 Chapter (30) Nuclear Physics

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Chapter (30) Nuclear Physics
T. Norah Ali Al moneef

the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles, electromagnetic radiation, or both. Radioactivity is a natural and spontaneous process by which the unstable atoms of an element emit or radiate excess energy in the form of particles or waves. These emissions 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. T. Norah Ali Al moneef

Atomic Structure T. Norah Ali Al moneef

Complete Symbols Contain the symbol of the element, the mass number and the atomic number. Mass number X Superscript → Atomic number Subscript → T. Norah Ali Al moneef

X A Z A = number of protons + number of neutrons Z = number of protons
A – Z = number of neutrons Number of neutrons = Mass Number – Atomic Number T. Norah Ali Al moneef

Subatomic Particles in Some Atoms
O P Zn 8 p+ 8 n0 8 e- 15 p+ 30 p+ 16 n0 35 n 15 e- 30 e- T. Norah Ali Al moneef

Br 35 80 Find each of these: number of protons number of neutrons
number of electrons Atomic number Mass Number Br 80 35 If an element has an atomic number of 34 and a mass number of 78, what is the: number of protons number of neutrons number of electrons complete symbol T. Norah Ali Al moneef

If an element has 78 electrons and 117 neutrons what is the
Atomic number Mass number number of protons complete symbol If an element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons complete symbol T. Norah Ali Al moneef

Isotopes Atoms of the same element can have different numbers of neutrons. Thus, different mass numbers. These are called isotopes. Chemically identical Isotopes: elements with the same number of protons, but a different number of neutrons. 12 6 C 13 14 T. Norah Ali Al moneef

Isotopes Frederick Soddy ( ) proposed the idea of isotopes in 1912 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials. T. Norah Ali Al moneef

U U 235 92 238 92 There are many types of uranium: A Z
Number of protons Number of neutrons A Z Number of protons Number of neutrons T. Norah Ali Al moneef

U U 235 92 238 92 There are many types of uranium: A 235 Z 92
Number of protons Number of neutrons 143 A 238 Z 92 Number of protons Number of neutrons 146 Isotopes of any particular element contain the same number of protons, but different numbers of neutrons. T. Norah Ali Al moneef

Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the man-made isotopes are unstable. Unstable isotopes can become stable by releasing different types of particles. This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radio nuclides. T. Norah Ali Al moneef

CHARACTERISTICS OF RADIOACTIVE DECAY
It is a natural process in our universe It is spontaneous – we cannot predict when an atom will undergo decay T. Norah Ali Al moneef

Alpha radiation -  Helium nuclei Description:
2 neutrons, 2 protons (helium nuclei) Electric Charge: +2 Relative Atomic Mass: 4 Penetration power: Stopped by paper or a few cm of air Ionisation effect: Strongly ionising Effects of Magnetic/Electric Field: Weakly deflected Helium nuclei

Alpha, Beta, and Gamma Historically, the products of radioactivity were called alpha, beta, and gamma when it was found that they could be analyzed into three distinct species by either a magnetic field or an electric field: T. Norah Ali Al moneef

Radioactive Decay It is not uncommon for some nuclides of an element to be unstable, or radioactive.We refer to these as radionuclides. There are several ways radionuclides can decay into a different nuclide. Unstable nuclei decay releasing energy and radiation. Three types of radiation alpha (α) particles - 42He nuclei(+2 charge beta (β) particles - electrons(- charge) positrons (+ charge) gamma (γ) particles - high frequency electromagnetic radiation. Increasing penetration (uncharged) Radioactive decay results in the emission of either: an alpha particle (a), a beta particle (b), or a gamma ray(g). T. Norah Ali Al moneef

Alpha Emission: Alpha Particle: Two protons and two neutrons bound together and emitted from the nucleus during some kinds of radioactive decay. Helium nuclei with charge of 2+ Symbol: 42He Net effect is loss of 4 in mass number and loss of 2 in atomic number. T. Norah Ali Al moneef

Alpha Decay An alpha particle is identical to that of a helium nucleus. It contains two protons and two neutrons. X A Z Y A - 4 Z - 2 + He 4 2 unstable atom alpha particle more stable atom T. Norah Ali Al moneef

