# Radiation/Cosmic rays

Cosmic rays are energetic charged subatomic particles, originating in outer space.
At right is an image indicating the range of cosmic-ray energies. The flux for the lowest energies (yellow zone) is mainly attributed to solar cosmic rays, intermediate energies (blue) to galactic cosmic rays, and highest energies (purple) to extragalactic cosmic rays.
“Cosmic ray astronomy attempts to identify and study the sources of ultrahigh energy cosmic rays. It is unique in its reliance on charged particles as the information carriers.”

## Astronomy

"Astronomy based on cosmic rays with the highest energies [above 6 x 10$^{19}$ electron volts] opens a new window on the nearby universe."

## Cosmic rays

"Cosmic rays arise from galactic source accelerators."
Cosmic rays may be upwards of a ZeV (10$^{21}$ eV).
About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei of alpha particles, and 1% are the nuclei of heavier elements. Solitary electrons constitute much of the remaining 1%.
Def. cosmic rays that originate from astrophysical sources are called primary cosmic rays.
Def. cosmic rays that are created when primary cosmic rays interact with interstellar matter are called secondary cosmic rays.
Def. low energy cosmic rays associated with solar flares are called solar cosmic rays.
Cosmic rays are not charge balanced; that is, positive ions heavily outnumber electrons. The positive ions are
* free protons,
* alpha particles (helium nuclei),
* lithium nuclei,
* beryllium nuclei, and
* boron nuclei.
Def. a nuclear reaction in which a nucleus fragments into many nucleons is called spallation.
Cosmic rays cause spallation when a ray particle (e.g. a proton) impacts with matter, including other cosmic rays. The result of the collision is the expulsion of large numbers of nucleons (protons and neutrons) from the object hit.
Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium and boron in a process termed cosmic ray spallation. Spallation is also responsible for the abundances of scandium, titanium, vanadium, and manganese ions in cosmic rays produced by collisions of iron and nickel nuclei with interstellar matter.

## Planetary sciences

"Production rates of $^{22}$Na (T$_{1/2}$ = 2.6 years) from aluminium by the action of cosmic rays are measured at the Mont Blanc (altitude 4600 m), the Aiguille du Midi (3840 m), and the Col du Lautaret (2070 m). They are 2.3±0.5, 1.8±0.3, and 0. 77±0.18 atoms min$^{−1}$ kg$^{−1}$, respectively, in good agreement with the calculated production rates, 2.4, 1.7 and 0.6 atoms min$^{−1}$ kg$^{−1}$, respectively, at the three stations."

## Colors

"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."

## Larmor radius

The Larmor radius is the radius of the circular motion of a charged particle] in the presence of a uniform magnetic field. “[F]or a particle of energy E in EeV and charge Z in a magnetic field B in µG [the Larmor radius (R$_L$)] is roughly”
    $R_{L}=1kpc{\frac {E}{ZB}}$
where
   * $R_{L}\$ is the Larmor radius,
   * $E\$ is the energy of the particle in EeV
   * $Z\$ is the charge of the particle, and
   * $B\$ is the constant magnetic field.

## Greisen-Zatsepin-Kuzmin limits

Notation: let the symbol GZK represent Greisen-Zatsepin-Kuzmin.
Based on interactions between cosmic rays and the photons of the cosmic microwave background radiation (CMB) cosmic rays with energies over the threshold energy of 5x10$^{19}$ eV interact with cosmic microwave background photons $\gamma _{\rm {CMB}}$ to produce pions via the $\Delta$ resonance.
    $\gamma _{\rm {CMB}}+p\rightarrow \Delta ^{+}\rightarrow p+\pi ^{0},$
or
    $\gamma _{\rm {CMB}}+p\rightarrow \Delta ^{+}\rightarrow n+\pi ^{+}.$
Pions produced in this manner proceed to decay in the standard pion channels—ultimately to photons for neutral pions, and photons, positrons, and various neutrinos for positive pions. Neutrons decay also to similar products, so that ultimately the energy of any cosmic ray proton is drained off by production of high energy photons plus (in some cases) high energy electron/positron pairs and neutrino pairs.
The pion production process begins at a higher energy than ordinary electron-positron pair production (lepton production) from protons impacting the CMB, which starts at cosmic ray proton energies of only about 10$^{17}$eV. However, pion production events drain 20% of the energy of a cosmic ray proton as compared with only 0.1% of its energy for electron positron pair production. This factor of 200 is from two sources: the pion has only about ~130 times the mass of the leptons, but the extra energy appears as different kinetic energies of the pion or leptons, and results in relatively more kinetic energy transferred to a heavier product pion, in order to conserve momentum. The much larger total energy losses from pion production result in the pion production process becoming the limiting one to high energy cosmic ray travel, rather than the lower-energy light-lepton production process.
The pion production process continues until the cosmic ray energy falls below the pion production threshold. Due to the mean path associated with this interaction, extragalactic cosmic rays traveling over distances larger than 50 Mpc (163 Mly) and with energies greater than this threshold should never be observed on Earth. This distance is also known as GZK horizon.

## Askaryan effects

The Askaryan effect is the phenomenon whereby a particle traveling faster than the phase velocity of light in a dense dielectric (such as salt, ice or the lunar regolith) produces a shower of secondary charged particles which contain a charge anisotropy and thus emits a cone of coherent radiation in the radio or microwave part of the electromagnetic spectrum. It is similar to the Cherenkov effect.
So far the effect has been observed in silica sand, rock salt, and ice.

## Galactic cosmic rays

The "effect of time-variations in galactic cosmic rays on the rate of production of neutrons in the atmosphere [was studied using] a series of balloon and airplane observations of the [fast neutron] flux and spectrum of 1-10 MeV neutrons, in flights at high geomagnetic latitude, during [quiet times as well as during Forbush decreases, which are rapid decreases in the observed galactic cosmic rays following a coronal mass ejection (CME), and solar particle events for] the period of increasing solar modulation, 1965-1969. It also included latitude surveys in 1964-1965 and in 1968."
In the image on the right for Forbush decreases, data include GOES-15 X-rays, energetic particles, and magnetometer. Cosmic Rays from the Moscow station show a Forbush Decrease.
The graph on the right shows an inverse correlation between sunspot numbers (solar activity) and neutron production from galactic cosmic rays.
Notation: let the symbol Z stand for atomic number.
          let the symbol PeV stand for 10$^{15}$ electron volts.
"The most dominant group is the iron group (Z = 25 − 27), at energies around 70 PeV more than 50% of the all-particle flux consists of these elements."
In the graph on the right, the black line is cosmic-ray data and the red line is temperature. Ulysses data is included.

