Ratio In Cosmic Rays Research Articles

Data driven approach for the measurement of Be10/Be9 in cosmic rays with magnetic spectrometers

Cosmic rays (CRs) are a powerful tool for the investigation of the structure of the magnetic fields in the galactic halo and the properties of the interstellar medium. Two parameters of the CR propagation model---the galactic halo (half-)thickness $H$ and the diffusion coefficient $D$---are loosely constrained by current CR flux measurements; in particular, a large degeneracy exists being only $H/D$ well measured. The $^{10}\mathrm{Be}/^{9}\mathrm{Be}$ isotopic flux ratio (thanks to the 2 My lifetime of $^{10}\mathrm{Be}$) can be used as a radioactive clock, providing the measurement of CR residence time in the galaxy. This is an important tool for solving the $H/D$ degeneracy. Past measurements of the $^{10}\mathrm{Be}/^{9}\mathrm{Be}$ isotopic flux ratio in CRs are scarce, limited to low energy, and affected by large uncertainties. Here, a new technique to measure the $^{10}\mathrm{Be}/^{9}\mathrm{Be}$ isotopic flux ratio with a data-driven approach in magnetic spectrometers is presented. The analysis with the data driven approach of beryllium events collected by the PAMELA experiment is shown as an example. It is possible to measure the $^{10}\mathrm{Be}/^{9}\mathrm{Be}$ flux ratio avoiding the uncertainties related to the Monte Carlo simulation.

Cosmic rays across the star-forming galaxy sequence – I. Cosmic ray pressures and calorimetry

ABSTRACT In the Milky Way (MW), cosmic rays (CRs) are dynamically important in the interstellar medium (ISM), contribute to hydrostatic balance, and may help regulate star formation. However, we know far less about the importance of CRs in galaxies whose gas content or star formation rate (SFR) differ significantly from those of the MW. Here, we construct self-consistent models for hadronic CR transport, losses, and contribution to pressure balance as a function of galaxy properties, covering a broad range of parameters from dwarfs to extreme starbursts. While the CR energy density increases from ∼1 eV cm−3 to ∼1 keV cm−3 over the range from sub-MW dwarfs to bright starbursts, strong hadronic losses render CRs increasingly unimportant dynamically as the SFR surface density increases. In MW-like systems, CR pressure is typically comparable to turbulent gas and magnetic pressure at the galactic mid-plane, but the ratio of CR to gas pressure drops to ∼10−3 in dense starbursts. Galaxies also become increasingly CR calorimetric and gamma-ray bright in this limit. The degree of calorimetry at fixed galaxy properties is sensitive to the assumed model for CR transport, and in particular to the time CRs spend interacting with neutral ISM, where they undergo strong streaming losses. We also find that in some regimes of parameter space hydrostatic equilibrium discs cannot exist, and in Paper II of this series we use this result to derive a critical surface in the plane of star formation surface density and gas surface density beyond which CRs may drive large-scale galactic winds.

Cosmic ray driven outflows to Mpc scales from L* galaxies

ABSTRACT We study the effects of cosmic rays (CRs) on outflows from star-forming galaxies in the circum and intergalactic medium (CGM/IGM), in high-resolution, fully cosmological FIRE-2 simulations (accounting for mechanical and radiative stellar feedback, magnetic fields, anisotropic conduction/viscosity/CR diffusion and streaming, and CR losses). We showed previously that massive ($M_{\rm halo}\gtrsim 10^{11}\, \mathrm{M}_{\odot }$), low-redshift (z ≲ 1–2) haloes can have CR pressure dominate over thermal CGM pressure and balance gravity, giving rise to a cooler CGM with an equilibrium density profile. This dramatically alters outflows. Absent CRs, high gas thermal pressure in massive haloes ‘traps’ galactic outflows near the disc, so they recycle. With CRs injected in supernovae as modelled here, the low-pressure halo allows ‘escape’ and CR pressure gradients continuously accelerate this material well into the IGM in ‘fast’ outflows, while lower-density gas at large radii is accelerated in situ into ‘slow’ outflows that extend to >Mpc scales. CGM/IGM outflow morphologies are radically altered: they become mostly volume-filling (with inflow in a thin mid-plane layer) and coherently biconical from the disc to >Mpc. The CR-driven outflows are primarily cool ($T\sim \! 10^{5}\,$ K) and low velocity. All of these effects weaken and eventually vanish at lower halo masses ($\lesssim 10^{11}\, \mathrm{M}_{\odot }$) or higher redshifts (z ≳ 1–2), reflecting the ratio of CR to thermal + gravitational pressure in the outer halo. We present a simple analytical model that explains all of the above phenomena. We caution that these predictions may depend on uncertain CR transport physics.