X Y + He Ra Rn + He Rn + Y He Rn He + Po A Z A - 4 Z - 2 4 2 226 88
Alpha Decay X A Z Y A - 4 Z - 2 + He 4 2 Ra 226 88 Rn 222 86 + He 4 2 Rn 222 86 + Y A Z He 4 2 Rn 222 86 He 4 2 + Po 218 84 T. Norah Ali Al moneef

Alpha Decay  Daughter Nucleus Np-237 Th-234 Ra-228 Rn-222
Parent Nucleus Am-241 U-238 Th-232 Ra-226 Alpha Particle (Helium Nucleus) T. Norah Ali Al moneef

Beta Radioactivity Beta particles are just electrons from the nucleus, the term "beta particle" being an historical term used in the early description of radioactivity. The high energy electrons have greater range of penetration than alpha particles, but still much less than gamma rays. The emission of the electron's antiparticle, the positron, is also called beta decay. T. Norah Ali Al moneef

Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron. T. Norah Ali Al moneef

Beta Decay   Daughter Nucleus Osmium-187 Calcium-40
Antineutrino Parent Nucleus Rhenium-187 Potassium-40  Beta Particle (electron) T. Norah Ali Al moneef

b-particle production
The common modes of decay The net effect of b-particle production is to change a neutron to a proton. The nuclides lie above the zone of stability. The ratios of neutron/proton are too high. T. Norah Ali Al moneef

Beta radiation -  high energy electron Description:
Electric Charge: -1 Relative Atomic Mass: 1/1860th Penetration power: Stopped by few mm of aluminium Ionisation effect: Weakly ionising Effects of Magnetic/Electric Field: Strongly deflected high energy electron T. Norah Ali Al moneef

Gamma radiation -  Electromagnetic radiation Description:
High energy electromagnetic radiation Electric Charge: Relative Atomic Mass: Penetration power: Reduced by several cm’s of lead or several metres of concrete Ionisation effect: Very weakly ionising Effects of Magnetic/Electric Field: NO deflection Electromagnetic radiation T. Norah Ali Al moneef

γ-radiation γ radiation is high frequency electromagnetic radiation. When they are emitted from the nucleus the nuclear structure stays the same, it simply represents a loss of energy T. Norah Ali Al moneef

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The penetration power of the three types of radiation.
Skin or paper stops ALPHA Thin aluminium stops BETA Thick lead reduces GAMMA Thin mica

The effects of a field on radiation
Beta radiation has a –1 charge and a small mass so is strongly deflected Gamma radiation has no mass or charge so it is not deflected. Alpha radiation has a +2 charge but a RAM of 4 so is only weakly deflected. The effect of a magnetic or electric field on radiation depends upon the nature of the radiation.

Physical Half-Life Useful parameter related to the decay constant; defined as the time required for the number of radioactive atoms in a sample to decrease by one half Physical half-life and decay constant are inversely related and unique for each radionuclide If the particle’s lifetime is very short, the particles decay away very quickly. When we get to subatomic particles, the lifetimes are typically only a small fraction of a second! If the lifetime is long (like 238U) it will hang around for a very long time! T. Norah Ali Al moneef

Radioactive Decay The number of atoms in a sample that decay depends on the total number of atoms in the sample!! This fact yields a rate of decay called an exponential decay The Decay Constant, λ • The rate of decay is called the decay constant. It determines the half-life of a radioactive element. • The decay constant is unique for each radioactive element. Number of atoms decaying per unit time is proportional to the number of unstable atoms The decay constant of radioactive decay is equal to the reciprocal value of the half life time Constant of proportionality is the decay constant () dN/dt =-  N T. Norah Ali Al moneef

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The time it takes for one-half of a radioactive sample to decay Look at factors of 2 One half-life (1/2) Two half-lives (1/4) Three half-lives (1/8) For Example: A material has decreased by ¼ of its original amount it has gone through two half-lives T. Norah Ali Al moneef

T. Norah Ali Al moneef

Half-Life Number of atoms decaying per unit time is proportional to the number of unstable atoms Constant of proportionality is the decay constant () ∆N/ ∆ t =-  N dN/dt =-  N0 = -  t Nt N0 ln Nt = N0e-t (this is a decrease, since sign is - ) where: Nt = number of radioactive atoms at time t N0 = initial number of radioactive atoms e = base of natural logarithm = … t = time Note when t = 0, N = N0 T. Norah Ali Al moneef

