The effect of neutron irradiation on the magnetic properties of low carbon steels

The present work describes an experimental investigation of the effect of neutron irradiation on the change in particular magnetic properties of low carbon steels. The experimental work was carried out using samples of type SD-31 steel. The process of neutron exposure was iradiation followed by re-irradiation of up to twice the dose rate under the same exposure circumstances and exposure times.The experimental results show that there is a change in the magnetic properties, particularly in the area of the hysteresis loop as a measure of the loss factor due to the exposure to neutron irradiation. The megnetic loss factor increases as the neutron fluence increases in spite of the different irradiation rates. The increase in the hysteresis loop area reduced after the second irradiation to 12% of its value after the first irradiation. This reduction may be attributed to the formation of tiny voids which become significant at an integrated flux of 1.88 × 10¹⁸ n/cm².     

The biological effect of the phosphatidylinositol 3-kinase wortmannin following thermal neutron irradiation

PURPOSE: Wortmannin, a phosphatidylinositol 3-kinase inhibitor, has been found to inhibit DNA-dependent protein kinase (DNA-PKcs) and to be an efficient radiosensitizer. We investigated the radiosensitizing effect of wortmannin on cell killing by thermal neutrons and the occurrence of mutations at the HPRT locus of CHO cells. MATERIALS AND METHODS: Wortmannin was added to cells at a final concentration of 20 microM two hours before irradiation. Cells were irradiated with thermal neutrons. The biological end point of cell survival was measured by colony formation assay. Mutagenicity was calculated from the mutation frequency at the HPRT locus. RESULTS: Wortmannin promoted cell death following thermal neutron irradiation especially in the absence of boron. However, mutagenicity was decreased by the wortmannin treatment. CONCLUSION: Our results suggest that the inhibition of DNA-PKcs by wortmannin would be an effective radiosensitizer for BNCT and might bring about a reduction in the frequency of mutation by blocking the mis-joining of DNA damage during the repair process.     

Effects of neutron and combined gamma irradiation of rats

The effect of single neutron irradiation (2 Gy) alone and combined with continuous gamma irradiation (6 Gy accumulated during 10.5 days) was studied on the survival of rats and on nucleic acids both in the lymphoid organs and testes. After neutron irradiation alone the most profound changes in lymphoid organs and testes were found on the third and within the days 28-60, respectively. Regeneration has been undergone at a relatively fast rate. Continuous irradiation subsequent to neutron irradiation deepened only slightly the extent of the initial changes. The effect of combined irradiation manifested mainly a later times in marked slowing down of regeneration.     

Serum proteins in rats after combined neutron and gamma irradiation

Quantitative changes of some selected serum proteins in rats irradiated with a single dose of 2 Gy neutrons were compared with protein changes in rats irradiated with an equal single neutron dose and subsequent continuous gamma irradiation using daily dose rate of 0.574 Gy up to the total dose of 6 Gy. On the basis of the values obtained from the diagrams of two-dimensional immunoelectrophoresis it was found that both irradiations entailed approximately equal quantitative changes of the serum concentrations of the proteins followed. The differences found concerned time intervals of the adjustment of the changes produced. After neutron irradiation reparation of the serum albumin occurred on 14th day, of A1-globulin concentrations on 28th day and of haptoglobin on 90th day, yet after combined neutron and gamma irradiation reparation of the changes in albumin on 15th and A1-globulin occurred on 40th day and in haptoglobin only on 100th day after neutron irradiation.     

Dosimetric influence of secondary electrons during accelerator-produced fast neutron irradiation

1 MeV neutrons are produced by the ⁷Li(p, n)⁷Be nuclear reaction using 2.75 MeV protons and a target consisting of 3 × 10⁻⁴ g cm⁻² Li evaporated on 1 g cm⁻² Ta. The response due to secondary electrons was about 25% of the neutron response, but 1 mm polyethylene absorbs all these particles. This finding may be of particular interest for radiobiologists.     

Treatment results of fast neutron irradiation in soft tissue sarcomas

Purpose

Surgery is the standard treatment of soft-tissue sarcomas. Adjuvant radiotherapy with photons after less radical resection can improve local control. The rate of tumor control achieved in patients with G1 and G2 soft tissue sarcomas incompletely resected and treated postoperatively with neutron irradiation is similar to that seen in patients undergoing complete tumor resection and adjuvant photon irridiation.

Patients and Methods

At the Department of Radiotherapy and Radiation Oncology of the University of Münster, 61 patients with soft tissue sarcomas were irradiated postoperatively with fast neutrons. Mainly tumors of low or intermediate malignancy (R0; 27%; R1, 21%; R2, 52%) were treated. Malignant fibrous histiocytoma, liposarcoma, and neurogenic sarcomas dominated. 46 patients were irradiated with fast neutrons alone, and 15 patients were treated with mixed beam therapy (photons and neutrons).

