Artificial neural network-based method for discriminating Compton scattering events in high-purity germaniumγ-ray spectrometer

To detect radioactive substances with low activity levels,an anticoincidence detector and a high-purity germanium(HPGe)detector are typically used simultaneously to suppress Compton scattering background,thereby resulting in an extremely low detection limit and improving the measurement accuracy.However,the complex and expensive hardware required does not facilitate the application or promotion of this method.Thus,a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector,whereby Compton scattering background is suppressed and a low minimum detectable activity(MDA)is achieved without using an expensive and complex anticoincidence detector and device.The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location,as well as the characteristics of energy-deposition distributions for fulland partial-energy deposition events.This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification.To accurately determine the relationship between the deposited energy of gamma(γ)rays in the detector and the deposition location,we extract four shape parameters from the pulse signals output by the detector.Machine learning is used to input the four shape parameters into the detector.Subsequently,the pulse signals are identified and classified to discriminate between partial-and full-energy deposition events.Some partial-energy deposition events are removed to suppress Compton scattering.The proposed method effectively decreases the MDA of an HPGeγ-energy dispersive spectrometer.Test results show that the Compton suppression factors for energy spectra obtained from measurements on ^(152)Eu,^(137)Cs,and ^(60)Co radioactive sources are 1.13(344 keV),1.11(662 keV),and 1.08(1332 keV),respectively,and that the corresponding MDAs are 1.4%,5.3%,and 21.6%lower,respectively.

Evolution of Electron Phase Orbits Based on Multi-photon Nonlinear Compton Scattering

The electron movement based on the multi-photon nonlinear Compton scattering with the extra-intense stationary laser field is discussed by using KMR (Kroll-Morton-Rosenbluth) theory.We find that there exists only an evolution from periodicity to non-periodicity of the un-captured electron phase orbits after the energy exchange between the electron beam and laser fields.With the increase of the absorbed photon number n by an electron, this evolution will be more and more faster, while it is rapidly decreased with the enhancement of the collision non-flexibility ξ of the electrons and photons; When the electrons are captured by the laser fields, the evolution is finished, the electrons will stably transport,and the photons dont give up the energy to these electrons.

High‑accuracy measurement of Compton scattering in germanium for dark matter searches

Compton scattering with bound electrons contributes to a significant atomic effect in low-momentum transfer,yielding background structures in direct light dark matter searches as well as low-energy rare event experiments.We report the measurement of Compton scattering in low-momentum transfer by implementing a 10-g germanium detector bombarded by a^(137)Cs source with a radioactivity of 8.7 mCi and a scatter photon captured by a cylindrical NaI(Tl)detector.A fully relativistic impulse approximation combined with multi-configuration Dirac–Fock wavefunctions was evaluated,and the scattering function of Geant4 software was replaced by our calculation results.Our measurements show that the Livermore model with the modified scattering function in Geant4 is in good agreement with the experimental data.It is also revealed that atomic many-body effects significantly influence Compton scattering for low-momentum transfer(sub-keV energy transfer).

Dispersion Properties of TIRPCF under Compton Scattering

The dispersion properties in the short wavelength region of total internal reflective photonic crystal fiber(TIRPCF) in Compton scattering have been studied by using the model of the equivalent twin waveguide soliton coupling, dispersion management solitons and effective refractive index. It is shown that the positive dispersion of the cladding waveguide of TIRPCF and the negative dispersion of its core waveguide are quickly increased by the square of the collision non-elastic composition between the electron and photons, and they are lessened by the increase of the electron absorption photon number. Under the one-photon nonlinear Compton scattering, the method of the compensated probing laser diffraction by the phase hole induced by the stationary pumping laser in the cladding waveguide enables the average dispersion value of TIRPCF to be close to zero, and the zero dispersion point quickly shifts to the short wavelength region.

