Recoil Spectra Research Articles

Ion irradiation of electronic-type-separated single wall carbon nanotubes: A model for radiation effects in nanostructured carbon

The structural and electrical properties of electronic-type-separated (metallic and semiconducting) single wall carbon nanotube (SWCNT) thin-films have been investigated after irradiation with 150 keV 11B+ and 150 keV 31P+ with fluences ranging from 1012 to 1015 ions/cm2. Raman spectroscopy results indicate that the ratio of the Raman D to G′ band peak intensities (D/G′) is a more sensitive indicator of SWCNT structural modification induced by ion irradiation by one order of magnitude compared to the ratio of the Raman D to G band peak intensities (D/G). The increase in sheet resistance (Rs) of the thin-films follows a similar trend as the D/G′ ratio, suggesting that the radiation induced variation in bulk electrical transport for both electronic-types is equal and related to localized defect generation. The characterization results for the various samples are compared based on the displacement damage dose (DDD) imparted to the sample, which is material and damage source independent. Therefore, it is possible to extend the analysis to include data from irradiation of transferred CVD-graphene films on SiO2/Si substrates using 35 keV C+ ions, and compare the observed changes at equivalent levels of ion irradiation-induced damage to that observed in the SWCNT thin-film samples. Ultimately, a model is developed for the prediction of the radiation response of nanostructured carbon materials based on the DDD for any incident ion with low-energy recoil spectra. The model is also related to the defect concentration, and subsequently the effective defect-to-defect length, and yields a maximum defect concentration (minimum defect-to-defect length) above which the bulk electrical transport properties in SWCNT thin-films and large graphene-based electronic devices rapidly degrade when exposed to harsh environments.

DARWIN dark matter WIMP search with noble liquids

DARWIN (dark matter wimp search with noble liquids) is a design study for a next-generation, multi-ton dark matter detector in Europe. Liquid argon and/or liquid xenon are the target media for the direct detection of dark matter candidates in the form of weakly interacting massive particles (WIMPs). Light and charge signals created by particle interactions in the active detector volume are observed via the time projection chamber technique. DARWIN is to probe the spin-independent, WIMP-nucleon cross section down l0−48cm2 and to measure WIMP-induced nuclear recoil spectra with high-statistics, should they be discovered by an existing or near-future experiment. After a brief introduction, I will describe the project, selected R&D topics, expected backgrounds and the physics reach.

A first estimate of triply heavy baryon masses from the pNRQCD perturbative static potential

Within pNRQCD we compute the masses of spin-averaged triply heavy baryons using the now-available NNLO pNRQCD potentials and three-body variational approach. We focus in particular on the role of the purely three-body interaction in perturbation theory. This we find to be reasonably small and of the order 25 MeV. Our prediction for the Ω ccc baryon mass is 4900(250) MeV in keeping with other approaches. We propose to search for this hitherto unobserved state at B factories by examining the end point of the recoil spectrum against triple charm.

Analysis of neutron spectrum effects on primary damage in tritium breeding blankets

The effect of neutron spectrum on primary damages in a structural material of a tritium breeding blanket is investigated with a newly established recoil spectrum estimation system. First, a recoil spectrum generation code is developed to obtain the energy spectrum of primary knock-on atoms (PKAs) for a given neutron spectrum utilizing the latest ENDF/B data. Secondly, a method for approximating the high energy tail of the recoil spectrum is introduced to avoid expensive molecular dynamics calculations for high energy PKAs using the concept of recoil energy of the secondary knock-on atoms originated by the INtegration of CAScades (INCAS) model. Thirdly, the modified spectrum is combined with a set of molecular dynamics calculation results to estimate the primary damage parameters such as the number of surviving point defects. Finally, the neutron spectrum is varied by changing the material of the spectral shifter and the result in primary damage parameters is examined.

