Nuclear radiation - Revision history

Lwcamp at 19:04, 7 March 2026

2026-03-07T19:04:40Z

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	=References=		=References=
	[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:Medicine]]		[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:Physics & Math & Engineering]][[Category:Medicine]]

Lwcamp: /* References */

2026-02-17T16:35:40Z

References

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	=References=		=References=
	[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:~~Particle_Physics~~]]		[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:Medicine]]

Lwcamp: /* References */

2026-02-17T16:34:45Z

References

← Older revision		Revision as of 09:34, 17 February 2026
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	=References=		=References=
	[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:~~Life]][[Category:Medicine~~]]		[[Category:Physics & Engineering‏‎]][[Category:Physics]][[Category:Particle_Physics]]

Lwcamp: /* Threshold dose */

2025-08-16T17:36:33Z

Threshold dose

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	Cells can repair themselves after exposure to radiation. As living organisms, we appear to be well adapted to repair radiation damage at dose rates typical of our natural background radiation. Even at dose rates well above that for typical background levels (for example, for people living at high altitudes where there is less atmospheric protection from cosmic rays or for people living over bodies of radioactive ores or other naturally radioactive rock – particularly granite. Or for astronauts, flight crew on commercial aircraft, or people given medical procedures resulting in exposure to low dose radiation such as CAT scans or x-rays), there is no detectable increase in cancers or mutations. There appears to be some threshold above which the dose or dose rate can cause harm and below which it is harmless; although quite what this threshold dose rate is has not yet been teased out from the data.		Cells can repair themselves after exposure to radiation. As living organisms, we appear to be well adapted to repair radiation damage at dose rates typical of our natural background radiation. Even at dose rates well above that for typical background levels (for example, for people living at high altitudes where there is less atmospheric protection from cosmic rays or for people living over bodies of radioactive ores or other naturally radioactive rock – particularly granite. Or for astronauts, flight crew on commercial aircraft, or people given medical procedures resulting in exposure to low dose radiation such as CAT scans or x-rays), there is no detectable increase in cancers or mutations. There appears to be some threshold above which the dose or dose rate can cause harm and below which it is harmless; although quite what this threshold dose rate is has not yet been teased out from the data.

	Government agencies responsible for worker safety generally establish allowable regulatory dose limits; both for the general public and for radiation workers. This varies from country to country, but is usually set at a level thought to be well below the threshold of significant risk. While there are many specifics dealing with exposures to various body parts, as an example the allowable whole body dose set by the Nuclear Regulatory Commission (NRC) of the United States of America is 1 mSv/year for a member of the general public and 50 mSv/year for radiation workers above and beyond any background radiation, with a lifetime allowance of 250 mSv (this only applies to dose received at facilities under NRC jurisdiction, so it will not cover, for example, medical imaging or exposure at foreign sites). In the United States, at least, these values are usually set conservatively with the goal of avoiding harm. Individual institutions under the authority of U.S. law then often set even more stringent limits for their workers to avoid falling foul of federal regulations.		Government agencies responsible for worker safety generally establish allowable regulatory dose limits; both for the general public and for radiation workers<ref>[https://www.energy.gov/sites/prod/files/2018/01/f46/doe-ionizing-radiation-dose-ranges-jan-2018.pdf The DOE Ionizing Radiation Dose Ranges Chart]</ref>. This varies from country to country, but is usually set at a level thought to be well below the threshold of significant risk. While there are many specifics dealing with exposures to various body parts, as an example the allowable whole body dose set by the Nuclear Regulatory Commission (NRC) of the United States of America is 1 mSv/year for a member of the general public and 50 mSv/year for radiation workers above and beyond any background radiation, with a lifetime allowance of 250 mSv (this only applies to dose received at facilities under NRC jurisdiction, so it will not cover, for example, medical imaging or exposure at foreign sites). In the United States, at least, these values are usually set conservatively with the goal of avoiding harm. Individual institutions under the authority of U.S. law then often set even more stringent limits for their workers to avoid falling foul of federal regulations.

