Energy Neutrons Research Articles

Energy dispersive X-ray fluorescence and neutron activation analysis of surficial sediments of the Sea of Marmara and the Black Sea around Istanbul

Surficial sediment samples, collected from 27 sampling sites of the Sea of Marmara and the Black Sea nearby Istanbul area in 1996 and 1999 years, were analyzed quantitatively for some heavy metals and some other elements by using radioisotope excited energy dispersive X-ray fluorescence (EDXRF). The U and Th concentrations of the samples were determined by instrumental neutron activation (INAA). The results were compared with those from other contaminated and uncontaminated sedimentary materials. It is found that some elemental concentrations of the Sea of Marmara and the Black Sea sediments are comparable with those in most other sea sediments in the vicinity of densely populated regions.

Oxygen Vacancies in Perovskite and Related Structures: Implications for the Lower Mantle

AbstractThe oxygen vacancy ordering process and displacive transitions have been characterised in the system CaTiO3-CaFeO2.5 as a function of composition and temperature at atmospheric pressure using X-ray diffraction, Mössbauer spectroscopy, infrared spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, neutron diffraction and electrical conductivity methods. With increasing concentration of vacancies the following sequence is observed: isolated defects → short defect chains → infinite chains in layers. Similar experiments at high pressures and temperatures have been conducted to determine the nature of oxygen vacancies in the lower mantle phases (Mg,Fe)(Si,Al)O3-σ and Ca(Si,Fe)O3-σ perovskite.

Neutronic calculations for a final focus system

For heavy-ion fusion and for “liquid-protected” reactor designs such as HYLIFE-II (Moir et al., Fusion Technol. 25 (1994); HYLIFE-II-Progress Report, UCID-21816, 4-82-100), a mixture of molten salts made of F 10, Li 6, Li 7, Be 9 called flibe allows highly compact target chambers. Smaller chambers will have lower costs and will allow the final-focus magnets to be closer to the target with decreased size of the focus spot and of the driver, as well as drastically reduced costs of IFE electricity. Consequently the superconducting coils of the magnets closer to the chamber will suffer higher radiation damage though they can stand only a certain amount of energy deposited before quenching. The scope of our calculations is essentially the total energy deposited on the magnetic lens system by fusion neutrons and induced γ-rays. Such a study is important for the design of the final focus system itself from the neutronic point of view and indicates some guidelines for a design with six magnets in the beam line. The entire chamber consists of 192 beam lines to provide access of heavy ions that will implode the pellet. A 3-D transport calculation of the radiation penetrating through ducts that takes into account the complexity of the system, requires Monte Carlo methods. The development of efficient and precise models for geometric representation and nuclear analysis is necessary. The parameters are optimized thanks to an accurate analysis of six geometrical models that are developed starting from the simplest. Different configurations are examined employing TART 98 (D.E. Cullen, Lawrence Livermore National Laboratory, UCRL-ID-126455, Rev. 1, November, 1997) and MCNP 4B (Briesmeister (Ed.), Version 4B, La-12625-m, March 1997, Los Alamos National Laboratory): two Monte Carlo codes for neutrons and photons. The quantities analyzed include: energy deposited by neutrons and gamma photons, values of the total fluence integrated on the whole energy range, neutron fluence spectrum, total path length of neutrons in energy, neutron mean free path versus energy. The results of the two codes turned out to be in good agreement with each other for different zones and configurations of the system. The source restriction technique gives reliable results as it is proved comparing re-normalized results with results obtained with a 4π source and with sources emitting with different set of solid angles. For this reason, this technique is used in all the six models avoiding other variance reduction techniques. Finally, solutions are suggested for optimizing the system from the neutronic point of view, with respect to both relative position of the magnets and choice of shielding materials.

Possible explanation of the difference in nuclear fission induced by the intermediate energy protons and neutrons

A possible explanation is given of the experimentally observed differences between the the fission cross-sections in the reactions induced by the intermediate energy (hundreds MeV) neutrons and protons.

