Atomic Nucleus and Radioac1vity

Atomic Nucleus and Radioac1vity Chin- Sung Lin

X- Rays and Radioac1vity In 1895, a German physicist, W. C. Roentgen was working with a cathode ray tube in his lab and discovered X- rays produced by a beam of electrons striking the glass surface of a gas- discharge tube

X- Rays and Radioac1vity Roentgen found that X- rays could pass through solid materials, could ionize the air, showed no refrac1on in glass, and were undeﬂected by magne1c ﬁelds

X- Rays and Radioac1vity X- rays are high- frequency electromagne1c waves, usually emiled by the de- excita1on of the innermost orbital electrons of atoms

X- Rays and Radioac1vity An energe1c beam of electrons striking a solid surface excites the innermost electrons and produces higher- frequency photons of X- radia1on.

X- Rays and Radioac1vity X- ray photons have high energy and can penetrate many layers of atoms before being absorbed or scalered X- rays do this when they pass through your soo 1ssue to produce an image of the bones inside your body

X- Rays and Radioac1vity Radioac'vity Radioac1vity is the process of nuclear decay (radioac1ve decay) Nothing new in the environment; it s been going on since 1me zero It warms Earth s interior, is in the air we breathe, and is present in all rocks (some in trace amounts) It is natural

X-Rays and Radioactivity CHECK YOUR NEIGHBOR The radioac1ve decay of nature s elements occurs in the A. soil we walk on. B. air we breathe. C. interior of Earth. D. All of the above.

X-Rays and Radioactivity CHECK YOUR ANSWER The radioac1ve decay of nature s elements occurs in the A. soil we walk on. B. air we breathe. C. interior of Earth. D. All of the above.

Alpha, Beta, and Gamma Rays

Alpha, Beta, and Gamma Rays Radioac1ve elements emit three dis1nct types of radia1on: α alpha: posi1vely charged (helium nuclei) β beta: nega1vely charged (electrons) γ gamma: no charge(electromagne1c radia1on) Rela1ve penetra1on

Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR The origins of radioac1vity go back to A. military ac1vi1es in the mid- 20th century. B. the Industrial Revolu1on two centuries ago. C. the beginning of human error. D. before humans emerged on Earth.

Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER The origins of radioac1vity go back to A. military ac1vi1es in the mid- 20th century. B. the Industrial Revolu1on two centuries ago. C. the beginning of human error. D. before humans emerged on Earth.

Alpha, Beta, and Gamma Rays Alpha decay

Alpha, Beta, and Gamma Rays Beta decay

Alpha, Beta, and Gamma Rays Gamma decay

Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR Any atom that emits an alpha par1cle or beta par1cle A. becomes an atom of a different element, always. B. may become an atom of a different element. C. becomes a different isotope of the same element. D. increases its mass.

Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER Any atom that emits an alpha par1cle or beta par1cle A. becomes an atom of a different element, always. B. may become an atom of a different element. C. becomes a different isotope of the same element. D. increases its mass.

Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR Which of these is actually a high- speed electron? A. Alpha B. Beta C. Gamma

Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER Which of these is actually a high- speed electron? A. Alpha B. Beta C. Gamma

Radioac1ve Isotopes The number of protons in an atomic nucleus determine the number of electrons surrounding the nucleus in a neutral atom When there is a different number of electrons than the nuclear protons, the atom is charged and is called an ion When there is a same number of protons (atomic numbers) but different number of neutrons (mass numbers), they are called isotopes When an isotope is radioac1ve, it is called radioac-ve isotope

Radioac1ve Isotopes Three common isotopes of Hydrogen:

Radioac1ve Isotopes Tri1um is a radioac1ve isotope:

Exercise: Radioac1ve Isotopes The nucleus of beryllium- 8 (Be- 8) undergoes a special kind of radioac1ve decay: it split into two equal halves. What nuclei are the products of this decay? What is the form of this decay?

