RADIOACTIVITY1. DEFINE ATOM Atom is the matter made of very small particles. 2. PROPERTIES OF THE PARTICLES IN AN ATOM PARTICLE Proton NOTATION1

MASS 1.67x10-27kg

CHARGE IC +1.6x10-19

p1 1

RELATIVE MASS OF PARTICLE 1

Neutron Electron

n0 0

1.67x10-27kg 9.11x10-31kg

0 -1.6x10-19

1 1 1836

e-1

3. ELEMENT SYMBOL A X Z A = nucleon number Z = proton number X = chemical symbol of the element

4. DEFINE ISOTOPES Isotopes are atoms which have the same number of protons but different number of neutrons in the nucleus. 5. WHAT IS MEANT BY RADIOISOTOPES? Radioisotopes is isotope that are not stable and go through radioactive decay. 6. DEFINE RADIOACTIVITY The spontaneous disintegration of the nucleus on an unstable atom accompanied by radioactive emmisions. 7. UNSTABLE NUCLEI : Z>83 AND A>209 The nuclei of some atoms atre unstable.The nucleus of unstable atom will decay to become more stable by emitting radiation in the form of particle or electromagnetism.

8. RANDOM EMISSIONS OF RADIOACTIVE RAYS MEANSRandom process means there is no way to tell which nucleus will decay and cannot predict when it is going to decay.

9. THREE TYPES OF RADIOACTIVE EMISSIONS(RADIOACTIVE DECAYS):

i.alpha particlesA A-4 4

X ------>Z Z-2

X

+2

He

The daughter nuclide has 2 protons less than 2 neutrons less than parent nuclide.The proton number Z decreases by 2 and its nucleon number A decreases by 4.

ii.beta particlesA A 0

X ------>Z Z+1

Y

+-1

e

A neutron changes to proton and electron during beta decay.Proton stays within the nucleus and electron is emitted as beta particles.The nucleus loses a neutron but gains a proton.Proton number increase by 1,nucleon number remains unchanged.

iii.gamma rays(Electromagnetic waves)A A

X ------>Z Z

X

+

7

Gamma emissions does not change the structure of the nucleus. It just makes the nucleus stable. Gamma rays are emitted at the same time together with either an alpha or beta particle. When a nucleus ejects an alpha or beta particle, there is often some excess energy produced which will be released as gamma rays.

10. CHARACTERISTICS OF THE THREE TYPES OF RADIOACTIVE EMISSIONS. Characteristic Nature Alpha Helium nuclei or4

Beta Electrons,0

He 2 p and 2 n2 -1

e1/2000 -e Fast Medium Medium A few mm of aluminium foil Yes

Gamma Electromagnetic radiation. 0 Neutral Speed of light Low High A few cm of lead No

Mass Charge Speed Ionizing ability Penetrating power Stopped by Deflected by electric and magnetic fields

4 +2e Slow High Low A few cm of air or a piece of paper Yes

11. RADIOACTIVE DETECTOR-DIAGRAM AND WORKING PRINCIPLE. i.GM Tube (Geiger-Muller tube) The radioactive emission enters the tube through the mica window and ionizes the neon gas. - The electrons and positive ions are attracted towards the anode and cathode respectively. - When electrons are collected by the anode, a pulse of current is produces. - The pulses of current are counted by a scaler or ratemeter. - The scaler gives the number of counts over a certain period of time ie counts per minute /counts per second. - Initially the GM tube is switched on without the presence of any radioactive substance. The reading displayed by the ratemeter is known as the background count rates. - When the GM tube is used to detect radioactive emission, the background count rate is subtracted from the count rate obtained. Actual reading = Reading recorded Background Reading. Notes: Background radiation gives reading to the GM tube even though there is no radioactive source. Background radiation is always presentdue to natural radioactivity in the ground,bricks or buildings and cosmic radiation. -

ii.Cloud chamber It shows the path traveled by the ionizing radiation in air. The radioactive produces ions in the air that is saturated with alcohol vapour. The alcohol vapour condenses on the ions to make the tracks of the radiation visible. Alpha particles are best for this because it ionization power is high.

iii.Spark counter The spark counter consists of a wire gauze and a thin wire below it. A high voltage is applied between the gauze and the wire. The voltage is adjusted until it is just below the value required to produce sparks. When a radioactive source is brought near the wire gauze, the radiation ionizes the air below it.

The motion of the ions to the gauze and the wire causes sparks to be produced.

The spark can be seen and heard. - Spark counters are suitable for alpha particles. Beta particles and gamma rays produce too few ions to produce sparks. iv.Electroscope When an electroscope is charged, the gold leaf sticks out, because the charges on the gold repel the charges on the metal stalk. When a radioactive source come near, the air is ionized and starts to conduct electricity. This means the charge leak away, the electroscope discharged and the gold leaf falls.

v.Photographic plate Is worn by worker in nuclear power stations and in radiation laboratories. The badge contains a photographic film in a light-proof packet. The part of the film which had received radiation will be darkned.the degree darkening indicates the amount of radiation the person had been exposed to.