High-Energy Particles and Radiation in Star-Forming Regions

Non-thermal particles and high-energy radiation can play a role in the dynamical processes in star-forming regions and provide an important piece of the multiwavelength observational picture of their structure and components. Powerful stellar winds and supernovae in compact clusters of massive stars and OB associations are known to be favourable sites of high-energy particle acceleration and sources of non-thermal radiation and neutrinos. Namely, young massive stellar clusters are likely sources of the PeV (petaelectronvolt) regime cosmic rays (CRs). They can also be responsible for the cosmic ray composition, e.g., 22Ne/20Ne anomalous isotopic ratio in CRs. Efficient particle acceleration can be accompanied by super-adiabatic amplification of the fluctuating magnetic fields in the systems converting a part of kinetic power of the winds and supernovae into the magnetic energy through the CR-driven instabilities. The escape and CR propagation in the vicinity of the sources are affected by the non-linear CR feedback. These effects are expected to be important in starburst galaxies, which produce high-energy neutrinos and gamma-rays. We give a brief review of the theoretical models and observational data on high-energy particle acceleration and their radiation in star-forming regions with young stellar population.

Journey through the birth, growth and maturity of X-ray astronomy

In this biographical account, I recall my scientific journey that began in 1961 when I joined as a Physics Trainee in the BARC Training School and after one year course was admitted in TIFR as a Research Associate. During 1962–1967, I worked on determination of the He3/He4 ratio in cosmic rays using a gas Cerenkov counter and also used a scintillation + solid Cerenkov detector to measure flux of protons and helium nuclei in primary cosmic rays. I also developed a large area scintillation-Cerenkov detector with a spark chamber between them for measuring charge composition of primary cosmic rays. I joined the X-ray astronomy programme in 1967 initiated by Prof. B. V. Sreekantan and played a leading role in developing a balloon borne hard X-ray instrument for studying time variability and energy spectra of cosmic X-ray sources. We carried out a series of balloon experiments and studied temporal intensity variation and energy spectra of X-ray objects like Sco X-1, Cyg X-1, etc. Results on rapid intensity changes and spectra appeared in a series of publications based on which I obtained a Ph.D. degree in 1972. Immediately afterwards, I joined Prof. Gordon Garmire at Caltech as a Research Fellow (a post-doctoral position) to work with him on the low energy component of HEAO A-2 experiment. The instrument was developed and successfully realised. Working on this satellite experiment was a thrilling experience which exposed me to the technical complexities of space instruments. The HEAO-1 satellite was launched in 1978. During 1978–1979, Guenter Riegler and I, working at JPL, reported detection of intense soft X-rays from several classes of extragalactic and Galactic objects like new BL Lacs, a new AM Her binary, coronal X-rays from active stars, etc. After returning to TIFR, I developed a rocket experiment with K. P. Singh to map the spatial and spectral distribution of the Soft Diffuse X-ray Background. At the same time, I also designed 15 cm deep Xenon filled Proportional Counters (XPCs) of ∼ 2500 cm2 area for balloon experiments which were done during 1983–1990 and produced new results on several X-ray binaries. During this period I also developed a proportional counter (PC) based satellite instrument and submitted a proposal jointly with the astronomy group at the Indian Space Research Organization (ISRO) for an Indian X-ray Astronomy Experiment (IXAE). After success of the Polar Satellite Launch Vehicle (PSLV), the IXAE instrument was included on the top deck of the IRS-P3 satellite that was launched in March 1996. Despite the severe limitation of a polar orbit, the IXAE observed a good number of X-ray binaries and produced interesting results, with the most notable being quasi-regular bursts from a new transient, GRS 1915+105, which turned out to be an enigmatic black hole source. Following success of the IXAE, a proposal for an ambitious multiwavelength astronomy satellite, named ASTROSAT, with broad spectral coverage in the optical, NUV, FUV, soft X-ray and hard X-ray by a suite of instruments, was submitted to ISRO and finally approved by the Govt. of India in 2004. Over the next 10 years, the development and fabrication of the five ASTROSAT instruments were accomplished and a PSLV launch on Sept. 28, 2015 placed ASTROSAT in a 650 km circular orbit with 6 degree inclination. The ASTROSAT instruments have been performing well for ∼ 4 years and have observed more than 500 cosmic sources. Results from ASTROSAT have appeared in a large number of journal publications. Successful realization and performance of ASTROSAT marks culmination of my research career. I formally retired as a Senior Professor from TIFR on 2006 April 30 on attaining the age of superannuation. However by agreement with TIFR, ISRO designated me ‘ISRO Chair Professor’, which was later renamed as ISRO Satish Dhawan Professor, and asked me to continue to lead ASTROSAT as PI. At the end of my tenure as ISRO Professor on 2011 April 30, I relinquished the PI position. I am at present affiliated with the MU-DAE Centre of Excellence for Basic Sciences, Mumbai University Campus at Mumbai as an Emeritus Professor.

