B: Radioactive DecayB: Radioactive Decay

There are about 350 There are about 350 isotopes of 90 isotopes of 90 elements found in our elements found in our solar system.solar system.Of these, about 70 are Of these, about 70 are radioactive.radioactive.Naturally occurring Naturally occurring radioisotopes radioisotopes (elements with atomic (elements with atomic nos. of 83 or less) emit nos. of 83 or less) emit background radiation background radiation in relatively small in relatively small amounts.amounts.

B.2 Natural Radioactive DecayB.2 Natural Radioactive DecayAlpha particles have Alpha particles have two protons and two two protons and two neutrons.neutrons.

They are massive—They are massive—8000 x heavier than 8000 x heavier than beta particles, but can beta particles, but can only cause damage only cause damage over very short over very short distances.distances.

They are easily They are easily blocked, even by skin.blocked, even by skin.

Radium-226 loses Radium-226 loses two protons, so it’s two protons, so it’s atomic number atomic number drops from 88 to drops from 88 to 86.86.

Atoms of 2 Atoms of 2 elements, He and elements, He and Rn can be formed.Rn can be formed.

Beta particles are fast-Beta particles are fast-moving negatively charged moving negatively charged particles released during particles released during radioactive decay.radioactive decay.During beta decay, a During beta decay, a neutron changes into a neutron changes into a proton and an electron. proton and an electron. The proton remains in the The proton remains in the nucleus but the electron nucleus but the electron (beta particle) is ejected at (beta particle) is ejected at high speed.high speed.A third particle called an A third particle called an antineutrino is also antineutrino is also released.released.

A beta particle has a mass number of 0 and an A beta particle has a mass number of 0 and an atomic number (nuclear charge) of -1.atomic number (nuclear charge) of -1.The overall result of beta emission is that a The overall result of beta emission is that a neutron is converted into a proton.neutron is converted into a proton.Notice that the atomic number increases and Notice that the atomic number increases and Radium turns into Actinium.Radium turns into Actinium.

vvGamma emissions Gamma emissions do not change the do not change the mass or charge mass or charge balance in a balance in a nuclear equation nuclear equation because the rays because the rays have no mass or have no mass or charge.charge.

Of the three Of the three emissions: alpha, beta emissions: alpha, beta and gamma, alpha and gamma, alpha radiation is the most radiation is the most damaging at short damaging at short range but easy to range but easy to protect against. Beta protect against. Beta and gamma do less and gamma do less damage over a long damage over a long range but it’s harder range but it’s harder to protect against to protect against them.them.

New isotopes created New isotopes created from radioactive from radioactive decay can also be decay can also be radioactive and radioactive and undergo further undergo further decay.decay.Eventually, the result Eventually, the result will be a stable atom. will be a stable atom. In this case Uranium In this case Uranium decays into stable decays into stable lead—it just takes 14 lead—it just takes 14 steps to do so.steps to do so.

B.3 Ionizing Radiation—How Much B.3 Ionizing Radiation—How Much is Safe?is Safe?

Radiation can be measured with a Geiger Radiation can be measured with a Geiger counter in counts per minute (cpm).counter in counts per minute (cpm).

It can also be measured in rems when It can also be measured in rems when evaluating its effect on humans. Rems evaluating its effect on humans. Rems stand for Roentgen equivalent man and stand for Roentgen equivalent man and measures the ability of radiation to cause measures the ability of radiation to cause ionization in human tissue.ionization in human tissue.

A third way to measure radiation levels is A third way to measure radiation levels is in Becquerels.in Becquerels.

1986 Nuclear Meltdown at 1986 Nuclear Meltdown at ChernobylChernobyl

The accident released 1.1 x 10 The accident released 1.1 x 10 19 Becquerels of radioactive 19 Becquerels of radioactive material (one Becquerel is one material (one Becquerel is one molecule undergoing radioactive molecule undergoing radioactive decay per second).decay per second). About 116,000 people were About 116,000 people were evacuated from the area around evacuated from the area around the plant, and 134 were the plant, and 134 were hospitalized for acute radiation hospitalized for acute radiation sickness. The 31 deaths were sickness. The 31 deaths were mainly among fire fighters who mainly among fire fighters who fought the first fire without fought the first fire without radiation protection.radiation protection. The major health hazards came The major health hazards came from iodine 131 (I-131) , which from iodine 131 (I-131) , which accumulates in the thyroid gland, accumulates in the thyroid gland, and cesium 137 (Cs-137), which and cesium 137 (Cs-137), which gathers in bone. The accident gathers in bone. The accident released 1,760 * 10 15 released 1,760 * 10 15 Becquerels of I-131 and 85 * 10 Becquerels of I-131 and 85 * 10 15 Becquerels of Cs-137.15 Becquerels of Cs-137.

Radiation Damage Now and LaterRadiation Damage Now and LaterIonizing radiation Ionizing radiation tears molecules apart tears molecules apart by breaking chemical by breaking chemical bonds.bonds.

Damage to proteins Damage to proteins and nucleic acids are and nucleic acids are particularly particularly detrimental because detrimental because of their importance in of their importance in body functions and body functions and structures.structures.

Nucleic acids in DNA Nucleic acids in DNA can be damaged in can be damaged in two ways:two ways:Mutations result in the Mutations result in the synthesis of altered synthesis of altered proteins. Can result in proteins. Can result in killing the cell or if it’s killing the cell or if it’s a sperm or ovum, a sperm or ovum, cause birth defects.cause birth defects.If the exposure is high If the exposure is high enough and proteins enough and proteins cannot be cannot be synthesized, death synthesized, death follows.follows.

Sources of RadiationSources of Radiation

Cosmic raysCosmic rays

Radioisotopes from rocks and soilsRadioisotopes from rocks and soils

Radioisotopes from the atmosphereRadioisotopes from the atmosphere

Fallout from nuclear weapons testingFallout from nuclear weapons testing

Increased exposure to cosmic rays Increased exposure to cosmic rays through air travel.through air travel.

Radioisotopes released from nuclear Radioisotopes released from nuclear power technologies.power technologies.

Radioisotopes in the EnvironmentRadioisotopes in the EnvironmentOn average, people in On average, people in the U.S. receive above the U.S. receive above 360 mrem per year, of 360 mrem per year, of which 82% is naturally which 82% is naturally occurring.occurring.Radiation standard by Radiation standard by fed. Gov. is 500 mrem fed. Gov. is 500 mrem per year.per year.Maximum exposure Maximum exposure recommended by recommended by federal government is federal government is 5000 mrem (.5 rem) 5000 mrem (.5 rem) per year.per year.

Radioisotopes in the Human BodyRadioisotopes in the Human Body

ThyroidThyroid I-131I-131

LungsLungs Rn-222Rn-222 U-238U-238 Pt-239Pt-239 Kr-85Kr-85

MusclesMuscles K-40K-40 Cs-137Cs-137

LiverLiver Co-60Co-60

BonesBones Ra-226Ra-226 Sr-90Sr-90 P-32P-32 C-14C-14

Radon in HomesRadon in HomesRadon is a decay Radon is a decay product of uranium product of uranium and is always present and is always present in the atmosphere.in the atmosphere.Some radon dissolves Some radon dissolves into groundwater from into groundwater from the soil.the soil.Inhaled radon gas Inhaled radon gas goes through goes through radioactive decay radioactive decay causing health causing health problems such as lung problems such as lung cancer.cancer.