12. DEFINE HALF-DAY OF DAY RADIOACTIVE ELEMENT. Problem solving The half-life T1/2 of a radioactive substance is the time taken for the number of undecayed nuclei to be reduced to half of its original number. - The activity of a radioactive substance is the number of decays per second of the unstable nuclei. It is also known as the decay rate. - Each decay corresponds to the emission of one particle or one photon. - As the number of undecayed nuclei decreases with time, the activity of the radioactive substance also decreases with time. - The activity can be measured by using a GM tube connected to a ratemeter. - The SI unit for activity is the Becquerel (Bq). 1 Bq = 1 decay per second.

13. DRAW A DECAY CURVE

The decay curve for the radioactive gas radon-222 which has a half-life of 55 seconds. A radioactive nuclide with a shorter half-life will decay at a faster rate than another radioactive nuclide that has a longer half-life.

14. USAGE OF HALF-LIFE i. ii. iii. iv. v. vi. vii. Half -life in archeology Carbon-14 has a half-life of 5600 years. Humus,animals and palnt absorb carbon-14 through carbon dioxide gas in the atmosphere. A small amount of carbon in carbon dioxideaists as carbon-14 Living animals and vegetables have a constant amount of carbon-14 becausa carbon-14 decayed will always be replaced. However,for dead beings the amount of carbon-14 in it will decrease because new carbon-14 will not be absorbed causing its reactivity to decreases. When antique or human skills are found,their age can be determined by: Measuring the reactivity of carbon-14 in it. Determine the ratio of decay carbon-14 against intact carbon-14.

Problem solving. A radioiactives sorce gives a reading of 640 counts per second when measured using GM tube.One day later,the reading drops to 40 counts per second.What is half-life of this source? 640 counts per second 80 counts per second 320 counts per second 40 counts per second 160 counts per second

Therefore, 4 T =24 hours T1/2=24/4 hours =6 hours

15. DEFINE RADIOISOTOPES Radioisotopes are unstable isotopes which decay and give out radioactive emissions. Radioisotopes are isotopes of an element that are radioactive. Radioisotopes are naturally occurring or artificially produced.

16. STATE THE USES OF RADIOISOTOPES i.Medicine Radioactive Tracers Nuclear medicine is a branch of medicine that uses radiation to provide information about the function of the specific organs of a patient or to treat disease. Characteristics of radioisotope: a) half-life is medium, long enough to examine metabolic processes in the body and short enough to minimize the radiation dose to the patient. A radioisotope is taken in by a patient through the digestive system, by inhalation or through the blood vessels by injection. The radiation emitted enables organs such as thyroid, bones, heart, liver to be easily imaged by imaging equipment. Disorders can then be detected.

-

b) Emits low energy gamma rays which can pass through the body without much ionization of the molecules. Sterilizing - Medical instruments are sterilized after packing by a brief exposure to gamma rays. - Gamma rays can be used to kill bacteria, mould and insects in food. Cancer treatment - Gamma rays can kill living cells. They are used to kill cancer cells without having to resort to surgery. - This is called radiotherapy. - It is important to administer the correct dosage.Excessive radiation will damage too many healthy cells. Insufficient radiation will not stop the cancer from spreading. ii.Industry Smoke detectors - Contain a weak radioactive source such as americium-241. - Alpha particles emitted from the source ionize air molecules. The ionized air molecules conduct electricity and a small current flows in the smoke detector. - When smoke enters the detector, the soot particles in the smoke absorb some of the alpha particles. - This causes a decrease in the current that flows in the smoke detector and trigger the alarm. - Americium-241 has a long half-life, 460 years so that the substance will last longer.

Thickness control A radioactive sends radiation through the sheet material as it comes off the production line. Beta radiation are used for thin sheets. A radiation detector on

the other side of the sheet measures the intensity of the radiation passing through the sheet. The amount of radiation received by the detector depends on the thickness of the rubber sheet. If the sheet is too thin, the reading of the detector increases. A signal is sent from the roller control to the rollers so that the pressure on the sheets can be reduced.

Detecting leaks in underground water pipes. - A radioactive substance which emits beta particles is added to a fluid in a pipeline to measure the flow rate in the pipeline and to find leaks. - The radiation produced by the radioactive substance can be detected with a GM tube counter placed above ground. - A larger increase in the count rate will indicate that there is leak in that area.

iii.Agriculture By measuring the radioactivity of the stem and leaves, scientists can find out how much fertilizer has been absorbed b the plant. Radioisotopes are used to kill pests and parasites and to controls ripening of fruits.