## Ultra-high energy cosmic rays

The Oh-My-God particle was observed on the evening of 15 October 1991 over Dugway Proving Ground, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3×10$^{20}$ eV(50 joules)—in other words, a subatomic particle with kinetic energy equal to that of a baseball (142 g or 5 oz) traveling at 100 km/h (60 mph).
It was most probably a proton with a speed very close to the speed of light (approximately 0.9999999999999999999999951c), so close that in a year-long race between light and the cosmic ray, the ray would fall behind only 46 nanometers (5 x 10$^{-24}$ light-years), or 0.15 femtoseconds (1.5 x 10$^{-16}$ s).
“The energy spectrum of cosmic rays extends to ~10$^{20}$ eV (and smoothly to 10$^{19}$).”

## Primary cosmic rays

The data on the right "from the Climax, Colorado, surface neutron monitor [...] is an indicator of primary cosmic rays in the GeV range."
"Variation with the solar cycle [dotted curve of sunspot data] is evident."
"The tendency of the cosmic-ray modulation to lag sunspots (at least at times of sunspot decline) is visible, as is the somewhat more sawtooth form of the cosmic rays."
"The surface neutron flux [...] is largest at solar minimum and smallest at solar maximum, and [...] has the same sense as the $^{37}$Ar production variations."
"Primary cosmic rays below ~1 GeV are shielded by heliospheric currents which build up during solar maximum; see, e.g., Simpson 1989 and references there in."

## Secondary cosmic rays

Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium and boron in a process termed cosmic ray spallation. Spallation is also responsible for the abundances of scandium, titanium, vanadium, and manganese ions in cosmic rays produced by collisions of iron and nickel nuclei with interstellar matter.
Observations of the lunar shadowing of galactic cosmic rays (GCRs) has demonstrated that there does not appear to be an antiproton component of the galactic cosmic rays, but the antiprotons detected are instead produced by the GCR interaction with interstellar hydrogen gas.
For an interstellar medium "composed of 90% H and 10% He, [with a density of 0.3 atoms cm$^{-3}$] and using the most recently measured cross sections (Webber, 1989; Ferrando et al., 1988b), the escape length has been found equal to 34βR$^{-0.6}$ g cm$^{-2}$ for rigidities R above 4.4 GV, and 14β g cm$^{-2}$ below. ... where R and β are the interstellar values of the rigidity and the ratio of the velocity of the particle to the velocity of light."

## Minerals

"Bombardment by protostellar cosmic rays may make the rock precursors of [Calcium-aluminum-rich inclusions] CAIs and chondrules radioactive, producing radionuclides found in meteorites that are difficult to obtain with other mechanisms."
"The Earth is continually being bombarded by high-energy cosmic rays that originate predominantly from super nova explosions within our galaxy. Interactions between these high energy cosmic rays and the Earth's atmosphere creates secondary and tertiary cosmic rays, including neutrons and muons."
"When reaching the Earth's surface these high energy particles can penetrate meters into rock and sediment."
"Nuclear interactions between neutrons and muons and minerals [as in the diagram at the right] such as quartz, calcite, K-feldspar, and olivine, produce long-lived radionuclides such as Be-10, Al-26 and Cl-36."
"The production rates of these "in-situ produced terrestrial cosmogenic nuclides" are almost unimaginably small - a few atoms per gram of rock per year, however using accelerator mass spectrometry (AMS) we can detect and count cosmogenic nuclides down to levels of a few thousand atoms per gram (parts per million of parts per billion!)."
"The build-up of cosmogenic nuclides through time provides us with a way to measure exposure ages for rock surfaces such as fault scarps, lava flows and glacial pavements.Where surfaces are gradually evolving, cosmogenic nuclide measurements allow us to calculate erosion or soil accumulation rates.Where previously exposed rock or sediment is re-buried the relative decay between different cosmogenic nuclides can be used to date the burial time."

## Theoretical cosmic-ray astronomy

"The phenomenology of cosmic ray cascades ... reflects in an essential way processes governed by the strong force."
"Full multiple scattering theory must take account of the angular dependence of hadron-nucleon scattering, which affects the degree of screening."

## Sources

"Violent activity and Supernovae generate cosmic ray (suprathermal) particles. The speeds of individual particles may be ~ c, and their energy density, if they diffused uniformly through the universe, could well exceed 100 eV per baryon. Subrelativistic particles would be slowed down, and would transmit their energy to the thermal component. However, the relativistic particles could themselves exert a pressure if they were coupled (e.g. via magnetic fields) so that they constituted, with the thermal gas, a composite fluid, to which they contributed most of the pressure. Although there is here even less problem in fulfilling the energy density requirement than there is for ultraviolet radiation, there is uncertainty about how uniformly it can spread. If the cosmic-ray energy remains concentrated around the sources, it is irrelevant in the present context [of the cold dark matter cosmogony]; at the other extreme, if the particles diffuse too freely, they do not couple well enough to protogalactic gas for their pressure gradients to oppose gravitational collapse."

## Objects

"Comparison with the chemical composition of various astrophysical objects, such as the Sun, the interstellar medium, supernovae or neutron stars, can give clues about the site at which cosmic rays are injected into the acceleration process."

## Strong forces

"In field theory it is known that coupling constants “run”. This means that the values of the coupling constants that one measures depend on the energy at which the measurement is performed. [...] the three different coupling constants [one each for the strong force, electromagnetic force, and the weak force] of the standard model seem to converge to the same value at an energy scale of about 10$^{16}$ GeV [...] This suggests that there is only one coupling constant at high energies and most likely only one symmetry group. [...] The current belief [is] that the electromagnetic, weak and strong forces [are] unified at about 10$^{16}$ GeV [as such] one has to rely on [the] particle physics interactions which can lead to electromagnetic radiation and cosmic rays".

## Weak forces

"The feature that makes deep inelastic lepton scattering and e$^+$e$^-$ annihilation tractable is that these processes proceed via the electromagnetic and weak interactions."

## Continua

Continuum "radiation ... diffuse gamma rays with energies above 10 MeV. In the galaxy these are produced primarily by bremsstrahlung from cosmic ray electrons and from decay in flight of π$^0$'s produced by interactions of cosmic ray protons."

## Backgrounds

"The attenuation of photons in the microwave background via the process
    $\gamma +\gamma (3^{o}K)\rightarrow e^{+}e^{-}$
is strongly energy dependent, with a minimum attenuation length of ≈ 7 kpc around 2.5 PeV, as determined by the threshold for e$^+$e$^-$ production (Gould and Schreder, 1966; Jelley, 1966)."

## Meteors

"[T]he carbonaceous material [is] known from observation to dominate the terrestrial [micrometeorite (MM)] flux."
"Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."

