Dose Neutron Irradiation Research Articles

Neutron Radiation Can Activate K-ras via a Point Mutation in Codon 146 and Induces a Different Spectrum of ras Mutations than Does Gamma Radiation

Neutron radiation is known to produce tumors in animals and cause cell transformation. We have developed a protocol to efficiently induce thymic lymphomas in RF/J mice by a single acute dose of neutron irradiation. Activated ras genes were detected in 17% (4 of 24) of the tumors analyzed. One of the tumors contained a K-ras gene activated by a point mutation in codon 146. Activating ras mutations at position 146 have not been previously detected in any known human or animal tumors. The spectrum of ras mutations detected in neutron radiation-induced thymic lymphomas was different from that seen in thymic lymphomas induced by gamma radiation in the same strain of mice. These results may have important implications for the mechanisms by which different types of radiation damage DNA.

Neutron radiation can activate K-ras via a point mutation in codon 146 and induces a different spectrum of ras mutations than does gamma radiation.

Neutron radiation is known to produce tumors in animals and cause cell transformation. We have developed a protocol to efficiently induce thymic lymphomas in RF/J mice by a single acute dose of neutron irradiation. Activated ras genes were detected in 17% (4 of 24) of the tumors analyzed. One of the tumors contained a K-ras gene activated by a point mutation in codon 146. Activating ras mutations at position 146 have not been previously detected in any known human or animal tumors. The spectrum of ras mutations detected in neutron radiation-induced thymic lymphomas was different from that seen in thymic lymphomas induced by gamma radiation in the same strain of mice. These results may have important implications for the mechanisms by which different types of radiation damage DNA.

Effect of prior history on the response of some commercial aluminium alloys to low dose neutron irradiation

The materials under investigation were AlMg and AlMgSi alloys. Tensile specimens in the cold-rolled and annealed conditions were neutron irradiated to fast fluences of 8.7 {times} 10{sup 17} and 2.5 10{sup 18} neutron cm{sup {minus} 2} at about 50{degrees}C.

Infrared absorption properties of the EL2 and the isolated AsGa defects in neutron-transmutation-doped GaAs: Generation of an EL2-like defect.

The EL2 and the isolated ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects in neutron-transmutation-doped (NTD) GaAs were studied by using the infrared (ir) absorption technique concurrent with thermal annealing. The results show that irradiation with low thermal-neutron doses partially decomposes the EL2 complex in semi-insulating (si) GaAs grown by the liquid-encapsulated Czochralski (LEC) growth technique. On the other hand, a small amount of EL2 is generated in as-grown Ga-rich undoped p-type LEC GaAs. The EL2 defect in low-dose thermal-neutron-irradiated samples (both si and p-type) was found to be stable up to 850 \ifmmode^\circ\else\textdegree\fi{}C. High neutron-irradiation doses, however, completely annihilate EL2 but generate a different EL2-like defect (DL2). The DL2 defect is observed after annealing the high-dose NTD samples for 6 min at 600 \ifmmode^\circ\else\textdegree\fi{}C. The DL2 concentration is observed to be larger than that of EL2 in as-grown LEC si GaAs by a factor of 2.3 or higher. The photoquenching and thermal recovery properties of DL2 and EL2 defects are identical. However, the DL2 defect does not exhibit the same thermal stability or the zero-phonon line of the EL2 defect. Thermal annealing kinetics shows that DL2 is composed of three point defects. The residual absorption (unquenchable component) after photoquenching the EL2 (DL2) defect is interpreted as the photoionization of the isolated ${\mathrm{As}}_{\mathrm{Ga}}$ antisite. The present results support the identification of EL2 as a complex defect and cast further doubt on the validity of the model which identifies EL2 as the isolated ${\mathrm{AS}}_{\mathrm{Ga}}$ antisite defect.

Radiation does from medical in-vivo prompt gamma-ray activation using a mobile nuclear reactor.

A method of medical diagnosis of toxic elements, using a neutron beam from a mobile nuclear reactor to perform partial-body in-vivo prompt gamma-ray activation technique, has been developed. Both neutron and gamma-ray dose equivalents in an irradiated phantom and around medical researchers were measured and evaluated. Neutron flux at various kinetic energies was measured using an activation foil technique, and the neutron dose equivalents at tissues of risk inside the irradiated phantom were calculated by neutron transport code. Gamma-ray dose equivalents inside the irradiated phantom and around the nuclear reactor were measured by thermoluminescent dosimeters. The risk associated with the neutron and gamma radiation dose equivalents received by both the irradiated phantom and medical researchers were evaluated in detail. The radiation safety of the in-vivo medical diagnosis using the mobile nuclear reactor, under the context of radiation protection guidelines, is discussed.

