University Research Reactor Research Articles

屋内空気中のラドンとその娘核種濃度 ＩＩ 換気装置の始動または停止直後の過渡的状態

In the reactor room of the Kyoto University Research Reactor Institute, the measurements of radon (Rn) and its short-lived decay products (Rn-Dts) were carried out under ventilated and non-ventilated conditions. The indoor activities were equal to outdoor ones under ventilated condition and those activities increased till about 10 times of outdoors under non-ventilated condition. We attempted to explain these results on a basis of a simple model. The calculations were performed taking into account: (1) supply of Rn and Rn-Dts from outdoor, (2) the emanation rate of Rn from the wall materials of building, (3) the removal rate of Rn-Dts by ventilation and wall deposition, and (4) the attachment rate of unattached atom to aerosols. In addition, natural ventilation were considered during periods without artificial ventilation.

INAA determination of selenium via77mSe in plasma, semen and hair samples from beef and dairy bulls

Interest in the element selenium with respect to its biological significance has been steadily increasing for the last ten years. Neutron activation analysis has long been used for the accurate determination of selenium in biological samples usually via75Se. More recently activation analysts having access to high flux reactors with rapid delivery pneumatic tube facilities; have successfully employed77mSe. This approach, which is much faster, is particularly well suited to the Missouri University Research Reactor (MURR). The specific interest concerning bulls has to do with the involvement of selenium in the reproductive system. Selenium analysis methodology and data on plasma, semen and 22 tissues from both beef and dairy bulls are presented.

非破壊放射化分析法による臭化メチル暴露者の血液・毛髪中ブロム濃度

The bromine contained in blood and hair samples obtained from workers exposed to methyl bromide was analyzed by non-destructive activation analysis. The samples were irradiated for 1 min in pneumatic irradiation facility of Kyoto University research reactor with an estimated thermal neutron flux density at 2 X 10(13)n X cm-2 X sec-1. The irradiation was counted with Ge(Li) detector. The duration of measurement of radionuclide bromine in blood and hair was 200 sec within 2-10 min after irradiation. The bromine content of serum sample obtained from a worker suspected of methyl bromide poisoning was found to be 412 micrograms/g on 13 days apart from exposure to methyl bromide. The biological half-life of bromine in this case was found to be about 16 days. Then bromine contents in serum and hair samples obtained from workers exposed to methyl bromide were found to be 1.7 and 2.6 times higher respectively than those of nonexposed workers. Any correlations of bromine contents were not observed between serum and hair samples obtained from workers exposed to methyl bromide, nor between bromine amount in the serum of workers exposed to methyl bromide, and the terms exposed to it, but statistically significant positive correlation was observed between bromine amount in the hair of workers exposed to methyl bromide and the terms exposed to it.

Energy and angular flux density spectra of 6 MeV gamma-rays penetrating shielding materials

Double differential flux spectra are presented for 6 MeV gamma photons penetrating aluminium, steel, lead and lead-aluminium shielding slabs. A large diameter disc radiator filled with activated primary cooling water from the Universities Research Reactor provides the source of high energy photons. Experimental pulse height distributions from a NaI spectrometer have been unfolded with the code RADAK. Comparisons are made with theoretical values using the code PIPE. Good agreement is established for most of the energy range, but experimental results show the need for the inclusion of secondary sources of photons in theoretical calculations.

The Effect of the Azimuthal Angle on Fast-Neutron Concrete Albedos

Albedos have been experimentally measured for a spectrum of fast fission neutrons incident on a 24- x 24- x 9-in. concrete slab. The source of fast neutrons for the experimental studies was the Missouri University Research Reactor; the direct and reflected neutron spectra were detected using a 2- x 2-in. liquid-scintillation spectrometer system. Previously published Monte Carlo calculated albedos have indicated a weak dependence on the azimuthal angle of reflection. These experimental measurements have confirmed this result and identified the effect of the incident angle on this relationship.