## Anomalous cosmic rays

"While interstellar plasma is kept outside the heliosphere by an interplanetary magnetic field, the interstellar neutral gas flows through the solar system like an interstellar wind, at a speed of 25 km/sec. When closer to the Sun, these atoms undergo the loss of one electron in photo-ionization or by charge exchange. Photo-ionization is when an electron is knocked off by a solar ultra-violet photon, and charge exchange involves giving up an electron to an ionized solar wind atom. Once these particles are charged, the Sun's magnetic field picks them up and carries them outward to the solar wind termination shock. They are called pickup ions during this part of their trip."
"The ions repeatedly collide with the termination shock, gaining energy in the process. This continues until they escape from the shock and diffuse toward the inner heliosphere. Those that are accelerated are then known as anomalous cosmic rays."
"ACRs [may] represent a sample of the very local interstellar medium. They are not thought to have experienced such violent processes as GCRs, and they have a lower speed and energy. ACRs include large quantities of helium, oxygen, neon, and other elements with high ionization potentials, that is, they require a great deal of energy to ionize, or form ions. ACRs are a tool for studying the movement of energetic particles within the solar system, for learning the general properties of the heliosphere, and for studying the nature of interstellar material itself."

## Hadrons

The "problems plaguing (3 + 1)- dimensional quantum gravity quantization programs are solved by virtue of the fact that spacetime is dimensionally-reduced. Indeed, effective models of quantum gravity are plentiful in (2 + 1) and even (1 + 1) dimensions [11–13]. Similarly, the cosmological constant problem may be explained as a Casimir-type energy between two adjacent “foliations” of three-dimensional space as the scale size L > L4 opens up a fourth space dimension."
"What makes this proposal of evolving dimensions very attractive is that some evidence of the lower dimensional structure of our space-time at a TeV scale may already exist. Namely, alignment of the main energy fluxes in a target (transverse) plane has been observed in families of cosmic ray particles [18–20]. The fraction of events with alignment is statistically significant for families with energies higher than TeV and large number of hadrons. This can be interpreted as evidence for coplanar scattering of secondary hadrons produced in the early stages of the atmospheric cascade development."
In the image on the right, the "energy spectrum of hadrons in cosmic rays at sea level has been measured over the energy range 600 GeV - 8 TeV. The spectrum is found to be well represented in differential form by N(E)dE = AE$^{-𝛄}$dE where 𝛄 = 2.74 ± 0.16 with no suggested anomalous behaviour over the whole energy range."
"Incident hadrons either interact in the lead (15 cm thick) or iron (15 cm thick) targets and the resulting cascade traverses the plastic scintillators [...] which are both 5 cm thick. Using a burst of size > 400 equivalent muons traversing either scintillator as a master trigger a high voltage pulse was applied to the flash tubes, which are photographed, after a time delay of 330 𝛍s. From the resulting photograph the projected angle of incidence of the incident hadron could be determined and a decision taken a to whether is was in the acceptance geometry as defined [...]. [...] In converting the burst spectrum measurements to an estimate of the incident hadron spectrum the hadrons have been assumed to be nucleons. If charged pions are assumed the energies shown in [the image on the right] should be reduced by 0.8."

## Neutrons

Because free neutrons are unstable, they can be obtained only from nuclear disintegrations, nuclear reactions, and high-energy reactions (such as in cosmic radiation showers or accelerator collisions).
The Bonner Ball Neutron Detector "BBND ... determined that galactic cosmic rays were the major cause of secondary neutrons measured inside ISS. The neutron energy spectrum was measured from March 23, 2001 through November 14, 2001 in the U.S. Laboratory Module of the ISS. The time frame enabled neutron measurements to be made during a time of increased solar activity (solar maximum) as well as observe the results of a solar flare on November 4, 2001."
"BBND results show the overall neutron environment at the ISS orbital altitude is influenced by highly energetic galactic cosmic rays, except in the South Atlantic Anomaly (SAA) region where protons trapped in the Earth's magnetic field cause a more severe neutron environment. However, the number of particles measured per second per square cm per MeV obtained by BBND is consistently lower than that of the precursor investigations. The average dose-equivalent rate observed through the investigation was 3.9 micro Sv/hour or about 10 times the rate of radiological exposure to the average US citizen. In general, radiation damage to the human body is indicated by the amount of energy deposited in living tissue, modified by the type of radiation causing the damage; this is measured in units of Sieverts (Sv). The background radiation dose received by an average person in the United States is approximately 3.5 milliSv/year. Conversely, an exposure of 1 Sv can result in radiation poisoning and a dose of five Sv will result in death in 50 percent of exposed individuals. The average dose-equivalent rate observed through the BBND investigation is 3.9 micro Sv/hour, or about ten times the average US surface rate. The highest rate, 96 microSv/hour was observed in the SAA region."

## Protons

About 89% of cosmic rays are simple protons or hydrogen nuclei.
The free proton is stable and is found naturally in a number of situations. Free protons exist in plasmas in which temperatures are too high to allow them to combine with electrons. Free protons of high energy and velocity make up 90% of cosmic rays, which propagate for interstellar distances.
"Proton astronomy [since protons are also most cosmic rays] should be possible; it may also provide indirect information on inter-galactic magnetic fields."
Antiprotons have been detected in cosmic rays for over 25 years, first by balloon-borne experiments and more recently by satellite-based detectors. The standard picture for their presence in cosmic rays is that they are produced in collisions of cosmic ray protons with nuclei in the interstellar medium, via the reaction, where A represents a nucleus:
    p + A → p + p + p + A
The secondary antiprotons (p) then propagate through the galaxy, confined by the galactic magnetic fields. Their energy spectrum is modified by collisions with other atoms in the interstellar medium. The antiproton cosmic ray energy spectrum is now measured reliably and is consistent with this standard picture of antiproton production by cosmic ray collisions.
Kosmos 60 measured the gamma-ray background flux density to be 1.7×10$^4$ quanta/(m$^2$·s). As was seen by Ranger 3 and Lunas 10 & 12, the spectrum fell sharply up to 1.5 MeV and was flat for higher energies. Several peaks were observed in the spectra which were attributed to the inelastic interaction of cosmic protons with the materials in the satellite body.

## Electrons

Solitary electrons constitute much of the remaining 1% of cosmic rays.
"The conventional procedure of delta-ray counting to measure charge (Powell, Fowler, and Perkins 1959), which was limited to resolution sigma$_z$ = 1-2 because of uncertainties of the criterion of delta-ray ranges, has been significantly improved by the application of delta-ray range distribution measurements for $^{16}$O and $^{32}$S data of 200 GeV per nucleon (Takahashi 1988; Parnell et al. 1989)." Here, the delta-ray tracks in emulsion chambers have been used for "[d]irect measurements of cosmic-ray nuclei above 1 TeV/nucleon ... in a series of balloon-borne experiments".

