Behavior of Radium

[The Thing]

Why is it that radium emits heat and so the sample is always a few degrees warmer than its surroundings? Any explanation?

Also, what other elements or compounds exhibit this behavior? Are there any others besides radium?

Thanks a lot for any answers.

[swansont]

Why is it that radium emits heat and so the sample is always a few degrees warmer than its surroundings? Any explanation?

Also' date=' what other elements or compounds exhibit this behavior? Are there any others besides radium?

Thanks a lot for any answers.[/quote']

 

Anything radioactive will tend to do this to some extent. Ra-226 (which is probably the isotope involved) alpha decays, so the decay energy will be deposited fairly close the the parent atom as the alpha ionizes and collides with surrounding atoms. The resulting recoils, from conservation of momentum, increase the vibrational KE of the atoms, thus increasing temperature.

 

The degree to which the temperature will rise depends on the activity (decay rate) of the material and the amount of energy deposited. Gammas may not be deposited in the material, betas probably will, while alphas almost cetainly will.

[woelen]

Why is it that radium emits heat and so the sample is always a few degrees warmer than its surroundings? Any explanation?

Also' date=' what other elements or compounds exhibit this behavior? Are there any others besides radium?

Thanks a lot for any answers.[/quote']

Radium is a radioactive element and it slowly decays. While it decays, a lot of energy is produced. In fact any radioactive compound, which decays at an appreciable rate produces heat. The amount of energy produced this way is fantastic. E.g. a metal like plutonium produces quite some heat and a piece of that metal at the size of a fist feels warm. It does so for thousands of years! There is no chemical equivalent of this. The immense amounts of energy produced are due to nuclear reactions, in which elements are transformed from one to another.

[The Thing]

Thanks swansont & woelen. Those responses helped a lot.

The degree to which the temperature will rise depends on the activity (decay rate) of the material and the amount of energy deposited. Gammas may not be deposited in the material' date=' betas probably will, while alphas almost cetainly will.

[/quote']

So, the amount of heat given off is related to the half-life of the radioactive material? The shorter the half-life the more heat given off but for a shorter period? I am assuming that as time goes by its heat emission will be less and less...

Also, this means that alpha-decaying materials would produce more heat than a beta & gamma decaying material?

 

Which radioactive material has a nice ratio between the amount of heat given off and the time it can last?

[5614]

Which radioactive material has a nice ratio between the amount of heat given off and the time it can last?

That depends on your application. If you want to heat a cup of tea then you want a lot of heat and quickly... whereas if you just want a warm lump of metal just to look cool (as in trendy/cool... not cold!) then you'd want it warm for many years.

[The Thing]

Okay, let's say I want the lump of metal warm for at least a decade.

Oh also, is the radioactive lump of metal ALWAYS warmer than its surroundings, even if you heat its surroundings up its temperature will rise higher than the surroundings?

[5614]

I don't know an example.

 

Oh also, is the radioactive lump of metal ALWAYS warmer than its surroundings, even if you heat its surroundings up its temperature will rise higher than the surroundings?

 

Yes. Because the radioactive metal will have the same thermal energy as it's surroundings & then it will have energy from the radioactive decay on top of that.

 

This breaks down if you look at it on a nanosecondly basis, at some point the temperature of the surroundings may differ from the metal... but overall the metal will be at the same temperature as the surroundings & then it will have radioactive decay on top of that to increase it's thermal energy.

[swansont]

Pu-238 is used in spacecraft RTGs (I just saw a related thread on themocouples) - it has a half-life of 87.8 years.

 

The amount of energy depends also on the Q-value, or energy released in the decay. You wouldn't want tritium, with its 12 year half-life but only 18.6 keV of energy released. You'd get more from the Pu-238, and its 5.6 MeV of energy released.

[The Thing]

Doesn't Americium-241 have a nice half-life of 460 years? And I've heard that it has 5.5 MeV energy release.

What are some radioactive isotopes that has an even greater Q-value?

I am doing an experiment on this (okay, it's the one that YT posted a long time ago about the homemade atomic reactor). I'm NOT doing this at home, but I'm hoping to get a university or college sponsor so I can use their labs. So, where can I get these radioactive materials, such as Amercium 241, without collecting them from smoke detectors or radium painted watches? Does a university lab usually store these things?

[akcapr]

Depends what lab- a genetics lab wouldnt have any for example.

[The Thing]

Lol, yes indeed. Good point.

Let's say a chemistry / physics lab.

[5614]

I wouldn't expect the average university to stockpile radioactive metals, at the same time I'm sure if they don't have any they should have contacts and suppliers from which they could order some.

[swansont]

From a practical standpoint, Q and half-life are only the first requirements - you also have to have sufficient amounts of the material. It may be that you don't make certain isotopes in sufficient quantities, or that a macroscopic amount would be way too expensive.

[The Thing]

What's a good material to use for this experiment? That is, it is:

a) not too expensive & not too rare?

b) decent Q-value? (several MeV)

c) decent half-life? (several decades)

Thanks.

[The Thing]

Oh one more thing. Can someone tell me how to calculate the power (amount of watts) generated from a sample of radioactive materials, given the Q-value? What other values do you need for that calculation? I remember Swansont giving the result of his calculations in the original homemade atomic reactor thread, but how to actually do the calculation? Also, can someone suggest any sites for knowing more on this subject? I've done google searches but so far good sites have eluded me.

[swansont]

Oh one more thing. Can someone tell me how to calculate the power (amount of watts) generated from a sample of radioactive materials, given the Q-value? What other values do you need for that calculation? I remember Swansont giving the result of his calculations in the original homemade atomic reactor thread, but how to actually do the calculation? Also, can someone suggest any sites for knowing more on this subject? I've done google searches but so far good sites have eluded me.

