CHEM 120 Lecture Notes - Lecture 24: Spontaneous Emission, Alpha Particle, Positron

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15 Jun 2018

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Radioactivity: spontaneous emission of particles/electromagnetic radiation from unstable nuclei

- E.g. emission of; , , gamma rays, positrons & e capture

Radioactive Decay Series; sequence of nuclear reactions that result in the formation of stable

isotopes (contradicts atomic theory [transmutation occurs] → changing isotopes)

+ Particles – identical to He-4 nuclei (+ charge)

- Daughter nucleus = difference in alpha particle + mass number + A.N.

- Decay- high speed electrons (- charge)

- Mass number =0, no nucleus

- Because you release an electron, neutron disintegrates into proton (c14 to n14)

Positrons – + high-speed positrons (+ charged electrons)

- Daughter will have one less proton than the parent

- Releases a proton and forms a neutron

- No nucleus, mass number =0

Electron Capture – 1s electron captured by the nucleus, - low energy

- Same as positron emission

- p + e → n

Gamma rays – y, photons with high energy (no charge)

- Alpha Decay → decrease number of neutrons & protons by 2

- Beta Decay → increase number of protons by 1

- Positron Decay → increase number of neutrons & decrease # of protons by 1

- Gamma Emission → no charge in the number of neutrons/protons

o Α-particles; stopped by normal matter, destroyed by outer surface of skin

o B-particles; go through paper, 1 cm into flesh, what stops them is electrostatic

forces; stopped by metals

o G-rays; both paper and metal, ionizes other metals, damage DNA/protein etc.

Conserve Mass Number (A)- sum of protons & neutrons in the products = sum of protons &

neutrons in reactants

Atomic Number (Z) – sums of products/reactants are equal by nuclear charges

- Nuclei have magic numbers (stable); 2, 8, 20, 50, 82, 126 [pic]

- All isotopes with Z > 83 are unstable

Neutron-Rich Nuclides (N/Z > 1) → B- decay (neutron → proton reduce N/Z) mass number > avg.

atomic mass

Proton-Rich Nuclides (N/Z <1) → B+ emission (N/Z goes up, proton → neutron)

Heavy Nuclides (Z > 83) A decay (reduced N/Z by 2 units)

Radioactive Decay Kinetics: 1st order

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Radioactivity: spontaneous emission of particles/electromagnetic radiation from unstable nuclei. Radioactive decay series; sequence of nuclear reactions that result in the formation of stable. Because you release an electron, neutron disintegrates into proton (c14 to n14) Daughter nucleus = difference in alpha particle + mass number + a. n. E. g. emission of; (cid:573), (cid:574), gamma rays, positrons & e capture isotopes (contradicts atomic theory [(cid:498)transmutation(cid:499) occurs] changing isotopes) (cid:573)+ particles identical to he-4 nuclei (+ charge) (cid:574)- decay- high speed electrons (- charge) Positrons (cid:574)+ high-speed positrons (+ charged electrons) Electron capture 1s electron captured by the nucleus, (cid:574)- low energy. Gamma rays y, photons with high energy (no charge) Daughter will have one less proton than the parent. Releases a proton and forms a neutron. Alpha decay decrease number of neutrons & protons by 2. Beta decay increase number of protons by 1. Positron decay increase number of neutrons & decrease # of protons by 1.

Related Questions

Nuclear Decay Equations

Learning Goal:

To predict the products of alpha emission, beta emission, positron emission, and electron capture.

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. There are five major types of radioactive decay:

Alpha (Î±) radiation consists of helium nuclei. The helium nucleus is a small particle containing two protons and two neutrons (42He).

Beta (Î²) radiation consists of electrons. In nuclear equations, the standard format for representing a beta particle using superscripts and subscripts is 0â1e.

Positron emission results from the conversion of a proton in the nucleus to a neutron. The ejected positron is a particle that has the same mass as an electron but an opposite charge. In nuclear equations, the standard format for representing a positron using superscripts and subscripts is 01e .

Electron capture is the capture of an inner shell electron by a proton in the nucleus. The process emits gamma (Î³) radiation and results in a proton converting to a neutron. Gamma radiation consists of high-energy electromagnetic radiation.

Gamma (Î³) radiation consists of high-energy radiation, and contains no particles and thus they have no mass. In nuclear equations, the standard format for representing gamma radiation using superscripts and subscripts is 00Î³.

Balancing a decay equation

There are two main rules to remember when balancing nuclear equations:

The total of the superscripts in the reactants and products must be the same.

The total of the subscripts in the reactants and products must be the same.

For an isotope of an element, the superscripts are mass numbers, and the subcripts are atomic numbers:

Mass number â¶ AAtomic number â¶ Z X âµ Chemical symbol

Where the mass number (A) is the sum of the number of proton and number of neutrons in the nucleus, atomic number (Z) is the number of protons in the nucleus, and chemical symbol (X) is the symbol of the specific element.

Part A

Identify the nuclide produced when americium-241 decays by alpha emission:

241 95Amâ42He + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part B

Identify the nuclide produced when phosphorus-32 decays by beta emission:

3215Pâ 0â1e + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part C

Identify the nuclide produced when fluorine-18 decays by positron emission:

18 9Fâ01e + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part D

Identify the nuclide produced when thallium-201 decays by electron capture:

201 81Tl+ 0â1eâ00Î³ + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Following are some Parent - Daughter isotope pairs with their half life:

U-238 going to Pb-206 (T_1/2 = 4.5 x 10⁹ years)

U-235 going to Pb-207 (T_1/2 = 0.7 x 10⁹ years)

C-14 going to N-14 (T_1/2 = 5700 years)

Q-1: If the C-14 : N-14 ratio in a shell in a sandstone was found to be 1 : 3, how old is the shell?