## Positrons

A few antiprotons and positrons are in primary cosmic rays.
"In the first 18 months of operations, AMS-02 [image under Cherenkov detectors] recorded 6.8 million positron (an antimatter particle with the mass of an electron but a positive charge) and electron events produced from cosmic ray collisions with the interstellar medium in the energy range between 0.5 giga-electron volt (GeV) and 350 GeV. These events were used to determine the positron fraction, the ratio of positrons to the total number of electrons and positrons. Below 10 GeV, the positron fraction decreased with increasing energy, as expected. However, the positron fraction increased steadily from 10 GeV to 250 GeV. This increase, seen previously though less precisely by instruments such as the Payload for Matter/antimatter Exploration and Light-nuclei Astrophysics (PAMELA) and the Fermi Gamma-ray Space Telescope, conflicts with the predicted decrease of the positron fraction and indicates the existence of a currently unidentified source of positrons, such as pulsars or the annihilation of dark matter particles. Furthermore, researchers observed an unexpected decrease in slope from 20 GeV to 250 GeV. The measured positron to electron ratio is isotropic, the same in all directions."
A High-Energy Antimatter Telescope (HEAT) has been developed and tested in the mid 1990s to measure the positron fraction in cosmic rays.
There is an "unexpected rise of the positron fraction, observed by HEAT and PAMELA experiments, for energies larger than a few GeVs."
"[T]he HEAT balloon experiment [30] ... has mildly indicated a possible positron excess at energies larger than 10 GeV ... In October 2008, the latest results of PAMELA experiment [36] have confirmed and extended this feature [37]."
Earlier measurements indicate that "the positron fraction, [f = ] e$^+$/(e$^-$ + e$^+$), increases with energy at energies above 10 GeV. Such an increase would require either the appearance of a new source of positrons or a depletion of primary electrons." All results taken together suggest a slight decrease with increasing energy from about 1 GeV to 10 GeV, but overall the fraction may be constant, per Figure 2.

## Muons

At right is an image of the Moon's cosmic ray shadow, as seen in secondary muons generated by cosmic rays in the atmosphere, and detected 700 meters below ground, at the Soudan II detector.
The shadow is the result of approximately 120 muons missing from a total of 33 million detected in Soudan 2 over its 10 years of operation. The cross denotes the actual location of the Moon. The shadow of the Moon is slightly offset from this location because cosmic rays are electrically charged particles and were slightly deflected by the Earth's magnetic field on their journey to the upper atmosphere. The shadow is produced due to the shielding effect the Moon has on galactic and cosmic rays, which stream in from all directions.
"To reduce the background of ordinary cosmic ray showers, several large air shower experiments emphasize measurement of the muon content of the shower. Ironically, early indications are that the signal seems to have the same muon content as the background."

## Neutrinos

Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions, or when cosmic rays hit atoms.
Cosmic "ray neutrinos of local origin are also the background for neutrino astronomy."

## Gamma rays

"Over the last few years, the cold dark matter cosmogony has become a fiducial model for the formation of structure. [...] The problem with detecting dark matter using annihilation radiation gamma rays has been that the expected signal is comparable to the background (Stecker 1988) and it would be difficult to separate a "cosmic-ray halo" from a dark halo."
In gamma-ray astronomy, when cosmic rays [such as protons] interact with ordinary matter ... pair-production gamma rays at 511 keV [are produced that are included in] the gamma ray background.

## X-rays

Some "of the possible sources of the ultra-high energy cosmic rays, such as very young supernova remnants and X-ray binaries, are associated with relatively dense concentrations of matter and would therefore be likely point sources of secondary photons and neutrinos."

## Opticals

"An accelerator in this particular supernova [TeV range] could hardly be this powerful without having altered the behavior of the optical light curve, which was very successfully explained as being powered by the radioactive decay chain of $^{56}$Ni synthesized in the explosion (Pinto & Woosley, 1988)."
"Cygnus X-3 is obscured by the disk of the galaxy and is not visible in the optical. It is therefore impossible to determine unambiguously by what means it is powered."

## Blues

"The Broad LAteral Non-imaging Cherenkov Array (BLANCA) takes advantage of the CASA-MIA particle array installation by augmenting it with 144 angle-integrating Cherenkov detectors. Located in Dugway, Utah at an atmospheric depth of 870 g cm$^{−2}$, BLANCA uses the CASA trigger to collect Cherenkov light and records the Cherenkov lateral distribution from cosmic ray events in the energy range of the knee. The CASA trigger threshold imposes an energy threshold of ∼ 100 TeV on the Cherenkov array. However, BLANCA analysis uses events with a 200 TeV minimum to avoid composition bias introduced from the CASA trigger."
"Each BLANCA detector contains a large Winston cone [43] which concentrates the light striking an 880 cm$^2$ entrance aperture onto a photomultiplier tube. The concentrator has a nominal half-angle of 12.5° and truncated length of 60 cm. The Winston cones were aligned vertically with ∼ 0.5° accuracy. A two-output preamplifier increases the dynamic range of the detector. The minimum detectable density of a typical BLANCA unit is approximately one blue photon per cm$^2$."

## Greens

"Babcock, using a Fabry and Perot interferometer, determined very accurately the wave-length of the auroral green line 5577. ... After a careful examination of all the results obtained in these reports, we may only say that the exact nature of the cosmical rays, responsible for the aurora, remains a mystery. ... The origin of the most prominent and interesting line of the auroral spectrum, the line 5577, has hitherto remained unexplained. Vegard* has recently obtained a luminescent band from solid nitrogen, that he supposes, under very special conditions, may coincide with the auroral green line. ... spectra of pure helium and of pure oxygen were taken at different pressures and with various excitations, but no trace of 5577 or of any other new lines was obtained. ... Mixtures of helium, oxygen and nitrogen were excited, and it was found that the line 5577 could be photographed on the same plate with the nitrogen band system, thus reproducing in the laboratory practically the entire auroral spectrum. In ... mixtures of neon and oxygen ... neon enhanced the line 5577 in the same manner as helium. ... From Plate 20 it will be seen that all the lines except 5577 have been identified as strong lines in the spectrum of helium, hydrogen, oxygen, or mercury. ... It has been shown that this line must be attributed to some hitherto unknown spectrum of oxygen, and that it is not a limiting member of the ordinary band spectrum of oxygen. It has been observed faintly in highly purified oxygen when currents of high density have been used."
Airglow is caused by various processes in the upper atmosphere, such as the recombination of ions which were photoionized by the sun during the day, luminescence caused by cosmic rays striking the upper atmosphere, and chemiluminescence caused mainly by oxygen and nitrogen reacting with hydroxyl ions at heights of a few hundred kilometers. It is not noticeable during the daytime because of the scattered light from the Sun.

## Plasma objects

"When magnetic fields "reconnect" in a turbulent magnetohydrodynamic (MHD) plasma, electric fields are generated in which particles can be accelerated (Matthaeus et al., 1984; Sorrell, 1984)."

## Berylliums

The "presence in ... cosmic radiation [is] of a much greater proportion of "secondary" nuclei, such as lithium, beryllium and boron, than is found generally in the universe."

## Carbons

These "are nevertheless present in the cosmic radiation as spallation products of the abundant nuclei of carbon and oxygen (Li,Be,B) and of iron (Sc,Ti,V,Cr,Mn)."

