Exclusive Measurement of Quasifree Proton-Neutron Bremsstrahlung
M. VolkertsJ. C. S. BacelarM. J. van GoethemM.N. HarakehM. HoefmanH. HuismanN. Kalantar‐NayestanakiS. KopeckyH. LöhnerJ. G. MesschendorpK. NakayamaR. W. OstendorfS. SchadmandO. SchöltenH. W. Wilschut
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Abstract:
Data on proton-neutron bremsstrahlung have been obtained from a measurement of the quasifree breakup channel in proton-deuteron bremsstrahlung. This high-precision measurement, with an incident proton energy of 190 MeV, is fully exclusive; i.e., the protons, the neutron, and the photon have been detected. The quasifree differential cross sections obtained are compared with microscopic calculations and calculations based on soft-photon models. There are sizable differences between the models and also between the models and the data obtained for this simple process.Keywords:
Photon energy
It has been considered to be difficult to calculate the energy quantity, which is transfered to photons composing materials from incident photons, by means of present absorption coefficients. The ratio of transfered energy to photons composing water layer from incident photons (effective energy absorption ratio) was calculated theoretically. Consequently, the ratio of total exit energy to total incident energy as a function of thickness of layer was represented a sigmoid curve on semilogarithmic scale, and was saturated to the value of energy emerged from the layer by back scattered photons. It can be able to calculate the effective energy absorption ratio for given photon energy and for given thickness of layer by following equation, which is a function of photon energy and "effective energy absorption ratio coefficients" (k, n), obtained from the graphs. (effective energy absorption ratio) =1-k×E^n (E : primary photon energy [keV])
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The effects of target thickness on the shape of the bremsstrahlung energy spectrum in Pb for 89Sr beta particles are studied in the photon energy region of 1–100 keV. The thicknesses of the Pb targets chosen for present study are 53, 223, 552, 677, 908 and 1352 mg/cm2. The bremsstrahlung energy spectrum, only at target thickness of 677 mg/cm2 is found to be closer to the Avdonina and Pratt (1999) theory for total bremsstrahlung with the variation of +3%, −2%, +2%, −13%, −39% and 69% at 1, 4, 10, 30, 60 and 100 keV, respectively. The polarization bremsstrahlung is limited up to a particular target thickness at low-energy region, suppressing the bremsstrahlung at high-energy region.
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Energy spectrum
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Transmission data for 4‐MV bremsstrahlung beams have been measured with a combination of lead and aluminum attenuators. From these data, the original energy spectra have been reconstructed using an iterative least‐squares technique, previously evaluated by simulation studies. The spectra on the central axis for three similar 4‐MV linear accelerators indicated no significant differences. When studying the spectra at 5° and 9° off the central axis, that at 9° showed the expected increase of low‐energy photons. All these spectra showed a maximum photon energy of 4.5±0.2 MeV. When the magnetron power was reduced, the spectrum on the central axis shifted to lower energies and the maximum photon energy decreased to 3.5±0.2 MeV. The result of this experimental study confirms the conclusions from the previous simulation, that the numerical technique for analysis of transmission data can accurately represent 4‐MV bremsstrahlung spectra and detect differences in energy distribution with changes in machine tuning and position in the radiation field for a 4‐MV bremsstrahlung beam.
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Photon energy
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Photon energy
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The total bremsstrahlung photon yield in thick metallic targets (Al, Cu, Sn and Pb) produced by beta emitter 45Ca and 147Pm has been measured by using X-PIPS Si (Li) detector in the photon energy region 5-30 keV. The Z-dependence index ‘n’ and yield constant are determined in the photon energy region 5-30 keV. The Z-dependence index ‘n’ values obtained from experimental bremsstrahlung photon distributions shows better agreement with the index ‘n’ values obtained from the modified Elwert factor (relativistic) Bethe-Heitler theory, which includes the polarization bremsstrahlung into ordinary bremsstrahlung. It was observed, that a yield constant shows exponential decaying dependence on photon energy. Further, it has been found that the Z-dependence index ‘n’ values are not constant and decreases with increasing photon energy. The higher ‘n’ values than unity clearly indicates the inadequacy of theoretical models to represent the dependence of spectral shape of total bremsstrahlung on atomic number. It was observed that total bremsstrahlung photon yield increases with the increase in atomic number and with the decrease in photon energy.
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Using Monte Carlo simulation, reconstruction of photon conversions is studied, and the detection efficiency and energy resolution as a function of photon energy are obtained. The dE/dx correction for the electrons from photon conversions and the energy scale for the photons are calibrated with BES II data. An improved Crystal Ball function describes well the energy distribution of the photons. Photon energy resolutions in the range from 2.3 to 3.8MeV are found for the photons with energy from 100 to 260MeV at the BES II detector.
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Electron ion bremsstrahlung cross sections {beta}{sup 2}{divided_by}h{nu} d{sup 2}{sigma}(h{nu},1/2 mv{sup 2}, {theta}){divided_by}d(h{nu}) d({theta}) are evaluated for the fixed photon emission angle {theta}=90{degrees}, as relevant to experiments where the spectra are recorded perpendicularly to the electron trajectories. For a fixed photon energy h{nu}, the cross sections in the mildly relativistic regime are varying only very slowly with the incident electron energy 1/2 mv{sup 2} (contrary to the angular integrated cross section). Energy ranges and examples for which this property is found are indicated. As an application, we show how this enables more detailed and more rigorous interpretations of bremsstrahlung spectra.
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Sigma
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