	==Material effects==		==Material effects==

Lwcamp at 23:31, 8 April 2025

2025-04-08T23:31:20Z

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	Heavy neutron or ion bombardment can have dramatic effects on materials. The nuclear recoil from collisions knocks atoms out of place. This will produce crystal defects, make materials amorphous, and cause materials to become brittle. In addition, neutron capture transmutes the material into other isotopes. These can change the chemical composition of the material, potentially weakening it. And it also makes the material radioactive, generally decaying via beta decay to produce beta and gamma radiation.		Heavy neutron or ion bombardment can have dramatic effects on materials. The nuclear recoil from collisions knocks atoms out of place. This will produce crystal defects, make materials amorphous, and cause materials to become brittle. In addition, neutron capture transmutes the material into other isotopes. These can change the chemical composition of the material, potentially weakening it. And it also makes the material radioactive, generally decaying via beta decay to produce beta and gamma radiation.

	the amount of radiation needed to affect material changes depends strongly on the material. But for example, reactor steels experience embrittlement at neutron fluences of on the order of 10<sup>19</sup> to 10<sup>20</sup> fast neutrons (~~<math>~~E > 1~~</math>~~ MeV) per square centimeter. This corresponds to a neutron dose on the order of between 10,000,000 and 1,000,000,000 Gy. Naturally, reactor steels are chosen for their resistance to radiation so more typical materials may be more sensitive. But this is still many orders of magnitude less sensitive than biological tissue.		the amount of radiation needed to affect material changes depends strongly on the material. But for example, reactor steels experience embrittlement at neutron fluences of on the order of 10<sup>19</sup> to 10<sup>20</sup> fast neutrons (E > 1 MeV) per square centimeter. This corresponds to a neutron dose on the order of between 10,000,000 and 1,000,000,000 Gy. Naturally, reactor steels are chosen for their resistance to radiation so more typical materials may be more sensitive. But this is still many orders of magnitude less sensitive than biological tissue.

	The effects of gamma and beta radiation on materials are more subtle. They can activate F-center defects, causing transparent materials to change color and lose transparency. The ionization they create can also lower activation barriers to chemical reactions, directly break chemical bonds, and create free radicals that chemically attack the material, causing rubber and plastics to crack and become less bendable and more brittle, bleaching organics, and eventually causing organic materials to degrade. The lower activation barriers can also help to anneal disordered materials back into a crystalline lattice.		The effects of gamma and beta radiation on materials are more subtle. They can activate F-center defects, causing transparent materials to change color and lose transparency. The ionization they create can also lower activation barriers to chemical reactions, directly break chemical bonds, and create free radicals that chemically attack the material, causing rubber and plastics to crack and become less bendable and more brittle, bleaching organics, and eventually causing organic materials to degrade. The lower activation barriers can also help to anneal disordered materials back into a crystalline lattice.

Lwcamp: /* Radiactive decay */

2025-04-08T23:30:48Z

Radiactive decay

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	===Radiactive decay===		===Radiactive decay===

	In any given span of time, a given fraction of the radioactive material in any sample (as measured from that present at the start of that span of time) will decay<ref name="Krane"></ref>. It is convenient to find the time it takes for exactly half of the radioactive material to decay, this is called the <i>half-life</i> and is commonly denoted with <~~math~~>~~t_{1/2}~~</~~math~~> in equations. In another half-life after the first, half of the remaining material will decay and thus you will be left with one-half of one-half of the original sample, or one quarter of the original amount. Similarly, after three half-lives, you will have 1/8<sup>th</sup> of the original material; after four half-lives, 1/16<sup>th</sup> of the original material, and so on. In general, after ~~<math>~~n~~</math>~~ half-lives, ~~<math>~~1/2^n</~~math~~> of the original sample will still be present. After many half-lives, a sample will have decayed away to the point where it is negligible.		In any given span of time, a given fraction of the radioactive material in any sample (as measured from that present at the start of that span of time) will decay<ref name="Krane"></ref>. It is convenient to find the time it takes for exactly half of the radioactive material to decay, this is called the <i>half-life</i> and is commonly denoted with t<sub>½</sub> in equations. In another half-life after the first, half of the remaining material will decay and thus you will be left with one-half of one-half of the original sample, or one quarter of the original amount. Similarly, after three half-lives, you will have 1/8<sup>th</sup> of the original material; after four half-lives, 1/16<sup>th</sup> of the original material, and so on. In general, after n half-lives, 1/2<sup>n</sup> of the original sample will still be present. After many half-lives, a sample will have decayed away to the point where it is negligible.

