Pure Research

In my past posts, I have  spoken about the research behind cosmic rays and information about them, their history, how they are detected, their origins, etc. What I have not addressed very well yet is the significance of all of this and research in general; something I hope to rectify in the coming weeks.

Often in government and funding agencies there is the debate of what sort of research should be actively funded. A portion of the research in the world today is started and funded with a specific goal in mind, such as whether drug A had harmful side effects, or what product is superior to its competitors. In general, this research is purpose driven. On the other hand, there is research that can be labeled in my mind as “pure” research. To me, this is research that is purely research for the sake of understanding. There not really any specific goal in mind other then to simply learn more about the topic. Pure research could also be seen as the desire to put a man on the moon, to explore deep space, and to understand the fundamental laws that govern the universe. Some people are critical of such endeavors, feeling that it is a waste of money to fund research and achievements that seem to have little measurable effect on the world  that could be better invested elsewhere. However, I feel that this is not true. While going to the moon or proving the existence of the Higgs boson may not be the straightforward and tangible results of other research, it is essential to human nature to understand the universe in which we live and satisfy our curiosity of the final frontier. Additionally, pure research has done more than just expand our understanding of the universe, it has also created industry, wealth, and commerce. For example, the Large Hadron Collider, according to an article about the subject on the Telegraph website, involves 10,000 scientists from over 100 counties at an estimated cost of £4.4 billion. If people had been focused solely on improving their lives then we might not have many of the commodities that augment our understanding of the world, from something as simple as fundamental algebra and calculus to the transistors that power modern electronics.

-Source http://www.telegraph.co.uk/science/large-hadron-collider/3351899/Large-Hadron-Collider-thirteen-ways-to-change-the-world.html

Detecting Cosmic Rays

As stated before, a cosmic ray, after entering the atmosphere, colliding with an atom, and breaking into subatomic particles is not visible to the naked eye. However, physicists are able to use two distinct methods to detect the resulting air showers and byproducts that the collisions produce.

How a PMT amplifies the signal of a single photon

The first is the air shower array method. Since the particle showers produced from upper atmosphere collisions can be quite large, on the order of several miles wide when they hit the ground, air shower arrays typically cover a large area (“Detecting Cosmic Rays” 13). The best example of a large array is the Akeno Giant Air Shower Array (AGASA) in Akeno Japan (“Detecting Cosmic Rays” 12). Using 111 detectors spread over forty miles, physicists are able to collect a variety of data from the array, such as concentration and angle of the air shower (“Detecting Cosmic Rays” 12). Physicists can do this because in each detector there is four layers of scintillators, special plastics that emit a pulse of weak light when a charged particle passes through them (“Detecting Cosmic Rays” 12). Therefore, AGASA detects and is most sensitive to muons and other highly energized particles (“Detecting Cosmic Rays” 12).

A similar method can observe cosmic rays in a slightly different manner. Called the air fluorescence method, the passage of the air shower through the atmosphere excites adjacent molecules and this excitation energy is emitted in the form of ultraviolet (UV) light (“Detecting Cosmic Rays” 13). However, because this light is very dim photo multiplier tubes (PMTs) are needed to amplify the electrical signal from a small amount of light to an easily detectable pulse (“Detecting Cosmcic Rays” 13). By arranging these PMTs adjacent to each other in large grids, physicists are able to record the the time of the lights arrival and the amount of light collected in each tube and then reconstruct the origin of the initial particle (“Detecting Cosmic Rays” 13). This method works best in secluded areas far from light pollution, such as the Utah desert, where, starting in 1997, the High Resolution Fly’s Eye Observatory (HiRes) has been dectecting rays using the air fluorescence method (“Detecting Cosmic Rays” 13).

-Source “Detecting Cosmic Rays” pages 12-13 from the University of Columbia Physics Department

Community Response

Recently, my blog has acquired some readers and I have received my first question via email about cosmic rays.

The reader asks,

Perhaps my understanding of atom smashing is a bit out of date. I am having a hard time understanding your statement that a cosmic ray will smash an atom into bits.  I know that relatively recent understanding of particle physics has changed the understanding of atoms, but is the concept of electrons orbiting a nucleus completely out the window?  If not, just what is split into bits, the nucleus or the orbiting electrons or both?  Or are the components of the nucleus along with the electrons freed to become something else or to combine with other freed particles?

 I will try to answer you questions to the best of my ability and understanding. Your understanding of the atom is still correct, electrons circle the nucleus in an atom. However, in their light-speed interstellar travels, most cosmic rays have their electrons stripped off, and all that is left in the majority of cosmic rays is a single hydrogen proton. According to websites such as this, when this proton collides with a molecule in the upper atmosphere, the proton fragments into various quarks (subatomic particles) that quickly decay into more stable particles. The molecule fragments into various other molecules and ions that also quickly decay into more stable states; any electrons that are hit in the molecule are simply knocked off and shoot away. Both Wikipedia and this website offer lots of places to explore for further information.

