COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been copied and communicated to you by or on behalf of The University of Southern Queensland pursuant to Part VA of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further copying or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. NSC1951 Lecture 11 Atoms & Nuclear Radiation Objectives • To recognize the properties of the three types of radiation. • To determine the nature of shielding appropriate for each type of radiation. • To show that the intensity of radiation decreases with the square of the distance from the radioactive material. • Understand basic nuclear equations. • Understand the concept of half-life of radioisotopes. 1. ISOTOPES & ATOMIC WEIGHT • Isotopes Atoms of same element that have different numbers of neutrons n0 Same Atomic Number Z p+ Different Mass Number A p+ + n0 • Isotope Symbols A 24 Element Mg Z 12 25 Mg 12 • Same p+ but 1 extra n0 12 12+1=13 Isotopes of Hydrogen Marieb, Fig 2.3 Atomic Weight • An element contains: – Large numbers of atoms – Various isotopes • Averaged out Atomic Mass (Atomic Weight) • Atomic Weight of an element = average weight of naturally occurring isotopes of that element, expressed in amu Eg chlorine (Cl) 35.45amu (rounded off to 2 decimal places) Atoms & Elements Key Concepts: Elements consist of Atoms that have Subatomic particles Protons Neutrons Electrons determine Make up the differs in Atomic Nucleus Number Isotopes has a that average to give Mass Number Atomic Mass 2. ALPHA (), BETA () & GAMMA () RADIATION Elements with Z 20 contain mixture of isotopes & also some with Z 20. Eg C, O, Mg • Radioisotope Unstable nucleus of isotope is radioactive emits radiation stable • Radiation Alpha () particle or Beta () particle or Gamma ( ) particle (pure energy • Particle 2p+ + 2n0 4 4 or or He 2 2 Same as helium nucleus • Emitted from nucleus • Particle a high energy e- 0 0 or or e -1 -1 • Produced when n0 changes to p+ e- comes from nucleus!! Normally around nucleus 1 1 0 n p + e 0 1 -1 Neutron in New proton Electron formed & Nucleus remains in emitted as particle nucleus • Rays energy alone no mass or charge • Similar to X-rays but Unstable nucleus stable nucleus + rays Characteristics of alpha, beta and gamma radiation Type of Nature Charge Mass Penetration radiation Helium nuclei +2 4 Very Low particle (42He) Electron -1 Effectively 0 Low particle ray Electromagnetic 0 0 Very High radiation Cree & Rischmiller, Table 13.1 3. SHIELDING REQUIRED FOR DIFFERENT TYPES OF RADIATION • Many body cells sensitive to radiation, eg sperm, ova, rapidly dividing cells of embryo, foetus proper shielding required • : slowest, least penetration • : intermediate speed & penetration • : fastest, most penetration Also : thin plastic Timberlake, Table 3.3 :thick plastic gloves, aprons Timberlake, Figure 3.1 (7th Ed); Cree & Rischmiller, Fig 13.1 4. INVERSE SQUARE LAW • Time exposed to radiation & KEEP YOUR DISTANCE • Greater the distance from source, the lower the intensity of radiation received Timberlake Figure 3.3; (7th Ed); Cree & Rischmiller Fig 13.7 Inverse Square Law • Intensity of radiation = 1/d² = 1/dxd • Double the distance from source • intensity of radiation to which you were originally exposed by 1/2x2 =1/4 @ 2m 1/2x2 ¼ @4m 1/4x4 @8m 1/8x8 See Cree & Rischmiller, Fig 13.7 5. NUCLEAR EQUATIONS • Radioactive Decay Spontaneous break down of nucleus radiation released • Radioactive nucleus new nucleus + radiation (, , ) Alpha Emitters Timberlake Page 73 Lab session Exp 1 Alpha Emitters (cont) 241 • Americium-241 Am-241 Am 95 (In smoke detectors) 241 237 4 Am Np + He 95 93 2 particle Beta Emitters Timberlake Page 75 Lab session Exp 1 Beta Emitters (cont.) 90 • Strontium-90 Sr-90 Sr 38 * Bone scans 90 90 0 Sr Y + e 38 39 -1 particle Gamma Emitters • Very few pure gamma emitters but rays accompany &/or 198 • Gold-198 Au-198 Au 79 *Treating lung pleura & peritoneal cancers 198 198 Au Au + 79 79 Stable nucleus, same element Gamma Emitters (cont) 131 • Iodine-131 I-131 I 53 *Treating thyroid cancer 131 131 I I + 53 53 Stable nucleus, same element Timberlake Fig 3.2 Changes in the nucleus for alpha, beta and gamma radiation 6. HALF-LIFE OF RADIOISOTOPES Cree & Rischmiller Fig 13.4 Timberlake Figure 3.4 Time it takes for one half of a given amount of a radioactive sample to decay Importance to nurses: • Patients isolated until radiation to safe level * See Table 13.4 (Cree & Rischmiller) Radioisotopes commonly used in diagnosis and therapy for some half-life values • Liquid radioisotopes urine, faeces, dressings, etc Precautions with disposal etc until safe level. 7. EFFECTS OF RADIATION ON LIVING TISSUE • Direct radiation damage Damage by physical impact of radiation on molecules in cells. • Indirect radiation damage Ionising radiation passes H2O in a cell & removes an e- H2O H2O+ + e- • H2O+ is very reactive! • It combines with a protein molecule in the cell, destroying the protein Useless &/or dangerous. Eg proteins in DNA • Damage desirable??? Target cells of cancer. Please bring Cree & Rischmiller or Instructional Guide to Lectures 12, 13, 14 *PERIODIC TABLE* REFERENCES • Cree & Rischmiller, 2001 Ch. 13 pp 375-382; 385; 390-393; 397-401 • Marieb, 2004 Ch. 2 pp 30-31 Key Concepts Nuclear Radiation Radioisotopes emit decay by one-half in one Radiation and Energy Half-life and are used in from the nucleus as Nuclear medicine Alpha Beta Gamma } differ in where exposure is reduced by as shown in Penetration Distance and require Nuclear equations different and Shielding and Time Review questions 1. Define: isotopes, atomic weight. 2. Describe alpha (), beta () & gamma () radiation. 3. Describe the types of shielding required to protect a person from , & radiation. 4. Understand the significance of the Inverse Square Law in relation to distance from a radio active source. 5. Write basic nuclear equations of radioactive decay, showing emissions of , & radiation. 6. Define: half-life of a radioisotope. 7. Briefly summarise the effects of radiation on living tissue.