Results

The median follow-up period was 44 months. Overall five-year survival probability analysed by Kaplan-Meyer method was 42.5%. The local control rate was 57.7%. 15 patients showed complete remission, 18 patients had a partial remission. Only 11% of the patients showed grade III and IV side effects during neutron irradiation.

Conclusion

Neutron irradiation is efficocious in treating highly and intermediately differentiated soft tissue sarcomas. The result of surgical resection seems to be a very important prognostic factor for patients with soft tissue sarcomas.

     

Changes of the peripheral blood picture after combined neutron and gamma irradiation

Changes of the peripheral blood picture of rats irradiated with a single dose of 2 Gy of neutrons were followed in comparison with a group of rats irradiated with a single dose of 2 Gy of neutrons followed by continuous gamma irradiation (daily dose rate 0.574 Gy, total dose 6 Gy). The decisive factor for the organism damage was the single 2 Gy neutron dose. The subsequent continuous gamma irradiation retarded the reparation of the peripheral blood elements.     

Fractionation of high-dose electron beam irradiation of BPTB grafts provides significantly improved viscoelastic and structural properties compared to standard gamma irradiation

Purpose

Irradiation >30 kGy is required to achieve sterility against bacterial and viral pathogens in ACL allograft sterilization. However, doses >20 kGy substantially reduce the structural properties of soft-tissue grafts. Fractionation of irradiation doses is a standard procedure in oncology to reduce tissue damage but has not been applied in tissue graft sterilization.

Methods

Forty-four human 10-mm wide bone-patellar-tendon-bone grafts were randomized into four groups of sterilization with (1) 34 kGy of ebeam (2) 34 kGy gamma (3) 34 kGy fractionated ebeam, and (4) non sterilized controls. Graft´s biomechanical properties were evaluated at time zero. Biomechanical properties were analyzed during cyclic and load-to-failure testing.

Results

Fractionation of ebeam irradiation resulted in significantly higher failure loads (1,327 ± 305) than with one-time ebeam irradiation (1,024 ± 204; P = 0.008). Compared to gamma irradiation, significantly lower strain (2.9 ± 1.5 vs. 4.6 ± 2.0; P = 0.008) and smaller cyclic elongation response (0.3 ± 0.2 vs. 0.6 ± 0.4; P = 0.05), as well as higher failure loads (1,327 ± 305 vs. 827 ± 209; P = 0.001), were found. Compared to non-irradiated BPTB grafts, no significant differences were found for any of the biomechanical parameters. Non-irradiated controls had significantly lower cyclic elongation response and higher failure loads than ebeam and gamma irradiation.

Conclusions

In this study, it was found that fractionation of high-dose electron beam irradiation facilitated a significant improvement of viscoelastic and structural properties of BPTB grafts compared to ebeam and gamma irradiation alone, while maintaining levels of non-irradiated controls. Therefore, this technique might pose an important alternative to common methods for sterilization of soft-tissue allografts.     

Early repair kinetics of intestine and lung in mice, after fast neutron and photon irradiation

Early repair (Elkind repair) kinetics of an early and a late responding tissue after gamma and d(50) + Be neutron irradiation were compared in mice. LD50 at five days after abdominal irradiation and LD50 at 180 days after thoracic irradiation were chosen as biological endpoints to study intestinal and lung tolerance, respectively. Elkind repair is assessed from the additional dose Dr to reach LD50 when a single dose Ds is split into two equal fractions Di separated by time intervals "i" ranging from 0 to 24 hours (Dr = 2Di-Ds). Dr is greater for lung than for intestine after both gamma and neutron irradiations. Our data are consistent with an exponential early repair with an half-life (T 1/2) of 0.5 h for intestine and 1.5 to 2 h for lung.     

Morphologic alterations in rat bone marrow and spleen after neutron and gamma irradiation

Morphologic alterations were studied in rat bone marrow and spleen after wholebody neutron irradiation (2 Gy dose). Neutron irradiation causes damage of hemapoietic organs changing their morphological structure already in the first hours after irradiation. The damage is further intensified reaching its maximum on 3rd day. Recovery of the hemopoiesis in the bone marrow and spleen begins approximately on 5th day being complete by 15th to 21st day after irradiation. Continuous gamma irradiation for 10.5 days following single neutron irradiation (total accumulated dose of 6 Gy, daily input dose of 0.574 Gy) results in prolonged inhibition of the hemopoietic activity until termination of the irradiation. Reparation of the damaged bone marrow is seen only on about day 5 after cessation of continuous irradiation; this implies that continuous irradiation following neutron irradiation delays the onset of reparative processes by approximately 5 days. In the spleen reparation of erythropoiesis begins already during the irradiation.     