Dual-phase argon ionization detector for measurement of coherent elastic neutrino scattering and medium-energy nuclear recoils

We propose to build and deploy a 10-kg dual-phase argon ionization detector for the detection of coherent neutrino-nucleus scattering, which is described by the reaction; ( ν ) + ( Z , N ) → ( ν ) + ( Z , N ) . Our group would be the first to make this measurement. Its detection would validate (or refute) central tenets of the Standard Model. The existence of this process is also relevant to astrophysics, where coherent neutrino scattering is assumed to impede energy transport within neutron stars. We have built a gas-phase argon ionization detector to determine the feasibility of measuring small recoil energies (∼1keV) predicted from coherent neutrino scattering, and to characterize the recoil spectrum of the argon nuclei induced by scattering from medium-energy neutrons. We present calibrations made with 55-Fe, a low energy x-ray source, and describe a planned measurement of the recoil spectra from the 60keV Lithium-target neutron generator at LLNL. A high signal-to-noise measurement of the recoil spectrum will not only serve an important milestone in achieving the sensitivity necessary for measuring coherent neutrino-nucleus scattering, but will break new scientific ground by providing a first ever measurement of low-energy quenching factors in argon.

What can(not) be measured with ton-scale dark matter direct detection experiments

Direct searches for dark matter have prompted in recent years a great deal of excitement within the astroparticle physics community, but the compatibility between signal claims and null results of different experiments is far from being a settled issue. In this context, we study here the prospects for constraining the dark matter parameter space with the next generation of ton-scale detectors. Using realistic experimental capabilities for a wide range of targets (including fluorine, sodium, argon, germanium, iodine and xenon), the role of target complementarity is analysed in detail while including the impact of astrophysical uncertainties in a self-consistent manner. We show explicitly that a multi-target signal in future direct detection facilities can determine the sign of the ratio of scalar couplings fn/fp, but not its scale. This implies that the scalar-proton cross-section is left essentially unconstrained if the assumption fp ∼ fn is relaxed. Instead, we find that both the axial-proton cross-section and the ratio of axial couplings an/ap can be measured with fair accuracy if multi-ton instruments using sodium and iodine will eventually come online. Moreover, it turns out that future direct detection data can easily discriminate between elastic and inelastic scatterings. Finally, we argue that, with weak assumptions regarding the WIMP couplings and the astrophysics, only the dark matter mass and the inelastic parameter (i.e. mass splitting) may be inferred from the recoil spectra — specifically, we anticipate an accuracy of tens of GeV (tens of keV) in the measurement of the dark matter mass (inelastic parameter).

Determining ratios of WIMP-nucleon cross sections from direct dark matter detection data

Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for Dark Matter. So far the usual procedure for constraining the WIMP-nucleon cross sections in direct Dark Matter detection experiments have been to fit the predicted event rate based on some model(s) of the Galactic halo and of WIMPs to experimental data. One has to assume whether the spin-independent (SI) or the spin-dependent (SD) WIMP-nucleus interaction dominates, and results of such data analyses are also expressed as functions of the as yet unknown WIMP mass. In this article, I introduce methods for extracting information on the WIMP-nucleon cross sections by considering a general combination of the SI and SD interactions. Neither prior knowledge about the local density and the velocity distribution of halo WIMPs nor about their mass is needed. Assuming that an exponential-like shape of the recoil spectrum is confirmed from experimental data, the required information are only the measured recoil energies (in low energy ranges) and the number of events in the first energy bin from two or more experiments.

Dark discrete gauge symmetries

We investigate scenarios in which dark matter is stabilized by an Abelian ${Z}_{N}$ discrete gauge symmetry. Models are surveyed according to symmetries and matter content. Multicomponent dark matter arises when $N$ is not prime and ${Z}_{N}$ contains one or more subgroups. The dark sector interacts with the visible sector through the renormalizable kinetic mixing and Higgs portal operators, and we highlight the basic phenomenology in these scenarios. In particular, multiple species of dark matter can lead to an unconventional nuclear recoil spectrum in direct detection experiments, while the presence of new light states in the dark sector can dramatically affect the decays of the Higgs at the Tevatron and LHC, thus providing a window into the gauge origin of the stability of dark matter.

