ferrous ion in 0.8 N H2S04 with a small amount of NaCl added) has gained universal acceptance for work in radiation chemistry that involves X-rays, y-rays, or energetic electrons. G(Fe3+), the number of ferric ions produced per 100 ev deposited in the dosimeter, is a well-studied and monotonically decreasing function of ILET (initial linear energy transfer). G(Fe3+) decreases from 15.6 for lightly ionizing radiation, such as the y-rays from Co60, to an asymptotic value of about 4 for densely ioning particles such as the recoil a's and lithium atoms from the B10(n, a)Li7 reaction. Allen has summarized the work on the Fricke dosimeter through 1959 (2). Other, more sensi-

Neutron spectrum of a plutonium-beryllium source

The neutron spectrum of a plutonium-beryllium source (containing 80 g of plutonium) was obtained with the use of nuclear emulsions. Intensity maxima exist at less than 1.0 MeV and at 3.2, 4.7, 7.7 and 9.7 MeV. Maxima at 4.7, 7.7 and 9.7 MeV are well accounted for in a calculated spectrum. Those at less than 1.0 and at 3.2 MeV are partially explained. Comparison with other published spectra shows more low-energy neutrons for a source with 80 g of plutonium than for a source containing 13 g of plutonium.