Radioac1ve Isotopes The electric force of repulsion between the protons in a heavy nucleus acts over a greater distance than the alrac1ve forces among the neutrons and protons in the nucleus Each proton is repelled by every other proton in the nucleus, but is alracted only by the nucleons closest to it In a large nucleus, electric repulsion can exceed nuclear alrac1on This instability makes all the heaviest atoms radioac1ve

The Atomic Nucleus and the Strong Force The strong force is more effec1ve with smaller nuclei. par1cles occupying the nucleus is nucleons Mass=2000 1mes the mass of electrons

The Atomic Nucleus and the Strong Force The strong force holds nucleons together Nuclear force holds the nucleus together called the strong interac1on which is an alrac1ve force and is a short range force Electrical interac1on is a long range force

The Atomic Nucleus and the Strong Force A lone neutron is radioac1ve and spontaneously transforms to a proton and an electron A neutron needs protons around to keep this from happening

The Atomic Nucleus and the Strong Alpha emission Force

The Atomic Nucleus and the Strong Force CHECK YOUR NEIGHBOR The strong force is a force in the A. atom that holds electrons in orbit. B. nucleus that holds nucleons together. C. Both A and B. D. Neither A nor B.

The Atomic Nucleus and the Strong Force CHECK YOUR ANSWER The strong force is a force in the A. atom that holds electrons in orbit. B. nucleus that holds nucleons together. C. Both A and B. D. Neither A nor B.

The Atomic Nucleus and the Strong Force CHECK YOUR NEIGHBOR In the nucleus of an atom, the strong force is a rela1vely A. short- range force. B. long- range force. C. unstable force. D. neutralizing force.

The Atomic Nucleus and the Strong Force CHECK YOUR ANSWER In the nucleus of an atom, the strong force is a rela1vely A. short- range force. B. long- range force. C. unstable force. D. neutralizing force.

Radioac1ve Half- Life The rate of decay for a radioac1ve isotope is measured in terms of a characteris1c 1me, the half- life, the 1me for half of an original quan1ty of an element to decay

Radioactive Half-Life CHECK YOUR NEIGHBOR Suppose the number of neutrons in a reactor that is star1ng up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion? A. 1 minute B. 2 minutes C. 5 minutes D. 9 minutes

Suppose the number of neutrons in a reactor that is star1ng up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion? A. 1 minute B. 2 minutes C. 5 minutes D. 9 minutes Explana;on: Radioactive Half-Life CHECK YOUR ANSWER This ques1on would be appropriate with Appendix D, Exponen1al Growth and Doubling Time. Can you see that working backward, each minute has half the number of neutrons?

Radiation Half-Life CHECK YOUR NEIGHBOR A certain isotope has a half- life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be A. zero. B. one- quarter. C. Half. D. the same.

Radiation Half-Life CHECK YOUR ANSWER A certain isotope has a half- life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be A. zero. B. one- quarter. C. Half. D. the same.

Exercise: Radioac1ve Half- Life If a sample of radioac1ve isotope has a half- life of 1 year, how much of the original sample will be leo at the end of the second year?

Exercise: Radioac1ve Half- Life If a sample of radioac1ve isotope has a half- life of 1 year, how much of the original sample will be leo at the end of the second year? (1/2) 2 = 1/4

Exercise: Radioac1ve Half- Life If Fukushima Daiichi nuclear power plant in Japan releases a certain amount of radioac1ve iodine (I- 131), how many percent of the original material will be leo at the end of the 50 days? (The half- life of I- 131 is 8.02 day)

Exercise: Radioac1ve Half- Life The half- life of Th- 227 is 18.2 day. How many days are required for 0.70 of a given sample to decay?

Exercise: Radioac1ve Half- Life The half- life of Th- 227 is 18.2 day. How many days are required for 0.70 of a given sample to decay? (1/2) (t/18.2 days) = (1.0 0.7) t = 31.61 days

Radioac1ve Half- Life Radioac-ve decay series: Uranium- 238 to lead- 206 through a series of alpha and beta decays In 4.5 billion years, half the uranium presently in Earth will be lead

Alpha, Beta, and Gamma Rays Irradia1on is the process by which an item is exposed to radia1on Food irradia1on kills microbes, but doesn t make the food radioac1ve

Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR Which of these is the nucleus of the helium atom? A. Alpha B. Beta C. Gamma D. All are different forms of helium.