Interpreting dark matter direct detection independently of the local velocity and density distribution

We demonstrate precisely what particle physics information can be extracted from a single direct detection observation of dark matter while making absolutely no assumptions about the local velocity distribution and local density of dark matter. Our central conclusions follow from a very simple observation: the velocity distribution of dark matter is positive definite, $f(v)\ensuremath{\ge}0$. We demonstrate the utility of this result in several ways. First, we show a falling deconvoluted recoil spectrum (deconvoluted of the nuclear form factor), such as from ordinary elastic scattering, can be ``mocked up'' by any mass of dark matter above a kinematic minimum. As an example, we show that dark matter much heavier than previously considered can explain the CoGeNT excess. Specifically, ${m}_{\ensuremath{\chi}}<{m}_{\mathrm{Ge}}$ can be in just as good agreement as light dark matter, while ${m}_{\ensuremath{\chi}}>{m}_{\mathrm{Ge}}$ depends on understanding the sensitivity of xenon to dark matter at very low recoil energies, ${E}_{R}\ensuremath{\lesssim}6\text{ }\text{ }\mathrm{keVnr}$. Second, we show that any rise in the deconvoluted recoil spectrum represents distinct particle physics information that cannot be faked by an arbitrary $f(v)$. As examples of resulting nontrivial particle physics, we show that inelastic dark matter and dark matter with a form factor can both yield such a rise.

Micro-channel development and hydrogen adsorption properties in templated microporous carbons containing platinum nanoparticles

Ordered microporous carbons containing dispersed platinum nanoparticles were fabricated and chosen as suitable models to investigate micro-structure development and hydrogen transport properties of zeolite-templated carbons. X-ray photoelectron spectroscopy analysis revealed that the enhanced heat of adsorption is related to the narrow micro-channels templated from the zeolite and the presence of certain C O groups on the carbon. The lack of a well-defined and intense rotational transition line and the persistent broad H 2 recoil spectrum in neutron scattering results suggests a distribution of binding sites. Most interestingly, hydrogen diffusion occurs on two time scales, consisting of a fast liquid-like jump diffusion on the timescale of picoseconds along with an even faster bulk-like diffusion. The liquid-like motion is characterized by a diffusion constant of (2.1 ± 0.3) × 10 −8 m 2/s with an activation energy of ca. 77 K; both values indicate somewhat lower mobility than similar dynamics of H 2 on nanotubes, activated carbon XC-72, or Grafoil, yet greater mobility than that of bulk liquid. These unusual characteristics for hydrogen in carbons are believed to arise from the network of narrow pores in this zeolite-templated image of the zeolite. In fact, the diffusion constants of the templated carbons are extremely similar to those measured for zeolite 13X.

Non-relativistic effective theory of dark matter direct detection

Dark matter direct detection searches for signals coming from dark matter scattering against nuclei at a very low recoil energy scale ∼ 10 keV. In this paper, a simple non-relativistic effective theory is constructed to describe interactions between dark matter and nuclei without referring to any underlying high energy models. It contains the minimal set of operators that will be tested by direct detection. The effective theory approach highlights the set of distinguishable recoil spectra that could arise from different theoretical models. If dark matter is discovered in the near future in direct detection experiments, a measurement of the shape of the recoil spectrum will provide valuable information on the underlying dynamics. We bound the coefficients of the operators in our non-relativistic effective theory by the null results of current dark matter direct detection experiments. We also discuss the mapping between the non-relativistic effective theory and field theory models or operators, including aspects of the matching of quark and gluon operators to nuclear form factors.