A chopper for neutron pulse propagation experiments

An intense neutron pulse with a wide frequency spectrum was required for pulse propagation experiments. The neutron beam emanating from the thermal column of the Universities Research Reactor (URR) was modulated by an improved rotary chopper of 86 cm diameter, operating at 2000 rev min-1 and containing boron and cadmium absorbers. The cross-sectional area of the pulsed beam was 26 cm2. The pulses has a 3 dB cut-off frequency of about 1000 Hz and a signal-to-background ratio of about 400.

Measured Fast-Neutron Penetration Spectra for Water—Comparison with Calculations

Fast-neutron angular penetration spectra were experimentally determined for a fast-neutron spectrum incident on 4-, 8-, and 12-in. (102-, 203-, and 305-mm)-thick water slabs. The experimental spectra were compared with MORSE Monte Carlo calculations using readily available multigroup cross sections.The source of fast neutrons for the experimental study was the Missouri University Research Reactor; the incident and penetration neutron spectra were detected using a 2- X 2-in. (51- X 51-mm) NE-213 liquid scintillation spectrometer system. A comparison of the Monte Carlo and experimental results showed excellent agreement for all but the thickest slabs. All results showed similar trends and structure, and only for the 12-in. slab did the experimental and calculated result vary by as much as 40% for shallow angle penetrations. Integrated spectral results are generally within ±15% for all reported angles and thicknesses.A modification to the well-known MORSE code has been utilized to calculate group-to-group transfer probabilities for each of the experimental geometries. These probabilities have been converted to dose and are tabulated to permit calculation of the penetration dose for any incident neutron spectrum for the comprehensive set of angles considered in this work.

Lattice dynamics of BaO

The frequency-wave vector dependence of the normal modes of vibration have been measured for BaO at room temperature. A total of 99 phonons were examined in the high symmetry directions using coherent inelastic neutron scattering techniques on the triple axis diffractometer at the Missouri University Research Reactor. Very good fits to the data were possible, both with a normal shell model and with a three body force shell model. The normal shell model produced a slightly better fit but required a total of 15 adjustable parameters; the three body force shell model was fit with 8 adjustable parameters. The phonon density of states was calculated and used to determine the temperature dependence of the Debye Temperature.

A 6 MeV gamma photon facility

The 16N radiation facility provides a source of 6 MeV gamma photons for shielding and dosimetry studies. It utilises the 16N produced in the cooling water of the 300 kW Universities Research Reactor, Risley, as it flows through the fuel element assemblies. The facility incorporates a specially designed disc radiator providing an isotropic uniform disc source suitable for benchmark experiments. A shielded cell houses a lead collimator weighing 1.6 Mg which is capable of being moved in three directions by a traversing gear with external control and position indicator.

Pulsed-source experiments in a reflected coupled-core reactor-I. reactivity measurements

The behaviour has been studied of the Universities Research Reactor (URR) at Risley, Lancs., when subjected to pulses of fast neutrons. The URR is an enriched-uranium, water-cooled and moderated, graphite-reflected system, the core consisting of two coupled fuel slabs spaced 1 ft apart and containing approximately 3300 g of 235U. The work is reported in two parts. In the work reported in this first section the pulsed source was located symmetrically relative to the core slabs (so that the coupled-core nature of the reactor was suppressed) and the results analysed using the more conventional point-reactor models. A reflector decay mode, as predicted by a three-region Cohn model was not observed. The delayed critical prompt decay constant of the URR was found to be 33·5 ± 0·6 sec −1. The experiments showed that, for sub-critical core loadings in a highly reflected system such as the URR, the data is analysed most readily and reliably by the Simmons-King method supplemented by calculated changes in the generation time. For this reactor, the Gozani method corrected for kinetic distortion was found to be the most suitable of the modified pulse techniques. METHUSELAH II—GOG multigroup-diffusion poison-removal calculations gave prompt and delayed flux distributions which accounted well for the observed spatial dependence of the modified-pulse-technique reactivities. The experimental and calculated decay constants, although substantially in agreement at critical, diverged by as much as 15–25 per cent for the subcritical core loadings. Part 11 of this work will examine the coupled, two-slab, nature of the URR.