## Aluminums

"The dominant reactions for making $^{26}$Al by [cosmic-ray] proton and α bombardment of refractory rocks in impulsive flares are $^{27}$Al(p, pn)$^{26}$Al (β=0.92), $^{26}$Mg(p, n)$^{26}$Al (β=1.0), $^{24}$Mg(α, pn)$^{26}$Al (β=2.5 and y$_{CR}$ = 0.1), $^{28}$Si(p, 2pn)$^{26}$Al (β=0.10), and $^{28}$Si(α, αpn)$^{26}$Al (β=0.41)."
Aluminium-26, $^{26}$Al, is a radioactive isotope of the chemical element aluminium, decaying by either of the modes beta-plus or electron capture, both resulting in the stable nuclide magnesium-26. The half-life of $^{26}$Al is 7.17×10$^5$ years. This is far too short for the isotope to survive to the present, but a small amount of the nuclide is produced by collisions of argon atoms with cosmic ray protons.
Aluminium-26 also emits gamma rays and X-rays, and is one of the few radionuclides to emit X-rays.

## Ions

"Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids."

## Atmospheres

Atmospheric neutrinos result from the interaction of cosmic rays with atomic nuclei in the Earth's atmosphere, creating showers of particles, many of which are unstable and produce neutrinos when they decay. A collaboration of particle physicists from the Tata Institute of Fundamental Research (India), Osaka City University (Japan) and Durham University (UK) recorded the first cosmic ray neutrino interaction in an underground laboratory in Kolar Gold Fields in India in 1965.
"The major problems associated with the balloon borne positron measurements are (i) the unique identification against a vast background of protons, and (ii) corrections for the positrons produced in the residual atmosphere."
"[T]o account for the atmospheric corrections ... first [use] the instrument to determine the negative muon spectrum at float altitude. ... [Use this] spectrum ... to normalize the analytically determined atmospheric electron-positron spectra. ... most of the atmospheric electrons and positrons at small atmospheric depths are produced from muon decay at [the energies from 0.85 to 14 GeV]."

## Materials

"The two groups of elements Li, Be, B and Sc, Ti, V, Cr, Mn are many orders of magnitude more abundant in the cosmic radiation than in solar system material."

## Meteorites

Cosmic ray exposure history established with noble gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years.
Imaged at lower right is an igneous Martian shergottite meteorite. "The perimeter exhibits a fusion crust from the heat of entry into the Earth’s atmosphere. It is a fresh sample of NWA 6963, an igneous Martian shergottite meteorite found in September 2011 in Morocco. Meteorites are often labeled NWA for North West Africa, not because they land there more often, but because they are easy to spot as peculiar objects in the desert sands. From the geochemistry and presence of various isotopes, the origin and transit time is deduced. The 99 meteorites from Mars exhibit precise elemental and isotopic compositions similar to rocks and atmosphere gases analyzed by spacecraft on Mars, starting with the Viking lander in 1976. Compared to other meteorites, the Martians have younger formation ages, unique oxygen isotopic composition (consistent for Mars and not for Earth), and the presence of aqueous weathering products. A trapped gas analysis concluded that their origin was Mars quite recently, in the year 2000."
"The formation ages of meteorites often come from their cosmic-ray exposure (CRE), measured from the nuclear products of interactions of the meteorite in space with energetic cosmic ray particles. This one is particularly young, having crystallized only 180 million years ago, suggesting that volcanic activity was still present on Mars at that time. Volcanic flows are the youngest part of a planet, and this one happened to be hit by a meteor impact, ejecting" it from the youthful Mars.

## Spectrometers

Using Germanium detectors - a crystal of hyperpure germanium that produces pulses proportional to the captured photon energy; while more sensitive, it has to be cooled to a low temperature, requiring a bulky cryogenic apparatus. When exposed to cosmic rays (charged particles in space that come from the stars, including our sun), chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. The gamma ray spectrometer looks at these signatures, or energies, coming from the elements present in the target soil. By measuring gamma rays coming from the target body, it is possible to calculate the abundance of various elements and how they are distributed around the planet's surface. Gamma rays, emitted from the nuclei of atoms, show up as sharp emission lines on the instrument's spectrum output. While the energy represented in these emissions determines which elements are present, the intensity of the spectrum reveals the elements concentrations. Spectrometers are expected to add significantly to the growing understanding of the origin and evolution of planets like Mars and the processes shaping them today and in the past.

## Solar cosmic rays

"A persistent problem of solar cosmic-ray research has been the lack of observations bearing on the timing and conditions in which protons that escape to the interplanetary medium are first accelerated in the corona."
"For solar cosmic-rays, the apparent lack of proton acceleration in the corona seems justified, in contrast to the electrons, proton bremsstrahlung and gyrosynchrotron emission are negligible. This suggests a transit time anomaly, ΔT$_A$, defined as follows:
    ΔT$_A$ = ΔT$_{onset}$ - 11 min,
where ΔT$_{onset}$ is the deduced Sun-Earth transit time for the first arriving relativistic protons and 11 min is the nominal transit time for a ~2 GeV proton traversing a 1.3 AU Archimedes spiral path."
"The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. ΔT$_A$ may have values from "7-19 min for a small sample of well-connected ... cosmic-ray flares." The transit time anomaly may be explained by a rise time associated with the ground-level events (GLEs). "The average GLE rise time ... for well-connected ... events ... defined to be the time from event onset to maximum as measured by the neutron monitor station showing the largest increase and whose asymptotic cone of acceptance ... includes the nominal direction of the Archimedean spiral path, is 21.3 min."
"Data from an extensive air shower detector of ultrahigh-energy cosmic rays shows shadowing of the cosmic-ray flux by the Moon and the Sun with significance of 4.9 standard deviations. This is the first observation of such shadowing."
"The ... solar proton flare on 20 April 1998 at W 90° and S 43° (9:38 UT) was measured by the GOES-9-satellite (Solar Geophysical Data 1998), as well as by other experiments on WIND ... and GEOTAIL. Protons were accelerated up to energies > 110 MeV and are therefore able to hit the surface of Mercury."
Here's a quote from Bowman's "Radiocarbon Dating" book from 1990, p. 19: "High sunspot activity increases the weak magnetic field that exists between the planets, and at such times there is a greater deflection of cosmic rays and hence $^{14}$C decreases."
"Cosmic rays originate from the Sun as well as from galactic sources."
Here's a quote from Aitken's "Radiocarbon Dating" article from 2000, "Cosmic-ray variations are associated with changes in the strength of the Earth's magnetic field. A weak field allows more cosmic radiation to reach the upper atmosphere, and the production of carbon-14 is consequently enhanced--causing raw radiocarbon ages to be underestimates of calendar ages. The short-term wiggles mentioned above are associated with sunspot activity."
"Direct observations of cosmic rays within the heliosphere over several decades have revealed a great deal of information about the acceleration and propagation of cosmic radiation through the interstellar space and the heliosphere. We now know that the cosmic radiation incident at the top of the earth’s atmosphere comes to us through several “filters”:
* Galactic magnetic fields,
* Interstellar magnetic fields,
* Solar magnetic plasma within the heliosphere, regulated by solar activity, and finally,
* the Terrestrial geomagnetic field."
"Additionally, cosmic ray particles are frequently accelerated by the sun, and sometimes in a nearby supernova to make an appreciable difference in the total cosmic ray flux at the earth!"
"Since fairly extensive cosmic-ray data on primary and secondary cosmic rays are available for more than the past five decades, covering five solar cycles, it is fairly easy to make reliable calculations of the magnitude of variations in cosmogenic production rates in terrestrial solids due to solar modulation of galactic cosmic-ray flux. This exercise is based on a study of relative changes in the primary cosmic-ray flux at the top of the atmosphere, and flux of low energy neutrons as measured by neutron monitors. Solar modulation of galactic cosmic-ray flux is conveniently described in terms of a modulation potential, ∅, which is a phase-lagged function of solar activity (see Castagnoli and Lal 1980; Lal 1988b, 2000 and references therein). Continuous data are available for several neutron monitors at sea-level and mountain altitudes located at different latitudes, and these data have been analyzed in terms of transfer functions relating changes in the secondary nucleon fluxes in the atmosphere to those in the primary cosmic-ray spectra (cf. Webber and Lockwood 1988; Nagashima et al. 1989). For a recent discussion on changes in cosmic-ray fluxes as measured on spacecrafts and in neutron monitor counting rates, the reader is referred to Lal (2000). The manner in which the primary and secondary cosmic-ray flux changes occur with the march of solar activity is described in detail by Lal and Peters (1967), who also estimate the changes in the isotope production rates as a function of altitude and latitude during 1956 (a period of solar minimum) and 1958 (a period of unusually high solar activity). Using this approach, and using the neutron monitor data available to date, one can improve on the earlier estimates of solar temporal variations in cosmogenic nuclide production rates at sea level and at mountain altitudes. We must mention here that several direct experiments are also being made at present by exposing targets to cosmic radiation at different altitudes and latitudes (cf. Lal 2000)."

