T ½ Time taken by radioactive substance for its : Activity of atoms HALF LIFE CONCEPT HALF LIFE Time taken by radioactive substance for its : Activity of atoms Mass OR Number OR to decrease to half of its original value T ½

HALF LIFE CONCEPT EXAMPLE 100 g 50 g 10 January 3000 20 January 3000 A radioactive decay for a radioactive sample 100 g 50 g 10 January 3000 20 January 3000 Half life,T1/2 = 10 days

HALF LIFE CONCEPT EXAMPLE 700/minutes 350/minutes Time 8.00 p.m A radioactive decay for a radioactive sample 700/minutes 350/minutes Time 8.00 p.m Time 12.00 p.m Half life,T1/2 = 4 hours

HALF LIFE CONCEPT EXAMPLE 20 g 10 g 5 g Half life of a radioactive sample is 2 days.Mass of the radioactive sample on 11th January 3000 is 5 g. What was it mass on 7th January 3000 ? 7th January 3000 20 g 9th January 3000 10 g 11th January 3000 5 g

HALF LIFE CONCEPT EXAMPLE 5 g 2.5 g 1.25 g Half life of a radioactive sample is 2 days.Mass of the radioactive sample on 11th January 3000 is 5 g. What will it mass on 15th January 3000 ? 11th January 3000 5 g 13th January 3000 2.5 g 15th January 3000 1.25 g

HALF LIFE CONCEPT EXERCISE 0 day 1000 500 250 250/s A sample of radioactive has a half life of 5 days. What is the activity of 1000/s substance after 10 days ? 1000 0 day 5 days 500 5 days 250 250/s

HALF LIFE CONCEPT EXERCISE 200 g 150 g 100 g Year 3000 Year 4000 Below is a record of radioactive decay for a sample recorded by a student 200 g 150 g 100 g Year 3000 Year 4000 Year 5000 What is the half life of the radioactive sample ? 5000 – 3000 = 2000 years

HALF LIFE CONCEPT EXERCISE A radioactive sample has a half life of 3 years.If mass of the sample is 10 g.What was the mass of the sample 15 years ago ? 320 g 15 years ago 160 g 12 years ago 80 g 9 years ago 40 g 6 years ago 20 g 3 years ago 10 g now

HALF LIFE CONCEPT EXERCISE 100 % T ½ 2T ½ = 5 hours 5 hours 50 % A sample of radioactive left 25 % residual after 5 hours. What is the half life of the sample ? 100 % T ½ 2T ½ = 5 hours 5 hours 50 % T ½ = 5/2 hours T ½ 25 %

HALF LIFE CONCEPT EXERCISE 100 % 2T ½ = 6 days 75 % 50 % T ½ = 3 days A radioactive isotope took 6 days to decay 75 % of its sample. What was the mass of 5 g sample 9 days ago ? 9 days ago 40 g 100 % 6 days ago 20 g 2T ½ = 6 days 75 % 50 % T ½ = 3 days 3 days ago 10 g 25 % Now 5 g

HALF LIFE GRAPH(DECAY CURVE) HALF LIFE CONCEPT HALF LIFE GRAPH(DECAY CURVE) A sample of radioactive has a half life of 2 days. If its activity now is 50/s.What is its activity after 5 days ? 0 day 2 days 4 days 6 day ANSWER CAN NOT BE OBTAINED BY CALCULATION. THE ANSWER ONLY CAN BE FOUND BY USING HALF LIFE GRAPH.

HALF LIFE GRAPH(DECAY CURVE) HALF LIFE CONCEPT HALF LIFE GRAPH(DECAY CURVE) Activity 50 40 30 20 10 Time/day 1 2 3 4 5 6

HALF LIFE CONCEPT EXERCISE If half life of a radioactive sample is 1 hour. What is the activity of 25/s sample after 1.5 hours ? Activity 25 20 15 10 5 1 2 3 Time/hour

What is the half life of the sample ? HALF LIFE CONCEPT EXERCISE Activity 500 400 300 200 100 1 2 4 6 Time/hour 5 hours What is the half life of the sample ?

IT IS NOT AN ANCIENT GOAT HALF LIFE CONCEPT EXERCISE GM tube reads 2080/s of carbon-14 atoms in a fresh bone of a goat. Background reading is 80/s. A student from a school claimed that he has found a bone of an ancient goat at the back yard of his house. The reading of GM tube for the sample is 1080/s. If the half life of carbon-14 is 5 years,estimate the age of the ancient goat. The actual reading of fresh bone = 2080 – 80 = 2000/s The actual reading of ancient bone = 1080 – 80 = 1000/s 2000 1000 SORRY ! IT IS NOT AN ANCIENT GOAT 5 years

HALF LIFE CONCEPT APPLICATIONS OF HALF LIFE Understanding the half life for a radioactive substance in medical field is very important.Radioactive substance with longer half life tends to stay longer in human body and will cause a side effect. If the half life is too short,it will disappear too fast before any test can be done. 2. Archeology. Carbon-14 isotope is used to determine the age of the fossil based on carbon-14 half life.

