Nuclear Chicago Research Articles

Computational spectrometry and dosimetry, of neutrons and γ rays, outside a subcritical nuclear reactor with water and polyethylene moderators

An external neutron source is necessary to start up and run a subcritical thermal nuclear reactor. The external neutron source can be a neutron generator, a radionuclide having spontaneous fission or an isotopic neutrons source. Turning off the neutron generator or removing the neutron source shuts down the reactor. In subcritical reactors for teaching, fuel tubes and items for irradiation can be inserted or removed even when the reactor is running because are radiological safe. The aim of this work was to estimate, using Monte Carlo methods, the neutron and γ-ray spectra at five sites outside a Subcritical thermal neutron reactor Nuclear Chicago model 9000 using water and polyethylene moderators. In addition, the ambient dose equivalent and the ambient dose, for neutrons and γ-rays were calculated. For neutrons, the ambient dose equivalent were calculated with the neutron fluence-to-ambient dose equivalent coefficients from the ICRP 74 and the neutron fluence-to-ambient dose response of the neutron area monitor LB 6411; while, the ambient dose was calculated using the ICRU 95 neutron fluence-to-ambient dose coefficients. For γ-rays, was calculated the ambient dose equivalent using the ICRP 74 photon fluence-to-ambient dose equivalent coefficients; while, the ambient dose was calculated with the photon fluence-to-ambient dose coefficients from the ICRU 95. Outside the reactor, neutron spectra have fast, epithermal and thermal neutrons, and gamma ray spectra have γ rays induced in the inelastic scattering and capture of neutrons with the reactor materials. Neutron and γ-ray fluence rates and dose rates are larger in the water-moderated reactor. The ambient dose rates, due to neutrons and γ-rays, are smaller than the ambient dose equivalent, because the ambient dose resembles the maximum effective dose.

Effect of changing the neutron moderator in a thermal subcritical nuclear reactor

Subcritical thermal nuclear reactor is the combination of nuclear fuel, moderator and external neutron source. Nevertheless, the amount of neutrons increases through nuclear fissions in the 235U in the fuel, the absorption and leakage of neutrons maintain the subcriticality condition. There are several subcritical reactors with different features and purposes. The open tank subcritical reactor Nuclear Chicago model 9000 is the heterogeneous combination of natural uranium, in hexagonal lattice, and light water, acting as moderator and reflector of neutrons, that uses a239PuBe neutron source. Worldwide there are several of these reactors mainly used in education, where due to the contact with water the Al tubes have corrosion. A possible solution is to use polyethylene as moderator. Aiming to evaluate the effect of changing the moderator, in this work Monte Carlo methods were used to model the reactor with polyethylene and water as moderators increasing the fuel load. For each model were estimated the keff and the μ parameters, and for Case 10a model was calculated the power, the Ambient dose equivalent and the fluence, of neutrons and γ-rays at five sites outside the reactor.

Mini Subcritical Nuclear Reactor

A mini subcritical nuclear reactor was designed using Monte Carlo methods. The reactor has light water as moderator, natural uranium as fuel, and a 239PuBe neutron source. In the design uranium fuel was modeled in an arrangement of concentric rings: 8.5, 14.5, 20.5 26.5, 32.5 cm-inner radius, 3 cm-thick, and 36 cm-high. Different models were made from a single ring of natural uranium to five rings. For each case, the neutron spectra, the neutron fluence distribution, the effective multiplication factor, the amplification factor, and the reactor power were estimated. The ambient dose equivalent rate outside the mini reactor was also estimated. The maximum value for the keff (0.78) was obtained when five rings of fuel were used; this value is close to 0.86 which belongs to a Nuclear Chicago subcritical reactor which requires almost twice the amount of uranium than the mini subcritical reactor.

