Nucleosynthesis Essays - Nuclear Physics, Nuclear Chemistry

Nucleosynthesis Essays - Nuclear Physics, Nuclear Chemistry Nucleosynthesis The big bang which created the universe, only created the elements Hydrogen (H) and Helium (He) and possibly a very small amount of Lithium (Li). However, a glance at the periodic table of the elements shows that today (some 15 billion years after the big bang) there are at least 108 known elements. Every atom of every element heavier than Li has been produced since the big bang! The factories which make these elements are stars. Nucleosynthesis or the synthesis of nuclei, is the process by which stars (which start out consisting mostly of H and He) produce all other elements. The key is nuclear fusion, in which small nuclei are joined together to form a larger nucleus. (This contrasts with nuclear fission, in which a large nucleus breaks apart to form two smaller nuclei). Fusion requires an extremely large amount of energy (see fig. 1), and can typically only take place in the centers of stars. FIGURE 1 a) Low energy proton is strongly repelled by the 7Be nucleus.b) High energy proton moves so fast that it can strike the 7Be nucleus. Once the proton touches the nucleus, it has a chance to stick. If the proton sticks, the 7Be becomes a 8B nucleus.c) 8B is radioactive and changes into 8Be plus a positron (b+) and a neutrino (n). 8Be is itself radioactive, and almost immediately breaks into two 4He nuclei. Protons repel each other. This repulsion becomes stronger as the protons get closer together (just like when you try to stick two magnets together north to north, or south to south. Try this! As you push the magnets closer together, it becomes harder to do). However, if the protons can actually touch each other, they have a chance to stick together! This is because of the strong nuclear force which attracts nucleons (protons or neutrons) together, and is much stronger (at close range) than the electromagnetic force repulsion that makes protons repel other protons. (Magnets do not do this: two like poles will never stick together). In order to get a proton to strike another proton (or a nucleus that contains several protons) they must be traveling at high relative speeds; if their closing velocity is not great enough, they will never get close enough to stick together, because they strongly repel each other. But, just as you can make two of the same magnetic poles touch each other by providing sufficient force, so too can protons touch when they have sufficient relative speed. This can take place in the center of the sun, where the temperature is extremely high. Temperature is related to atomic motion: the hotter something is, the faster its atoms are moving [] see demo food coloring in water[]. Table 1 shows the nuclear reactions that are taking place in our sun, as well as nuclear reactions that take place in stars that are either older than our sun, or hotter than our sun. The reactions in columns 2 and 3 occur after a star has entered the red giant phase. How fast a star evolves to this point depends on its mass: stars heavier than the sun can reach this phase in less than 5 billion years (the age of the sun) whereas stars with about our sun's mass take about 10 billion years to get there. The particles you may be unfamiliar with are: n the neutrino, g a gamma ray (high energy light wave), and b+ the positron (the antimatter version of the electron). TABLE 1. NUCLEAR REACTIONS IN STARS OUR SUN NOW OLDER, OR HOTTER STARS p + p 2H + b+ + n 4He + 4He 8Be + g 12C + p 13N + g 2H + p 3He + g 8Be + 4He 12C + g 13N 13C + b+ + n 3He + 3He 4He + p + p 12C + 4He 16O + g T1/2 = 10 min 16O + 4He 20Ne + g 13C + p 14N + g 3He + 4He 7Be + g 20Ne + 4He 24Mg + g 14N + p 15O + g 7Be + p 8B + g 15O 15N + b+ + n 8B 8Be + b+ + n T1/2 = 120 ms 8Be 4He + 4He 15N + p 12C + 4He He burning (core) H

First-Year Residency Requirements for College

First-Year Residency Requirements for College At many colleges and universities, you will need to live in the residence halls for your first year or two of college. A few schools require campus residency for all four years. Even if your school allows students to live off campus, consider the pros and cons of living on campus before making a final decision. Why Youre Required to Live on Campus Your First Year of College Students are most likely to stay at a college when they feel like they belong. This sense of belonging has a direct impact on a colleges retention rate and graduation rate. When new students live off campus, they are less likely to get involved in campus clubs and activities and will have a harder time making friends among fellow students.When a student lives on campus, the college has an easier time helping out should that student encounter trouble on the academic or social front. Resident Advisors (RAs) and Resident Directors (RDs) are trained to intervene and assist when students are struggling, and they can help direct students to the appropriate people and resources on campus.A college education is about much more than taking classes and earning a degree. Residential life teaches many important life skills: resolving conflicts with a roommate, suitemates, and/or students on your hall; learning to live with people who may be quite different from you; building a living and learnin g community; and so on. At most schools, campus residence halls are much closer to important facilities (library, gym, health center, etc.) than off-campus apartments.Colleges have little ability to monitor illegal behavior off campus, but within the residence halls, activities such as underage drinking and illegal drug use can be detected and responded to much more readily.  When you are a new student, it can be a huge benefit to be living in the same building with upper-class students and/or RAs who know the campus and academic expectations well. Youre also more likely to find mentors in a campus residence hall than in an off-campus apartment.Along with having upper-class mentors, youll also have a peer group that will include students taking some of the same classes as you. Living on campus gives you ready access to study groups, and peers can often help if you are forced to miss a class or if you find material from a lecture confusing. Along with the obvious benefits of living on campus, colleges have a few reasons for keeping students on campus that may be a bit less altruistic. Specifically, colleges dont make all of their money from tuition dollars. For the great majority of schools, significant revenues also flow from room and board charges. If dorm rooms sit empty and not enough students are signed up for meal plans, the college will have a harder time balancing its budget. If more states move forward with free tuition plans for in-state students at public universities (such as New Yorks Excelsior Program), all college revenue will come from room, board, and associated fees. Exceptions to College Residency Requirements Keep in mind that very few colleges have residential policies that are set in stone, and exceptions are often made. If your family lives very close to the college, you can often get permission to live at home. Doing so obviously has significant cost benefits, but dont lose sight of the valuable experiences you might miss out on by choosing to commute. By living at home, you wont be getting the full college experience, including learning how to be independent.Some colleges with two- or three-year residency requirements allow strong students to petition to live off campus sooner. If youve proven your academic and personal maturity, you may be able to move off campus earlier than many of your classmates.At some schools, it may also be possible to petition to live off campus for reasons related to specific health and wellness needs. For example, you might be able to petition to live off campus if the college cant meet your atypical dietary requirements or if you need access to regular healthcare that simply isnt feasible in a college residence hall.   A Final Word About Residency Requirements Every college has residency requirements that were developed for the unique situation of the school. Youll find that some urban schools as well as some universities that have been experiencing rapid expansion, simply dont have enough dormitory space to handle all of their students. Such schools often cannot guarantee housing and may be happy for you to live off campus. At any school, its important to weigh the pros and cons of living off campus before making a decision. Time spent cooking meals and commuting to campus is time that wont be spent on your studies, and not all students do well with too much independence.