## Coronal clouds

"[C]oronal magnetic bottles, produced by flares, [may] serve as temporary traps for solar cosmic rays ... It is the expansion of these bottles at velocities of 300–500 km/s which allows fast azimuthal propagation of solar cosmic rays independent of energy. A coronagraph on Os 7 observed a coronal cloud which was associated with bifurcation of the underlying coronal structure."
"A persistent problem of solar cosmic-ray research has been the lack of observations bearing on the timing and conditions in which protons that escape to the interplanetary medium are first accelerated in the corona."

## Mercury

From the Mariner 10 observations in electron astronomy, it is concluded that "[d]ue to the limited shielding provided by its relatively weak magnetic dipole moment, the surface of Mercury is everywhere subject to bombardment by cosmic rays and solar energetic particles with energies greater than 1 MeV/nucleon."
"Galactic cosmic rays should have very similar fluxes on Mercury and the Moon." "Solar Cosmic Rays which result in the formation of particle tracks also increase by a factor of up to 10 when compared to the Moon. However, surface temperatures reach 700 K, which can result over millions of years in the annealing of irradiation effects."

## Venus

Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation. This radiation may result in cloud-to-cloud lightning discharges.

## Earth

The Earth's atmosphere is a relatively bright source of gamma rays produced in interactions of ordinary cosmic ray protons with air atoms.
When cosmic rays enter the Earth’s atmosphere they collide with molecules, mainly oxygen and nitrogen, to produce a cascade of billions of lighter particles, a so-called air shower.
An air shower is an extensive (many kilometres wide) cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray (i.e. one of extraterrestrial origin) enters the atmosphere.
There is "a decrease in thunderstorms at the time of high cosmic rays and an increase in thunderstorms 2-4 days later."
It is believed that proton energies exceeding 50 MeV in the lower belts at lower altitudes are the result of the beta decay of neutrons created by cosmic ray collisions with nuclei of the upper atmosphere. The source of lower energy protons is believed to be proton diffusion due to changes in the magnetic field during geomagnetic storms.
The PAMELA experiment detected orders of magnitude higher levels of antiprotons than are expected from normal particle decays while passing through the SAA. This suggests the van Allen belts confine a significant flux of antiprotons produced by the interaction of the Earth's upper atmosphere with cosmic rays. The energy of the antiprotons has been measured in the range from 60 - 750 MeV.

## Moon

“The lunar surface also lends itself well to cosmic ray astronomy (as it lies outside the Earth's magnetosphere) and other astronomies requiring large, bulky detectors (eg gamma-ray astronomy).”
Observations of the lunar shadowing of galactic cosmic rays (GCRs) has demonstrated that there does not appear to be an antiproton component of the galactic cosmic rays, but the antiprotons detected are instead produced by the GCR interaction with interstellar hydrogen gas.
The Compton Gamma Ray Observatory has imaged the Moon in gamma rays of energy greater than 20 MeV. These are produced by cosmic ray bombardment of its surface.
Gamma-ray spectrometers have been widely used for the elemental and isotopic analysis of airless bodies in the Solar System, especially the Moon These surfaces are subjected to a continual bombardment of high-energy cosmic rays, which excite nuclei in them to emit characteristic gamma-rays which can be detected from orbit. Thus an orbiting instrument can in principle map the surface distribution of the elements for an entire planet. They are able to measure the abundance and distribution of about 20 primary elements of the periodic table, including silicon, oxygen, iron, magnesium, potassium, aluminum, calcium, sulfur, and carbon. The chemical element thorium [is] mapped [by a GRS], with higher concentrations shown in yellow/orange/red in the left-hand side image shown on the left.
At right is the result of an all Moon survey by the Lunar Prospector using an onboard neutron spectrometer (NS). Cosmic rays impacting the lunar surface generate neutrons which in turn lose much of their energy in collisions with hydrogen atoms trapped within the Moon's surface. Some of these thermal neutrons collide with the helium atoms within the NS to yield an energy signature which is detected and counted. The NS aboard the Lunar Prospector has a surface resolution of 150 km.

## Mars

"NASA's Curiosity rover ... Radiation Assessment Detector instrument, or RAD, collected data for about 3 1/2 hours on Wednesday (Aug. 8)". As the Sun was relatively quiet in the direction of Mars, most of the spikes in the collected, unprocessed temporal spectrum are considered to be from galactic cosmic-radiation.
"The data show that the radiation levels measured on Mars during this period of quiet solar activity are reduced from the average radiation detected in space during Curiosity's cruise to Mars. This is explained by the rover being on the planet versus out in space, where it would have more exposure to radiation from all directions. Red arrows point to spikes in the radiation dose rate from heavy ion particles, which would be the most dangerous to astronauts. ... RAD measures 26 kinds of charged particles as well as neutrons and gamma rays."

