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At least 235 records · Page 13Linked to original sources
PubMed1976

Measurements of neutron spectra at depths in tissue equivalent material for fast neutron beams generated by deuterons on beryllium.

The threshold foil technique has been used to investigate the behaviour in tissue of the spectra of neutron beams produced by the bombardment of thick Be targets with 13-0 and 20-5 MeV deuterons. The results indicate a gradual "softening" with depth in tissue of the spectrum generated by 20-5 MeV deutrons which contrasts with a gradual hardening as reported by other authors. This is discussed in terms of the significance of field size and the methods used for data collection and analysis.

Beryllium↗
PubMed1975

[Neutron therapy in the G.D.R. Fundamentals of fast neutron application in radiation treatment (author's transl)].

In 1972 GDR started with the treatment of tumor patients with fast neutrons on the base of oxygen-effect. That means a better sensitivity of radiation of anoxic cells against radiation with high LET in comparison to radiation of thin ionization. Every tumor contains some anoxic cells. Therefore a better effect is possible with doses that are tolerated by normal tissue. In the following the details of the problems are discussed.

Anaerobiosis↗
PubMed1990

Results of fast neutron therapy of adenoidcystic carcinomas of the head and neck at the neutron facility Hamburg-Eppendorf.

Between July 1977 and March 1988, 31 patients with an adenoidcystic carcinoma were treated with fast neutrons of a 14 MeV-DT-generator at our department. Primary locations were: parotid gland eight cases, paranasal sinus five cases, submandibular gland five cases, trachea four cases and other locations nine cases. The median follow-up of our patients was 16 months. Most of the patients had advanced tumors. The calculated local control rate is 65% at two years.

Adult↗
PubMed1977

Study on the biological effect of fast neutrons 1. Effect of fast neutrons on germinability of barley seeds and on the chlorophyll content of the seedlings according to the dose used.

Barley seeds were irradiated in the active zone of the reactor at 500 watt, at favourable flux of fast neutrons in the dose interval of 823--2144 rad. Seeds after irradiation were "cooled" for 48 hours, then germinated, and the length of shoots of the seven days old seedings was measured. The value of the half lethal dose is 1130 rad, estimated from the growth curve. There is a well-defined relation of chlorophyll content (calculated for fresh weight unit) to the dose used. It was concluded from the phenotype of the leaves that the decrease of chlorophyll content was due first of all to the presence of chlorophyll-less cells and cell lines and not to the decrease of chlorophyll content of the individual cells. Irradiation yielded genetically defected cells.

Chlorophyll↗
PubMed2005

Measurement and analysis of induced activities in concrete irradiated using high-energy neutrons at KENS Neutron Spallation Source Facility.

Precise estimation of induced activities in concrete shields for high-energy accelerator facilities is one of the most important issues that need to be solved, not only for the reduction of exposure for workers, but also for the reduction of radioactive wastes. Irradiation experiments have been performed by using the 500 MeV Neutron Spallation Source Facility in KEK. The large concrete assembly was placed in the direction of 0 degrees to the beamline. Two kinds of samples were placed at several positions in the assembly. The irradiation period was about 1 week and induced activities in the samples were measured until approximately 1.5 y after irradiation. From the comparison between the experiment and the available Monte Carlo calculation code system, good agreement was obtained for 24Na, 47Sc, 47Ca and 54Mn within a factor 2; however, large discrepancies were observed for some other nuclides.

Computer Simulation↗
PubMed1992

Neutron dosimetric quantities for several radioisotopic neutron sources.

The fluence-weighted and dose equivalent-weighted average energies, and the spectrum-averaged fluence-to-dose equivalent conversion factors have been calculated for 52 spectrum variations of 20 different radioisotopic neutron sources. An internally consistent method of determination enables comparison of values for different spectra. The methodology and results are presented.

Neutrons↗
PubMed2000

Prospects for gravitational-wave observations of neutron-star tidal disruption in neutron-star-black-hole binaries.