Alpha, Beta, and Gamma Rays CHECK YOUR ANSWERS Which of these is the nucleus of the helium atom? A. Alpha B. Beta C. Gamma D. All are different forms of helium Explana;on: Contrary to the failures of alchemists of old to change elements from one to another, this was going on all around them unno;ced

Transmuta1on of the Elements Transmuta-on: The changing from one chemical element to another With alpha or beta par1cle, a different element is formed. This is transmuta1on, which occurs in natural events and is also ini1ated ar1ficially in the laboratory Uranium naturally transmutes to Thorium when an alpha par1cle is emiled

Transmuta1on of the Elements Uranium naturally transmutes to Thorium when an alpha par1cle is emiled

Transmuta1on of the Elements Natural transmuta1on Thorium naturally transmutes to protac1nium when a beta par1cle is emiled. An electron is e Superscript 0 indicates electron s mass is insignificant compared with nucleons Subscript - 1 is the electric charge of the electron

U-238 Radioac1ve Radioactive decay Half- Life series

Transmutation of the Elements CHECK YOUR NEIGHBOR When an element ejects an alpha par1cle, the atomic number of the resul1ng element A. reduces by 2. B. reduces by 4. C. increases by 2. D. increases by 4.

Transmutation of the Elements CHECK YOUR ANSWER When an element ejects an alpha par1cle, the atomic number of the resul1ng element A. reduces by 2. B. reduces by 4. C. increases by 2. D. increases by 4. Explana;on: An alpha par1cle (a helium nucleus) has atomic number 2. Ejec1on of an alpha par1cle means a loss of 2 protons, so the atomic number of the element is lowered by 2

Transmutation of the Elements CHECK YOUR NEIGHBOR When an element ejects an alpha par1cle and a beta par1cle, the atomic number of that element A. reduces by 1. B. increases by 1. C. reduces by 2. D. increases by 2.

Transmutation of the Elements CHECK YOUR ANSWER When an element ejects an alpha par1cle and a beta par1cle, the atomic number of that element A. reduces by 1. B. increases by 1. C. reduces by 2. D. increases by 2. Explana;on: Alpha emission reduces atomic number by 2, and beta emission increases atomic number by 1, so net result is - 1.

Exercise: Transmuta1on of the Elements Write the nuclear reac1ons from Uranium- 238 to lead- 206 through a series of alpha and beta decays

Transmuta1on of the Element Ar1ficial transmuta1on An alpha par1cle fired at and impac1ng on a nitrogen atom, which transmutes to oxygen and hydrogen

Transmutation of the Elements CHECK YOUR NEIGHBOR Atoms can transmute into completely different atoms in A. nature. B. laboratories. C. Both A and B. D. Neither A nor B.

Transmutation of the Elements CHECK YOUR ANSWER Atoms can transmute into completely different atoms in A. nature. B. laboratories. C. Both A and B. D. Neither A nor B. Explana;on: Atomic transmuta1on occurs in nature, in laboratories, and as far as we know, throughout the cosmos

Transmutation of the Elements CHECK YOUR NEIGHBOR An element emits 1 beta par1cle, and its product then emits 1 alpha par1cle. The atomic number of the resul1ng element is changed by A. 0. B. - 1. C. - 2. D. None of the above.

Transmutation of the Elements CHECK YOUR ANSWER An element emits 1 beta par1cle, and its product then emits 1 alpha par1cle. The atomic number of the resul1ng element is changed by A. 0. B. - 1. C. - 2. D. None of the above. Explana;on: Beta emission increases atomic number by 1, then alpha emission decreases atomic number by 2, so the net change is 1.