	When doing calculations, the half-life can be inconvenient to use. It is more convenient to define a characteristic decay time ~~<math>\tau</math>~~ which is related to the half-life by		When doing calculations, the half-life can be inconvenient to use. It is more convenient to define a characteristic decay time τ which is related to the half-life by
	<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><~~math~~>		<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
	~~\tau = \frac{t_{1~~/~~2}}{\~~ln[2]}.		τ = t<sub>½</sub> / ln[2].
	~~</math>~~</div>		</div>
	After any arbitrary amount of time ~~<math>~~t~~</math>~~ when starting with an amount <~~math~~>~~N_0~~</~~math~~> of radioactive material, the amount of remaining material will be		After any arbitrary amount of time t when starting with an amount N<sub>0</sub> of radioactive material, the amount of remaining material will be
	<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"~~><math~~>		<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
	N(t) = ~~N_0 \~~exp[-t/~~\tau~~].		N(t) = N<sub>0</sub> exp[-t/τ].
	~~</math>~~</div>		</div>
	If ~~<math>~~N~~</math>~~ is measured in number of atoms, the rate at which the decays occur is		If N is measured in number of atoms, the rate at which the decays occur is
	<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"~~><math~~>		<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
	A = N/~~\tau~~.		A = N / τ.
	~~</math>~~</div>		</div>
	This rate is called the <i>activity</i> of the sample. Note that while a long half-life means that you need to deal with the radioactivity for a long time, the overall activity will be low. Meanwhile, an isotope with a short half life may go away quickly but will have a high activity during that time.		This rate is called the <i>activity</i> of the sample. Note that while a long half-life means that you need to deal with the radioactivity for a long time, the overall activity will be low. Meanwhile, an isotope with a short half life may go away quickly but will have a high activity during that time.

	It is also occasionally useful to note that ~~<math>\tau</math>~~ is the average life span of any given radioactive particle.		It is also occasionally useful to note that τ is the average life span of any given radioactive particle.

	===Decay chains===		===Decay chains===

Lwcamp: /* Decay chains */

2025-04-08T23:26:13Z

Decay chains

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	An example of a decay chain from one of the most common naturally occurring radioactive isotopes on our planet is<ref>[https://www.nndc.bnl.gov/nudat3/ National Nuclear Data Center Chart of Nuclides]</ref>		An example of a decay chain from one of the most common naturally occurring radioactive isotopes on our planet is<ref>[https://www.nndc.bnl.gov/nudat3/ National Nuclear Data Center Chart of Nuclides]</ref>
	<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><~~math~~>		<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
	~~\,^{~~238~~}{\rm~~ U~~} \to \,^{~~234~~}{\rm~~ Th~~} \to \,^{~~234~~}{\rm~~ Pa~~} \to \,^{~~234~~}{\rm~~ U~~} \to \,^{~~230~~}{\rm~~ Th~~} \to \,^{~~226~~}{\rm~~ Ra~~} \to \,^{~~222~~}{\rm~~ Rn~~} \to \,^{~~218~~}{\rm~~ Po~~} \to \,^{~~214~~}{\rm~~ Pb~~} \to \,^{~~214~~}{\rm~~ Bi~~} \to \,^{~~214~~}{\rm~~ Po~~} \to \,^{~~210~~}{\rm~~ Pb~~} \to \,^{~~210~~}{\rm~~ Bi~~} \to \,^{~~210~~}{\rm~~ Po~~} \to \,^{~~206~~}{\rm~~ Pb}.		<sup>238</sup>U →
	<~~/math~~></div>		<sup>234</sup>Th →
			<sup>234</sup>Pa →
			<sup>234</sup>U →
			<sup>230</sup>Th →
			<sup>226</sup>Ra →
			<sup>222</sup>Rn →
			<sup>218</sup>Po →
			<sup>214</sup>Pb →
			<sup>214</sup>Bi →
			<sup>214</sup>Po →
			<sup>210</sup>Pb →
			<sup>210</sup>Bi →
			<sup>210</sup>Po →
			<sup>206</sup>Pb
			<br>
			</div>
	The final daughter product, <sup>206</sup>Pb is stable.		The final daughter product, <sup>206</sup>Pb is stable.

Lwcamp: /* Muon */

2025-03-12T05:12:29Z

Muon

← Older revision		Revision as of 22:12, 11 March 2025
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	==Muon==		==Muon==

	Muons are particles that behave like heavy electrons. They are far too energetic to be produced by nuclear radioactive decay, but they are commonly produced by the decays of some sub-atomic particles and in the collisions of particles created by particle accelerators or from cosmic rays. In particular, they are ~~the most~~ common form of natural background radiation on earth coming from the cosmic rays bombarding our atmosphere from space. Muons are extremely penetrating, leaving sparse ionization trails like electrons but with far more mass giving them more momentum and more energy to shed. It can take hundreds of meters of rock to screen out most of the muons created by cosmic radiation that manage to reach ground level.		Muons are particles that behave like heavy electrons. They are far too energetic to be produced by nuclear radioactive decay, but they are commonly produced by the decays of some sub-atomic particles and in the collisions of particles created by particle accelerators or from cosmic rays. In particular, they are a common form of natural background radiation on earth coming from the cosmic rays bombarding our atmosphere from space. Muons are extremely penetrating, leaving sparse ionization trails like electrons but with far more mass giving them more momentum and more energy to shed. It can take hundreds of meters of rock to screen out most of the muons created by cosmic radiation that manage to reach ground level.