Neutron interstitial brachytherapy for malignant gliomas: a pilot study.

Fifty-six patients with malignant glioma were treated with implantation of the neutron-emitting element californium-252 (252Cf) within 2 weeks after surgical debulking of the tumor. Implantation was performed using computerized tomography-guided placement of afterloading catheters, and the 252 Cf sources were removed after approximately 300 neutron rads were delivered. Patients then received 6000 to 7000 conventional photon rads by external beam. The total photon-equivalent dose to the tumor ranged from 8100 to 9100 rads. The median survival time was 10 months, with 18-and 24-month survival rates of 28% and 19%, respectively. The results of reoperation or autopsy showed that patients had recurrence of the tumor but that radiation necrosis was restricted to the area of the original tumor. Serious complications occurred in five patients (9%) and consisted of wound infections in three, cerebral edema in one, and radiation necrosis beyond the original tumor margin in one. Previous studies using external-beam neutron radiation have shown that neutrons are capable of totally eradicating malignant gliomas; however, in most cases, unacceptable widespread radiation necrosis has resulted. Neutron implants are a logical way to increase the dose to the tumor and decrease the dose to normal brain. Interstitial neutron radiation can be given safely with 252Cf, and the survival results achieved by radiation alone using relatively low doses of interstitial neutron radiation from 252Cf implants plus conventional photon radiation were equal to the results attained with any currently available conventional therapy.

Irradiation-induced defects in amorphous Fe 40Ni 40P 20

During fast neutron damage, defects are generated in amorphous Fe 40Ni 40P 20. These defects cause a macroscopic swelling, but the crystallization enthalpy, the crystallization temperature and the ductility remained unchanged. Moreover, since specimens which had been thermally embrittled prior to irradiation became completely ductile again after low dose neutron irradiation, these defects appear to be beneficial for ductile behaviour. From small-angle neutron scattering experiments the average radius of the irradiation-induced defects, which are not visible in the transmission electron microscope, is 10 nm. The nature of these defects can be described as density fluctuations. A phase separation or the formation of crystallites during neutron irradiation can be ruled out.

Early ultrastructural changes in axodendritic synapses of the rat sensomotor cortex after high doses of fast neutron irradiation

Early ultrastructural changes in axodendritic synapses of the rat sensomotor cortex after high doses of fast neutron irradiation

Dielectric properties of neutron irradiated insulators

Abstract The dielectric properties (eand tan δ) of aluminium oxynitride (AlON), and two grades of commercial alumina (99.9% and 97.5% A1203) have been measured after neutron irradiation doses to faiences ranging from 1017 to 1020 n/cm2. The measurements span the frequency range 0.1 to 65 MHz and thus include the ion cyclotron resonance frequencies currently being considered for plasma heating in fusion reactors. The permittivity (Ψ) has been measure by a two fluid technique with an accuracy of better than + / - 1%. A 2% increase in permittivity has been observed after irradiation to 1019 n/cm2. The dielectric loss in AlON increased by approximately × 10 while that for the alumina increased by approximately × 3. After neutron irradiation to 1019 n/cm2, there was little difference in the loss factor of the irradiated alumina and AlON. The less pure ceramic (97.5%) was found to have lower loss than the high purity material. This may indicate the contribution of grain boundaries to the loss as the 99.9% mater...

Performance Characteristics of a High-Level Solid-State Personnel Dosimetry System in Pulsed Radiation Environments

The Health Physics Research Reactor at Oak Ridge National Laboratory was used to evaluate performance characteristics of a high-level, solid-state, personnel dosimetry system developed for the US Army for the rapid measurement of total (gamma plus neutron) radiation doses to soldiers in locations where tactical nuclear weapons could be used. The gamma sensitive element of the dosemeter consists of a silver-activated phosphate glass and the neutron detector is a silicon diode. Areas considered in this evaluation included pre-irradiation dose indication; accuracy and precision of gamma, neutron, and total dose measurements; time dependence; and temperature effects. Study results indicate that for doses above about 0.4 Gy, the system can provide rapid and accurate dose estimates within accuracy limits specified by several international regulatory and standards agencies for criticality accident dosimetry. However, theoretical and observed lower limits of detection for this system are somewhat higher than the 0.25 Gy minimum dose of interest for general accident dosimetry.

