Radioactivity and laws of radioactivity

radioactivity

1. RADIOACTIVITY AND LAWS OF RADIOACTIVITY Dr. Jitendra Patil Associate Professor Dr, D.Y.Patil Medical College, Hospital and Research Institute

2. Discovery of Radioactivity Henri Bequerel (1852-1908) During his studies of phosphorescence (1896), found a mineral (uranium) would darken a photographic plate even if the plate was wrapped. Found that this mineral emitted a new kind of radiation (X-rays needed an external stimulus)

3. Discovery of Radioactivity Marie (1867-1934) and Pierre (1859-1906) Curie isolated two previously unknown radioactive materials, polonium and radium Radioactivity was found to be unaffected by chemical and physical testing, showing that the radiation came from the atom itself – specifically from the disintegration or decay of an unstable nucleus

4. Discovery of Radioactivity 1898 – Ernest Rutherford began studying the nature of the rays that were emitted Classified into three distinct types according to their penetrating power. Alpha decay (α) – positively charged;can barely penetrate a piece of paper Beta Decay (β) – negatively charged; pass through as much as 3mm of aluminium Gamma Decay (γ) – neutral; Extremely penetrating

5. Radioactivity The n u clei of naturally occurring heavy el e ments l i ke U , unstable and T h , Ra and P o are keep on emitt i ng spontaneously invisible rays or radiations and give more stable elements .

6. Radioactivity These heavy elements radioactive elements. are ca l led The property o f emit t ing these rays is called radioactivity of the elements.

7. Radioactivity cont…. It is the nucleus of an atom of an element which spontaneously disintegrates to emit α, β or γ-rays. The rays emitted by radioactive element are called radioactive rays

8. Thus radioact i vity can be defined as:- The phenomenon in which the nucleus of the atom of an element undergoes spontaneous and uncontrollable disintegration (or decay) and emit α, β or γ-rays .

9. Radioactivity cont…. The emitted α, β or γ-rays from unstable nuclei are collectively called ionizing radiations . Depending on how the nucleus loses this excess energy either a lower energy atom of the same form will result , or a completely different nucleus and atom can be formed .

10. Radioactivity cont…. Ionization is the addition or removal of an electron to create an ion . Ionizing radiation is any type of particle (α, β) or electromagnetic wave ( γ ) that carries enough energy to ionize or remove electrons from an atom. .

11. Radioactivity cont…. These radiations are of such high energy that when they interact with materials, they can remove electrons from the atoms in the material . This effect is the reason why ionizing radiation is hazardous to health

12. Rad i oactivi t y i s o f the f ollowi n g two ty p es which are: a) Natural radio a ctivity b)Artificial Radioactivity

13. Natural Radioactivity is the process of spontaneous (i.e. without external means, by it self) disintegration of the nuclei of heavy elements with the emission of radiation. -these are unstable nuclei found in nature.

14. Natural radioactivity

15. Natural radioactivity cont….. All heavy elements above Z=82 show the phenomenon of radioactivity. the emission of radiation changes the structure of the nucleus and transforms the atom into a lighter atom .

16. Natural radioactivity cont….. The heavy element are unstable therefore they disintegrate to acquire a more stable state .

17. Artificial Radioactivity Is t he process i n which a stab l e ( no n - nucleus i s c h a n g e d into an ( rad i o a ct i ve) nucleus by radioactive) unstable bombard i ng i t with ap p ropria t e atomic projectiles like α, neutron, proton .

18. Example of Artificial radioactivity

19. The diffe r ences be t ween natural and artificial radioactivity Natural radioactivity Artificial radioactivity Is spontaneous, since in natural radioactivity, the nuclei of heavy atom disintegrate on their own accord, forming slightly lighter and more stable nuclei and emitting α,β,ᵞ radiations. Is not spontaneous, since in it the nuclei of the atoms have to be bombarded by fast moving particles like α, neutrons, protons, deuterons. Is uncontrolled and hence it can not be slowed down or accelerated by any means. Can be controlled by controlling the speed of the bombarding particles used for bringing about the artificial radioactivity Is usually shown by heavy elements. Can be induced even in light element.

20. Units of Radioactivity The standard unit of radioactivity is CURIE (c) It is defined as mass of radioactive substance that produces 3.7 x 10 10 disintegrations per second

21. Equivalent dose Is a dose quantity representing the stochastic health effects of low levels of ionizing radiation on the human body. It is derived from the physical quantity absorbed dose , but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. The SI unit of measure is the Sievert (Sv).

22. Other Common Radiation Units – SI 1. Gray (Gy) To measure absorbed dose. (the amount of energy actually absorbed in some material) and is used for any type of radiation and any material (does not describe the biological effects of the different radiations) Gy = J / kg (one joule of energy deposited in one kg of a material)

23. 2. Roentgen (R) -Is used to measure exposure but only to describe for gamma and X-rays , and only in air . R = depositing in dry air enough energy to cause 2.58 𝑥10−4 coulombs per kg

24. 3. Rem (Roentgen Equivalent Man) - to derive equivalent dose related the absorbed dose in human tissue to the effective biological damage of the radiation. .

25. 4. Sievert (Sv) T o d e r i ve e q uivale n t dose related to the a b so r b e d d o se i n h u man tissue t o the e f fe c t i ve Biological damage of the radiation. S v = g y x q ( q = quality f a c tor unique to the type of incident radiation) ( Gy = Gray unit)

26. 5. Becquerel (Bq) - to measure a radioactivity (the quantity of a ra d i oact i ve material that have 1 transformations /1s) Bq = one transformation per second, there are 3.7 x 10 10 Bq in one curie.

27. Few conversions 1 curie = 3.7 x 10 10  disintegrations per second 1 roentgen (R) = 0.000258 coulomb/ kilogram (C/kg) 1 megabecquerel (MBq) = 0.027 millicuries (mCi) 1  gray  ( Gy ) = 100 rad 1  sievert  (Sv) = 100 rem

28. Detection and Measurement of Radioactivity The r adioact i vi t y of su b stance i s d e t e c ted the ra d ioa c t i ve an d me a s ured by instruments like:- Geiger-Muller (G-M) counter Wilson Cloud Chamber. Scintillation Counters. Dosimeter.

29. Geiger-Muller (G-M) counter

30. Scintillation Counters

31. Dosimeters

32. Fundamental laws of radioactivity Rutherford Soddy Law of Radioactive Decay  In  1902 , Rutherford and Soddy studied the disintegrating of many radioactive substance and found the conclusion regarding radioactive decay known as Rutherford and Soddy Rules.

33. According to the fundamental law of radioactivity decay: 1. Radioactivity is a nuclear phenomenon and the rate of emission of radioactive ray cannot be controlled by physical or chemical process that mean neither can it be extended nor can it be reduced. 2. The nature of the disintegration of radioactive substance is statistical, this is, it very difficult to say which nucleus will be disintegrated and which particle will emit α,β and γ With the emission of α,β and γ rays in the process of disintegration one element change into another new element, its chemical and radioactive quantities are completely new. 3. At any time the rate of decay of radioactive atom is proportional to the number of atoms present at that time.

34. The radioactive decay scheme includes: Alpha decay Beta decay Positron decay Neutron decay Proton decay