Evaluation of thermal neutron irradiation field using a cyclotron-based neutron source for alpha autoradiography

It is important to measure the microdistribution of ¹⁰B in a cell to predict the cell-killing effect of new boron compounds in the field of boron neutron capture therapy. Alpha autoradiography has generally been used to detect the microdistribution of ¹⁰B in a cell. Although it has been performed using a reactor-based neutron source, the realization of an accelerator-based thermal neutron irradiation field is anticipated because of its easy installation at any location and stable operation. Therefore, we propose a method using a cyclotron-based epithermal neutron source in combination with a water phantom to produce a thermal neutron irradiation field for alpha autoradiography. This system can supply a uniform thermal neutron field with an intensity of 1.7×10⁹ (cm⁻² s⁻¹) and an area of 40 mm in diameter. In this paper, we give an overview of our proposed system and describe a demonstration test using a mouse liver sample injected with 500 mg/kg of boronophenyl-alanine.     

Sensitizing effect of the phosphatidylinositol 3-kinase inhibitor wortmannin on thermal neutron irradiation with or without boron compound

Wortmannin, a phosphatidylinositol 3-kinase inhibitor, has been found to be an efficient radiosensitizer. We have investigated the radiosensitizing effect of wortmannin on cell killing against thermal neutrons produced by the Kyoto University Research (KUR) reactor. Wortmannin was added to cells 2 hours before irradiation and removed 16 hours after irradiation. Cells were irradiated by thermal neutrons with or without boron at 0, 10, and 20 ppm. The biological end point of cell survival was measured by colony formation assay. The D0 values of thermal neutrons in different boron concentrations, 0, 10, and 20 ppm were 1.2, 1.1, and 1.0 Gy, respectively. When cells were treated with wortmannin, the D0 values decreased to 0.5, 0.6, and 0.8 Gy at boron concentrations of 0, 10, and 20 ppm, respectively. Wortmannin enhanced cell death against thermal neutron irradiation especially in the absence of boron. Thus, our results suggest that wortmannin may be useful to combine with boron neutron capture therapy (BNCT) treatment when boron uptake by cells is limited.     

Reactivation of neutron killed mammalian cells by gamma irradiation: the observations, possible mechanism and implication

We have observed that combinations of neutron plus gamma ray exposure can significantly increase the colony forming ability of monkey and human cell cultures over the neutron dose alone. The "reactivation" of neutron killed mammalian cells by gamma rays is analogous to observations made in lower eukaryotic organisms and fits the pattern termed "T repair" previously postulated for yeast and protozoans.     

Microdosimetric measurements in the thermal neutron irradiation facility of LENA reactor

A twin TEPC with electric-field guard tubes has been constructed to be used to characterize the BNCT field of the irradiation facility of LENA reactor. One of the two mini TEPC was doped with 50 ppm of ¹⁰B in order to simulate the BNC events occurring in BNCT. By properly processing the two microdosimetric spectra, the gamma, neutron and BNC spectral components can be derived with good precision (~6%). However, direct measurements of ¹⁰B in some doped plastic samples, which were used for constructing the cathode walls, point out the scarce accuracy of the nominal ¹⁰B concentration value. The influence of the Boral^® door, which closes the irradiation channel, has been measured. The gamma dose increases significantly (+51%) when the Boral^® door is closed. The crypt-cell-regeneration weighting function has been used to measure the quality, namely the RBE_µ value, of the radiation field in different conditions. The measured RBE_µ values are only partially consistent with the RBE values of other BNCT facilities.     

Effects of neutron irradiation on optical and chemical properties of CR-39: Potential application in neutron dosimetry

Effects of high-dose neutron irradiation on chemical and optical properties of CR-39 were studied using FTIR (Fourier Transform Infrared) and UV–vis (Ultraviolet–Visible) spectroscopy. The primary goal was to find a correlation between the neutron dose and the corresponding changes in the optical and chemical properties of CR-39 resulted from the neutron irradiation. The neutrons were produced by bombarding a thick Be target with 22-MeV protons. In the FTIR spectra, prominent absorbance peaks were observed at 1735 cm⁻¹ (CO stretching), 1230 cm⁻¹(C–O–C stretching), and 783 cm⁻¹(C–H bending), the intensities of which decreased with increasing neutron dose. The optical absorbance in the visible range increased linearly with the neutron dose. Empirical relations were established to estimate neutron doses from these optical properties. This technique is particularly useful in measuring high doses, where track analysis with an optical microscope is difficult because of track overlapping.