CHAPTER 8: RADIOACTIVITY
Transcript of CHAPTER 8: RADIOACTIVITY
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ENGLISH VERSION:
CHAPTER 8: RADIOACTIVITY
8.1 WHAT IS RADIOACTIVITY?
1. We shall study the contribution of 3 individuals:
Wilhelm Roentgen: - discovered X-ray
Henri Becquerel: - discovered radioactivity
Marie & Pierre Curie: - detected gamma ray - discovered polonium & radium as radioactive substance
2. Radioactivity = spontaneous decay of unstable to stable nuclei & emitting radioactive radiations (α,β,γ) - normal phenomenon occurred in the environment - the process is also known as radioactive decay
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3. Examples of radioactive substances (contain unstable nuclei):
Uranium-238 Carbon-14 Polonium-210 Plutonium-239 Thorium-234 Radium-223
4. Units of radioactivity: - we use Curie (Ci) & becquerel (Bq) (Bq is chosen as the SI unit) - unit is used to measure the rate of radioactive decay per second - Conversion:
1 Ci = 3.7 x 1010 Bq 1 Bq = 3.7 x 10-10 Ci
Example: A radioactive substance decays at 15 Ci. Convert this into becquerel
1 Ci = 3.7 x 1010 Bq
So, 15 Ci = 15 x 3.7 x 1010 Bq = 5.55 x 1011 Bq 5. Half-life - Definition = time taken for unstable nucleus to decay by half the value - Time is always constant - Question example: The original mass of a radioactive substance is 2000g with half-life of 3 hours. Calculate the mass after 12 hours:
2000g 1000g 500g 250g 125g
Answer: 125g
3h 3h 3h 3h
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8.2 WHAT ARE THE RADIOACTIVE RADIATIONS?
1. Comparing the radioactive radiations (α, β, γ)
ALPHA (α)
BETA (β) GAMMA (γ)
What is it? Helium nucleus High speed electron
Electromagnetic wave
Charge + - Neutral
Ionising power Strong Medium Weak
Penetration power
Weak Medium Strong
Can it be deflected by electric & magnetic field?
Yes (because + charge
Yes (because – charge)
No (because neutral)
2. Diagram showing penetration & deflection of radioactive radiations:
a. Penetration power
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b. Deflection by electric field
c. Deflection by magnetic field
8.3 WHAT ARE IONISING & NON-IONISING RADIATION?
1. Ionising radiation = radiation that can cause formation of ions in the air - Strong ionising radiations can be hazardous because they can cause cancer in human - Examples
Ionising radiation (hazardous!) Non-ionising radiation (safe…) Radioactive radiations (α,β,γ) X-ray, ultraviolet
Radio, micro, infrared, visible light
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2. Source of ionising radiations in the environment:
Natural Man-made
- Cosmic ray (high altitude & space) - background radiation (nature)
- Nuclear power plant - Nuclear explosion - Smoking - background radiation from: a. TV/ computer b. food c. X-ray machine
3. We use microSievert/hour (µSv/h) to measure the dose of radiation Application of background (BG) radiation: - Pilots are not advised to stay at high altitude too long because of high dose - Don’t smoke due to high dose of BG radiation that can cause cancer - X-ray machine has protective layers to protect patients from high dose of BG radiation
8.4 ATOM & NUCLEUS – HOW IONS ARE FORMED?
1. Atom structure:
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2. Formation of ions:
How? Example Positive ion (cation)
Losing electrons Na+, Ca2+
Negative ion (anion)
Gaining extra electrons Cl-, O2-
*atom is neutral if number of proton = electron
3. In human being, too much ionisation by ionising radiations can alter the cells & DNA & this can lead to cancer & disease! - that’s why we should not smoke & handle carefully the radioactive wastes
8.5 HOW TO USE & HANDLE RADIOACTIVE MATERIALS?
1. They are used in 6 fields:
Archeology: -Use carbon-14 to determine the age of fossil/ artifacts
Industry: -Use beta radiation to detect thickness of metal sheets
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Agriculture: -Phosphorus-32 is used to check fertiliser absorption -radiations are used to kill pests
Defence: -Uranium & plutonium is used to make nuclear bombs
Food industry: -Gamma ray can kill bacteria & preserve food (food is safe to eat because of short half-life)
Medical: -Cobalt-60 to kill cancer cells & pathogens -Sodium-24 to check blood clot -Iodine-131 to treat thyroid gland
2. How to handle radioactive substance & radioactive waste?
a. Wear protective clothing & radiation badges b. Use robotic hands to handle them c. Keep them in lead & concrete containers d. Store them at safe locations (underground)