Physical Half-Life Useful parameter related to the decay constant; defined as the time required for the number of radioactive atoms in a sample to decrease by one half  = ln 2/T1/2 = 0.693/T1/2 Physical half-life and decay constant are inversely related and unique for each radionuclide The half-life of such a process is: = t1/2 0.693 T. Norah Ali Al moneef

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Half-life is the time it required for half the atoms of a radioactive nuclide to decay. It can be measured in seconds, minutes, days, or years. decay curve 8 mg 4 mg 2 mg mg initial 1 half-life 2 3 T. Norah Ali Al moneef

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Half-Life Problem Ra-223 has a half-life of 12 days. If today, you had 100 grams of this isotope, how much would remain after 36 days? How many half-life periods has it undergone in 36 days? 36 days = 3 half life periods days/half-life 100 g g g g 12.5 g T. Norah Ali Al moneef

• 99mTc (technetium) : 6.4 hours • 140Xe (Xenon) : 13.6 seconds
Physical Half Life • Longer the half life, the longer the isotope will continue to emit radiation • Half Life REMAINS the same, no matter how many atoms present • The Half Life and Decay Constant of a material are related! Physical Half-Life • 238U (Uranium) : 4.47 x 109 years • 226Ra (Radium) : 1600 years • 99mTc (technetium) : 6.4 hours • 140Xe (Xenon) : 13.6 seconds • 212Po (Polonium) : 299 x 10-9 secs • Wait a minute…….. A negatively charge particle from the nucleus? • A neutron decomposes into a proton and an electron. The proton stays in the nucleus and the electron is released. • Beta Particles can pass through paper, but are stopped by metals T. Norah Ali Al moneef

Physical Half-Life Biological Half-Life Effective Half-Life
Time (in minutes, hours, days, or years) required for the activity of a radioactive material to decrease by one half due to radioactive decay Biological Half-Life Time required for the body to eliminate half of the radioactive material (depends on the chemical form) Effective Half-Life The net effect of the combination of the physical and biological half-lives in removing the radioactive material from the body 1 HL = 50% 2 HL = 25% 3 HL = 12.5% T. Norah Ali Al moneef

Half-life, effective The period during which the quantity of a radionuclide in a biological system is reduced by half by interaction of radioactive decay and excretion due to biological processes. Tbiol: biological half-life Tphys:physical half-life 1. Tphysical the time taken for half of the atoms in a radioactive material to undergo decay. 2. T biological the time required for half of a quantity of radioactive material absorbed by a living tissue or organism to be naturally eliminated (biological half-life) or removed by both elimination and decay (effective half-life) T. Norah Ali Al moneef

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The half life of radium Ra is 1. 6x103 yr. If the sample contains 3
The half life of radium Ra is 1.6x103 yr. If the sample contains 3.00x1016 nuclei find the decay constant T. Norah Ali Al moneef

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?
t1/ = 13 hrs 26 hours = 2 x t1/2 Amount initial = 64mg Amount remaining = 64 mg x ½ x ½ = 16 mg T. Norah Ali Al moneef

Nt /N0= e-t = e-0.693x10/2.5 =1/16 Nt = N0e-t
The half-life of a radioactive substance is 2.5 minutes. What fraction of the original radioactive substance remains after 10 minutes? (1) ½ (2) 1/ (3) ¼ (4) 1/16 Nt = N0e-t Nt /N0= e-t = e-0.693x10/2.5 =1/16 T. Norah Ali Al moneef

What is the half-life of an isotope if it decays to 12
What is the half-life of an isotope if it decays to 12.5% of its radioactivity in 18 minutes? (a) 9 minutes (b) 8 minutes (c) 12 minutes (d) 6 minutes (e) 0.17 minutes T. Norah Ali Al moneef

The half life of radium Ra is 1. 6x103 yr. If the sample contains 3
The half life of radium Ra is 1.6x103 yr. If the sample contains 3.00x1016 nuclei. Find the number of nuclei after 4.8x103 yr. T. Norah Ali Al moneef