Features of a subcritical nuclear reactor

A subcritical nuclear reactor is a device where the nuclear-fission chain reaction is initiated and maintained using an external neutron source. It is a valuable educational and research tool where in a safe way many reactor parameters can be measured. Here, we have used the six-factor formula to calculate the effective multiplication factor of a subcritical nuclear reactor Nuclear Chicago model 9000. Using the MCNP5 code, a three-dimensional model of the subcritical reactor was developed to estimate the effective multiplication factor, the neutron spectra, and the total and thermal neutron fluences along the radial and axial axis. The MCNP5 results of the effective multiplication factor were compared with those obtained from the six-factor formula. The effective dose and the Ambient dose equivalent, at three sites outside the reactor, were estimated; the Ambient dose equivalent was also measured and compared with the calculated values.

Temporolimbic Activation by Intracranial Electrical Stimulation

To evaluate the results of intracranial electrical stimulation (ICES) as a pre-surgical tool in order to select the side of the operation in bitemporal lobe epilepsy (BTLE) patients who underwent depth electrode (DE) implantation. We reviewed the files of 77 medically intractable BTLE patients who underwent ICES with positive results through implanted DEs and then were under surgical treatment. One year or more after surgery, we evaluated the outcome. ICES was performed through: 1) Square-wave bipolar stimulation with symmetrical pulses of 60 Hz for 0.5 ms was delivered by a constant current Nuclear Chicago stimulator; 2) An initial intensity of 0.5 mA, and subsequently progressively stronger currents at 1-2 and occasionally 3 or 4 mA; 3) The duration of a single stimulation was usually 5 seconds; 4) The volume of tissue effectively stimulated did not exceed 5 mm. We obtained habitual auras or seizures (clinical responses, CRs) in 74 patients and after-discharges, ADs in 61 of them, according to Engel's classification for post surgery outcomes. If CRs or ADs were obtained by stimulation of only one temporal lobe the result of epilepsy surgery tended to be better (Engel classes I or II) when the operation was done on the same side of positive CRs (15 cases) or ADs (14 cases), and tended to be worse (Engel classes III or IV) when the ICES had provoked bilateral responses or when the side operated on was contra-lateral to positive CRs (33 cases) or ADs (28 cases). Statistical analyses were performed in order to test these results and we found better post-operative results when the resection took place in the same side of positive responses to ICES (CRs: chi2 4.74 and p=0.0295; ADs: chi2 7.57 and p=0.0059). In addition to other methods (PET, MRI and neuropsychology) presurgical ICES can provide useful data in the process of identifying the temporal lobe to be targeted for resection in BTLE patients.

Measurement of neutron flux and albedo of water for thermal neutrons with foils of indium in a subcritical nuclear reactor

A subcritical nuclear reactor, Model 9000, Nuclear Chicago, is installed and operating at the Aristotle University of Thessaloniki, in the Atomic and Nuclear Physics Laboratory, at Thessaloniki, Northern Greece. The fuel is about 5500 lbs (2495 kgs) natural uranium metal (U3U8), the moderator about 3600 lbs (1633 kgs) light water, H2O and the reflector is also light, water, H2O. The lattice core is hexagonal, 42 inches (1.07 m) high and of 35 inches (88.90 cm) maximum diameter. The neutron source at the core is Am-Be 5 curies (185 GBq), 1.1·107n·s−1. The reactor is used for the activation of various materials by neutrons such as indium, the determination of the thermal neutrons flux, the horizontal and the vertical distribution of the neutron flux, material buckling, B, and geometric buckling, B, the parameters of the reactor, and the albedo of water for thermal neutrons with foils of indium.

Assessment of the extent of bone marrow haemopoietic activity in normal subjects

A method, introduced by the authors, for assessment of the extent of bone marrow haemopoietic activity in normal subjects is reported. 99mTc-sulfur colloid is injected, and the bone marrow visualized on gamma camera, type Phogamma-HP, which is equipped with 4096 channel analyzer (Nuclear Chicago). By use of a standard and by registering the activity in "zones of interest" from the arm, forearm, thigh and lower leg bones, indices and mean normal values in 26 normal subjects were calculated and reported.