Robotic hand Protective clothing & radiation badges
Lead & concrete containers
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VERSI BAHASA MELAYU
BAB 8: KERADIOAKTIFAN
8.1 APA ITU KERADIOAKTIFAN?
1. Kita akan kaji sumbangan 3 individu:
Wilhelm Roentgen: - menemui sinar-X
Henri Becquerel: - menemui radioaktif
Marie & Pierre Curie: - mengesan sinar gamma - menemui polonium & radium sebagai bahan radioaktif
2. Keradioaktifan = pereputan spontan nukleus yang tidak stabil menjadi stabil & memancarkan sinar radioaktif (α, β, γ) - fenomena biasa berlaku di persekitaran - proses ini juga dikenali sebagai pereputan radioaktif
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3. Contoh bahan radioaktif (mengandungi nukleus tidak stabil):
Uranium-238 Karbon-14 Polonium-210 Plutonium-239 Thorium-234 Radium-223
4. Unit keradioaktifan: - Unit Curie (Ci) & becquerel (Bq) (Bq dipilih sebagai unit SI) - unit digunakan untuk mengukur kadar pereputan radioaktif sesaat - Penukaran unit:
1 Ci = 3.7 x 1010 Bq 1 Bq = 3.7 x 10-10 Ci
Contoh: Bahan radioaktif mereput sebanyak 15 Ci. Tukarkan unit ini ke becquerel
1 Ci = 3.7 x 1010 Bq
Maka, 15 Ci = 15 x 3.7 x 1010 Bq = 5.55 x 1011 Bq 5. Separuh hayat - Definisi = masa yang diambil untuk nukleus tidak stabil untuk mereput menjadi separuh daripada nilai asal - Masa separuh hayat adalah malar - Contoh soalan: Jisim asal bahan radioaktif ialah 2000g dengan separuh hayat 3 jam. Hitung jisim selepas 12 jam:
2000g 1000g 500g 250g 125g
Jawapan: 125g
3j 3j 3j 3j
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8.2 APA ITU SINAR RADIOAKTIF?
1. Jom bandingkan sinar radioaktif (α, β, γ)
ALFA (α)
BETA (β) GAMMA (γ)
Ciri? Nukleus helium Elektron halaju tinggi
Gelombang elektromagnet
Cas elektrik + - Neutral
Kuasa pengionan Kuat Sederhana Lemah
Kuasa penembusan
Lemah Sederhana Kuat
Pesongan dlm medan elektrik & magnet
Ya (kerana cas +) Ya (kerana cas - ) Tidak (kerana neutral)
5. Rajah menunjukkan penembusan & pesongan sinaran radioaktif:
a. Kuasa penembusan
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b. Pesongan dlm medan elektrik
c. Pesongan dlm medan magnet
8.3 APA ITU SINARAN MENGION & SINARAN TIDAK
MENGION?
1. Sinaran mengion = sinaran yang boleh menyebabkan ion terbentuk di udara - Sinaran mengion yg kuat adalah merbahaya kerana boleh menyebabkan kanser - Contoh:
Sinaran mengion (bahaya!) Sinaran tidak mengion (selamat…)
Sinar radioaktif (α, β, γ) Sinar-X-, ultralembayung
Radio, mikro, inframerah, cahaya nampak
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2. Sumber sinaran mengion di persekitaran:
Semula jadi Buatan manusia
- Sinaran kosmik (altitud tinggi & angkasa lepas) - sinaran latar belakang (alam semula jadi)
- Loji nuklear - letupan nuklear - Merokok - sinaran latar belakang daripada: a. TV / komputer b. makanan c. mesin x-Ray
3. Unit microSievert/jam (µSv /j) untuk mengukur dos sinaran Aplikasi sinaran latar belakang (LB): - Juruterbang tidak disarankan untuk terbang terlalu lama kerana dos LB yang tinggi - Jangan merokok kerana dos sinar LB yang tinggi boleh menyebabkan barah - Mesin sinar-X mempunyai lapisan pelindung untuk melindungi pesakit dari dos sinaran LB yg tinggi
8.4 ATOM & NUKLEUS – BAGAIMANA ION TERBENTUK?
1. Struktur atom:
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2. Pembentukan ion:
Bagaimana terbentuk? Contoh Ion positif (kation)
Atom kehilangan elektron Na+, Ca2+
Ion negatif (anion)
Atom memperoleh elektron tambahan
Cl-, O2-
* atom adalah neutral sekiranya bilangan proton = elektron
3. Dalam manusia, pengionan berpanjangan akibat terdedah kepada sinar radioaktif akan mengubah sel & DNA & ini boleh mengakibatkan penyakit & kanser - kita disarankan utk tidak merokok & kendalikan sisa radioaktif dgn berhati-hati.
8.5 APAKAH KEGUNAAN BAHAN RADIOAKTIF?
1. Digunakan dalam 6 bidang:
Arkeologi: -Guna karbon-14 untuk menentukan usia fosil / artifak
Industri: -Guna sinaran beta untuk mengesan ketebalan kepingan logam
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Pertanian: -Fosforus-32 digunakan untuk memeriksa penyerapan baja -Guna sinar untuk bunuh makhluk perosak
Pertahanan: -Uranium & plutonium digunakan untuk membuat bom nuklear
Industri makanan: -sinar gamma dapat membunuh bakteria & mengawet makanan (makanan selamat dimakan kerana jangka hayat yang pendek)
Perubatan: -Cobalt-60 untuk bunuh sel barah & patogen -Natrium-24 untuk mengesan darah beku -Iodin-131 untuk merawat kelenjar tiroid
2. Bagaimana mengendalikan bahan radioaktif & sisa radioaktif?
a. Pakai pakaian pelindung & lencana radiasi b. Gunakan tangan robot memegang bahan c. Simpan dalam bekas plumbum & konkrit d. Simpan di lokasi selamat (bawah tanah)
Guna robot Pakaian pelindung & lencana radiasi
Bekas plumbum & konkrit