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30.9 radioactive decays Einstein - mass IS energy E = mc2
In all nuclear processes , the following quantities must be conserved 1- energy (including mass energy) 2- momentum ( both linear and angular) 3- electric charge the number of elementary positive and negative charges must be equal before and after NT 4- number of nucleons , - A is the same before and after NT Einstein - mass IS energy E = mc2 m is the mass difference between the parent nuclei and the daughters. The equation gives the energy released. Mass is converted into energy! T. Norah Ali Al moneef

BASIC TYPES OF RADIOACTIVE DECAY
Alpha () decay Occurs when atomic nuclei have too many protons and neutrons (i.e., Are heavy) (A > 150) and is often followed by gamma and characteristic x-ray emission Consist of 2 protons and 2 neutrons Mass of an alpha particle is ~8000 me Charge = +2 charge Are highly ionizing Have low penetrating abilities (only cm in air and mm in water) Easily shielded; common types of shielding are paper, cardboard, air, clothing; will not penetrate skin Changes both the mass and identity of the nucleus of the parent radionuclide This means that the decay results in the formation of a new element as the daughter product T. Norah Ali Al moneef

Alpha Decay A Z X A4 Z2 Y 4 2 He alpha particles are very heavy and very energetic compared to other common types of radiation. These characteristics allow alpha particles to interact readily with materials they encounter, including air, causing many ionizations in a very short distance. α-particles are relatively large particles, thus they have lots of collisions with atoms of the materials through which they pass. During these collisions the α-particles energy can cause ionisation of the materials. α- particles cause lots of ionisation Are deflected by electric and magnetic fields (i.e. are charged T. Norah Ali Al moneef

Only a hazard when inside your body
Alpha Radiation Only a hazard when inside your body (internal hazard) can’t penetrate skin internal hazard stopped by paper found in soil, radon and other radioactive materials T. Norah Ali Al moneef

Converting protons and neutrons
There are certain combinations of protons and neutrons that are more stable than others If the number of protons :neutrons is not correct the nucleus is unstable. The solution is to release certain types of radioactivity. Note: proton (11p), neutron (10n) 10n  11p + 0–1e (– emission) 11p  10n + 01e (+ emission) 11p + 0–1e  10n (EC – electron capture) T. Norah Ali Al moneef

What makes unstable nuclei unstable?
. Each nuclear energy level can contain four particles: two protons (s=½) and two neutrons (s=½). energy r The potential experienced by nucleons is a 3D potential well. The ground-state configuration of the carbon-16 nucleus : If a nucleus is allowed to decrease its energy by transforming “excessive” protons (neutrons) into neutrons (protons), it will do it! The processes responsible for these transformations are driven by weak interaction (the fourth fundamental interaction): protons neutrons Some important transformation processes driven by weak interaction:

Why N  Z for light nuclei
protons neutrons energy protons neutrons energy If the electrostatic repulsion of protons can be neglected (this is the case of light nuclei: recall that the positive electrostatic energy Z2), the nucleus tends to keep approximately equal numbers of protons and neutrons. energy energy Even in this case, the nucleus can still lower its total energy: the rest energy of neutron is slightly more than the rest energy of a proton and an electron. protons neutrons protons neutrons

β- radiation β – particles are high speed electrons ejected from the nuclei of radioactive atoms It occurs when a neutron in the nucleus splits to become a proton and an electron. The proton remains in the nucleus and the electron (β- particle) is emitted at high speeds Β – particles are more penetrating than α – particles (since they are smaller particles they have less collisions and so penetrate further). The fact that they have less collisions means that they cause less ionisation. They are deflected by electric and magnetic fields (i.e. they are charged particles) T. Norah Ali Al moneef

neutron decay (-, lowers the N/Z ratio
When a β particle is emitted the mass no. stays the same (since the mass of an electron is very small) and the atomic no. increases by one (as an extra proton is created with the β particle. Beta Particles: Electrons or positrons having small mass and variable energy. Electrons form when a neutron transforms into a proton and an electron or: neutron decay (-, lowers the N/Z ratio T. Norah Ali Al moneef

skin, eye and internal hazard stopped by plastic found in natural food, air and water T. Norah Ali Al moneef