-Source http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html

A Quick History of Cosmic Rays

In previous posts I have focused on the current studies and impacts of cosmic rays, so I thought that it would be a good time to talk about the history and discovery of cosmic rays. 

For his work on cosmic rays, Victor Hess won the Nobel Prize for Physics in 1936

At the beginning of the 20th century, French physicists Henri Becquerel and Marie and Pierre Curie discovered that certain elements transformed into other elements over time, and in the process, emitted particles (“How Were Cosmic Rays Discovered?” 4). These emitted particles were called radiation and the process itself was called radioactive decay (“How Were Cosmic Rays Discovered?” 4). During the following studies of radioactivity, scientists noticed that electroscope (instruments used to measure electric charge) spontaneously lost their charge in the presence of radioactive materials (“How Were Cosmic Rays Discovered?” 4). Thus the electroscope became the standard instrument for studying radiation and radioactive materials in the first decades of the 20th century (“How Were Cosmic Rays Discovered?” 4). 

Continuing to study radiation and electroscope, physicists soon found that electroscopes slowly lost their charge under all conditions; it didn’t matter if radioactive material was present or not (“How Were Cosmic Rays Discovered?” 4). This observation suggested that there existed some king of low-level background radiation everywhere on the Earth’s surface (“How Were Cosmic Rays Discovered?” 4). At the time, the radiation was thought to come from the Earth itself. This gave rise to the hypothesis that the radiation level would decrease as one traveled further and further from Earth’s surface (“How Were Cosmic Rays Discovered?” 4). In 1912, the Austrian physicist Victor Hess decided to test this hypothesis. Using his hot air balloon to ascend to as high as 17,500 feet, Hess used an electroscope to measure the radiation levels at different altitudes (“How Were Cosmic Rays Discovered?” 4). What Hess found was the opposite of what was believed at the time, the radiation levels actually increased as he climbed higher (“How Were Cosmic Rays Discovered?” 4). Hess interpreted these results to mean that radiation enters the atmosphere from outer space (“How Were Cosmic Rays Discovered?” 5). He named this phenomenon cosmic radiation, which later evolved into cosmic rays. Although these rays were later understood to be particles, the term “cosmic rays” has remained.

-Source “How Were Cosmic Rays Discovered?” pages 4-5 from the University of Columbia Physics Department

Cosmic Ray Interactions in the Atmosphere

Bound by the forces of gravity to the Earth’s surface, we cannot detect cosmic rays directly. Instead, we observe and study the products of the rays’ interaction with our atmosphere (“What Happens to Cosmic Rays in the Atmosphere” 6).

When a cosmic ray enters the outer atmosphere of the Earth it will eventually smash into a nitrogen or oxygen atom (“What Happens to Cosmic Rays in the Atmosphere” 6). This high energy collision causes a chain reaction in which the broken bits of the atom move on to break apart other atoms and so on (“What Happens to Cosmic Rays in the Atmosphere” 6). The result is an air shower of particles in the atmosphere. You can see animations of showers at this website.

Most of these particles have a very low energy, and they decay into other atoms or are absorbed in the atmosphere before they reach the surface of the Earth (“What Happens to Cosmic Rays in the Atmosphere” 6). The only particles that reach the ground are either very energetic or relatively stable (“What Happens to Cosmic Rays in the Atmosphere” 6). One such particle is the muon. The muon is one of the many exotic particles that were discovered in studies of cosmic radiation. The muon is a heavier version of the electron, with the same electric charge but about two hundred times more mass (“What Happens to Cosmic Rays in the Atmosphere” 6). Like the electron, it is a fundamental elementary particle. In contrast to electrons, muons are not stable. They decay in about two millions of a second, turning into their lighter partners, electrons (“What Happens to Cosmic Rays in the Atmosphere” 6). At sea level, the flow of high-energy muons from air showers is about six muons per square inch per minute (“What Happens to Cosmic Rays in the Atmosphere” 6).

Because a muon decays after two millions of a second, Newton’s laws of mechanics tell us that it can travel only about half a mile before it decays, even if it is travelling at 99.9999996% the speed of light (“What Happens to Cosmic Rays in the Atmosphere” 6). Therefore, we would not expect any muons to hit the Earth, since many interactions first happen at least 30 miles up in the atmosphere (“What Happens to Cosmic Rays in the Atmosphere” 6). But even the simplest detectors detect about six muons per square inch, one would ask, how is this possible? Albert Einstein provided the answer. His theory of relativity states that as things move faster, time slows down for them. Since muons are traveling very close to the speed of light, they take five times longer to decay (“What Happens to Cosmic Rays in the Atmosphere” 6).

