CHEM 1R03 Lecture Notes - Lecture 33: Scintillation Counter, Particle Accelerator, Positron

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 α (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 β (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 β (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 α 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 + α = (1 point)

C-12 + 2 α = (1 point)

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

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

Pu-244 = ________ + 2α + 2β (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). *