When does atom disintegrate

[CarbonCopy]

When does an atom disintegrate into smaller ones and how can we predict the nature of radiation ( alpha, beta or gamma)

[swansont]

When does an atom disintegrate into smaller ones and how can we predict the nature of radiation ( alpha, beta or gamma)

It will disintegrate if there is a lower energy state available to it (that is allowable within the constraint of, and sometimes modified by conservation laws/selection rules). Generally the half life, within a decay type, will be shorter as the released energy increases. The type of radiation depends on the type of instability. Alpha happens (with a few notable exceptions) for nuclei that are very large; the instability is due to excess charge repulsion as compared to the nuclear attraction. Beta happens because of an excess or shortage of neutrons and there is a lower energy state available if a nucleon changes identity (best interpreted with the shell model). Gamma decay occurs when a nucleus is in an excited state.

[CarbonCopy]

How do we know that an atom is at a lower energy ? And how do we know a nucleus is heavy ?

[swansont]

How do we know that an atom is at a lower energy ? And how do we know a nucleus is heavy ?

We know the energy is lower because total mass of the constituents has decreased. Large/heavy nuclei have large numbers of neutrons and protons in them. Alpha decay begins to be important above Z=82

[Enthalpy]

Nuclei masses are measured with great precision in spectrometers. With an electric and a magnetic field, the deflection tells the mass with many places accuracy.

 

Because energy in a nucleus is very concentrated, the variation of mass is significant and spectrometers observe it accurately.

 

As a side remark, energy is always mass. Air blown by wind is heavier, water loses mass as it produces electricity in the dam, a stone is heavier hot than cold... But this variation is tiny, generally impossible to measure, and certainly the faint variation is not convenient for energy computations. Mass default is convenient, and commonly used, only for nuclear reactions like radioactivity.

[O'Nero Samuel]

E"nergy is always mass?" Could you elaborate on that?

[CarbonCopy]

_{mass energy conservation, Einstein's equation e=mc2.}

[Phi for All]

!

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