For an inspiraling neutron-star-black-hole (NS-BH) binary, we estimate the gravity-wave frequency f(td) at the onset of NS tidal disruption. We model the NS as a tidally distorted, homogeneous, Newtonian ellipsoid on a circular, equatorial geodesic around a Kerr BH. We find that f(td) depends strongly on the NS radius R, and estimate that LIGO-II (ca. 2006-2008) might measure R to 15% precision at 140 Mpc ( approximately 1 event/yr under current estimates). This suggests that LIGO-II might extract valuable information about the NS equation of state from tidal-disruption waves.

Astronomical Phenomena↗
PubMed1985

Life shortening in mice exposed to fission neutrons and gamma rays. IV. Further studies with fractionated neutron exposures.

When mice were exposed to a total dose of 240 rad of fission neutrons divided into two, four, or six fractions given at 1-week intervals, more life shortening was observed than was seen after a single exposure. Maximum life shortening was observed with four fractions, although the value for six fractions was not significantly lower. Much of the augmentation effect was attributable to an increase in early deaths during the first 200-300 days after exposure, although differences persisted throughout the lifetime of the animals. The changes in life shortening were associated with changes in the distribution of causes of death; however, decrementation of the populations for any given specific cause of death failed to eliminate completely the differences in mean aftersurvival time.

Animals↗
PubMed1982

[Computer-assisted irradiation planning for tumor therapy with fast neutrons at the Neutron Therapy Unit CIRCE in Essen].

A series of programs for the irradiation planning in tumor therapy with fast neutrons is presented. With these programs it is possible to calculate the dose distribution of single and multiple field as well as of uni- and biaxial rotating irradiations. The programs consider the patient's contour and calculate the total dose, the gamma dose and the gamma/total dose ratio. The output of the calculated dose distributions is made on a colour graph terminal. A hardcopy output by line printer is also possible.

Computers↗
PubMed1995

A novel approach to the microdosimetry of neutron capture therapy. Part I. High-resolution quantitative autoradiography applied to microdosimetry in neutron capture therapy.

A novel approach to the microdosimetry of neutron capture therapy has been developed using high-resolution quantitative autoradiography (HRQAR) and two-dimensional Monte Carlo simulation. This approach has been applied using actual cell morphology (nuclear and cytoplasmic cell structures) and the measured microdistribution of boron-10 in a transplanted murine brain tumor (GL261) containing p-boronophenylalanine (BPA) as the boron compound. The 2D Monte Carlo transport code for the alpha and 7Li charged particles from the 10B(n,alpha)7Li reactions has been developed as a surrogate to a full 3D approach to calculate a variety of different microdosimetric parameters. The HRQAR method and the surrogate 2D Monte Carlo approach are described in detail and examples of their use are presented.

Animals↗
PubMed2004

Determination of 4.438 MeV gamma-ray to neutron emission ratio from a (241)Am-(9)Be neutron source.

Gamma-ray (gamma-ray) spectra of a 1.49 x 10(11)Bq (241)Am-(9)Be source and background were measured using a 2 in x 2 in, NaI(Tl) detector. Backgrounds due to the neutron interactions and energy deposition were calculated with MCNP4C. By subtracting the backgrounds from the experimental spectra, the S(gamma) is obtained and the R=S(gamma)/S(n) was estimated. The final result of R=S(gamma)/S(n)=0.596 is in agreement with result reported in literature.

Journal Article↗
PubMed2005

Variation of the thermal neutron diffusion cooling properties of wet rock material (Monte Carlo simulations of the pulsed neutron experiments).

The water content in a rock material can significantly change the thermal neutron diffusion parameters with respect to those of the dry medium. The effect has been studied for dolomite, CaMg(CO3)2, by Monte Carlo simulations of the variable buckling experiments for 10 series of samples. The density-removed diffusion cooling coefficient C(M) varies hyperbolically by two orders of magnitude with water content in the range of 0-20%.

Journal Article↗
PubMed2001

A new approach for the synthesis of isonitrile carborane derivatives. Ligands for metal based boron neutron capture therapy (BNCT) and boron neutron capture synovectomy (BNCS) agents.