The effect of tityustoxin from scorpion venom on the release of acetylcholine from subcellular fractions of rat brain cortex

TITti~usroxtr., a potent neurotoxin purified from the venom of the scorpion Tityus serrulatus increases the release of cellular acetylcholine (GOMEZ el a1., 1971, 1973). The effect of the toxin is dependent on several factors and is blocked by tetrodotoxin and absence of Na+ or Cat+ in the incubation medium. Acetylcholine occurs in subcellular fractions of brain tissue in three forms : free form obtained front the high speed supernatant ; bound form present in the synaptic vesicles and a labile bound form, present in the cytoplasm of synaptosomes (CHAKRIN and WHTITAKER, 1969). Since tityustoxin reduces bound acetylcholine from incubated slices of brain tissue, we decided to investigate on which of the above subcellular fractions it acts . Tityustoxin was purified as previously described by a combination of extraction and chromatographic techniques using Sephadex G-25 and CM-cellulose (GontEZ and DtNtz, 1966) . The preparation of brain slices, incubation procedure and acetylcholine assay was performed as described (GOMEZ et a1., 1973, 1975) . Acetylcholine was extracted from each fraction according to the procedure of McLErttvAx and ELhIOT (1950) . The subcellular fractionation was conducted according to the procedure described by DE ROBERTIS et al., (1962) . The fraction that sedimented at 11,5008 containing myelin, nerve endings, mitochondria and lysosomes was termed the crude mitochondrral fraction . The microsomal fraction sedimented at 100,0008 for 30 min aad the supernatant was the high speed supernatant . Synaptic vesicle membranes (M=fraction) were prepared according to the method of DE RoBEttns er al., (1963) . The procedure allowed the isolation of myelin, mitochondria, nerve ending ghosts (Ml), synaptic vesicles and membranes (M~ and soluble material (M,) . Radioactivity experiments : brain slices were incubated in the medium described with dusopropylphosphofluoridate in the presence of acetylcholine (methyl-taC) chloride (AmershamJSearle ; 54 mCi/mM). After 60 min, the slices were rinsed with gold incubation medium, digested with Nuclear Chicago Solubiliur or again incubated in the absence (control) or presence of tityustoxin. After 15 min of incubation, they wen homogeniud and the subcellular fractions Ml, M=and M, prepared according to the procedure previously described .

Fitting a 60Co external source to a Liquid Scintillation System for the estimation of the 32P Čerenkov effect detection efficiency

This paper deals with the fitting of a 1.4 μCi 60Co external source on the sample elevator of the Nuclear Chicago Liquid Scintillation System (model 724) for the estimation of the 32P Čerenkov effect detection efficiency, using an external standard method for correcting the color quenching.

A simple method of evaluating the penetrability of Spitz-Holter drains with the aid of radioisotopes.

A simple, reliable, and innocuous method is described for evaluating the penetrability of cerebrospinal shunts with the use of 99mTc O4. After introducing 25 muCi of 99mTc O4 in a volume of about 0.2 ml into Rickham's reservoir, series scintigrams in the lateral or AP direction are made with the aid of a Nuclear Chicago Pho Gamma HP Scintillation Camera. The results are in satisfactory agreement with the surgical findings. No complications have so far been observed.

Purification of conjugated bilirubin: a new approach utilizing albumin-agarose gel affinity chromatography.