Theoretical and experimental study on Compton scattering of a binary powder mixture

The relationship between Compton scattered photon counts per unit mass and the content of a component in a binary powder mixture is deduced based on the Compton scattering theory.This relationship can be regarded linear after some approximations.The scattered photon counts per unit mass increases faster with the content when the difference of the atomic numbers of the two components in the binary powder mixture is larger.The relationship was verified with Compton scattering experiments on a series of Ni-Cu and Fe-C binary powder mixtures.The method of using this linear dependene of scattered photon counts on the content of a binary powder mixture to ascertain the component content in a binary mixture was introduced.

Nonlinear Propagation of Coupling Optical Pulse under Compton Scattering in Laser Medium

After considering Kerr nonlinear effect, group velocity dispersion of host and gain distribution of active particle in laser amplifying medium, a basic equation describing propagation of the coupling optical pulse under the multi-photon nonlinear Compton scattering in the laser amplifying medium has been deduced. Besides, the profile and power spectrum of a picosecond-level super-Gaussian coupling pulse in the laser amplifying medium have been discussed when its central frequency coincides with the gain peak frequency of the laser amplifying medium.

Evolution of Electron Phase Orbits of Multi-photon Nonlinear Compton Scattering in High Power Laser-plasma

The evolution of the electron phase orbits based on the multi-photon nonlinear Compton scattering with the high power laser-plasma is discussed by using Kroll-Morton-Rosenbluth theory. The random evolution of the un-captured electron phase orbits from periodicity to non-periodicity is found after the energy has been exchanged between the electron and photons. With the increase of the absorbed photon number n by an electron,this evolution will be more and more intense, while which is rapidly decreased with the enhancement of the collision non-flexibility ξ and their initial speeds of the electrons and photons,but this evolution is lower than that in the high power laser field. When the electrons are captured by the laser field,the evolution is finished,and the electrons will stably transport,and the photons don’t provide the energy for these electrons any more.

The effect of Compton scattering on gamma-ray spectra of the 2005 January 20 flare

Gamma-ray spectroscopy provides a wealth of information about acceler- ated particles in solar flares, as well as the ambient medium with which these energetic particles interact. The neutron capture line （2.223 MeV）, the strongest in the solar gamma-ray spectrum, forms in the deep atmosphere. The energy of these photons can be reduced via Compton scattering. With the fully relativistic GEANT4 toolkit, we have carried out Monte Carlo simulations of the transport of a neutron capture line in solar flares, and applied them to the flare that occurred on 2005 January 20 （X7.1/2B）, one of the most powerful gamma-ray flares observed by RHESSI during the 23rd solar cycle. By comparing the fitting results of different models with and without Compton scattering of the neutron capture line, we find that when including the Compton scat- tering for the neutron capture line, the observed gamma-ray spectrum can be repro- duced by a population of accelerated particles with a very hard spectrum （s ≤ 2.3）. The Compton effect of a 2.223 MeV line on the spectra is therefore proven to be sig- nificant, which influences the time evolution of the neutron capture line flux as well. The study also suggests that the mean vertical depth for neutron capture in hydrogen for this event is about 8 g cm-2.

A Compton scattering image reconstruction algorithm based on total variation minimization

Compton scattering imaging is a novel radiation imaging method using scattered photons.Its main characteristics are detectors that do not have to be on the opposite side of the source,so avoiding the rotation process.The reconstruction problem of Compton scattering imaging is the inverse problem to solve electron densities from nonlinear equations,which is ill-posed.This means the solution exhibits instability and sensitivity to noise or erroneous measurements.Using the theory for reconstruction of sparse images,a reconstruction algorithm based on total variation minimization is proposed.The reconstruction problem is described as an optimization problem with nonlinear data-consistency constraint.The simulated results show that the proposed algorithm could reduce reconstruction error and improve image quality,especially when there are not enough measurements.