Study of neutron irradiation effect on Morin transition in hematite

It is established by Mossbauer spectroscopy and slow neutron diffraction that temperature range of Morin transition in hematite changes depending on neutron irradiation dose, and above some critical values the transition is not observed at all. A fraction of iron ions with high-temperature orientation of moments which cause the sample weak-ferromagnetic characteristics decreases with temperature fall but does not disappear completely, and near 4 K it even rises. It is established that radiation defects causing the changes in Morin transition disappear at annealing of hematite on air at temperatures of 400–500 K.

Ion beam exposure characteristics of resists: Experimental results: T M Hall et al,J Appl Phys, 53 (6), 1982, 3977–4010

Results of DLTS and high-resolution Laplace DLTS measurements of electrically active defects induced in phosphorus-doped dilute Ge-rich SiGe (0⩽[Si]⩽6 at%) samples by irradiations with 60Co gamma-rays, fast neutrons and 1–3 MeV Si ions and by ensuing annealing are presented in the work. It has been found that the DLTS spectra of these germanium rich SiGe samples irradiated with gamma-rays are qualitatively similar to the spectra of similarly irradiated Ge samples, which do not contain Si. The DLTS spectra of the gamma-irradiated samples are dominated by the E-center (vacancy–phosphorus pair). This indicates that silicon impurity atoms are not effective traps for vacancies in Ge at room temperature. Further, we have found no evidence for possible interactions of Ge self-interstitial atoms with Si atoms upon room temperature electron irradiation of SiGe samples. The presence of Si impurity atoms does not influence significantly the annealing behavior of the E center in Ge-rich SiGe. Thirty-minute heat treatments of the gamma-irradiated samples at 300 °C have resulted in complete removal of radiation-induced damage.DLTS spectra of the SiGe samples after low dose neutron irradiation resemble those observed after gamma irradiations, however, in the neutron-irradiated samples a few more minor DLTS peaks have been observed. The neutron-radiation-induced defects can be removed by anneals at 300 °C. The situation in ion-implanted material is more complex. Point defects, which dominate the DLTS spectra of electron-irradiated SiGe samples, are not the main electrically active traps in the ion-implanted samples. The Laplace DLTS spectra of the implanted samples show evidence of broader features characteristic of defect clusters. The implantation-induced damage is much harder to remove by heat treatments compared to the radiation-induced one. Significant concentration of electrically active traps remain in SiGe samples implanted with high doses of ions even after anneals at 500 °C.

Nuclear Responses in INTOR Plasma Stabilization Elements

Nuclear responses in the plasma stabilization elements were studied in a parametric fashion as a part of the transient electromagnetics critical issue C of ETR/INTOR activity. The main responses are neutron fluence and radiation dose in the insulator material, induced resistivity and atomic displacement in the conductor material, nuclear heating and life analysis for the elements. Copper and aluminum conductors with either MgAl/sub 2/O/sub 4/ or MgO insulating material were investigated. Radiation damage and life analysis for these elements were also discussed.

Californium-252 interstitial implants in carcinoma of the tongue

A clinical study using 252Cf sources in brachytherapy of tumors began in the Research Institute of Medical Radiology of the Academy of Medical Sciences of the USSR in 1973. 252Cf afterloading cells were utilized by the method of simple afterloading. Dosimetry and radiation protection of medical personnel were developed. To substantiate optimal therapeutic doses of 252Cf neutrons, a correlation of dose, time, and treatment volume factors with clinical results of 252Cf interstitial implants in carcinoma of the tongue for 47 patients with a minimum follow-up period of 1 year was studied. Forty-nine interstitial implants have been performed. Seventeen patients received 252Cf implants alone (Group I), 17 other patients received 252Cf implants in combination with external radiation (Group 1I), and 15 patients were treated with interstitial implants for recurrent or residual tumors (Group III). Complete regression of carcinoma of the tongue was obtained in 48 patients (98%). Recurrences occurred in 1 patient (6°k) in Group 1, 6 patients (35%) in Group II, and 5 patients (33%) in Group III. Thirteen patients (27%) developed radiation necrosis. The therapeutic dose of neutron radiation from 252Cf sources in interstitial radiotherapy of primary tongue carcinomas (Group I) was found to be 7 to 9 Gy. Optimal therapeutic neutron dose in combined interstitial and external radiotherapy of primary tumors (Group II) was 5 to 6 Gy with an external radiation dose of 40 Gy. For recurrent and residual tumors (Group III), favorable results were obtained with tumor doses of 6.5 to 7 Gy.