Bilirubin, an organic anion and breakdown product of heme, is excreted chiefly by the liver by a process involving uptake by the hepatocyte and subsequent conjugation to form a more polar compound (1). The availability of purified preparations of bilirubin, especially of radiolabeled bilirubin, has greatly facilitated studies of its metabolism (1-5). Study of the transport of bilirubin from blood to bile, however, must also include consideration of the mechanisms for excretion of bilirubin conjugates. Such study has been limited because of difficulty in obtaining conjugated bilirubin free of significant quantities of contaminants (6-19). Recent studies of albumin-agarose gel affinity chromatography have revealed that the gels have a high affinity for bilirubin and a relatively low affinity and capacity for tri-and dihydroxy bile acids (20, 21), suggesting that this method might effectively separate bilirubin conjugates from other components in bile. We describe here, a rapid and relatively simple method for purification of conjugated bilirubin from bile. Materials and methods. Albumin-agarose gel was prepared by a modification of the cyanogen bromide method (20, 22), and packed in small columns of 0.9-cm i.d. Bile acids were quantitated in bile and column eluates by gas-liquid chromatography (23), cholesterol by the method of Zak et al. (24), and phospholipids by a modification of the method of Chen et al. (25, 26). Absorption spectra were obtained with a Beckman Acta III spectrophotometer, and fluorimetric analyses with a Farrand Mark I spectrofluorimeter. Tritium was quantitated by adding up to 0.5 ml of sample to 15 ml of Aquasol (New England Nuclear) and by counting in a liquid scintillation counter (Nuclear Chicago). All samples were recounted after addition of [3H]toluene (New England Nuclear) and results were corrected for background and quenching.

Marine Resources Research Institute Radiocarbon Dates I

In January 1975 a radiocarbon dating laboratory was established at the Marine Resources Research Institute for geochemical and geologic studies. A liquid scintillation system is employed according to the method of Noakes, Kim, and Akers (1967). A Searle (Nuclear Chicago) Isocap 300 liquid scintillation counter is currently being used for counting. This system is a duplicate of the one formerly used at Texas A & M University except for the counter (Mathews et al, 1972)

Estimation of body fat in rats by whole-body counting.

A method for determining body fat in vivo in rats by whole-body counting of 40K is described. The technique utilizes a Nuclear Chicago Corporation TOBOR system with 5-in thallium-activated sodium iodide crystals. To test the method a regression equation was developed using the 40K counts and body weight of young adult rats weighing 333-788 g; the results were compared with those obtained from the gravimetric determination of fat in the carcass. The correlation coefficient between the two methods was 0.945.

Nuclear Medicine Imaging with Pressurized Multiwire Proportional Chambers

The pressurized xenon-filled multi-wire proportional chamber (MWPC) is an imaging detector with high intrinsic spatial resolution and good uniformity of response. We describe the design and operation of a 20 x 20 cm2 MWPC with a mass of 0.14 g/cm2 of xenon, maintained at 60 psi absolute. Electromagnetic delay-lines are used to obtain position information. Imaging studies have been performed using a Nuclear Chicago low-energy high-resolution collimator. The intrinsic resolution of the system was determined for 60 keV and 140 keV photons using bar phantoms, and was found to be 1 mm and 2 mm respectively. The Modulation Transfer Function for 140 keV is down to 70 percent response at 1.4 cycles per cm. Stopping-power is about 65 percent for 1-125 and 10 percent for Tc-99m. The distribution of thyroid hormones in the rat was clearly demonstrated. Picker thyroid phantoms filled with 1-125 and TC-99m were imaged with good detail. Preliminary 1-125 thyroid studies in humans have shown a promising potential. Other studies in rats have included liver/spleen imaging with Tc-99m-sulfur colloid and skeletal imaging with Tc-99m-polyphosphate. The excellent spatial resolution of the detector, together with the addition of higher efficiency collimators and operation at higher pressures realize a system with characteristics that are adequate for clinical use. These components are now being incorporated in a 30 x 30 cm2 MWPC.

The Clinical Evaluation of 99mTc-Pyrophosphate Scintigraphy for Skeletal Diseases