Element 112 evidence starts a rush on proton beam stops

Suppose you bombard a tungsten target with very high‐energy protons. Sometimes a tungsten nucleus might receive enough energy to climb the Coulomb barrier in a second tungsten nucleus and produce some superheavy nucleus. That was the hypothesis of Amnon Marinov (on leave from Hebrew University at the Rutherford High Energy Laboratory) and his collaborators, C. J. Batty and A. I. Kilvington (Rutherford), G. W. A. Newton and V. J. Robinson (University of Manchester) and J. D. Hemingway (Universities Research Reactor, Risley, Lancashire), who examined two tungsten beam stops from the CERN proton synchrotron. After studying their alpha‐decay properties and also observing spontaneous fission, they concluded that they may have observed production of element 112 by secondary reactions in tungsten targets irradiated by 24‐GeV protons (Nature 229, 464, 1971).

On-Line, Digital Data Handling and Optimal Control Investigations at the Missouri University Research Reactor

An on-line, digital data handling and optimal control system based upon a PDP8s, general purpose, programmable digital computer, has been developed and tested at the Missouri University Research Reactor (MURR), a 5 megawatt, thermal, flux-trap type nuclear reactor. The instrumentation which has been successfully interfaced to the small digital computer includes a 100 channel, 250 Hz, randomly addressable reed scanner; a 10-bit, 100 kHz, analog-to-digital converter; a 60 Hz real time clock which provides a hardware interrupt every 16.7 milliseconds; and two relay contact outputs. Software which has been implemented includes a real-time executive which schedules eight different tasks in a specified priority and periodic scheme, a console utility package which allows direct, on-line, communication between computer core memory and the ASR-33 teletype, an analog signal input task, various control algorithms, an output task, and a systems log task. The automatic control algorithms are dependent upon the physical parameters of the reactor system. These parameters may be periodically identified by on-line dynamic testing and the control decision algorithm may be modified accordingly. Methods of z-transform analysis are applied in a linearized approach to the problem of representing each component of the closed-loop reactor, computer control system. The optimization theory based on the maximum principle of L. S. Pontryagin has been applied in an effort to improve the control calculations with respect to minimum time response. Testing methods used were hybrid computer simulation and on-line parameter input studies at the MURR.

Investigation of In-Band Resonant Modes in Cr-W Alloys by Inelastic Neutron Scattering

Transverse phonon groups in the [001] and [011] symmetry directions have been measured for Cr and three Cr-W alloys by inelastic neutron scattering using the triple-axis neutron diffractometer at the Missouri University Research Reactor. The tungsten concentration for the alloys are 0.3-, 0.8-, and 1.6- at.% W. The shifts in the phonon frequencies for each alloy showed the expected in-band resonant mode behavior. However, on extending the measurements of the shifts to the zone boundary in the [011] direction, additional structure was observed as well as a substantial increase in the magnitude of the negative shifts as one approaches the zone boundary. These frequency shifts are compared to the theory of Elliott and Maradudin using the frequency distribution function of chromium. The agreement between theory and experiment is no better for the lower tungsten concentrations than for previous results for Cr-3-at.% W. Thus, for the Cr-W system the mass-defect theory appears to be inadequate to predict the measured frequency shifts.

25-Minute Isomer ofSe83

BS>Se/sup 83/ was produced by irradiation of a selenium sample, enriched to 75% in Se/sup 82/, in the Pennsylvania State University research reactor. The gamma-ray spectrum of the 25-minute isomer was investigated by means of a 3-in. thick x 3-in. diameter NaI(Tl) crystal scintillation spectrometer. Gamma rays of 2.294 sintering time (0.833 sintering time 0.005, 0.712 sintering time 0.010, 0.524 sintering time 0.012, 0.358 sintering time 0.005, and 0.225 sintering time 0.005 Mev were found. The beta-ray spectrum was investigated by means of a plastic scintillator. In order to eliminate a competing activity from Se/sup 81/ it was found essential to restrict the observation of beta rays to those in coincidence with the Se/sup 83/ gamma spectrum. A coincidence circuit of 0.25microsecond resolving time was developed for this purpose. The beta spectrum was found to be complex with end-point energies of approximately 0.45, 1.0, and 1.7 Mev. From these data, together with gammagamma coincidence measurements, a decay scheme is proposed. (auth)