	==Exotic particles==		==Exotic particles==

Lwcamp: /* Radiactive decay */

2025-01-13T05:27:34Z

Radiactive decay

← Older revision		Revision as of 22:27, 12 January 2025
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	===Radiactive decay===		===Radiactive decay===

	In any given span of time, a given fraction of the radioactive material in any sample (as measured from that present at the start of that span of time) will decay<ref name="Krane"></ref>. It is convenient to find the time it takes for exactly half of the radioactive material to decay, this is called the <i>half-life</i> and is commonly denoted with <math>t_{1/2}</math> in equations. In another half-life after the first, half of the remaining material will decay and thus you will be left with one-half of one-half of the original sample, or one quarter of the original amount. Similarly, after three half-lives, you will have ~~<math>~~1/8~~</math>~~<sup>th</sup> of the original material; after four half-lives, ~~<math>~~1/16~~</math>~~<sup>th</sup> of the original material, and so on. In general, after <math>n</math> half-lives, <math>1/2^n</math> of the original sample will still be present. After many half-lives, a sample will have decayed away to the point where it is negligible.		In any given span of time, a given fraction of the radioactive material in any sample (as measured from that present at the start of that span of time) will decay<ref name="Krane"></ref>. It is convenient to find the time it takes for exactly half of the radioactive material to decay, this is called the <i>half-life</i> and is commonly denoted with <math>t_{1/2}</math> in equations. In another half-life after the first, half of the remaining material will decay and thus you will be left with one-half of one-half of the original sample, or one quarter of the original amount. Similarly, after three half-lives, you will have 1/8<sup>th</sup> of the original material; after four half-lives, 1/16<sup>th</sup> of the original material, and so on. In general, after <math>n</math> half-lives, <math>1/2^n</math> of the original sample will still be present. After many half-lives, a sample will have decayed away to the point where it is negligible.

	When doing calculations, the half-life can be inconvenient to use. It is more convenient to define a characteristic decay time <math>\tau</math> which is related to the half-life by		When doing calculations, the half-life can be inconvenient to use. It is more convenient to define a characteristic decay time <math>\tau</math> which is related to the half-life by

Lwcamp at 05:26, 13 January 2025

2025-01-13T05:26:06Z

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	==Fission==		==Fission==
	[[File:Watt_energy_spectrum.png\|thumb\|The spectrum of neutrons coming off of nuclear fission of <~~math~~>~~\,^{~~235~~}{\rm U}~~</~~math~~> by thermal neutrons. The neutrons from the fission of other nuclei are very similar in shape.]]		[[File:Watt_energy_spectrum.png\|thumb\|The spectrum of neutrons coming off of nuclear fission of <sup>235</sup>U by thermal neutrons. The neutrons from the fission of other nuclei are very similar in shape.]]
	[[File:Fission_gamma_spectrum_lin.png\|thumb\|The spectrum of gamma rays coming off of spontaneous nuclear fission of <~~math~~>~~\,^{~~252~~}{\rm Cf}~~</~~math~~>. The gamma ray spectra from the fission of other nuclei are broadly similar.]]		[[File:Fission_gamma_spectrum_lin.png\|thumb\|The spectrum of gamma rays coming off of spontaneous nuclear fission of <sup>252</sup>Cf. The gamma ray spectra from the fission of other nuclei are broadly similar.]]
	When a very heavy nucleus is disturbed, it can deform and elongate. Because the two ends of the elongated nucleus are both very highly positively charged, they strongly electrically repel each other. Normally, this is countered by the strong nuclear force gluing the nuclear particles together, but if the nucleus elongates it gives a lower cross sectional area for the nuclear force to stick the nucleus together. This leads to a runaway process, with the two ends pushing each other apart as the center thins out, forms a neck, and finally snaps. Which leaves two now separate new nuclei where once there was one; usually with one nucleus a bit heavier than the other. This process is called fission<ref name="Krane"></ref>.		When a very heavy nucleus is disturbed, it can deform and elongate. Because the two ends of the elongated nucleus are both very highly positively charged, they strongly electrically repel each other. Normally, this is countered by the strong nuclear force gluing the nuclear particles together, but if the nucleus elongates it gives a lower cross sectional area for the nuclear force to stick the nucleus together. This leads to a runaway process, with the two ends pushing each other apart as the center thins out, forms a neck, and finally snaps. Which leaves two now separate new nuclei where once there was one; usually with one nucleus a bit heavier than the other. This process is called fission<ref name="Krane"></ref>.