86 cases of several kinds of bone and joint diseases were scanned with 99mTc-pyrophosphate as bone imaging agent, and evaluated in comparison with clinical and radiological findings.These include 9 cases of inflammatory disease of bone, 5 cases of rheumatoid arthritis, 11 cases of osteoarthritis of knee, 8 cases of avascular femoral head necrosis, 15 cases of primary bone tumor (benign 10 and malignant 5), 32 patients with cancer and 6 cases of the other diseases.Using Hitachi dual 5 in. whole body scanner and Nuclear Chicago Pho/gamma camera, bone scans have been carried out routinely 3-5 hours after intravenous administration of 5-10mCi of 99mTc-pyrophosphate.The image obtained with 99mTc-pyrophosphate is more sensitive and effective than those of 85Sr, 87mSr and 18F. High concentration of tracer was more clearly demonstrated in the presence of abnormal X-ray views as inflammatory disease, bone necrosis, degenerative joint disease and malignant bone tumor. However, even in little or no evidence of definite X-ray view, abnormal uptake of 99mTc could early represent the existence of bone involvement and its extent. With 99mTc-bone scanning, the beneficial informations were obtained in early diagnosis, activity or process of the diseases.

Clinical myocardial imaging with nitrogen-13 ammonia.

Myocardial infarcts may be clearly imaged using intravenous nitrogen-13 as carrier-free ammonia in doses of 10–30 mCi. This positron emitter is well imaged with the Nuclear Chicago HP Anger Camera with heavy collimation. The rapid blood disappearance of the agent gives good image contrast, and the short half-life and high isotope dosage give high-count density images with little radiation absorbed dose (5 mrad∕mCi total body).

Device for recording multiple (16) dynamic or multiple static images from a gamma camera on one piece of X-ray film

The method described records sixteen images on one piece of 11*14 inch X-ray film by electronically reducing the oscilloscope image and moving in through a 4*4 matrix of locations. The oscilloscope images are enlarged onto the X-ray film by using a lens and mirror system (standard Photoscope attachment for a Nuclear Chicago Pho-Gamma III camera) attached to one of the recording oscilloscopes of the Anger camera.

Infiltration into a nonsaturated soil

1. The basic content of most of the papers is related to the wetting of a soil by rainfall, with the exception of the paper presented by S. V. Izbash and I S. Ronzhin (USSR), which deals with the operation of hydraulic structures. 2. From the theoretical viewpoint the most interesting papers were those by N. I. Druzhinin and S. V. Nerpin (USSR), and by G. Kovach (Hungary), in which attempts are made to study in a general manner the laws governing infiltration into a fine soil. The paper presented by S. V. Izbash and I. S. Ronzhin upheld the priority of the USSR in the investigation of infiltration into a large-pore medium (rock fill). 3. Of great interest was the paper presented by Daian and Vachand (France), which describes the use of neutron probing by means of the Nuclear Chicago P19 instrument, produced in the United States. 4. In the paper presented by T. Boker (Hungary), the authors confirm the data previously obtained by V. I. Aravinyim and G. M. Lomize (USSR).

Synaptosomal proteins and axoplasmic flow: Fractionation by SDS polyacrylamide gel electrophoresis