THE USES OF RADIOACTIVE SUBSTANCE HALF LIFE CONCEPT THE USES OF RADIOACTIVE SUBSTANCE Detect the leaking pipes Small amount of radioactive is injected into the pipe Geiger-Muller counter (G-M Counter) will detect the radioactive at the leaking area

HALF LIFE CONCEPT THE USES OF RADIOACTIVE SUBSTANCE Explain with example the applications of radioactive substances in the following fields : 1. medical 2. agriculture 3. industrial

THE HARMFULL EFFECTS OF RADIOACTICE SUBSTANCE HALF LIFE CONCEPT THE HARMFULL EFFECTS OF RADIOACTICE SUBSTANCE The effects of radioactive depends on : 1. Types of radiation 2. Dosage 3. Exposure time 4. Parts of body Common effects are : 1. Fatigue 4. Infertility in male 7. Genetic defect - Down syndrome - Klinefelter syndrome - Turner syndrome 2. Vomiting 5. Severe skin burn 3. Hair loss 6. Leukemia 8. Death

HALF LIFE CONCEPT PRECAUTION STEPS IN HANDLING RADIOACTICE SUBSTANCE 1. Keep radioactive substance in a room enclosed by concrete 2. Wear protective suits and gloves 3. Use robotic arms to handle a strong radioactive 4. Shield of radioactive container has to be made of lead 5. Do not eat and drink in radioactive lab 6. Dispose radioactive substances in safe method 7. Do not make fun of radioactive substance to your friends 8. Put a radioactive sign or symbol at the place where radioactive is handled 9. Wear photographic film to monitor the amount of radiation exposed.

PAST YEARS QUESTION A. P B. Q C. R D. S Which isotope is suitable to detect the blood clotting ? A. P P will disappear too fast R and S will stay too long in blood stream It is too dangerous. Q is fine because it will not stay too long in blood stream and enough time for it to travel in the blood stream B. Q C. R D. S

PAST YEARS QUESTION A. J B. K C. L D. M Which radioisotope is most suitable as a tracer in human body ? A. J J,K and L are too long.Thus,they will stay longer in human body.This will cause undesirable effect to human body. B. K C. L D. M

PAST YEARS QUESTION A. 400 B. 200 C. 100 D. 50 E. 25 What is the activity after 1 hour ? A. 400 0 min --- 15 min --- 30 min --- 45 min --- 60 min B. 200 800 --- 400 ---- 200 --- 100 -------- 50 C. 100 D. 50 E. 25

What is the radioisotope that can be used to determine the PAST YEARS QUESTION What is the radioisotope that can be used to determine the age of a fossil ? A. Radon-222 B. Uranium-238 C. Carbon-14 D. Iodine-131

PAST YEARS QUESTION A. 160 g 0 day 160 g B. 90 g 18 days 80 g C. 80 g Half life of arsenic is 18 days. After 72 days only 72 g arsenic still remains. What is the initial mass of arsenic ? A. 160 g 0 day 160 g B. 90 g 18 days 80 g C. 80 g D. 72 g 36 days 40 g 54 days 20 g 72 days 10 g

PAST YEARS QUESTION a 2b a How many alpha and beta particles are emitted in this process ?

PAST YEARS QUESTION a. What is meant by half life ? Time taken by radioactive substances to reduce its activity to half of its initial value. b. The initial iodine-131 is 1600 counts per second. Calculate the time taken for the iodine-131 activity to decrease to 100 counts per second if half life of iodine-131 is 8 days. 1600 ---- 800 ---- 400 ---- 200 ---- 100 4 half life Time taken = 4 x 8 days = 32 days

PAST YEARS QUESTION Diagram shows the radioisotope detected in the kidneys of a patient. A normal kidney can expel radioisotope in 20 minutes. a. Which kidney is not function properly ? Give reason for your answer. Right kidney because the radioisotope still can be detected in the kidney after 20 minutes.

PAST YEARS QUESTION Explain the suitability of characteristics of radioisotope to be used in the sterilization of medical equipments. Choose the most suitable radioisotope.Justify your choice.

PAST YEARS QUESTION Reason characteristics Reason State of matter is solid Easy to handle Type of ray is gamma High penetration power Half life is long Economical Therefore,the most suitable radioisotope is Cobalt-60 because it is in solid,produces gamma ray and has a long half life a. Explain whether gamma ray is suitable for taking photograph of human organ. Not suitable because it has high penetrating power and able to kill the body cells