Overview of Fluence to Dose Conversion Coefficients for High Energy Radiations

In and around high energy accelerator facilities, high energy radiation dose estimation is important to the radiological protection of workers. The contribution of high energy protons and neutrons to the radiation exposure of astronauts can not also be disregarded inside a spacecraft. Effective doses are adequate radiological quantities to evaluate radiation risks of individuals, exposed to radiation not only of low and intermediate energy but also of high energy. The conversion coefficients of fluence to effective doses have not been specified for all kinds of radiation in any publications of ICRP or ICRU, except the data up to 180 MeV of neutron in the ICRP74.This report provides an overview of calculational methodologies and estimated results of dose conversion coefficient of effective doses for high energy radiation such as photon, neutron, proton, alpha particle, electron, muon and pion in five groups: USA group (LAHET code), German group (LAHET), Japanese group (HERMES), Italian group (FLUKA) and Russian group (HADRON). This overview also summarized the calculational conditions and data such as computer codes, data libraries, mathematical phantoms and energy range of each particle for estimating dose conversion coefficient for each particle. Comparison of effective dose conversion coefficients of neutron, photon and proton in five groups were performed up to 10 GeV. These results will be helpful to establish an authoritative dose equivalent conversion coefficient for high energy radiation up to 10 GeV.

Measurements of low-energy (d,n) reactions for BNCT. Boron Neutron Capture Therapy.

Neutron yields and energy spectra have been measured for various deuteron-induced reactions at low energy. Neutrons of energy > 100 keV emitted in the 9Be(d,n)10B, 12C(d,n)13N, and 13C(d,n)14N reactions at Ed= 1.5 MeV were detected at five angles by means of liquid scintillator detectors. While low-energy neutrons were observed in all studied reactions, only 13C(d,n)14N is characterized by a relatively large yield with spectral features potentially interesting for an accelerator-based neutron source for BNCT.

Neutron carcinogenesis: past, present, and future.

An interest in the possible cancer causing ability of neutrons began soon after their discovery. Early use of neutrons from radioactive sources and from cyclotrons led to a need to define risk for such exposures. This need was soon followed by a more tangible need to define risk to the general population of high LET radiation from nuclear fall out and use of the Atomic bomb and possible use of the H-bomb. Neutrons were soon found to be very effective cell killing agents compared to conventional ionizing radiation. However High LET radiation sources and neutrons in particular, come in many different energies and from many types of sources. I will survey the differences between different energy neutrons and conventional types of radiation, particularly with respect to the dose rate of exposures and the influence of repair or lack thereof and more recently the effect of cell cycle distribution on the carcinogenic outcome. I will illustrate these ideas with examples of carcinogenicity studies and mutation studies from my own laboratory and in some cases from the work of others. Lastly I will introduce some possible avenues for molecular studies of neutron effects that might answer such vexing questions as the real risk at very low doses, is repair error free or error prone, do neutrons cause genetic instability for many cell generations after exposure, and others? There remain many questions about the biology of neutron action that require answers if we are to protect the ever increasing number of people exposed to them because of their growing use in medicine, in the military and in commercial industry.

Radioisotope X-ray fluorescence and neutron activation analyses of the trace element concentrations of the rainbow trout

The muscles and livers of the ten rainbow trouts (Oncorhynchus mykiss; N, 1752) obtained from Sapanca, Aquaculture Facility of Aquatic Products Faculty, The University of Istanbul (Turkey), have been analysed quantitatively for some minor elements using the radioisotope energy dispersive X-ray fluorescence (EDXRF) and neutron activation analysis (NAA) methods. It was found that samples contain Na, K, Ca, Sc, Cs, Fe, Co, Cu, Zn, Se, Br, Rb, Sr, Au, La and Ce in different amounts. Comparison of the results with those of reference river fish samples indicated that agricultural rainbow trout samples from Sapanca region have higher Fe level.