High-brightness photo-injector with standing-wave buncher-based ballistic bunching scheme for inverse Compton scattering light source

We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short standing-wave buncher between the RF gun and first booster in a conventional S-band photo-injector,electron bunches with a 500 pC charge can be compressed to the sub-picosecond level with very limited input RF power and an unchanged basic layout of the photo-injector.Beam dynamics analysis indicates that fine tuning of the focusing strength of the gun and linac solenoid can well balance additional focusing provided by the standing wave buncher and generate a well-compensated transverse emittance.Thorough bunching dynamics simulations with different operating conditions of the buncher show that a buncher with more cells and a moderate gradient is suitable for simultaneously obtaining a short bunch duration and low emittance.In a typical case of a 9-cell buncher with a 38 MV/m gradient,an ultrashort bunch duration of 0.5 ps(corresponding to a compression ratio of>5)and a low emittance of<1 mm mrad can be readily obtained for a 500 pC electron pulse.This feasible ballistic bunching scheme will facilitate the implementation of an ultrashort pulse mode inverse Compton scattering X-ray source on most existing S-band photo-injectors.

The polarization effect of a laser in multiphoton Compton scattering

The multiphoton Compton scattering in a high-intensity laser beam is studied by using the laser-dressed quantum electrodynamics （QED） method, which is a non-perturbative theory for the interaction between a plane electromagnetic field and a charged particle. In order to analyze in the real experimental condition, a Lorentz transformation for the cross section of this process is derived between the laboratory frame and the initial rest frame of electrons. The energy of the scattered photon is analyzed, as well as the cross sections for different laser intensities and polarizations and different electron velocities. The angular distribution of the emitted photon is investigated in a special velocity of the electron, in which for a fixed number of absorbed photons, the electron energy will not change after the scattering in the lab frame. We obtain the conclusion that higher laser intensifies suppress few-laser-photon absorption and enhance more-laser-photon absorption. A comparison between different polarizations is also made, and we find that the linearly polarized laser is more suitable to generate nonlinear Compton scattering.

Applications of Compton scattering

Compton scattering is used very widely. In this article, we depict an overall picture for its applications which are based on two basic theories. The first is the electron densitometry theory related to electron density. According to this theory its applications are in two fields: one is Compton scatter densitometry (CSD), the other is Compton scatter imaging (CSI). The second technique involves the electron momentum distribution and Compton profile. Applications of this technique are mainly the Compton profile analysis (CPA) and the Compton profile or the electron momentum distribution in physics and chemistry. Future research fields are suggested according to the current situation and limits of this technique and a promising prospect is unfolded.

Photon Polarizationin Photonic Crystal Fibers under Compton Scattering

Using the quantum invariant theory and unitary transformation means, we study the influences of multi-photon nonlinear Compton scattering on the photon polarization in photonic crystal fibers(PCF). The results show that the photon polarization of the incident photon changes a lot due to scattered optical, and its general geometric phase factor, Hamiton number and evolution operator are definited both by the incident and scattered optical.

Photon Acceleration of Laser-plasma Based on Compton Scattering

The one-dimensional electron density disturbance is studied by using the inelastic collision model of the relativity electron and photon group, the relativity theory, the momentum equation and the continuity equation, which is generated by a driving laser pulse and scattered laser pulse propagating through a tenuous plasma, and the electron density disturbance is closely associated with the incident laser and scattering laser. The electron plasma wave(EPW)is formed by the propagation of the electron density disturbance. Owing to the action of EPW, the increasing of the frequency of the photons in the incident laser pulses that there is a distance with the driving laser pulses is studied by using optical metric. The results show that it is possible that the photon will gain higher energy from the EPW when photon number is decreased and one-photon Compton scattering enters, the photon will be accelerated.

Influences of Uncaptured Electron on Energy Conversion of Photon Compton Scattering in High Power Laser-plasma

Using the single particle theory and the non-flexibility collision model of electron and photon, the influence of the uncaptured electrons on the energy conversion efficiency of multi-photon nonlinear Compton scattering in the extra stationary laser-plasma is investigated. It shows that in extra stationary laser-plasma,the uncaptured electrons make the Δω of the scattering frequency of the multi-photon Compton fall down with the increases of the incident radiation electron speed,the materials of the incident collision of electron and photon, and the number of the photons which work with the electrons at the same time. Under the modulation of the uncaptured electrons to the laser field, the energy conversion efficiency between electrons and photons will fall down with the increase of the electron incident radiation speed, using the low-power electrons for incident source, the loss can be efficiently reduced.

