Yield Of Photoneutrons Research Articles

Characteristics of the photoneutron contamination present in a high-energy radiotherapy treatment room

The photoneutron contamination arising from a high-energy medical lineal accelerator is calculated using Monte Carlo simulation, as a function of the radiation field size. The information is used to model the neutron propagation in a radiotherapy treatment room and the transmission across concrete mazes. The Monte Carlo code MCNP4C is used to model the main components of a medical lineal accelerator. Simulations were performed to calculate the photoneutron yields and spectra as a function of the radiation field size. The yield of contaminant photoneutrons is observed to increase with the size of the radiation beam, but the energy spectra remain the same, suggesting that the contamination arises from above the movable collimator. The transport of the photoneutrons across a treatment room corroborates the validity of empirical models, but the transmission across a concrete maze produces a dose-equivalent tenth-value layer that differs from previous data.

Photoneutron source based on a compact 10 MeV betatron

Accelerator-based photoneutron sources have enjoyed wide use and offer the advantages of long term stability, ease of control and absence of radioactive materials. We report here measurements of the yield of photoneutrons from a neutron generator using a compact betatron. Electrons were accelerated to energies up to 10 MeV and produced a bremsstrahlung beam with a dose rate of 0.16 Gy/min (at 10 MeV, 1 m from the bremsstrahlung target) to irradiate LiD, Be, depleted U, and Pb neutron-producing targets. The angular distributions of photoneutrons produced by bremsstrahlung beams were measured with a “long” counter and integrated to determine neutron yield. In addition, neutron time of flight spectra were recorded from all targets using a 15.5 m flight path perpendicular to the photon beam. The maximum observed yields were 4.6×10 7 n/s obtained with 1 kg of LiD, 5.7×10 7 n/s from a 3.3 kg Be block, 6.2×10 6 n/s from 1.5 kg of depleted U, and 7.0×10 6 n/s from 10.7 kg of Pb. Optimization of target dimensions, shape, and positioning is expected to increase the yield from the LiD target by a factor of 35, while optimization of the other targets is expected to yield at most a factor of 10. With the increased yield and a deuteride target, this compact betatron-based system could find application in the interrogation of waste containers for fissile material.

Photoneutron production in tissue during high energy bremsstrahlung radiotherapy

The total yield of photoneutrons from soft-tissue-equivalent material irradiated with bremsstrahlung of end-point energy from 6 to 28 MeV has been measured. The results are compared with calculations based on the cross sections for neutron production of the constituent elements of tissue (H,C,N and O). It is shown that the less common isotopes of the constituent elements (2H, 13C, 15N, 17O, 18O) must be included to obtain agreement with the measured yields. The dose imparted to tissue by the photoneutrons is calculated for the energy range from 6 to 30 MeV and is compared with other available estimates. Further, the dose equivalent due to all photonuclear reactions in tissue is estimated for energies of 24 and 30 MeV.

Photoneutron Production and Dosimetry in Tissue During High Energy Bremsstrahlung Radiotherapy

Abstract The total yield of photoneutrons from soft-tissue-equivalent material irradiated with bremsstrahlung of end point energy from 6 MeV to 28 MeV has been measured using the 35 MeV University of Melbourne Betatron and a 4p Halpern type neutron detector. The results are compared with calculations based on the cross sections for neutron production of the constituent elements of tissue (H, C, N and O). It is shown that the less common isotopes of the constituent elements (2H, 13C, 15N, 17O, 18O) must be included to obtain agreement with the measured yields. The dose imparted to tissue by the photoneutrons is estimated for the energy range from 6 MeV to 30 MeV and compared with other available measurements/estimations. Further, the dose equivalent due to all photonuclear reactions in tissue is estimated for energies of 24 MeV and 30 MeV.

Galculation of the neutron yield from thick targets bombarded by electrons with energies up to 500 MeV

A procedure was proposed for mathematical modeling of the yield of photoneutrons from thick targets, prepared from different materials, for a wide range of energies of the primary electrons. The method was tested on experimental data.