The neuronal cell body is known to supply the axon and the nerve terminal with various materials which migrate through the axon at several different velocities. A perikaryal origin of an important part of the syn- aptic proteins has been suggested and substantiated [1 ]. Using the visual system of the pigeon as a model, it was shown that proteins labelled in one retina reach the optic nerve terminals in the contralateral optic lobe in at least two waves. The first, corresponding to the fast axoplasmic flow, has a peak at 24 hr while the second, having the characteristics of slow axo- plasmic flow, has its maximum at 14 days [2-4], Previous attempts to fractionate the synaptosomal proteins [5-8] have not dealt with the source of origin of these proteins, i.e. the problem was not in- vestigated whether the proteins arrive with the fast or slow axonal flows or whether they are synthesized in the nerve endings. This report is concerned with the characterization, by sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis, of the synaptic proteins migrating from the perikaryon. 2. Materials and methods Each pigeon was injected intraocularly [2] with 50/aCi of aH-leucine (1-4,5-3H-leucine, specific activity 22 Ci[mM) or 50/aCi 14C-leucine (1-1- 14C- leucine, specific activity 62 mCi/rnM, both Radio- chemical Centre, Amersham, England) in 50 pl H20. Subcellular fractionation of the optic lobe's homo- genate was performed by the slightly modified [2] method of Gray and Whittaker [9]. The fraction enriched in synaptosomes, containing about 1.5 mg protein, was solubilized in 200/al of SUCK solution (1% SDS, 8 M urea, 0.01 M dithiotreitol and 0.05 M K2CO3) [10~ 11] by gentle agitation at room temper- ature for 30 min and used immediately for the electro- phoresis. An ORTEC SLAB electrophoresis unit was used with a pulsed constant-power source. 0.1% SDS acrylamide discontinuous gradient gel was prepared according to Grossfeld and Shooter [12]. In each cell, 7.5 ml of 12% acrylamide, 7.5 ml of 9.6%, 6 ml of 7.5% and 3 ml of 4.2% were layered on top of each other and polymerized simultaneously. The stacking gel, 8 ml of 2.5% acrylamide, was then polymerized with light. 50/al of synaptosomes solubilized in SUCK were applied on the stacking gel. Electrophoresis was performed in the discontinuous Tris glycine buffer system [12] using 300 pulses/see at 120 V, 10 mA and 0.1 /aF discharge capacitance. The proteins moved towards the anode at room temperature for 16 hr. The gels were fixed in concentrated acetic acid for 12 hr and stained with 1% amido black B in 7% (v/v) acetic acid for 3 hr. They were destained in 7% acetic acid and sectioned between successive bands, where mechanical separation was possible. The pieces of gel were solubilized [13] and counted in a Mark I Nuclear Chicago Scintillation Counter. The dpm were

The reaction of α-, δ-, and acetylated-δ-chymotrypsin with radioactive formaldehyde

Many investigations into the reaction of proteins and their amino acid constituents with formaldehyde have led to the conclusion that formaldehyde reacts primarily with the free amino group during short-term exposure and mild conditions 1–4. Recently, Martin and Marini 5 presented spectral and kinetic results for the reaction of α-chymotrypsin (EC 3.4.4.5) with formaldehyde which indicate that formaldehyde also reacts with the imidazole side chains of the enzyme to produce N-hydroxymethyl derivatives. This is particularly interesting in light of the fact that the enzyme remains catalytically active 6. Titrimetric results of imidazole in the presence of formaldehyde have also been analyzed in terms of N-hydroxymethylation 7,8. Because of the catalytic role assigned to histidine residues in a number of enzymes, a more definitive identification of the formaldehyde reaction product(s) has been undertaken. NMR techniques 9 have been used to study the formaldehyde reaction product(s) of several imidazole derivatives; however, the studies could only be conducted on model compounds. To extend the results observed in the NMR studies to enzyme systems, the binding of radioactive formaldehyde to the imidazole and amino functions of α-, δ-, and acetylated-δ-chymotrypsin has been observed as a function of pH. Radioactive [ 14C]formaldehyde was obtained from New England Nuclear Corp. and diluted with 12.4 M formaldehyde to 10 ml to give a final specific activity of 886 disint./min per μmole of formaldehyde. 15 mg of protein were dissolved in 0.3 ml of water and the pH adjusted with HC1 or KOH. The [ 14C]formaldehyde (0.1 ml) was added and the reaction mixture allowed to sit for 1 min. The protein reacted under acidic conditions was precipitated with 10% trichloroacetic acid; the protein reacted under basic conditions was precipitated with ice-cold absolute ethanol. The precipitated material was spun down, the supernatant layer decanted, and the precipitate washed by resuspension in absolute ethanol. The material was washed until no radioactivity could be detected in the supernatant layer. Washing with alcohol does not hydrolyze the hydroxymethylated derivatives 2. After the washing, the precipitate was prepared for scintillation counting by the addition of Nuclear Chicago Solubilizer. The solubilized sample was taken up in 15 ml of scintillation fluid and counted on a Beckman dual channel counter with predetermined isosets for 14C and 3H + 14C and an external standard set on automatic quench correction. Each sample was run in duplicate and a cold formaldehyde sample run simultaneously for protein determinations. This procedure was run on three separate occasions.