Measurement of the D/p ratio in Cosmic rays with the AMS-02 experiment

The deuteron (D) over proton (p) flux ratio in cosmic rays (CR) is one of the most valuable tools for understanding the propagation of CR in the galaxy and constrain the models that describe it. In this work, two new preliminary measurement of D/p flux ratios is presented, each obtained from the data of the AMS-02 experiment.

Precision Measurement of the Boron to Carbon Flux Ratio in Cosmic Rays from 1.9GV to 2.6TV with the Alpha Magnetic Spectrometer on the International Space Station.

Knowledge of the rigidity dependence of the boron to carbon flux ratio (B/C) is important in understanding the propagation of cosmic rays. The precise measurement of the B/C ratio from 1.9GV to 2.6 TV, based on 2.3million boron and 8.3million carbon nuclei collected by AMS during the first 5years of operation, is presented. The detailed variation with rigidity of the B/C spectral index is reported for the first time. The B/C ratio does not show any significant structures in contrast to many cosmic ray models that require such structures at high rigidities. Remarkably, above 65GV, the B/C ratio is well described by a single power law R^{Δ} with index Δ=-0.333±0.014(fit)±0.005(syst), in good agreement with the Kolmogorov theory of turbulence which predicts Δ=-1/3 asymptotically.

Determination of the proton-to-helium ratio in cosmic rays at ultra-high energies from the tail of the Xmax distribution

We present a method to determine the proton-to-helium ratio in cosmic rays at ultra-high energies. It makes use of the exponential slope, Λ, of the tail of the Xmax distribution measured by an air shower experiment. The method is quite robust with respect to uncertainties from modeling hadronic interactions and to systematic errors on Xmax and energy, and to the possible presence of primary nuclei heavier than helium. Obtaining the proton-to-helium ratio with air shower experiments would be a remarkable achievement.To quantify the applicability of a particular mass-sensitive variable for mass composition analysis despite hadronic uncertainties we introduce as a metric the ‘analysis indicator’ and find an improved performance of the Λ method compared to other variables currently used in the literature. The fraction of events in the tail of the Xmax distribution can provide additional information on the presence of nuclei heavier than helium in the primary beam.

High energy deuterons in cosmic rays registered by the SOKOL satellite experiment

We present the first measurement of the deuterium to proton ratio in cosmic rays, above 500GeV/nucleon. The data were obtained as part of the SOKOL satellite experiment. The cascade curves generated by single charged particles in the calorimeter were analysed. A hadronic showers’ simulation was performed. Simulated and experimental cascade curves were compared. Neural networks were used to select proton and deuteron events. The deuterium to proton ratio was evaluated as 0.114±0.023, whilst the deuterium to helium ratio was evaluated as 1.64±0.30 for energies between 500and2000GeV/n.

Constraints on dark matter annihilation from AMS-02 results

We use recently released data on the positron-to-electron ratio in cosmic rays from the AMS-02 experiment to constrain dark matter annihilation in the Milky Way. Due to the yet unexplained positron excess, limits are generally weaker than those obtained using other probes, especially gamma rays. This also means that explaining the positron excess in terms of dark matter annihilation is difficult. Only if very conservative assumptions on the dark matter distribution in the Galactic Center region are adopted, it may be possible to accommodate dark matter annihilating to leptons with a cross section above 10^-24 cm^3/sec. We comment on several theoretical mechanisms to explain such large annihilation cross sections.