An air shower is a chain reaction caused by a cosmic ray entering our atmosphere. This image of a simulation uses time-lapse to model the path of an air shower one hundred microseconds at a time. Air showers last only a few hundred microseconds but can cover many square miles. This image shows only one millionth of the number of particles in an actual shower.

 

 -Source “What Happens to Cosmic Rays in the Atmosphere” pages 6-7 from the University of Columbia Physics Department

Why Study Cosmic Rays?

While cosmic rays are invisible to the naked eye, they are all around us, about six hundred particles from cosmic ray air showers hit your body every minute, and they influence our lives in various ways (How do Cosmic Rays Affect Us?” 17).

Everything from the climate of the Earth to DNA replicating are influenced by cosmic rays. For example, when a charged particle from a cosmic ray air shower travels through a cloud, water droplets are left in its wake, increasing the frequency of rain (How do Cosmic Rays Affect Us?” 17). Such particles may also cause genetic mutation in organisms and even accelerate their evolution (How do Cosmic Rays Affect Us?” 17). These effects while subtle, have greatly influenced the Earth’s history and our own existence.

Cosmic rays also adversely affect computers. A cosmic rays that passes through a computer can swap a single digit in the computer’s memory (How do Cosmic Rays Affect Us?” 17). These so-called soft fails are not too much of a concern of Earth, where the protective ozone layer and other particles block most cosmic rays (How do Cosmic Rays Affect Us?” 17). However, in space, satellites on interstellar flights are unprotected and therefore subject to large amounts of cosmic rays, increasing the change of a soft fail (How do Cosmic Rays Affect Us?” 17). Cosmic rays are a part of the natural radiation we are exposed to here on Earth. However, much like satellites, a higher altitude will result in a higher dose of radiation, specifically fifteen to thirty times greater than at sea level (How do Cosmic Rays Affect Us?” 17).

Since cosmic rays have such a interesting impact upon our lives, there is a natural curiosity to learn more about them, such as where they come from and why they exist. These particles may also help us to better understand the laws of physics and discover unknown objects both in our own galaxy and in the distant regions of the universe.

By replicating the collisions and interactions between cosmic rays and our atmosphere scientists hope to prove the exsistence of the Higgs boson, a fundamental particle predicted by theorist Peter Higgs (Haber 40). Many believe that this particle is the key to understanding why elementary particles have mass (Haber 40). Howard Haber of the University of California, Santa Cruz explains the connection by referencing the riddle. “If sound cannot travel in a vacuum, then why are vacuum cleaners so noisy?” This riddle touches on the profound insight of modern physics: the vacuum of space is far from empty. It is indeed ”noisy” and full of virtual particles and force fields (Haber 40). The origin of mass seems to be related to this phenomenon (Haber 40).

In Einstein’s theory of relativity, there is an important difference between massless and massive particles: All massless particles must travel at the speed of light, whereas massive particles can never attain this ultimate speed (Haber 40). The question is how do massive particles arise then? Higgs proposed that the vacuum contains an omnipresent field that can slow down some (otherwise massless) elementary particles, much like a vat of molasses slowing down a high-speed bullet (Haber 40). The particles that are slowed would behave like massive particles travelling at less than light speed (Haber 40). Particles such as photons of light are immune to the field and do not slow down and therefore remain massless (Haber 40).

Although the Higgs field is not measurable directly, accelerators such as the LHC can excite the field and, in terms of Dr. Haber, “shake loose” detectable particles called Higgs bosons (Haber 40).

Humans have a natural drive to make what is unknown known. It is that drive that pushes us to explore cosmic rays so that we may learn more about how we were created, the origin of the universe, and the fundamental laws of physics.

-Source “How do Cosmic Rays Affect Us?” page 17 from the Univeristy of Columbia Physics Department

Haber. “The Higgs Boson.” Symmetry 03.6 (2006): 40. Print.

Types of Cosmic Rays

NASA divides separates cosmic rays into three groups: Galactic Cosmic Rays (GCRs), Anomalous Cosmic Rays (ACRs), and Solar Energetic Particles (SEPs). 

Galactic Cosmic Rays 

According to NASA, Galactic Cosmic Rays are the type that are most discussed and what scientists usually are referring to when they merely say “cosmic rays”. These rays come from within our Milky Way galaxy, but from outside of our solar system (Cosmicopia). These GCRs are only the nuclei of atoms, having had their electron 

Anomaouls Cosmic Rays

 

s stripped in their near lightspeed passage across the galaxy (Cosmicopia). Supernova remnants probably accelerated these particles and the magnetic field of the galaxy keeps them trapped and sends them across the galaxy many times (Cosmicopia). Detection of these particles is possible because of the thin interstellar gas in space, where some of the nuclei interact with the gas and emit gamma rays (Cosmicopia). 