Answer-1: _____________ years

Q-2: If the U-235:Pb-207 ratio in a rock from Massachussets was determined to be 1 : 15, how old is the rock?

Answer-2: __________years

Q-3: (a) If the U-238:Pb-206 ratio in a crystal of zircon found in a sandstone was determined to be 1 : 7, what radiometric age will this give for the zircon?

Answer-3: ___________years.

(b) Does the determined age realistic? If no why not? If yes, how? (Explain briefly).

Answer-4: ________________________.

Link to online Periodic Table: https://www.ptable.com/

Three main types of decay processes involve:

1. Alpha decay: nucleus spontaneously emits an Î± (alpha) particle, same as Helium nuclei, which is 2 p+ and 2 n.

Result: atomic number decreases by 2 (lost 2 p+); atomic mass decreases by 4 (lost 2 p+ and 2n = 4 amu)

2. Beta decay: neutron in nucleus spontaneously emits a Î² (beta) particle , which is essentially an electron trapped in a neutron. The neutron, therefore, turns itself into a proton.

Result: atomic number increases by 1 (gained 1 p+); atomic mass stays same.

3. Beta or electron capture: : proton in nucleus captures a Î² (beta) particle which is essentially an electron that can become part of a neutron. The proton, therefore, turns itself into a neutron.

Result: atomic number decreases by 1 (lost 1 p+); atomic mass stays same.

For example: Po-206 (atomic number = 84) with Î± decay makes Pb-202 (atomic number = 82)

Based on the above information, complete the following radioactive transformations ( You may need to refer to a periodic table): Please write your responses as "element symbol" followed by "atomic mass" as written in this problem itself, e.g. Boron (atomic number 5 and atomic mass 11) is written as B-11.

Be-9 + Î± = (1 point)

C-12 + 2 Î± = (1 point)

Bi-206 = _________ + Î² (Note: Î² on the product side means decay from Bi) (1 point)

Tl-202 + Î² = ________ (Note:Î² on the reactant side means nucleus captured a beta particle) (1 point)

Pu-244 = ________ + 2Î± + 2Î² (Note: there are two types of particle decaying twice) (2 point)

1. (1 point) What might be damaged by ionizing radiation? * paper soft tissue wood lead

2. (1 point) When an atom emits an beta particle, what is the change in the atomic number? * no change decrease by 1 decrease by 2 increase by 1 increase by 2

3. (1 point) What is the change in atomic mass caused by the emission of gamma radiation? * no change decrease by 1 decrease by 2 increase by 1 increase by 2

4. (1 point) Which of the following materials would effectively stop gamma radiation? * one foot of concrete single sheet of paper thin pieces of wood three inches of lead

5. (1 point) When the ratio of neutron-to-proton dictates that a neutron must break down it will form _________. * A helium nucleus An alpha particle A proton and an electron Two protons

6. (1 point) What determines the type of decay if a nucleus falls outside the band of stability? * the ratio of alpha particles to beta particles the ratio of beta particles to alpha particles the ratio of neutrons to protons the ratio of protons to neutrons

7. (1 point) A positron is emitted when ____________. * an alpha particle forms a beta particle forms proton converts to a neutron neutron converts to a proton

8. (1 point) How does an atom with too few neutrons relative to protons undergo radioactive decay? * by converting proton to a neutron by converting a neutron to a proton by emitting an alpha particle by emitting a beta particle

9. (1 point) How much of the original sample would remain after two half lives have past? * There would be nothing of the original left There would be half of the original sample still there There would be one quarter of the sample still present There would only be one eighth of the original sample still present

10. (1 point) What is the approximate half life of carbon- 14? * hundreds of years thousands of years million of years billion of years

11. (1 point) A reaction where a heavier nucleus splits into smaller nuclei is called ___________. * a chemical reaction background radiation fission fusion

12. (1 point) __________ and ___________ are used as moderators to capture neutrons in a nuclear reactor. * Cadmium and other metal Carbon and water Liquid sodium and water Plutonium and neptunium

13. (1 point) For a person working in a place where they might be exposed to radiation a _________ is routinely used to check their exposure. * film badge Geiger counter moderating rod scintillation counter

14. (1 point) Radioisotopes are used to do all of the following except __________. * analyze matter. diagnose medical problems. improve the flavor of food. treat diseases. study plant growth. Open response questions: Answer the following with complete sentences or if math is involve show the work

15. (3 point) The radioisotope radon-222 has a half-life of 3.8 days. How much of a 198.6 g sample of radon -222 would be left after approximately 23 days? ( Show your work) * Your answer

16. (3 point) How can an element be artificially transmuted? Give an example that has an element and what it is transmuted into. * Your answer

17. (4 point) Why does the mass and charge of an alpha particle make it less penetrating than a beta or gamma? Discuss both the mass and the charge(2 points each). *

CHEM 120 Lecture Notes - Lecture 24: Spontaneous Emission, Alpha Particle, Positron

CHEM 120 Full Course Notes

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