Comprehensive constraints on a spin-3/2 singlet particle as a dark matter candidate

We consider the proposal that dark matter (DM) is composed of aspin-3/2 Dirac-type particle that is a singlet of the standard model(SM). Its leading effective interactions with ordinary matterinvolve a pair of their fields and a pair of SM fermions, in theform of products of chiral currents. We make a comprehensiveanalysis on possible phenomenological effects of the interactions invarious experiments and observations. These include collidersearches for monojet plus missing transverse energy events, directdetections of DM scattering off nuclei, possible impacts on thegamma rays and antiproton-to-proton flux ratio in cosmic rays, andthe observed relic density. The current data already set strongconstraints on the effective interactions in a complementary manner.The constraint from collider searches is most effective at arelatively low mass of DM, and the antiproton-to-proton flux ratiooffers the best bound for a heavy DM, while the spin-independentdirect detection is the best in between. Putting all constraintstogether, a DM mass less than ∼ 1TeV has been excluded,leaving behind a small window for a heavy DM particle of spin-3/2.

Proton to helium ratio in cosmic rays: analysis of the PAMELA data

In our previous papers we proposed an anomalous diffusion model for solution of the knee problem in the primary cosmic-rays spectrum and explanation of different values of spectral exponent of protons and other nuclei at wide energy region. The anomaly results from large free paths (Levy flights) of particles between magnetic domains. The physical arguments and the calculations indicate that the bulk of observed cosmic rays with energy 108 – 1010 eV is formed by numerous distant (r > 1 kpc) sources. It means that the contribution of these sources to the observed flux may be evaluated in the framework of the steady-state approach (JG). The contribution of the nearby (r < 1 kpc) relatively young (t < 105 yrs) sources defines the spectrum in the high energy region and provides the knee (JL). Consequently the cosmic rays intensity from all galactic sources for some group of nuclei consists of local JL and global JG components.We show that in the framework of our anomalous diffusion model with two-component representation of CR intensity the behavior of proton to helium ratio observed by PAMELA can be reproduced.

Spin 3/2 particle as a dark matter candidate: an effective field theory approach

There is no indication so far on the spin of dark matter particles. We consider the possibility in this work that a spin-3/2 particle acts as dark matter. Employing the approach of effective field theory, we list all possible 4-fermion effective interactions between a pair of such fields and a pair of ordinary fermion fields. We investigate the implications of the proposal on the relic density, the antiproton to proton flux ratio in cosmic rays, and the elastic scattering off nuclei in direct detection. While the relic density and flux ratio are sensitive to all interactions albeit at different levels, the direct detection is only sensitive to a few of them. Using the observed data and experimental bounds, we set constraints on the relation of couplings and dark particle mass. In particular, we find that some mass ranges can already be excluded by jointly applying the observed relic density on the one side and the measured antiproton to proton flux ratio or the upper bounds from direct detection on the other.

Measurements of He isotopic ratio in cosmic rays in the 100 MeV &amp;ndash; 1 GeV range with the PAMELA experiment

The PAMELA satellite-borne experiment was launched on 15 June 2006 from the Baikonur cosmod- rome and it has been collecting data since then. The apparatus comprises a time-of-flight system, a silicon- microstrip magnetic spectrometer, a silicon-tungsten electro- magnetic calorimeter, an anticoincidence system, a shower tail counter scintillator and a neutron detector. The com- bination of these devices allows precision studies of the charged cosmic radiation to be conducted over a wide en- ergy range (100 MeV 1 TeV) with high statistics, with par- ticular focus on the antiparticle component. In this work we present 3 He/ 4 He isotopic ratio in the energy range from 100 MeV nucleon -1 to 1 GeV nucleon -1 . The mea- sured abundances are compared with different interstel- lar/heliospheric propagation calculations which are tuned on previous proton and helium measurements.

On the structure and scale of cosmic ray modified shocks

Strong astrophysical shocks, diffusively accelerating cosmic rays (CRs) ought to develop CR precursors. The length of such precursor Lp is believed to be set by the ratio of the CR mean free path λ to the shock speed, i.e. Lp ∼ cλ/Vsh ∼ crg/Vsh, which is formally independent of the CR pressure Pc. However, the x-ray observations of supernova remnant shocks suggest that the precursor scale may be significantly shorter than Lp which would question the above estimate unless the magnetic field is strongly amplified and the gyroradius rg is strongly reduced over a short (unresolved) spatial scale. We argue that while the CR pressure builds up ahead of the shock, the acceleration enters into a strongly nonlinear phase in which an acoustic instability, driven by the CR-pressure gradient, dominates other instabilities (at least in the case of low β plasma). In this regime the precursor steepens into a strongly nonlinear front whose size scales with the CR pressure as Lf ∼ Lp · (Ls/Lp)2(Pc/Pg)2, where Ls is the scale of the developed acoustic turbulence and Pc/Pg is the ratio of CR to gas pressure. Since Ls ≪ Lp, the precursor scale reduction may be strong in the case of even a moderate gas heating by the CRs through the acoustic and (possibly also) the other instabilities driven by the CRs.