## Interplanetary medium

The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the interplanetary medium varies. For dust particles within the asteroid belt, typical temperatures range from 200 K (−73 °C) at 2.2 AU down to 165 K (−108 °C) at 3.2 AU The density of the interplanetary medium is very low, about 5 particles per cubic centimeter in the vicinity of the Earth; it decreases with increasing distance from the sun, in inverse proportion to the square of the distance. It is variable, and may be affected by magnetic fields and events such as coronal mass ejections. It may rise to as high as 100 particles/cm³.

## Uranus

"[F]or the regions of the giant planets, especially Uranus and Neptune, ... ionization is due mainly to cosmic rays."

## Oort clouds

Cosmic "ray protons at energies up to 10 GeV [may be] able to build-up large amount of organic refractory material at depth of several meters in a comet during [its] long life in the Oort cloud (~4.6 x 10$^7$ yr). Ion bombardment might also lead to the formation of a substantial stable crust (Johnson et al., 1987)."

## Heliospheres

"The sun emits a plasma wind with an embedded magnetic field that tends to exclude low energy galactic cosmic rays from the heliosphere."
The "observed cosmic ray flux at Earth is inversely correlated with solar activity. [...] At a period of high solar activity (for example in 1983), the flux below a GeV can be suppressed by as much as an order of magnitude."
The "flux of cosmic rays in the heliosphere varies with the eleven year solar cycle".

## Interstellar medium

In astronomy, the interstellar medium (or ISM) is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding [Intergalactic medium] intergalactic space.
In astronomy, the interstellar medium (or ISM) is the gas and cosmic dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic medium. The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions, atoms, molecules, larger dust grains, cosmic rays, and (galactic) magnetic fields. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field.
The first gamma-ray telescope carried into orbit, on the Explorer 11 satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. They appeared to come from all directions in the Universe, implying some sort of uniform "gamma-ray background". Such a background would be expected from the interaction of cosmic rays (very energetic charged particles in space) with interstellar gas.

## Milky Way

"As with solar system cosmic rays, it is likely that both extended and point sources play a role in acceleration of particles in the Galaxy."

## Large Magellanic Cloud

Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from cosmic rays and other background radiation.

## Active galactic nuclei

There is "a correlation between the arrival directions of cosmic rays with energy above 6 x 10$^{19}$ electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs."
Some low energy cosmic rays originate or are associated with solar flares. Even these cosmic rays have too high an energy to originate from the solar photosphere. The coronal cloud in close proximity to the Sun may be a source or create them as it bombards the chromosphere from above.
"In particular we recognize a first trace of Vela, brightest gamma and radio galactic source, and smeared sources along Galactic Plane and Center [as a source of ultra high energy cosmic rays (UHECR)]."
"The main correlated map is the 408 MHz one. The first astronomical source that seem to correlate is the main multiplet along Cen$_A$. This AGN source, the nearest extragalactic one, sits in the same direction of a far Centaurus Cluster (part of the Super-Galactic Plane). The blurring by random galactic magnetic field might spread the nearest AGN event along the same Super-Galactic Plane, explaining the AUGER group miss-understanding [3]."

## Locations on Earth

Ice cores contain thin nitrate-rich layers that can be analyzed to reconstruct a history of past events [such as solar cosmic ray events] before reliable observations; [this includes] data from Greenland ice cores and others. These show evidence that events of [the magnitude of the solar storm of 1859—as measured by high-energy proton radiation, not geomagnetic effect—occur approximately once per 500 years, with events at least one-fifth as large occurring several times per century. Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported.

## Technology

The Cherenkov telescopes do not actually detect the gamma rays directly but instead detect the flashes of visible light produced when gamma rays are absorbed by the Earth's atmosphere.

## Fred Lawrence Whipple Observatory

The Fred Lawrence Whipple Observatory is an astronomical observatory owned and operated by the Smithsonian Astrophysical Observatory (SAO) with research activities that include imaging and spectroscopy of extragalactic, stellar, and planetary bodies, as well as gamma-ray and cosmic-ray astronomy.

## Pierre Auger Observatory

The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles (protons or atomic nuclei) with energies beyond 10$^{20}$ eV (about the energy of a tennis ball traveling at 80 km/h). These high energy particles have an estimated arrival rate of just 1 per km$^2$ per century, therefore the Auger Observatory has created a detection area the size of Rhode Island — over 3,000 km$^2$ (1,200 sq mi) — in order to record a large number of these events. It is located in western Argentina's Mendoza Province, in one of the South American Pampas.
The basic set-up consists of 1600 water tanks (water Cherenkov Detectors, similar to the Haverah Park experiment) distributed over 3,000 square kilometres (1,200 sq mi), along with four atmospheric fluorescence detectors (similar to the High Resolution Fly's Eye) overseeing the surface array.

## Major Atmospheric Gamma-ray Imaging Cherenkov Telescopes

MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov Telescopes) is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on [La Palma, one of the Canary Islands, at about 2200 m above sea level. MAGIC detects particle showers released by gamma rays, using the Cherenkov radiation, i.e., faint light radiated by the charged particles in the showers. With a diameter of 17 meters for the reflecting surface, it is the largest in the world. MAGIC is sensitive to cosmic gamma rays with energies between 50 GeV and 30 TeV due to its large mirror; other ground-based gamma-ray telescopes typically observe gamma energies above 200-300 GeV. Satellite-based detectors detect gamma-rays in the energy range from keV up to several GeV. MAGIC has found pulsed gamma-rays at energies higher than 25 GeV coming from the Crab Pulsar. The presence of such high energies indicates that the gamma-ray source is far out in the pulsar's magnetosphere, in contradiction with many models. A much more controversial observation is an energy dependence in the speed of light of cosmic rays coming from a short burst of the blazar Markarian 501 on July 9, 2005. Photons with energies between 1.2 and 10 TeV arrived 4 minutes after those in a band between .25 and .6 TeV. The average delay was .030±.012 seconds per GeV of energy of the photon. If the relation between the space velocity of a photon and its energy is linear, then this translates into the fractional difference in the speed of light being equal to minus the photon's energy divided by 2 x 10$^{17}$ GeV.

## Balloons

The various background effects OSO 1 encountered prompted the flight of similar detectors on a balloon to determine the cosmic-ray effects in the materials surrounding the detectors.
Measurements "of the cosmic-ray positron fraction as a function of energy have been made using the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument."
"The first flight took place from Fort Sumner, New Mexico, [on May 3, 1994, with a total time at float altitude of 29.5 hr and a mean atmospheric overburden of 5.7 g cm$^{-2}$] ... The second flight [is] from Lynn Lake, Manitoba, [on August 23, 1995, with a total time at float altitude of 26 hr, and a mean atmospheric overburden of 4.8 g cm$^{-2}$]".

