Read the contents below first, then answer question: Is there any mistake in the top table “Radioactive Decay and Nuclear Change” on Page 89 of Barron’s SAT book?
Positron emission or beta plus decay (β+ decay) is a particular type of radioactive decay and a subtype of beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron . The positron is a type of beta particle (β+), the other beta particle being the electron (β–) emitted from the β– decay of a nucleus.
An example of positron emission (β+ decay) is shown with magnesium decaying into sodium:
12Mg → 11Na + β+
Because positron emission decreases proton number relative to neutron number, positron decay happens typically in large “proton-rich” radionuclides. Positron decay results in changing an atom of a chemical element into an atom of an element with an atomic number that is less by one unit.
Positron emission should not be confused with electron emission or beta minus decay (β– decay), which occurs when a neutron turns into a proton and the nucleus emits an electron.
Electron capture (sometimes called inverse beta decay) is also occasionally classified as a type of beta decay. (In some ways, electron capture can be regarded as the “opposite” of positron emission. It can only occur when electrons are available and requires less energy difference between parent and daughter, so occurs much more often in smaller atoms than positron emission does.)
In the process of electron capture, one of the orbital electrons, usually from the inner shell orbital, is captured by a proton in the nucleus, forming a neutron.
- Read “Decay Series, Transmutations and Half-life on Page 88, Barron’s SAT book,
- Read entire page 89 and 90.
- Then do Practice Excises #10 through #19 on page 92 and 93.
Every student is required to write an essay (>= 250 characters) for midterm exam on Nov. 03. Please have your daughter/son submit her/his essay in Microsoft Word file to my email adress, before 12 noon on Nov. 03. S/he can choose any topic for the essay. S/he is also required to bring the paper copy of her/his essay to the class on Nov. 03.
I also hope you encourage your daughter/son participate 作文比赛. 参赛作文 automatically fulfills the midterm essay requirement, i.e. 参赛作文 is his/her midterm essay.
三、比赛方法: 比赛的作文命题分别是“我眼中的中国”和“记一件有意义的事”。参赛者可任选一题写一篇叙述文，儿童组300字；少儿组400字；少年组 600字。
五、评奖方式： 我们将组织本校资深老师和校有关行政人员组成评审委员会，本着公开、公平、公正的原则评选出优秀和获奖作品。 儿童组，少儿组以及少年组各设一等奖一名，二等奖2名，三等奖3名，优秀奖若干名，学校将发给奖状和一定的物质奖品，予以表彰和鼓励！。
The 2014 AP Chemistry exam will be the first administration of a redesigned test as a result of a redesigning of the AP Chemistry course. The exam format will be different from the past years.
Section I: Multiple Choice; 90 minutes; Number of Questions: 60
Section II: Free Response; 90 minutes; Number of Questions: Long Free Response: 3 and Short Free Response: 4
Section II contains two types of free-response questions (short and long), and each student will have a total of 90 minutes to complete all of the questions. This section also contains questions pertaining to experimental design, analysis of authentic lab data and observations to identify patterns or explain phenomena, creating or analyzing atomic and molecular views to explain observations, articulating and then translating between representations, and following a logical/analytical pathway to solve a problem.
Beginning with the May 2014 administration of the AP Chemistry Exam, multiple-choice questions will contain four answer options, rather than five. This change will save students valuable time without altering the rigor of the exam in any way. A student’s total score on the multiple choice section is based on the number of questions answered correctly. Points are not deducted for incorrect answers or unanswered questions.