Aim:How can we determine the particles emitted from radioactive

Transcription

1 Aim:How can we determine the particles emitted from radioactive decay? Nuclear Stability: The larger (more massive) a nucleus is, the harder it is for it to stay together. Natural transmutation (natural radioactive decay) When a nucleus is RADIOACTIVE, it gives off decay particles and changes from one element to another.

2 Alpha Decay 226 Ra 222 Rn + 4 He alpha Practice: Identify substance X X 4 He At 2 85

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4 Beta Decay 234 Th 234 Pa + 0 e Practice: Identify substance X X 14 N e beta

5 Gamma Radiation Technetium-99 (used to locate brain tumors) Tc --> 43 Tc + 0 g 0 **Gamma rays are not particles, they are high energy radiation.**

6 Positron Decay: 234 Pa --> 234 Th e positron How is the positron similar/different from an electron?

7 Identify substance X U 4 He X Fe --> X + 53 Mn 26 25

8 Suppose a beam of radioactive emissions contains alpha, beta and gamma decay. What kind of experiment could one design to separate the three emissions as they travel through the air? Type of Decay Alpha 2He 4 Beta -1e 0 Gamma Ray g Mass Charge Speed Penetrating Power Damage

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10 Artificial Transmutation Changing one element into another by bombarding it with another particle. 35 Cl + 1 n 35 S + X N + 4 He 17 O + X Pu 4 2He Cm + X

11 Aim: How can we solve problems involving half-life? Half life of a radioactive isotope: The period of time that must go by for half of the nuclei (half the mass) in the sample to undergo decay.

12 Problem #1 : The half-life of Rn-222 (a carcinogenic house pollutant) is 3.8 days. If today your basement contains 20.0 grams of Rn-222, how much will remain after 19 days assuming no more leaks in? # half-lives = time elapsed/half-life time Problem # 2: A laboratory sample of 32P triggers 400 clicks per minute in a Geiger-Mueller counter. How many days will it take for the 32P to decay enough so that there are only 50 clicks per minute?

13 Problem # 3: The half-life of Tc-99m* (used to locate brain tumors) is 6.0 hours. If 10. micrograms are left after 24 hours, how much Tc-99m was administered originally? Problem # 4: A laboratory sample of P-32 triggers 100. clicks per minute in a Geiger-Mueller counter. How many days ago did the P-32 to decay enough to produce clicks per minute?

14 Problem # 5: A sample of pure radioactive isotope is left to decay. After 40.0 days, the sample is placed in a mass spectrometer, and it is determined that the sample only 25% of the original isotope remains. How long is the half-life? Radioactive Dating: An ancient scroll is discovered, and it is found that only 25% percent of the original concentration of C-14 (a radioactive isotope found in equal concentration in all living beings) remains. How old is the scroll?

15 USES OF RADIOACTIVE ISOTOPES Many radioactive isotopes are very useful to us! Irradiation of food: kills bacteria, allowing it to be stored for a longer time without having to pasteurize. Irradiation does not change the flavor of food like pasteurization would. Radioactive isotopes are often used medically in the body to either treat cancer or to detect potential problems. **Since radioactivity itself can cause cancer with exposure, any isotopes administered to a person should have a short half- life and be quickly eliminated from the body (usually via urination).**

16 Aim: What is the difference between nuclear fusion and nuclear fission?

17 Nuclear Fission The splitting of a nuclei. The splitting of a nucleus is accompanied by the release of energy. Example: 235 U + 1 n 141 Ba + 92 Kr n This is the basis for a chain reaction. A chain reaction is started by a single neutron, however three neutrons are released in the next step. Each step releases three times as much energy as the previous step.

18 Chain reaction Neutron Capture 3 Neutrons 9 Neutrons

19 Nuclear Fusion: The joining of small nuclei to form a larger one. At temperatures of about 20 million Kelvin four hydrogen nuclei combine to form Helium H 2He + 2-1e + energy (Hence the name, Helios, the sun god). This reaction also liberates energy.

20 Mass- Energy Relation Einstein showed that nuclear changes can convert mass into energy. E = mc 2

21 Unique to Nuclear Fission Common to both Unique to Nuclear Fusion Unstable nucleus undergoes decay all by itself, turning into a new element. The left side of the equation has only the unstable nucleus, the right side has both the decay particle and the new, more stable nucleus Both form new elements from old ones The masses on top of each and the charges on the bottom of each side add up to the same. Stable nucleus is forced to change into a less stable nucleus of a new element. The left side of the equation has the target nucleus and the particle bullet, the right side shows the results of that collision. Produces energy through the destruction of mass. Both follow Einstein s equation E=mc2. A tiny bit of mass (mass defect) is destroyed and energy is created. Produces energy through the destruction of mass, however much more energy has to go into the process than comes out of it.

22 What are the risks and benefits of using radioactive materials? Everyday sources of radiation X-rays - medical uses Sunlight- do you protect your skin well enough? Microwaves- cell phones and microwave ovens Nuclear Waste- Nuclear power plants

23 Biological Uses Radiation therapy for cancer I-131 as a tracer for thyroid problems

24 Others uses C-14- Radioactive dating of organic materials up to about 60,000 years old. H-3 helpful in determining the ages of wines U-238 is useful for determining the age of rocks and the earth

25 ACCIDENTS CAN HAPPEN! 1. Chernobyl 2. Three mile island

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