Self-trapping Characteristics of Partially Coherent Optical Beam in Photonic Crystal Fiber under Compton Scattering

Using the mutually coherent function, the self-trapping of the circle partially coherent optical beam in the total internal reflective photonic crystal fiber(TIRPCF) under Compton scattering is studied. The study shows that the composition of the non-coherent optical beam in the optical spectrum and the diffraction effect are decreased by Compton scattering, and the probability of forming the soliton is greatly increased. The vibration peak value in the propagation, compressed degree, changed cycle, and radius of the soliton are all smaller than those before the scattering, but its coherent radius is larger than that before the scattering. In this propagation, the self-focusing plays a key role.

Influence on Atomic Inversion Evolution in Medium System from Compton Scattering

In Jaynes-Cummings model,by using the modulation of the coupling coefficient formed by the atom,medium and scattering optical,atomic inversion evolution of arbitrary forms has been worked out.Its feasibility has been proved,and the curvature of the atomic inversion evolution of the arbitrary forms is obtained.It announces that the atom and coupling medium system are to express the operators of the atom and optical field quantum in Jaynes-Cummings model.These operators can express arbitrary medium system.In these systems,the coupling coefficient can be changed and exactly controlled in the longer coherent times.

Influence of Heat-radiating on Multi-photon Compton Scattering High-energy Electron

Using the model of the inverse Compton scattering between high-energy electrons and heat-radiation photons, the influence of heat-radiating photons on multi-photon Compton scattering high-energy electrons is studied . The results show that the energy loss, power loss, light resistance and light pressure of the high-energy electron formed by heat radiating are all proportional to the temperature T4 of the vacuum cavity of the electron,the Lorentz factor γ2 of the high-energy electrons, the scattering section of the electron and the number of photons acting at the same time with high-energy electrons. A good method for lessening the energy loss of the high-energy electron by using the one-photon Compton scattering between high-energy electrons and heat radiation photons is proposed.

Free Electrons Compton Scattering Can Produce an Illusion of Expanding Universe

The high-precision measurements of the Hubble parameter make the theory of cosmic expansion more and more confusing, which bolsters the idea that new physics may be needed to explain the mismatch. Astronomical observations show that the Universe is expanding exponentially. Free electron Compton scattering (FEC) can produce the illusion of exponentially expanding Universe: FEC causes photons to redshift exponentially, and the photon beam exponentially expands along the propagation direction. Is this a coincidence? The redshift factor of the FEC is z = (1+z);the beam length stretch factor (time dilation of the supernova curve) of the FEC is z = (1+z);the expansion factor of the beam volume of the FEC is z = (1+z)3, and the FEC effect does not blur the image of distant galaxies. The reason for rejecting the “tired light” does not hold in FEC.

Simultaneous fluorescence and Compton scattering computed tomography based on linear polarization X-ray

Purpose To propose a method for simultaneous fluorescence and Compton scattering computed tomography by using linearly polarized X-rays.Methods Monte Carlo simulations were adopted to demonstrate the feasibility of the proposed method.In the simulations,the phantom is a polytetrafluoroethylene cylinder inside which are cylindrical columns containing aluminum,water,and gold(Au)-loaded water solutions with Au concentrations ranging between 0.5 and 4.0 wt%,and a parallel-hole collimator imaging geometry was adopted.The light source was modeled based on a Thomson scattering X-ray source.The phantom images for both imaging modalities were reconstructed using a maximumlikelihood expectation maximization algorithm.Results Both the X-ray fluorescence computed tomography(XFCT)and Compton scattering computed tomography(CSCT)images of the phantom were accurately reconstructed.A similar attenuation contrast problem for the different cylindrical columns in the phantom can be resolved in the XFCT and CSCT images.The interplay between XFCT and CSCT was analyzed,and the contrast-to-noise ratio(CNR)of the reconstruction was improved by correcting for the mutual influence between the two imaging modalities.Compared with K-edge subtraction imaging,XFCT exhibits a CNR advantage for the phantom.Conclusion Simultaneous XFCT and CSCT can be realized by using linearly polarized X-rays.The synergy between the two imaging modalities would have an important application in cancer radiation therapy.