) Beta decay ( b- is a stream of negatively charged electrons. has a very light mass of an electron has a -1 charge can be stopped by a piece of aluminum has a speed that is 90% of the speed of light. can ionize air and other particles. - release of anti-neutrino (no charge, no mass) ) A Z X Z1 Y 1 e T. Norah Ali Al moneef

Beta-minus (-) decay characteristically occurs with radionuclide's that have an excess number of neutrons compared with the number of protons (i.e., high N/Z ratio) Any excess energy in the nucleus after beta decay is emitted as gamma rays, internal conversion electrons or other associated radiations

Po 218 84 Rn 85 + b -1 Th 234 90 Pa 91 + b -1 Tl 210 81 Pb 82 + b -1

- release of neutrino ( )
Beta-plus (+) decay characteristically occurs with radionuclides that are “neutron poor” (i.e., low N/Z ratio)

proton decay (+, raises the N/Z ratio):
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A Z X Z1 Y +1 e T. Norah Ali Al moneef

Beta Particles: Electrons or positrons having small mass and variable energy. Electrons form when a neutron transforms into a proton and an electron or: T. Norah Ali Al moneef

NEGATIVE BETA (ß-) DECAY
Occurs when atoms have too many neutrons (i.e., Are “neutron-rich”) and decay by emitting a negative beta particle (ß-) During negative beta decay, excess neutrons are converted into protons, electrons, and antineutrinos. The protons remain in the nucleus but the new electrons are emitted as negative beta particles (ß-) or negatrons. Less ionizing than alphas due to decreased mass of negatrons Changes the identity of the nucleus but not the mass The z number is increased due to onversion of neutrons into protons T. Norah Ali Al moneef 17

POSITRON (ß+) EMISSION
Occurs when the nucleus of the atom has too many protons (i.e., is proton-rich). It is also known as positive beta decay. Results in a positive electron emitted from the nucleus of the proton rich atom. This positive electron is known as a positron. An additional particle, a neutrino, is also emitted from the nucleus. Neutrinos are very small particles with no electric charge. They have little or no mass and participate in weak interactions. Positrons have same mass as electrons Positrons have charge +1 Positrons are less ionizing than alphas Positrons are more penetrating than alpha decay but less than gamma The best shielding is lead with thickness of 1 inch or more T. Norah Ali Al moneef

Electron Capture electron capture: (inner-orbital electron is captured by the nucleus) Electron capture is one form of radioactivity. A parent nucleus may capture one of its orbital electrons and emit a neutrino. This is a process which competes with positron emission and has the same effect on the atomic number. Most commonly, it is a K-shell electron which is captured, and this is referred to as K-capture. Addition of an electron to a proton in the nucleus As a result, a proton is transformed into a neutron. electron capture (raises the N/Z ratio): p 1 + e −1  n T. Norah Ali Al moneef

 decay - three types 1) - decay
- converts one neutron into a proton and electron - no change in mass number, but different element - release of anti-neutrino (no charge, no mass) 2) + decay - converts one proton into a neutron and electron - no change in mass number, but different element - release of neutrino 3) Electron capture T. Norah Ali Al moneef

Gamma Radioactivity X* X
Gamma radioactivity is composed of electromagnetic rays. It is distinguished from x-rays only by the fact that it comes from the nucleus. Most gamma rays are higher in energy than x-rays and therefore are very penetrating. Gamma rays are not charged particles like a and b particles. A Z X* X T. Norah Ali Al moneef

Gamma ray release Gamma ray – high energy photon Examples Net effect is no change in mass number or atomic number. T. Norah Ali Al moneef

GAMMMA () -ray GAMMMA RAYS AND X RAYS
Is a form of pure electromagnetic radiation emitted from nuclei that have excess energy. It is sometimes called gamma photon radiation. Are photons emitted from unstable nuclei to rid themselves of excess energy. Gamma photons are subatomic packets of pure energy. They are higher in energy of ~ 1 x J). with high frequency and more penetrating than the photons that make up visible light. When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. GAMMMA RAYS AND X RAYS Have the same properties except for their origin Gammas come from within the nuclei of atoms X-rays come from outside the nuclei Both are electromagnetic energy in the form of emitte photons T. Norah Ali Al moneef 27 25