The Relationship Between Growth Hormone Kinetics and Sarcopenia in Postmenopausal Women

Sarcopenia, the decline in body cell mass (BCM) and especially in muscle mass with age, is an important age-related cause of frailty and loss of independence in the elderly. Because the decline in BCM with age parallels a decline in GH secretion from young adulthood to old age, loss of GH secretion has been considered an important contributory cause of sarcopenia in the elderly. To test this hypothesis in a group of healthy postmenopausal women (n = 15; mean +/- SD age, 66.9 +/- 7.8 yr), 24-h GH concentrations and secretory kinetics were correlated with BCM (measured by whole body counting of 40K) and percent body fat (measured by dual energy x-ray absorptiometry or neutron inelastic scattering). Serum leptin levels were determined as a measure of adipocyte mass. Contrary to prediction, GH secretion was lower in women with higher BCM (r = 0.50; P < 0.05), whereas their mean fat mass was higher (r = 0.51, P < 0.05). These data indicate that sarcopenia in postmenopausal women is not associated with reduced GH secretion and is inversely correlated with fat mass. Serum leptin levels were inversely associated with GH secretion (r = -0.67; P < 0.006). Although a causal relationship has not been demonstrated, these data suggest that leptin could modulate GH secretion through its action on the aging hypothalamic-pituitary axis, or that GH regulates leptin secretion.

The relationship between growth hormone kinetics and sarcopenia in postmenopausal women: the role of fat mass and leptin.

Sarcopenia, the decline in body cell mass (BCM) and especially in muscle mass with age, is an important age-related cause of frailty and loss of independence in the elderly. Because the decline in BCM with age parallels a decline in GH secretion from young adulthood to old age, loss of GH secretion has been considered an important contributory cause of sarcopenia in the elderly. To test this hypothesis in a group of healthy postmenopausal women (n = 15; mean +/- SD age, 66.9 +/- 7.8 yr), 24-h GH concentrations and secretory kinetics were correlated with BCM (measured by whole body counting of 40K) and percent body fat (measured by dual energy x-ray absorptiometry or neutron inelastic scattering). Serum leptin levels were determined as a measure of adipocyte mass. Contrary to prediction, GH secretion was lower in women with higher BCM (r = 0.50; P < 0.05), whereas their mean fat mass was higher (r = 0.51, P < 0.05). These data indicate that sarcopenia in postmenopausal women is not associated with reduced GH secretion and is inversely correlated with fat mass. Serum leptin levels were inversely associated with GH secretion (r = -0.67; P < 0.006). Although a causal relationship has not been demonstrated, these data suggest that leptin could modulate GH secretion through its action on the aging hypothalamic-pituitary axis, or that GH regulates leptin secretion.

Total cross section measurements with cold neutrons on solid and powder samples and on hydrogen containing compounds

Abstract Transmission measurements with cold neutrons of mean energy of 0.57 meV on solid and powder samples were performed to deduce the inelastic scattering cross sections σinel and the absorption cross sections σγ for 43 chemical elements and 27 of their isotopes. The Debye-temperature ΘD could be deduced from measurements. From similar experiments on water, alcohole and carbon hydrogen compounds the proton scattering cross section for cold neutrons was determined.

Nonlinearity of pulse height of recoil helium in /sup 3/He proportional counters

The pulse height distribution in /sup 3/He proportional counters has been investigated to accurately quantify the response function to be used in fast neutron spectroscopy. The measurements were performed as a function of the operating voltage, the counting gas mixture, and the incident neutron energy. The special emphasis of this study has been put on the nonlinearity of the pulse height of a recoil helium induced by the /sup 3/He(n,n)/sup 3/He reaction. A distinct deviation of 14% at maximum to lower energies was found in the position of the recoil edge with the energy axis calibrated by the full energy peaks of the /sup 3/He(n,p)T reaction produced with neutrons of thermal energy and 2.413 MeV. It was confirmed that the nonlinear effects, such as an initial recombination and a space-charge effect, take place more significantly in the energy loss process of a recoil helium because of its higher linear energy transfer (LET) in the filling gas compared to that of a proton and triton pair emitted from the /sup 3/He(n,p)T reaction. The deviation becomes larger with an increase of the average LET in the gas mixture. The experimental results suggested that the nonlinear effect caused by a higher LET recoil helium is inevitable for the filling gas, even if the operating voltage is changed to an acceptable range.