A Deep Level Transient Spectroscopy Study of Electron and Proton Irradiated ${\hbox {p}} ^{+} {\hbox {n}}$ GaAs Diodes

Defects produced by 0.6 MeV, 1 MeV, and 5 MeV electrons are compared with those produced by 2 MeV proton irradiations in p+n GaAs diodes using Deep Level Transient Spectroscopy (DLTS). The introduction rates are determined as a function of electron energy and compared with the nonionizing energy loss (NIEL). It has been determined that a majority of the electron-induced defects (E-traps) are similar to those observed following proton irradiation (PR-traps). However, a new defect emerges in the 5 MeV electron DLTS spectrum with a peak maximum occurring at ∼ 163 K which is not observed at the other electron energies. It has been determined that this new electron-induced defect which has previously not been detected is the proton-induced PR4'' defect. This defect emerges as the incident electron energy is increased suggesting it is formed by higher energy recoils and may be a complex defect. The recoil spectra are analyzed.

Peaked signals from dark matter velocity structures in direct detection experiments

In direct dark matter detection experiments, conventional elastic scattering of WIMPs results in exponentially falling recoil spectra. In contrast, theories of WIMPs with excited states can lead to nuclear recoil spectra that peak at finite recoil energies ER. The peaks of such signals are typically fairly broad, with ΔER/Epeak ∼ 1. We show that in the presence of dark matter structures with low velocity dispersion, such as streams or clumps, peaks from up-scattering can become extremely narrow with FWHM of a few keV only. This differs dramatically from the conventionally expected WIMP spectrum and would, once detected, open the possibility to measure the dark matter velocity structure with high accuracy. As an intriguing example, we confront the observed cluster of 3 events near 42 keV from the CRESST commissioning run with this scenario. Inelastic dark matter particles with a wide range of parameters are capable of producing such a narrow peak. We calculate the possible signals at other experiments, and find that such particles could also give rise to the signal at DAMA, although not from the same stream. Over some range of parameters, a signal would be visible at xenon experiments. We show that such dark matter peaks are a very clear signal and can be easily disentangled from potential backgrounds, both terrestrial or due to WIMP down-scattering, by an enhanced annual modulation in both the amplitude of the signal and its spectral shape.

Disentangling dark matter dynamics with directional detection

Inelastic dark matter reconciles the DAMA anomaly with other null direct detection experiments and points to a non-minimal structure in the dark matter sector. In addition to the dominant inelastic interaction, dark matter scattering may have a subdominant elastic component. If these elastic interactions are suppressed at low momentum transfer, they will have similar nuclear recoil spectra to inelastic scattering events. While upcoming direct detection experiments will see strong signals from such models, they may not be able to unambiguously determine the presence of the subdominant elastic scattering from the recoil spectra alone. We show that directional detection experiments can separate elastic and inelastic scattering events and discover the underlying dynamics of dark matter models.

Hydrogen analysis in diamond like carbon by elastic recoil detection

Among the available surface analytic instruments, elastic recoil detection (ERD) is known as a reliable method for hydrogen analysis. Since conventional fluence determination i.e. beam current integration is incredible at a large tilt angle, ion fluence is determined by the scattering spectrum that is simultaneously measured with recoil spectrum. However scattering cross sections deviate Rutherford values in the ERD energy of 1–3 MeV. Carbon scattering cross section is different from Rutherford value for higher beam energies over 1.8 MeV. As a result hydrogen content is exaggerated when fluence is determined by carbon matrix because of fluence underestimation due to lower value of scattering cross section than Rutherford’s. Therefore in order to quantify hydrogen in diamond like carbon (DLC) incident beam energy lower than 1.6 MeV should be used where carbon scattering cross sections are well agreed with Rutherford’s.

Using the energy spectrum measured by DAMA/LIBRA to probe light dark matter

A weakly interacting massive particle (WIMP) weighing only a few GeV has been invoked as an explanation for the signal from the DAMA/LIBRA experiment. We show that the data from DAMA/LIBRA are now powerful enough to strongly constrain the properties of any putative WIMP. Accounting for the detailed recoil spectrum, a light WIMP with a Maxwellian velocity distribution and a spin-independent interaction cannot account for the data. Even neglecting the spectrum, significant parameter space is excluded by a limit that can be derived from the DAMA unmodulated signal at low energies. Appreciable modification to the astrophysics or particle physics can open light mass windows.