The yield of resonance neutrons from a thick copper target bombarded by electrons with energies up to 100 GeV

The yield of low-energy neutrons at 90° from a copper target bombarded by high-energy electrons varies from 0.015 GeV −1·sr −1 at 20 GeV to 0.035 GeV −1·sr −1 at 100 GeV. This yield is higher than would be expected from calculations based on the yield of giant resonance photo-neutrons alone. It is also shown that simple estimates of the yield from high-energy photon spallation interactions are unable to account for the measured values or their apparent dependence on energy. The measured yields are not incompatible with the approximate value of 0.33 GeV −1 recommended for use in shielding assessment at high-energy electron accelerators.

Yield and angular distributions of photoneutrons from thick lead targets

Yield and angular distributions of photoneutrons from thick lead targets

An Estimate of the Yield of Photoneutrons from Beryllium Using a LINAC as the X-Ray Source

A procedure is described for calculating approximate photoneutron yields from thick beryllium targets exposed to the x radiation produced in thick tungsten targets bombarded with 2- ..-->.. 8-MeV electrons. It is based on empirical relations developed for predicting the average thick tungsten target radiation yield and the average beryllium photoneutron cross section for the selected incident electron energy.

Bremsstrahlung and Photoneutrons from Thick Tungsten and Tantalum Targets

Monte Carlo calculations have been made of electron-photon cascades in thick tungsten targets bombarded by electrons with energies up to 60 MeV. The following information has been obtained: (1) the bremsstrahlung efficiency, (2) the angular distribution of the emitted bremsstrahlung intensity, (3) the spectra of the bremsstrahlung emitted in various directions, (4) the transmission of primary and secondary electrons through the target, (5) energy deposition as function of the depth in the target, (6) the differential photon track length distribution inside the target, and (7) the yield of photoneutrons. The paper also includes various comparisons with experimental data.

Fast neutron spectroscopy using the yale electron linac and a new nanosecond time-of-flight system

The Yale electron linac has been modified to provide pulses ⪝ 10 ns wide and ⪞ 1.5 A peak current. The useful range of electron energy is from 10 to 70 MeV. A time-to-time converter and synchronized oscillator provide a flexible timing system with channel widths between 2 and 10 ns. An overall resolution of 0.2 ns/m is achieved. The favorable ratio of signal-to-background observed for the system permits investigations of a wide range of fast neutron experiments previously the prerogative of Van de Graaff accelerators. The differential elastic scattering of neutrons from the 12C(n,n) 12C reaction has been measured with high resolution at several angles for energies between 1 and 10 MeV. As a further example, polarization effects in the yield of photoneutrons from the giant dipole resonance region of the 16O(γ,n) 15O reaction have been studied by left-right scattering from a 12C analyser.

Fast neutron spectroscopy using the yale electron linac and a new nanosecond time-of-flight system

The Yale electron linac has been modified to provide pulses ⪷10 ns wide and ⪸1.5 A peak current. The useful range of electron energy is from 10 to 70 MeV. A time-to-time converter and synchronized oscillator provide a flexible timing system with channel widths between 2 and 10 ns. An overall resolution of 0.2 ns/m is achieved. The favorable ratio of signal-to-background observed for the system permits investigations of a wide range of fast neutron experiments previously the prerogative of Van de Graaff accelerators. The differential elastic scattering of neutrons from the 12C(n,n) 12C reaction has been measured with high resolution at several angles for energies between 1 and 10 MeV. As a further example, polarization effects in the yield of photoneutrons from the giant dipole resonance region of the 16 O(γ, n) 15 O reaction have been studied by left-right scattering from a 12C analyser.