A new approach for the synthesis of carborane isonitrile derivatives was developed. This approach involved the dehydration of both boron and carbon derived formamides using the Burgess reagent. The products, some of which were characterized by X-ray crystallography, can now be used as ligands for the synthesis of transition metal based boron neutron capture therapy and synovectomy agents and targeted radiopharmaceuticals.

Journal Article↗
PubMed2002

Characterization of neutron flux spectra in irradiation sites of MNSR reactor using the Westcott-formalism for the k0 neutron activation analysis method.

For the general applicability of the k0-NAA method to deal with "non-l/v" (n,gamma) reaction nuclides, the modified spectral index r(alpha) square root (Tn/T0) and g(Tn) factor for monitoring neutron temperature Tn for the inner and outer irradiation sites of the Ghana MNSR reactor (GHARR-1) were measured using the Cd-ratio method. Using the measured Cd ratio for lutetium and the modified spectral index, the reduced resonance integral of lutetium s0,Lu was also calculated. The computed result of 1.64 was in good agreement with the reported value of 1.67. Based on the assumption that the definitions of reaction rates in the Westcott-formalism and in Nisle's unified formulation are equal, a theoretical verification of the accuracy of the measured modified spectral indices for our data and those reported in the literature for other research reactors was carried out. Employing 197Au, 96Zr and 94Zr as "1/v" monitors, the theoretical values which depend on the choice of the monitor, followed the trend for measured values of the sub- to epi-cadmium flux ratio f for nine irradiation sites of four different research reactors. The computed and experimental modified spectral indices for the different flux ratios associated with irradiation sites within the range 18.8-152 fitted well to a simple exponential relationship. Calculated and measured data are in good agreement when appropriate correction factors are used.

Journal Article↗
PubMed2000

Rearrangement of the Fermi Surface of Dense Neutron Matter and the Direct Urca Cooling of Neutron Stars.

It is proposed that a rearrangement of single-particle degrees of freedom may occur in a portion of the quantum-fluid interior of a neutron star. Such a rearrangement is associated with the pronounced softening of the spin-isospin collective mode which, under increasing density, leads to pion condensation. Arguments and estimates based on fundamental relations of many-body theory show that one realization of this phenomenon could produce very rapid cooling of the star via a direct nucleon Urca process displaying a T5 dependence on temperature.

Journal Article↗
PubMed1999

Neutron reflectivity studies of critical adsorption: the correspondence between a critical adsorption profile and specular neutron reflection.

For interfacial order parameter profiles which decay as Az(-mu), such as the composition profile of the noncritical interface of a binary liquid mixture at a critical end point, there is a reported one-to-one correspondence between the profile and the reflectivity which can be described by an analytical theory [S. Dietrich and R. Schack, Phys. Rev. Lett. 58, 140 (1987)]. Evidence for mu=0.53+/-0.02 for adsorption at the hydrophilic silicon/liquid surface of the mixture (2-butoxyethanol+deuterium oxide) near its lower critical end point, determined from neutron reflectivity measurements, is presented. This value is in good agreement with the theoretical prediction of mu=0.516+/-0.004. Further examination of the data permits the determination of the asymptotic surface enrichment scaling factor amplitude P0 approximately 0.11, which is not in agreement with the theoretical value P(0) = 0.94+/-0.05 and values determined by other experimental methods.

Journal Article↗
PubMed2006

How low-energy weak reactions can constrain three-nucleon forces and the neutron-neutron scattering length.

We show that chiral symmetry and gauge invariance enforce relations between the short-distance physics that occurs in a number of electroweak and pionic reactions on light nuclei. Within chiral perturbation theory, this is manifested via the appearance of the same axial isovector two-body contact term in pi(-)d --> nngamma, p-wave pion production in NN collisions, tritium beta decay, pp fusion, nud scattering, and the hep reaction. Using a Gamow-Teller matrix element obtained from calculations of pp fusion as input, we compute the neutron spectrum obtained in pi(-)d --> nngamma. With the short-distance physics in this process controlled from pp --> de(=)nu(e), the theoretical uncertainty in the nn scattering length extracted from pi(-)d --> nngamma is reduced by a factor larger than 3, to approximately < or = 0.05 fm.

Journal Article↗