Positron fraction in cosmic rays and models of cosmic-ray propagation

The positron fraction observed by PAMELA and other experiments up to $\ensuremath{\sim}100\text{ }\text{ }\mathrm{GeV}$ is analyzed in terms of models of cosmic-ray propagation. It is shown that generically we expect the positron fraction to reach $\ensuremath{\sim}0.6$ at energies of several TeV, and its energy dependence bears an intimate but subtle connection with that of the boron to carbon ratio in cosmic rays. The observed positron fraction can be fit in a model that assumes a significant fraction of the boron below $\ensuremath{\sim}10\text{ }\text{ }\mathrm{GeV}$ is generated through spallation of cosmic-ray nuclei in a cocoonlike region surrounding the sources, and the positrons of energy higher than a few GeV are almost exclusively generated through cosmic-ray interactions in the general interstellar medium. Such a model is consistent with the bounds on cosmic-ray anisotropies and other observations.

Constraints on WIMP Dark Matter from the High Energy PAMELAp¯/pData

A new calculation of the p[over ]/p ratio in cosmic rays is compared to the recent PAMELA data. The good match up to 100 GeV allows us to set constraints on exotic contributions from thermal weakly interacting massive particle (WIMP) dark matter candidates. We derive stringent limits on possible enhancements of the WIMP p flux: a mWIMP=100 GeV (1 TeV) signal cannot be increased by more than a factor of 6 (40) without overrunning PAMELA data. Annihilation through the W+W- channel is also inspected and cross-checked with e+/(e-+e+) data. This scenario is strongly disfavored as it fails to simultaneously reproduce positron and antiproton measurements.

Astrophysics: decoding the cosmos

Preface. Acknowledgments. Introduction. Appendix: dimensions, units and equations. PART I THE SIGNAL OBSERVED. 1 Defining the signal. 1.1 The power of light - luminosity and spectral power. 1.2 Light through a surface - flux and flux density. 1.3 The brightness of light - intensity and specific intensity. 1.4 Light from all angles - energy density and mean intensity. 1.5 How light pushes - radiation pressure. 1.6 The human perception of light - magnitudes. 1.7 Light aligned - polarization. Problems. 2 Measuring the signal. 2.1 Spectral filters and the panchromatic universe. 2.2 Catching the signal - the telescope. 2.3 The Corrupted signal - the atmosphere. 2.4 Processing the signal. 2.5 Analysing the signal. 2.6 Visualizing the signal. Problems. Appendix: refraction in the Earth's atmosphere. PART II MATTER AND RADIATION ESSENTIALS. 3 Matter essentials. 3.1 The Big Bang. 3.2 Dark and light matter. 3.3 Abundances of the elements. 3.4 The gaseous universe. 3.5 The dusty Universe. 3.6 Cosmic rays. Problems. Appendix: the electron/proton ratio in cosmic rays. 4 Radiation essentials. 4.1 Black body radiation. 4.2 Grey bodies and planetary temperatures. Problems. Appendix: derivation of the Planck function. 4.A.1 The statistical weight. 4.A.2 The mean energy per state. 4.A.3 The specific energy density and specific intensity. PART III THE SIGNAL PERTURBED. 5 The interaction of light with matter. 5.1 The photon redirected - scattering. 5.2 The photon lost - absorption. 5.3 The wavefront redirected - refraction. 5.4 Quantifying opacity and transparency. 5.5 The opacity of dust - extinction. Problems. 6 The signal transferred. 6.1 Types of energy transfer. 6.2 The equation of transfer. 6.3 Solutions to the equation of transfer. 6.4 Implications of the LTE solution. Problems. 7 The interaction of light with space. 7.1 Space and time. 7.2 Redshifts and blueshifts. 7.3 Gravitational refraction. 7.4 Time variability and source size. Problems. PART IV THE SIGNAL EMITTED. 8 Continuum emission. 8.1 Characteristics of continuum emission - thermal and non-thermal. 8.2 Bremsstrahlung (free-free) emission. 8.3 Free-bound (recombination) emission. 8.4 Two-photon emission. 8.5 Synchrotron (and cyclotron) radiation. 8.5.4 Synchrotron sources - spurs, bubbles, jets, lobes and relics. 8.6 Inverse Compton radiation. Problems. 9 Line emission. 9.1 The richness of the spectrum - radio waves to gamma rays. 9.2 The line strengths, thermalization, and the critical gas density. 9.3 Line broadening. 9.4 Probing physical conditions via electronic transitions. 9.5 Probing physical conditions via molecular transitions. Problems. PART V THE SIGNAL DECODED. 10 Forensic astronomy. 10.1 Complex spectra. 10.2 Case studies - the active, the young, and the old. 10.3 The messenger and the message. Problems. Appendix A: Mathematical and geometrical relations. A.1 Taylor series. A.2 Binomial expansion. A.3 Exponential expansion. A.4 Convolution. A.5 Properties of the ellipse. Appendix B: Astronomical geometry. B.1 One-dimensional and two-dimensional angles. B.2 Solid angle and the spherical coordinate system. Appendix C: The hydrogen atom. C.1 The hydrogen spectrum and principal quantum number. C.2 Quantum numbers, degeneracy, and statistical weight. C.3 Fine structure and the Zeeman effect. C.4 The l 21 cm line of neutral hydrogen. Appendix D: Scattering processes. D.1 Elastic, or coherent scattering. D.1.1 Scattering from free electrons - Thomson scattering. D.1.2 Scattering from bound electrons I: the oscillator model. D.1.3 Scattering from bound electrons II: quantum mechanics. D.1.4 Scattering from bound electrons III: resonance scattering and the natural line shape. D.1.5 Scattering from bound electrons IV: Rayleigh scattering. D.2 Inelastic scattering - Compton scattering from free electrons. D.3 Scattering by dust. Appendix E: Plasmas, the plasma frequency, and plasma waves. Appendix F: The Hubble relation and the expanding Universe. F.1 Kinematics of the Universe. F.2 Dynamics of the Universe. F.3 Kinematics, dynamics and high redshifts. Appendix G: Tables and Figures. References. Index.