Radia1on Detectors Geiger counter detects incoming radia1on by a short pulse of current triggered when radia1on ionizes a gas in the tube

Radia1on Detectors Scin1lla1on counter indicates incoming radia1on by flashes of light produced when charged par1cles or gamma rays pass through the counter

Radia1on Detectors Cloud chamber: Charged par1cles moving through supersaturated vapor leave trails When the chamber is in a strong electric or magne1c field, bending of the tracks provides informa1on about the charge, mass, and momentum of the par1cles

Radia1on Detectors Bubble chamber: Liquid hydrogen is heated under pressure in a glass and stainless steel chamber to a point just short of boiling If the pressure in the chamber is suddenly released at the moment an ion- producing par1cle enters, a thin trail of bubbles is leo along the par1cle s path

Radia1on Units Different units of measure are used depending on what aspect of radia1on is being measured The amount of radia1on being emiled The radia1on dose absorbed by a person The biological risk of exposure to radia1on

Radia1on Units Aspect Conven'onal SI The amount of radia1on being emiled The radia1on dose absorbed by a person The biological risk of exposure to radia1on Curie (Ci) Rad (rad) Rem (rem) Becquerel (Bq) Gray (Gy) Sievert (Sv)

Radia1on Units Ci and Bq The amount of radia1on being emiled, by a radioac1ve material is measured using the conven1onal unit curie (Ci), or the SI unit becquerel (Bq) of radioac1ve atoms in a radioac1ve material over a period of 1me 1 Bq = 1 disintegra1on per second 1 Ci = 37 X 10 9 Bq Ci or Bq may be used to refer to the amount of radioac1ve materials released into the environment

Radia1on Units rad and Gy The radia1on dose absorbed by a person (that is, the amount of energy deposited per unit of weight of human 1ssue by radia1on) is measured using the conven1onal unit rad or the SI unit gray (Gy) The rad, which stands for radia-on absorbed dose, was the conven1onal unit of measurement 1 Gy = 100 rad

Radia1on Units rem and Sv The biological risk of exposure to radia1on is measured using the conven1onal unit rem or the SI unit sievert (Sv) Scien1sts have assigned a number, Quality Factor (Q), to each type of ionizing radia1on (alpha and beta par1cles, gamma rays, and x- rays) depending on that type's ability to transfer energy to the cells of the body To es1mate a person's biological risk in rems rem = rad X Q 1 Sv = 100 rem

Environmental Radia1on Units of radia1on Par'cle Radia'on Quality Factor Health effect alpha 1 rad 10 = 10 rems beta 10 rad 1 = 10 rems Doses of radia1on Lethal doses of radia1on begin at 500 rems

Environmental Radia1on Source received annually Natural origin Typical dose (mrem) Cosmic radia1on 26 Ground 33 Air (Radon- 222) 198 Human 1ssues (K- 40; Ra- 226) 35

Environmental Radia1on Radon, a common environmental hazard Most radia1on from natural background About 1/5 from nonnatural sources

Environmental Radia1on Doses of radia1on Human origin Typical dose (mrem) Medical procedures Diagnos1c X- rays 40 Nuclear diagnos1cs 15 TV tubes, other consumer products 11 Weapons- test fallout 1 Commercial fossil- fuel power plants < 1 Commercial nuclear power plants << 1

Environmental Radia1on Radioac1ve tracers Radioac1ve isotopes used to trace such pathways are called tracers

Radiometric Da1ng Earth s atmosphere is con1nuously bombarded by cosmic rays, which causes many atoms in the upper atmosphere to transmute

Radiometric Da1ng A nitrogen that captures a neutron and becomes an isotope of carbon by emirng a proton:

Radiometric Da1ng Because living plants take in carbon dioxide, any C- 14 lost by decay is immediately replenished with fresh C- 14 from the atmosphere Dead plants con1nue emirng C- 14 without replenishment

Radiometric Da1ng Carbon- 14 is a beta emiler and decays back to nitrogen The half- life of Carbon- 14 is about 5730 years

Radiometric Da1ng Rela1ve amounts of C- 12 to C- 14 enable da1ng of organic materials

Radiometric Dating CHECK YOUR NEIGHBOR The half- life of carbon- 14 is about 5730 years, which means that the present amount in your bones will reduce to zero A. when you die. B. in about 5730 years. C. in about twice 5730 years. D. None of the above.

Radiometric Dating CHECK YOUR ANSWER The half- life of carbon- 14 is about 5730 years, which means that the present amount in your bones will reduce to zero A. when you die. B. in about 5730 years. C. in about twice 5730 years. D. None of the above. Explana;on: In theory, the amount never reaches zero. In eons to come, trace amounts of the carbon- 14 in your bones, even if completely dissolved, will s1ll exist.

The End