 

 

P = QA

 

A is the activity

 

[math]A =\lambda N[/math] where [math]\lambda[/math] is the decay constant = [math](ln 2)/t_{1/2}[/math] and N is the number of atoms

 

A is actually a function of time, since N is a function of time. [math]N = N_0 e^{-\lambda t}[/math]

[The Thing]

Thanks swansont. However, could you illustrate the usage of that formula by calculating, say, the power that can be generated from 1 gram of Pu-238? (half life and Q-value in previous posts). I'm not really getting the N part. Is it simply just the number of atoms in the sample, or is it something else? So could you show me how to use the formula please? Thanks.

[swansont]

Thanks swansont. However, could you illustrate the usage of that formula by calculating, say, the power that can be generated from 1 gram of Pu-238? (half life and Q-value in previous posts). I'm not really getting the N part. Is it simply just the number of atoms in the sample, or is it something else? So could you show me how to use the formula please? Thanks.

 

Yes, N is the number of atoms, so it really should not be all that difficult. You just have to do a few unit conversions.

 

1 kg of Pu is roughly 4 moles, or N = ~2.4 x 10²⁴ atoms

Q= 5.6 MeV = ~9 x 10^-13 J

t_1/2 = 2.77 x 10⁹s, so ^{[math]\lambda = 2.5*10^{-10}s^{-1}[/math]}

 

multiply them together and you get ~ 540 W

 

edit: oops. You said a gram. divide by 1000: roughly .5 W

[YT2095]

I`de also like to point out that Radium the Metal (element) is Very Reactive!

so you`ll need to use a salt of Radium in order to do this safely with water, I reccomend the Sulphate of Raduim, it`s hardly at all soluble (less so than Barium sulphate, and we`re given that to ingest before some X-Rays and Barium is poisonous!) so Radium Sulphate would be the way to go

 

just a friendly pointer

[The Thing]

Thanks swansont & YT.

I have just one more question. The P in watts, is that the amount of power given off over a time period (how long?) or at any given time?

Thanks a lot for your help.

[woelen]

Thanks swansont & YT.

I have just one more question. The P in watts' date=' is that the amount of power given off over a time period (how long?) or at any given time?

Thanks a lot for your help.[/quote']

The power is the number of Joules per second. So, this symbol stands for the rate at which energy is produced, not for the total amount of energy.

 

E.g. if an object has P=500 W for two seconds and next it has 300 W for 7 second and then it does not emit any energy anymore, then the total amount of energy released is 2*500+7*300 = 3100 J.

[The Thing]

Thanks a lot woelen. I didn't word the question right, but you answered it anyways. Should have known it was obvious from the unit (watt), but my brain short-circuited.

Anywayz, YT, in your original thread you said you were going to post the circuitry of the device with thermocouples and a valve, solenoid but you never did. Could you post them now?

[YT2095]

I have in fact answered that in a PM to you about 3 weeks ago when you asked me the exact same thing, what makes you think I`m going to say anything different now?

 

you`ll need to strip down an old washing machine to get the water inlet solenoid, that`ll work as an electrical water tap. the thermister to read the temperature electronicaly (so you don`t have to mess about with glass thermometers), and you`ll need a Fill Level sensor to activate/deactivate the water valve/solenoid.

 

ring a bell now?

[The Thing]

Yes YT. Sorry for harrassing you with PMs.

Anyways, I contacted a research facility in my city sponsored by 2 universities, and asked them to help me on this project (it has changed into a science fair project ) as well as using tritium and solar cells to generate electricity (my 2nd design). Here's what I got back from them:

 

[Tritium is an _extremely_ hazardous material that requires a tremendous

amount of care in handling. Here we have gone to long and

_expensive_ lengths to ensure that 3H is properly handled.It's safe to say

that there is _no_ chance that we'd be able to conduct any measurements

with tritium.

 

it makes sense that if there is enough radiation to heat up a flask of water

and run a radio, then there is enough radiation to heat up your body, which

is mostly water. You can imagine that if the radiation is heating up your

body, it is also causing a lot of biological damage. Which means that IF

you had a radioactive source (what we call) 'hot' enough to run your

electricity-generating turbine, it is logical to assume that for safety

sake, you would not be able to come within a country mile of it.

Understand that you must _handle_ the material before putting it into your

lead-shielded apparatus, and proper safety measures must be in place to

handle a very hot source.Non-trivial, to say the least]

 

And he said that there were "good ideas that we might be able to exploit" and he'll "get back to me".

And I have 2 questions:

 

1) I thought tritium is only dangerous when inhaled or somehow got into your body? I thought tritium's radiation is so weak that it's stopped by your skin?

 

2) I'm not getting the 2nd paragraph completely. A MILE? Why?

 

So, can anyone help?

[RyanJ]

1) Tritium decays with a beta decay to form [ce]He^3[/ce].

Beta radiation is the second most dangerous, it cna penetrate skin to a small extent but as with anything in high concentrations makes high ammounts of radiation and it could cause skin cancer or some other types of cancer, inside the body this is very dangerous and thus why Tritium is so dangerous, it also has quite a long half life at about 12.3 years its radioactive fro a long time.

 

2) I think he meant the term mile as in you should not be anywhere near the stuff, it was not meant literally by the looks of it. Beta radiation cna only traved a few centimeters in air but if you are using a different radioactive source that products gamma rays you'd need a lot of lead and concrete to block the gamma rays thus why you'd need to be a long way away from the stuff.

 

Trust me when I say radiaiton is not stuff too eb messed with, look what happened to the Curies who were experts on it... radiation si best left along unless in specialised lab conditions with the coreect shielding and equiptment, unless you like the idea of killing yourself or others.

 

Cheers,

 

Ryan Jones