Anomalous Cosmic Rays  

As NASA described on their website on the sunject, the greatest difference between GCRs and ACRs is their origin and relative location in the galaxy. GCRs are usually found all throughout the galaxy while ACRs are within the heliosphere, the magnetic field from the sun that creates a sort of bubble around our solar system (Cosmicopia). 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 (Cosmicopia). When closer to the Sun, these atoms undergo the loss of one electron in photo-ionization or by charge exchange (Cosmicopia). 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 (Cosmicopia). Once these particles are charged, the Sun’s magnetic field picks them up and carries them outward to the solar wind termination shock (Cosmicopia). The termination shock is the point where the solar wind slows down, this creates and area where the leading and receding edge of the shock have a higher density of particles and magnetism (Cosmicopia). The ions, now called pickup ions, repeatedly collide with the termination shock, gaining energy in the process (Cosmicopia). This continues until they escape from the shock and diffuse toward the inner heliosphere (Cosmicopia). Those that are accelerated are then known as ACRs (Cosmicopia). 

Solar Energetic Particles 

The final group NASA writes about are the Solar Energetic Particles. SEPs are accelerated by solar flares, or a gradual explosion in the sun’s atmosphere (Cosmicopia). These flares heat plasma and particles to tens of millions of degrees and cause acceleration of solar particles, in addition to numerous other forces (Cosmicopia). SEP’s composition differ from flare to flare and therefore help scientists to understand how flares and the sun work (NASA). Compared to other forms of cosmic radiation, such as GCRs, SEPs have a relatively low energy (Cosmicopia).

-Source NASA’s Cosmicopia at http://helios.gsfc.nasa.gov/cosmic.html

A Wealth of Research

Today in the Writing Center I really spent some time trying to find articles pertaining to my interest in cosmic rays. In fact, the first thing I learned is that the term “cosmic ray” is not the standard scientific term used, rather, scientists when refering to near-lightspeed particles call them Galactic Cosmic Rays (GCRs).

Anyway, for my own reference as well as others:

http://helios.gsfc.nasa.gov/cosmic.html

http://www.srl.caltech.edu/personnel/dick/cos_encyc.html

http://phy6.org/Education/wcosray.html

http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html

http://imagine.gsfc.nasa.gov/docs/features/topics/instrument_design/cosmic_design.html

What is a Cosmic Ray?

Cosmic rays collide with molecules in the atmosphere, creating a shower of secondary particles that quickly decay.

To understand the effects and applications of cosmic rays one must first understand what exactly a cosmic ray is.

Cosmic rays are the high-energy particles that flow into our solar system from far away in the galaxy (Cosmic Rays). “Cosmic ray” is actually somewhat of a misnomer, as they are mostly pieces of atoms: protons, electrons, and atomic nuclei which have had all of the surrounding electrons stripped during their high-speed (almost the speed of light) passage through the galaxy (Cosmic Rays). Almost 90% of all the incoming cosmic rays are protons, about 9% are helium nuclei (alpha particles) and nearly 1% are electrons (Cosmic Rays).. Most cosmic rays are probably accelerated in the blast waves of supernova remnants (Cosmic Rays). However, the explosion itself does not accelerate the particle to its near light speed velocity. The remnants of the explosions, expanding clouds of gas and magnetic field, can last for thousands of years; this is where cosmic rays are accelerated (Cosmic Rays). Bouncing back and forth in the magnetic field of the remnant randomly lets some of the particles gain energy, and become cosmic rays (Cosmic Rays). Eventually they build up enough speed that the remnant can no longer contain them, and they escape into the galaxy, eventually interacting with our own atmosphere (Cosmic Rays).

To study such interactions, scientists and researchers at CERN are using the Large Hadron Collider (LHC) to recreate the moments after the Big Bang and the particles resulting from high energy collisions.

-Sources NASA’s Imagine the Universe! “Cosmic Rays” at http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html

http://en.wikipedia.org/wiki/Cosmic_ray

My Intentions

I am still uncertain about what exactly I will investigate for my project but I was thinking about delving into the world of cosmic rays; how they are measured, where they come from, and possible applications for them. My interest in this topic started in the summer of my junior year, when I worked at the Quarknet Research Facility at the University of Notre Dame. My tasks and duties were wide ranging, but they consisted mainly of conducting experiments and analyzing the resulting data with programs such as Microsoft Excel. These experiments focused around the timing differences between two identical cosmic ray detectors. It was not only the research environment that was exciting, but also the daily seminars we would have with the professors during lunch. I want to perform this study to expand upon what I learned at Quarknet and to fuel my interest in science.