Both are electromagnetic energy in the form of emitted photons
Have the same properties except for their origin Gammas come from within the nuclei of atoms X-rays come from outside the nuclei Both are electromagnetic energy in the form of emitted photons T. Norah Ali Al moneef 27

- conversion of strong to coulombic E - no change of A or Z (element)
g decay - conversion of strong to coulombic E - no change of A or Z (element) - release of photon - usually occurs in conjunction with other decay T. Norah Ali Al moneef

Penetration of Matter Though the most massive and most energetic of radioactive emissions, the alpha particle is the shortest in range because of its strong interaction with matter. The electromagnetic gamma ray is extremely penetrating, even penetrating considerable thicknesses of concrete. The electron of beta radioactivity strongly interacts with matter and has a short range. T. Norah Ali Al moneef

T. Norah Ali Al moneef

Classification of Decays
a-decay: emission of Helium nucleus Z  Z-2 N  N-2 A  A-4 Classification of Decays Neutrons Protons b- EC e+ e--decay (or -decay) emission of e- and n Z  Z+1 N  N-1 A = const a e+-decay emission of e+ and n Z  Z-1 N  N+1 A = const Electron Capture (EC) absorbtion of e- and emiss n Z  Z-1 N  N+1 A = const

Four types of radioactive decay
1) alpha (a) decay - 4He nucleus (2p + 2n) ejected 2) beta () decay - change of nucleus charge, conserves mass 3) gamma (g) decay - photon emission, no change in A or Z 4) spontaneous fission - for Z=92 and above, generates two smaller nuclei T. Norah Ali Al moneef

An Example…. Parent U238 → 8 alpha beta = ? 92 protons 146 neutrons

8 {lose 2 protons} + 6 (add 1 proton)
An Example…. Parent U238 → 8 alpha beta 8 {lose 2 protons} + 6 (add 1 proton) {lose 2 neutrons} - 16 protons + 6 protons - 16 neutrons

8 {lose 2 protons} + 6 (add 1 proton)
An Example…. Parent U238 → 8 alpha beta 8 {lose 2 protons} + 6 (add 1 proton) {lose 2 neutrons} - 16 protons + 6 protons = - 10 protons - 16 neutrons - 32 atomic mass atomic number

8 {lose 2 protons} + 6 (add 1 proton)
An Example…. Parent U238 → 8 alpha beta 8 {lose 2 protons} + 6 (add 1 proton) {lose 2 neutrons} - 16 protons + 6 protons = - 10 protons - 16 neutrons - 32 atomic mass atomic number U238 – 32 = “X” 206

8 {lose 2 protons} + 6 (add 1 proton)
An Example…. Parent U238 → 8 alpha beta 8 {lose 2 protons} + 6 (add 1 proton) {lose 2 neutrons} - 16 protons + 6 protons = - 10 protons - 16 neutrons - 32 atomic mass atomic number U238 – 32 = “X” 206 92 protons – 10 protons = 82 protons

8 {lose 2 protons} + 6 (add 1 proton)
An Example…. Parent U238 → 8 alpha beta 8 {lose 2 protons} + 6 (add 1 proton) {lose 2 neutrons} - 16 protons + 6 protons = - 10 protons - 16 neutrons - 32 atomic mass atomic number U238 – 32 = “X” 206 92 protons – 10 protons = 82 protons “X” 206 with 82 protons

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(1) alpha particle (3) gamma ray (2) beta particle (4) neutron
Which type of radioactive emission has a positive charge and weak penetrating power? (1) alpha particle (3) gamma ray (2) beta particle (4) neutron When a neutron is transformed into a proton what else is emitted a) alpha b) position c) 1H d) electron e) none of these

What is the missing particle?
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A. Radioactive Decay T. Norah Ali Al moneef

A. They are massless particles. B. They are electromagnetic wave.
Which of the following statements about alpha particles (α) is correct? A. They are massless particles. B. They are electromagnetic wave. C. They are traveling at the speed of light. D. They will be deflected by electric and magnetic field. There are two radioactive sources A and B, both of them have the same number of active nuclei at the beginning. After 10 days, the number of active nuclei in B is more than A. Which of the following statements is correct? A. The mass of A is larger than B. B. The mass of B is larger than A. C. The half-life of B is longer than A. D. The half-life of A is longer than T. Norah Ali Al moneef