Boron neutron capture therapy of brain tumors: past history, current status, and future potential.

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when boron-10 is irradiated with low-energy thermal neutrons to yield alpha particles and recoiling lithium-7 nuclei. High-grade astrocytomas, glioblastoma multiforme, and metastatic brain tumors constitute a major group of neoplasms for which there is no effective treatment. There is growing interest in using BNCT in combination with surgery to treat patients with primary, and possibly metastatic brain tumors. For BNCT to be successful, a large number of 10B atoms must be localized on or preferably within neoplastic cells, and a sufficient number of thermal neutrons must reach and be absorbed by the 10B atoms to sustain a lethal 10B(n, alpha)7 Li reaction. Two major questions will be addressed in this review. First, how can a large number of 10B atoms be delivered selectively to cancer cells? Second, how can a high fluence of neutrons be delivered to the tumor? Two boron compounds currently are being used clinically, sodium borocaptate (BSH) and boronophenylalanine (BPA), and a number of new delivery agents are under investigation, including boronated porphyrins, nucleosides, amino acids, polyamines, monoclonal and bispecific antibodies, liposomes, and epidermal growth factor. These will be discussed, and potential problems associated with their use as boron delivery agents will be considered. Nuclear reactors, currently, are the only source of neutrons for BNCT, and the fission process within the core produces a mixture of lower-energy thermal and epithermal neutrons, fast or high (> 10,000 eV) energy neutrons, and gamma rays. Although thermal neutron beams have been used clinically in Japan to treat patients with brain tumors and cutaneous melanomas, epithermal neutron beams should be more useful because of their superior tissue-penetrating properties. Beam sources and characteristics will be discussed in the context of current and future BNCT trials. Finally, the past and present clinical trials on BNCT for brain tumors will be reviewed and the future potential of BNCT will be assessed.

Study of the efficiency and time resolution of an RPC irradiated with photons and neutrons

We present recent results on the efficiency and time resolution of an RPC operated with low gas gain under intense irradiation of photons and neutrons. These results are compared with previous measurements obtained using both high and low gain RPC. Results on the RPC sensitivity to photons and neutrons of energy around 1 MeV are also reported.

Test of a resistive plate chamber under irradiation of photons and neutrons

A resistive plate chamber operated at low gas amplification has been exposed to photon and neutron sources to study the detection efficiency and the time response in conditions close to those expected in experiments at the Large Hadron Collider. Results on the sensitivity to photons and neutrons of energy around 1 MeV are presented.

Confocal microscopy in the analysis of the etched nuclear particle tracks in polymers

SummaryThe possibility of the morphometric analysis of etched tracks, induced by protons and alpha particles in the organic polymer allyl diglycol carbonate (CR‐39), using the confocal scanning laser microscope (CSLM), was studied. The detectors were investigated in two groups of irradiation experiments, namely: (a) irradiated with mono‐energetic neutrons of energy 1–2 MeV, (b) exposed to the alpha radiation from 222Rn and its progeny. Both groups were irradiated at normal incidence. Radiation‐induced latent tracks were electrochemically etched, and their morphometric parameters were investigated in the reflection mode by using the 488‐nm spectral line of an argon ion laser. A constant number of up to 200 optical sections in Z‐scan mode was taken through each selected etched track at vertical spacings of 0·642 μm. Successive reconstructions of Z‐sections were used to determine the following parameters: the mean radius of the opening channel, the maximum diameter and the length of the track, and the angle of the track wall to the surface of the sample. The results show that tracks produced by alpha particles differ from those induced by protons. The radius of the opening channel of alpha‐particle‐induced tracks ranges from 7·9 to 11 μm, whereas for protons the same parameter ranges between 2·0 and 3·8 μm for a specific electrochemical etch procedure.