Direct Observation of the Optical Anisotropy of the Holmium Nucleus

The optical anisotropy of the holmium nucleus in the giant-resonance energy region has been shown to exist by measuring the yield of photoneutrons as a function of the orientation of the nucleus with respect to a bremsstrahlung beam direction. The nuclei were aligned by the Bleaney method using a continuously operating ${\mathrm{He}}^{3}$ refrigerator to cool a single crystal of holmium ethyl sulfate to 0.29\ifmmode^\circ\else\textdegree\fi{}K. The orientation effects observed could be explained if the absorption cross section for holmium was made up primarily of a component given by the dynamic collective theory, but also included a small scalar component (about 15% of the total) which had no orientation effects associated with it. In fitting the data, a reanalysis of previous data on the holmium absorption cross section was made.

Calculating the yield of photoneutrons from mixtures of SiO2 with small amounts of beryllium, water, lithium, carbon, uranium, and thorium

The Belen'kii-Tamm avalanche theory is used to calculate curves for the yield of photoneutrons from mixtures of sand with beryllium, water, lithium, carbon, uranium, and thorium. The paper discusses the possibilities of using the photoneutron method to determine the lithium, uranium, and thorium content of rocks.

Structure of Giant Resonance in Al27(γ, n) Reaction

The Al/sup 27/( gamma ,n) cross section was measured up to 24 Mev with good energy resolution. Using a 25 Mev betatron, the yield of photoneutrons from Al/sup 27/ was determined for bremsstrahlung with peak energies ranging from 12.5 to 24 Mev in steps of 0.25 and 0.1 Mev. Neutrons were detected with eight B/sup 10/ enriched BF/sub 4/ counters in parrafin. (W.D.M.)

Calculation of yield of photoneutrons from some substances bombarded by a monochromatic beam of electrons using the belen'kiitamm equilibrium spectrum

Calculation of yield of photoneutrons from some substances bombarded by a monochromatic beam of electrons using the belen'kiitamm equilibrium spectrum

On surface direct photoneutrons

Experimental results on the energy spectra of photoneutrons from Ca/sup 40/ and Rh/sup 103/ targets, irradiated with bremsstrahlung protons of 30 Mev max energy, show an unusually high yield of photoneutrons at 3.5 and 4 to 7 Mev, respectively. These results were studied in terms of El single particle transitions by taking into account off-resonance effects neglected in Wilkinson's theory. Surface effects in energy spectra of photoneutrons from Ca/sup 40/, Cr/ sup 52/ and Rh/sup 103/ were calculated by assuming j-j coupling for the initial shell model nuclear state and considering transitions from the last filled neutron shell only. The theoretical points fit reasonably well with the experimental results. (C.J.G.)

Yield and Angular Distribution of Fast Photoneutrons from Deuterium and Carbon

The yield and angular distribution of fast photoneutrons (with energies >20.6 Mev) from carbon and deuterium nuclei have been investigated at the 265-Mev synchrotron of the P. N. Lebedev Physical Institute (Academy of Sciences, Moscow). The experimental results obtained at photon energies below as well as above the threshold for meson production are discussed from the viewpoint of the two-nucleon model.

Yield of Photoneutrons from U235 Fission Products in Beryllium and Deuterium

The yield of photoneutrons from a sample of U235 fission products at the center of a 9-in. diameter Be sphere was measured. Samples of U235 were exposed to neutrons in the reactor for periods of 15 min, 6 hr, and 74 hr. The photoneutrons created by the fission product gamma rays acting upon the Be nuclei were observed from 0.3 sec to about 4 weeks after the end of the exposure. Curves showing the photoneutron yield as a function of time, relative to the delayed neutron yield, are given for these exposure and observation times. The attempt was made to account for the observed yields from Be in this experiment, and the yield from D2O observed in an earlier experiment, in terms of known fission product gamma emitters.

Photoneutrons from U233 and Pu239 Fission Products in Heavy Water

The yield of photoneutrons from U235, U233, and Pu239 fission products in heavy water were compared. The number of photoneutrons per delayed neutron was found to be approximately the same for all three, in spite of the previously known large variations in the relative numbers of delayed neutrons from these isotopes.