Molecular dynamics simulation of intragranular Xe bubble re-solution in UO 2

The homogeneous re-solution of Xe fission gas bubbles in UO 2 is investigated by combined Monte Carlo and molecular dynamics simulations. Using a binary collision model, based on the Ziegler–Littmark–Biersack potential [J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, Stopping and Ranges of Ions in Matter, vol. 1, Pergamon Press, New York, 1984], the recoil energy distribution of fission gas atoms is obtained. An extensive library of fission gas atom displacement cascades is then compiled using molecular dynamic simulations. It used for calculating recoil spectrum averaged quantities. The calculations yield a re-solution parameter for homogeneous re-solution and a displacement distribution of fission gas atoms around the fission gas bubbles. The results disagree considerably from past estimates. The importance of channeling and threshold energy for fission gas escape are discussed.

How to Simulate the Microstructure Induced by a Nuclear Reactor with an Ion Beam Facility : DART

AbstractEven if the Binary Collision Approximation does not take into account relaxation processes at the end of the displacement cascade, the amount of displaced atoms calculated within this framework can be used to compare damages induced by different facilities like pressurized water reactors (PWR), fast breeder reactors (FBR), high temperature reactors (HTR) and ion beam facilities on a defined material. In this paper, a formalism is presented to evaluate the displacement cross-sections pointing out the effect of the anisotropy of nuclear reactions. From this formalism, the impact of fast neutrons (with a kinetic energy En superior to 1 MeV) is accurately described. This point allows calculating accurately the displacement per atom rates as well as primary and weighted recoil spectra. Such spectra provide useful information to select masses and energies of ions to perform realistic experiments in ion beam facilities.

Effect of Proton and Silicon Ion Irradiation on Defect Formation in GaAs

Electrical and structural changes in GaAs are monitored using electron beam induced current (EBIC) and transmission electron microscopy (TEM) measurements after irradiation by protons and silicon ions. It has been determined that higher energy protons (E ges 10 MeV) and silicon ions disordered regions that are electrically and structurally different than those produced by lower energy protons. The data suggest that these disordered regions are responsible for causing the deviations between experimental data and NIEL. From analyses of the recoil spectra, high energy recoils appear to be responsible for the formation of these disordered regions.

Determining the WIMP mass from a single direct detection experiment; a more detailedstudy

The energy spectrum of nuclear recoils in weakly interacting massive particle (WIMP)direct detection experiments depends on the underlying WIMP mass. We studyhow the accuracy with which the WIMP mass could be determined by a singledirect detection experiment depends on the detector configuration and the WIMPproperties. We investigate the effects of varying the underlying WIMP mass andcross-section, the detector target nucleus, exposure, energy threshold and maximumenergy, the local circular speed and the background event rate and spectrum. Thenumber of events observed is directly proportional to both the exposure and thecross-section; therefore these quantities have the greatest bearing on the accuracy of theWIMP mass determination. The relative capabilities of different detectors fordetermining the WIMP mass depend not only on the WIMP and target masses, butalso on their energy thresholds. The WIMP and target mass dependence of thecharacteristic energy scale of the recoil spectrum suggests that heavy targets will beable to measure the mass of a heavy WIMP more accurately. We find, however,that the rapid decrease of the nuclear form factor with increasing momentumtransfer which occurs for heavy nuclei means that this is in fact not the case.Uncertainty in the local circular speed and non-negligible background would bothlead to systematic errors in the WIMP mass determination. For deviations of ± 20 km s−1 in the underlying value of the circular speed the systematic error is of order10%, increasing with increasing WIMP mass. This error can be reduced by also fitting for thecircular speed. With a single detector it will be difficult to disentangle a WIMP signal (andthe WIMP mass) from background if the background spectrum has a similar shape to theWIMP spectrum (i.e. exponential background, or flat background and a heavyWIMP).