## Orbital rocketry

Explorer 11 (also known as S15) was an American Earth-orbital satellite that carried the first space-borne gamma-ray telescope. This was the earliest beginning of space gamma-ray astronomy. Launched on April 27, 1961 by a Juno II rocket the satellite returned data until November 17, when power supply problems ended the science mission. During the spacecraft's seven month lifespan it detected twenty-two events from gamma-rays and approximately 22,000 events from cosmic radiation.
The HEAO 3 French-Danish C-2 experiment measured the relative composition of the isotopes of the primary cosmic rays between beryllium and iron (Z from 4 to 26) and the elemental abundances up to tin (Z=50). Cerenkov counters and hodoscopes, together with the Earth's magnetic field, formed a spectrometer. They determined charge and mass of cosmic rays to a precision of 10% for the most abundant elements over the momentum range from 2 to 25 GeV/c (c=speed of light).
The purpose of the HEAO 3 C-3 experiment was to measure the charge spectrum of cosmic-ray nuclei over the nuclear charge (Z) range from 17 to 120, in the energy interval 0.3 to 10 GeV/nucleon; to characterize cosmic ray sources; processes of nucleosynthesis, and propagation modes.
"The rigidity dependence of the escape length of cosmic rays in the galaxy has been derived in the framework of the leaky box model from the measured values of the B/C ratio."
For an interstellar medium "composed of 90% H and 10% He, [with a density of 0.3 atoms cm$^{-3}$] and using the most recently measured cross sections (Webber, 1989; Ferrando et al., 1988b), the escape length has been found equal to 34βR$^{-0.6}$ g cm$^{-2}$ for rigidities R above 4.4 GV, and 14β g cm$^{-2}$ below. ... where R and β are the interstellar values of the rigidity and the ratio of the velocity of the particle to the velocity of light."

## Extreme Universe Space Observatory

The Extreme Universe Space Observatory (EUSO) is the first Space mission concept devoted to the investigation of cosmic rays and neutrinos of extreme energy (E > 5×10$^{19}$ eV). Using the Earth's atmosphere as a giant detector, the detection is performed by looking at the streak of fluorescence produced when such a particle interacts with the Earth's atmosphere.

## Heliocentric rocketry

Helios 1 and Helios 2 are a pair of probes launched into heliocentric orbit for the purpose of studying solar processes. The probes are notable for having set a maximum speed record among spacecraft at 252,792 km/h (157,078 mi/h or 43.63 mi/s or 70.22 km/s or 0.000234c). Helios 2 flew three million kilometers closer to the Sun than Helios 1, achieving perihelion on 17 April 1976 at a record distance of 0.29 AU (or 43.432 million kilometers), slightly inside the orbit of Mercury. Helios 2 was sent into orbit 13 months after the launch of Helios 1. The probes are no longer functional but still remain in their elliptical orbit around the Sun. On board, each probe carried an instrument for cosmic radiation investigation (the CRI) for measuring protons, electrons, and X-rays to determine the distribution of cosmic rays.

## Exploratory rocketry

Pioneer 10 is a 258-kilogram robotic space probe that completed the first mission to the planet Jupiter and became the first spacecraft to achieve escape velocity from the Solar System.
Pioneer 10 was launched on March 2, 1972 by an Atlas-Centaur expendable vehicle from Cape Canaveral, Florida. Between July 15, 1972, and February 15, 1973, it became the first spacecraft to traverse the asteroid belt.
"In 1972, the return of the galactic cosmic rays in the inner solar system to solar minimum conditions and the launch of Pioneer 10 toward Jupiter coincided to make possible the measurements of the low-energy cosmic-ray charge spectra during solar quiet times." "Recent measurements using the Goddard-University of New Hampshire cosmic-ray telescope on the Pioneer 10 spacecraft have revealed an anomalous spectrum of nitrogen and oxygen nuclei relative to other nuclei such as He and C, in the energy range 3-30 MeV per nucleon."
"To eliminate [the solar cosmic-ray background] a very careful selection of times must be made to assure that solar cosmic rays are not obviously present [by] requiring that the 10-20 MeV proton intensity measured on the same experiment be essentially at background level."
The International Cometary Explorer (ICE) spacecraft was originally known as [the] International Sun/Earth Explorer 3 (ISEE-3) satellite.
ISEE-3 was launched on August 12, 1978. It was inserted into a "halo" orbit about the libration point some 240 Earth radii upstream between the Earth and Sun. ISEE-3 was renamed ICE (International Cometary Explorer) when, after completing its original mission in 1982, it was gravitationally maneuvered to intercept the comet P/Giacobini-Zinner. On September 11, 1985, the veteran NASA spacecraft flew through the tail of the comet. The X-ray spectrometer aboard ISEE-3 was designed to study both solar flares and cosmic gamma-ray bursts over the energy range 5-228 keV.
The instruments aboard ISEE-3 are designed to detect
* protons in the energy range 150 eV - 7 keV and electrons in the 10 eV - 1 keV range (Solar wind plasma experiment),
* Low, Medium and High-Energy Cosmic Rays (1-500 MeV/n, Z = 1-28, electrons 2-10 MeV, for Medium Energy; H to Ni, 20-500 MeV/n for High-energy),
* H-Fe 30 MeV/n - 15 GeV/n and electrons 5-400 MeV for the Cosmic-Ray Energy Spectrum experiment,
* 17 Hz - 100 kHz magnetic and electric field wave levels (Plasma Waves Spectrum Analyzer),
* low-energy solar proton acceleration and propagation processes in interplanetary space, Energetic Particle Anisotropy Spectrometer (EPAS),
* 2 keV to > 1 MeV interplanetary and solar electrons,
* radio mapping of solar wind disturbances (type III bursts) in 3-D, 30 kHz - 2 MHz,
* solar wind ion composition, 300-600 km/s, 840 eV/Q to 11.7 keV/Q, M/Q = 1.5 to 5.6,
* cosmic ray isotope spectrometer 5-250 MeV/n, Z=3-28, A=6-64 (Li-Ni),
* ground based solar studies with the Stanford ground-based solar telescope, and the comparison of these measurements with measurements of the interplanetary magnetic field and solar wind made by other experiments on this spacecraft,
* X- and gamma-ray bursts, 5-228 keV, and
* Gamma-ray bursts, 0.05-6.5 MeV direction, profile, spectrum.
The Voyager 1 spacecraft is a 722 kg (1,592 lb) space probe launched by NASA on September 5, 1977 to study the outer Solar System and interstellar medium.
The Cosmic Ray System (CRS) "[d]etermines the origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, the nucleosynthesis of elements in cosmic-ray sources, the behavior of cosmic rays in the interplanetary medium, and the trapped planetary energetic-particle environment.
"Measurements from the spacecraft revealed a steady rise since May in collisions with high energy particles (above 70 MeV), which are believed to be cosmic rays emanating from supernova explosions far beyond the Solar System, with a sharp increase in these collisions in late August. At the same time, in late August, there was a dramatic drop in collisions with low-energy particles, which are thought to originate from the Sun.

## Hypotheses

* Some cosmic rays are superluminals.