Estimation of mutation rates induced by large doses of gamma, proton and neutron irradiation of the X-chromosome of the nematode Panagrellus redivivus

The radiation-resistant free-living nematode Panagrellus redivivus was used to study mutation rates in oocytes, following gamma, proton and neutron irradiation in the dose range 45–225 grays. γ-Radiation produced approximately 0.001 lethal X-chromosomes per gray over the range tested. Proton or neutron irradiation produced approximately 0.003 lethal X-chromosomes per gray at lower doses, with the mutation rate dropping to 0.001 lethal X-chromosome per gray at the higher doses. These results suggest a dose-dependent mutation-repair system. Cell lethality was also examined. γ-Radiation produced the greatest amount of cell lethality at all doses, while neutron irradiation had no cell lethal effect at any of the doses examined.

Radiation Effects in Reactor Structural Alloys

Structural materials subjected to high doses of energetic neutron radiation in advanced fission reactors and in planned fusion reactors experience profound changes in mechanical and physical properties. The important phenomena are swelling, creep, and embrittlement. Extensive programs of basic and applied radiation effects research are underway in the United States and in a number of other countries. This research has led to both an understanding of the fundamental processes operating and to the broad result that the severity of radiation effects is quite sensitive to irradiation and materials parameters. By manipulating these sensitivities with guidance from a knowledge of the basic processes, physical metallurgists have been able to design improved alloys for radiation effects resistance.

Positron annihilation in Ge-S glasses

Positron lifetime and Doppler broadening measurements have been carried out on GeS1.375 and GeS1.5 glasses. A pronounced decrease of the mean lifetime was observed at crystallization of GeS1.375 glass into the GeS structure. Also the Doppler-broadened curves are strongly sensitive to this solid-solid phase transition. Unlike the situation for many metals, the positron annihilation parameters were found non-sensitive to fast neutron irradiation doses as high as 1019 n/cm2. No difference between positron annihilation parameters measured on GeS1.375 and GeS1.5 glasses was found. The state of the positron in the GeS glasses is discussed on the basis of these results. The idea is put forward, that the GeS-GeS2 system provides possibilities of sample parameter variations that might prove useful in the understanding of the positron state in non-metallic solids.

State primary standard for units of absorption power and equivalent dose of neutron radiation

State primary standard for units of absorption power and equivalent dose of neutron radiation

Effect of Ionizing Radiation on the Energy Metabolism of Hog Lymphocytes

The pattern of biochemical changes induced by irradiation was studied in a relatively broad dose range, from doses on the order of 1 rad up to doses of several kilorad, based on determinations of the content of free nucleotides. The lymphocyte was chosen as a model cell, due to the high radiosensitivity of this type of cell. Changes in the free nucleotide content of hog blood lymphocytes were examined after γ irradiation in the dose range of 50 rad to 7 krad, and after low doses of neutron irradiation. Special attention was paid to the ATP level in irradiated cells. Determinations were always performed 1 hr after irradiation. For adenine nucleotides, a decrease was noted at low doses and an increase in the dose range of several kilorad, with a maximal increase in the content of ATP and other adenine nucleotides at 3 krad of γ radiation. It was demonstrated that the energy charge of the adenine nucleotide system is a sensitive index of radiation-induced biochemical changes.

The influence of radiation induced atomic disorder on the superconducting properties of nb 3sn

After high dose neutron or ion irradiation of Nb 3Sn several authors have observed a marked depression of T c , H c2 and J c . By a model calculation within the framework of the linear chain model it is shown that these effects might be explained by the decrease of the electronic density of states at the Fermi level, E F, due to radiation induced atomic disorder. The influence of atomic disorder on E F, T c, and on the intrinsic superconducting material parameters λ, ξ, κ, h c , H c2 is calculated numerically and the results are compared with experiments. The depression of the critical current density for doses φ > 2 × 10 18 n/cm 2 , in spite of a softening of the elastic properties of the flux line lattice after irradiation, is shown to be due to a drastic decrease of the elementary pinning forces.