Kerma Associated with High Energy Neutrons

Abstract The kerma for monoenergetic neutrons of nominal energies 27, 42 and 63 MeV was measured with commercial tissue-equivalent and carbon proportional counters. By operating the detectors in helix mode and exposing them to pulsed beams of quasi-monoenergetic neutrons, time-of-flight (TOF) techniques enabled the unambiguous identification of pulse height events associated with the neutron energies of interest. The microdosimetric spectra so obtained were used to derive gas-to-wall dose conversion factors for the TE gas filled carbon proportional counter. Subsequently the kerma ratios for carbon to A-150 plastic at the three nominal neutron energies were determined with the monoenergetic data. The results concur with other published data using different techniques.

Measurement of Neutron Activation Cross Sections for Energies up to 40MeV for Natural Samples of Mg, Si, Ca, V, Cr, Cu and Zn.

The cross section measurements of 17 neutron induced reactions using an intense semi-monoenergetic neutron field were recently reported. Neutrons for energies up to 40 MeV were produced by a simple Be target system bombarded by protons of 9 different energies between 20 and 40 MeV. Successively in this neutron field, we measured the cross sections of 15 reactions of natMg(n, Xnp) 24Na, natSi(n, Xn2p) 27Mg, natSi(n, Xnp) 28Al, natSi(n, Xnp) 29Al, natCa(n, Xnp) 42K, natCa(n, Xnp) 43K, nat (n, Xn2p) 46Sc, natV(n, Xn2p) 47Sc, natCr(n, Xnp,) V52V, natCr(n, Xnp) 53V, natCu(n, Xn2p) 62mCo (T 1/2=14 min), natZn(n, Xn2p) 65Ni, natZn(n, Xnp)Cu,64Cu, natZn(n, Xnp)Cu,66Cu and natZn(n, Xnp) 68mCu ( T,1/2=3.8 min) by irradiating natural samples of Mg, Si, Ca, V, Cr, Cu and Zn. The excitation functions of these reactions were obtained by using the least- squares fitting (LSF) of the cross-section values calculated with the ALICE/LIVERMORE82 code, and also by using the SAND-II and the NEUPAC unfolding codes with the init...

Measurement of Neutron Activation Cross Sections for Energies up to 40 MeV for Natural Samples of Mg, Si, Ca, V, Cr, Cu and Zn

The cross section measurements of 17 neutron induced reactions using an intense semi-monoenergetic neutron field were recently reported. Neutrons for energies up to 40 MeV were produced by a simple Be target system bombarded by protons of 9 different energies between 20 and 40 MeV. Successively in this neutron field, we measured the cross sections of 15 reactions of natMg(n, Xnp) 24Na, natSi(n, Xn2p) 27Mg, natSi(n, Xnp) 28Al, natSi(n, Xnp) 29Al, natCa(n, Xnp) 42K, natCa(n, Xnp) 43K, nat (n, Xn2p) 46Sc, natV(n, Xn2p) 47Sc, natCr(n, Xnp,) V52V, natCr(n, Xnp) 53V, natCu(n, Xn2p) 62mCo (T 1/2=14 min), natZn(n, Xn2p) 65Ni, natZn(n, Xnp)Cu,64Cu, natZn(n, Xnp)Cu,66Cu and natZn(n, Xnp) 68mCu ( T,1/2=3.8 min) by irradiating natural samples of Mg, Si, Ca, V, Cr, Cu and Zn. The excitation functions of these reactions were obtained by using the least- squares fitting (LSF) of the cross-section values calculated with the ALICE/LIVERMORE82 code, and also by using the SAND-II and the NEUPAC unfolding codes with the initial guess values derived from the LSF results and empirical reference data.

Fast neutron damage of silicon PIN photodiodes

A Hamamatsu Photonics photodiode S1723 was tested with respect to the fast neutron radiation. The device was irradiated with neutrons of energies in the range of 0.5 to 12 MeV from a Po-Be source. The irradiation was performed in several steps starting from the relatively low fluence of 2.5×1010 n cm−2. The following characteristics were measured: leakage current vs bias voltage, capacitance vs bias voltage and vs frequency, noise vs time constant of a quasi-Gaussian shaper and spectral density of noise. Significant changes of the leakage current and of the noise were observed at the fluence of neutrons as low as 2.5 × 1010 n cm−2.