Hyper Physics

7/30/2019 Hyper Physics

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Radioactivity

Radioactivity refers to the particles which are

emitted from nuclei as a result of nuclear instability.

Because the nucleus experiences the intense conflict

between the two strongest forces in nature, it should

not be surprising that there are many nuclear

isotopes which are unstable and emit some kind of

radiation. The most common types of radiation are

called alpha,beta, and gamma radiation, but there

are several other varieties of radioactive decay.

Radioactive decay rates are normally stated in terms of theirhalf-lives, and the

half-life of a given nuclear species is related to its radiation risk. The different types

of radioactivity lead to different decay paths which transmute the nuclei into other

chemical elements. Examining the amounts of the decay products makes possibleradioactive dating.

Radiation from nuclear sources is distributed equally in all directions, obeying the

inverse square law.

Natural radioactive decay series. Radioactive items you can buy. Some history.

Illustration of alpha, beta and gamma radiation

Index

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Alpha Radioactivity

Composed of two protons and two neutrons, the

alpha particle is a nucleus of the element helium.

Because of its very large mass (more than 7000

times the mass of thebeta particle) and its
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charge, it has a very short range. It is not suitable

for radiation therapy since its range is less than a

tenth of a millimeter inside the body. Its main

radiation hazard comes when it is ingested into

the body; it has great destructive power within its

short range. In contact with fast-growing

membranes and living cells, it is positioned for

maximum damage.

Alpha particle emission is modeled as abarrier penetration process. The alpha

particle is the nucleus of the helium atom and is the nucleus ofhighest stability.

Alpha role in deuterium-tritium fusion Proton fusion Radioactivity

Index

Alpha

particle

concepts

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Alpha Barrier Penetration

The energy of emitted alpha particles

was a mystery to early investigators

because it was evident that they did not

have enough energy, according to

classical physics, to escape the nucleus.

Once an approximate size of the nucleus

was obtained by Rutherford scattering,one could calculate the height of the

Coulomb barrier at the radius of the

nucleus. It was evident that this energy

was several times higher than the

observed alpha particle energies. There

was also an incredible range of half lives

for the alpha particle which could not be

explained by anything in classical

physics.

Index

Alpha

Decay

Concepts

References

Blatt

Ch 15
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The resolution of this dilemma came

with the realization that there was a finite

probability that the alpha particle could

penetrate the wall by quantum

mechanical tunneling. Using tunneling,

Gamow was able to calculate a

dependence for the half-life as a

function of alpha particle energy whichwas in agreement with experimental

observations.

Modeling of tunneling in polonium

Tipler

Ch 40

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Alpha Binding Energy

The nuclearbinding energy of the alpha particle is extremely high, 28.3 MeV. It is

an exceptionally stable collection of nucleons, and those heavier nuclei which can

be viewed as collections of alpha particles (carbon-12, oxygen-16, etc.) are also

exceptionally stable. This contrasts with a binding energy of only 8 MeV forhelium-3, which forms an intermediate step in theproton-proton fusion cycle.

Nuclear units

Index

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Alpha, Beta, and Gamma

Historically, the products ofradioactivity 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.

Index


Penetration of Matter

Though the most massive and most energetic ofradioactive 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 ofbeta radioactivity strongly interacts with

matter and has a short range.Index

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