Actinides and the sources of cosmic rays

The abundances of the actinide elements in the cosmic rays can provide critical constraints on the major sites of their acceleration. Using recent calculations of the r-process yields in core-collapse supernovae (SNe), we have determined the actinide abundances averaged over various assumed time intervals for their supernovae generation and their cosmic-ray acceleration. Using standard Galactic chemical evolution models, we have also determined the expected actinide abundances in the present interstellar medium. From these two components, we have calculated the U/Th and other actinide abundances expected in the SN-active cores of superbubbles, as a function of their ages and mean metallicity. We calculate the expected actinide abundances in cosmic-rays accelerated by Galactic SNe. We find that the current measurements of actinide/Pt-group and preliminary estimates of the UPuCM/Th ratio in cosmic rays are all consistent with the expected values if superbubble cores have mean metallicities of around three times solar. Future measurements of the abundance ratios will help to solve these questions. First results of experiments performed on the MIR space station (ECCO) and with balloon flights (TIGER) are promising.

Actinides in the Source of Cosmic Rays and the Present Interstellar Medium

The abundances of the actinide elements in the cosmic rays can provide critical constraints on the major sites of their acceleration. Using recent calculations of the r-process yields in core collapse supernovae, we have determined the actinide abundances averaged over various assumed time intervals for their supernova generation and their cosmic-ray acceleration. Using standard Galactic chemical evolution models, we have also determined the expected actinide abundances in the present interstellar medium. From these two components, we have calculated the U/Th and other actinide abundances expected in the supernova-active cores of superbubbles, as a function of their ages and mean metallicity resulting from dilution with interstellar cloud debris. Then, using observations of the fractions of Galactic supernovae that occur in superbubbles and in the rest of the interstellar medium, we calculate the expected actinide abundances in cosmic rays accelerated by Galactic supernovae. We find that the current measurements of actinide/Pt-group and preliminary estimates of the UPuCm/Th ratio in cosmic rays are all consistent with the expected values if superbubble cores have mean metallicities of around 3 times solar. Such metallicities are quite comparable to the superbubble core metallicities inferred from other cosmic-ray observations. Future, more precise measurements of these ratios with experiments such as ECCO are needed to provide a better measure of the mean source metallicity sampled by the local Galactic cosmic rays. Measurements of the cosmic- ray actinide abundances have been favorably compared with the protosolar ratio, inferred from present solar system abundances, to infer that the cosmic rays are accelerated from the general interstellar medium. We suggest, however, that such an inference is not valid because the expected actinide abundances in the present interstellar medium are very different from the protosolar values, which sampled the interstellar medium 4.5 Gyr ago and included an additional fresh ejecta component from a neighboring supernova.