Humor Random Comments Thread

[Linguofreak]

Hydrogen is about the same mass as a neutron, so it absorbs about half the momentum of the neutron every time it hits a hydrogen nucleus. That adds up pretty quickly.

There's also a significant cross section for the two to stick together, which is why light water reactors need enriched uranium, while heavy-water-moderated reactors can use natural uranium.

Incidentally, this means that if the weak nuclear force were stronger, so that it was more likely for a proton to decay into a neutron while in contact with another proton, hydrogen fusion in the sun would proceed much more quickly. Likewise, if the ratio of strengths of the steering nuclear force and the electromagnetic force were even more lopsided in favor of the strong nuclear force, fusion would proceed more quickly on account of the diproton being stable.

 

[Urwumpe]

Science question: why do hydrogen and hydrogen compounds such as water make good neutron shields? Does the hydrogen absorb the neutrons? What goes on there?

Additionally to what was said, there is another factor, the neutron cross section of a material - how likely it is to interact with an neutron at all. Its measured in "barns" for the fun of it.

There is a capture cross section, that applies to atoms that simply capture a neutron and then do nothing or just decay a bit of energy away.

The fission cross section applies to nuclear fuels.

And the scatter cross section to all atoms, that are not absorbing neutrons, but simply bounce them away and absorb their energy. Hydrogen has a great scatter cross section, and it is pretty densly packed in water.

Hydrogen has a scatter cross section of 20 barns, Xenon-135 a capture cross section of 4 million barns for comparison - sadly it isn't stable enough to be used as shielding. The best stable absorber is Boron-10, that is why it is often used to "extinguish" nuclear reactions in reactors.

 

[Andy44]

I still miss Firefly.

 

[Linguofreak]

On the ninth day of Christmas my true love gave to me:

9 Ladies Dancing
8 Maids a-Milking
7 Swans a-Swimming
6 Geese a-Laying

? 5 Gold-en Rings ?

Four Calling Birds, three French Hens, two Turtle Doves

And a partridge in a pear tree.

 

[PhantomCruiser]

wait, wait, wait...

I thought it was;
5 Flannel shirts!
4 muddin' tires
3 shotgun shells
2 huntin' dogs
and some parts for muh Mustang GT

---------- Post added at 02:36 PM ---------- Previous post was at 02:47 AM ----------

Any Oregonians here? Why are they freaking out over having the ability to pump their own gasoline?

Full service gas stations are something that's only a distant memory here in TN.

 

[MaverickSawyer]

They're doing away with that stupid requirement? FINALLY. That is, hands down, the WORST part about travelling through Oregon.

 

[Andy44]

They're doing away with that stupid requirement? FINALLY. That is, hands down, the WORST part about travelling through Oregon.

Sitting in your warm car while somebody else pumps gas for you is a bad thing?

I used to live in, and frequently travel in, New Jersey, where it is illegal to pump your own gas. I'm cool with that when it's 7°F outside, and it's never a problem when I visit there.

When I was little they eliminated that rule in Pennsylvania, and I remember my grandfather uttering a string of swear words whenever he had to pump his own gas. The main reason being that despite promises to the contrary, gas prices did not drop when the need for paying attendants vanished.

Pay the same, but now do the work yourself.

In fact, for many years gasoline in NJ has remained among the cheapest gas anywhere, despite the employment of many attendants.

What's really funny is watching people from NJ try to figure out how to operate a gas pump when they venture out of state. It's like watching someone figure out how to use an escalator for the first time.

 

[Artlav]

Sitting in your warm car while somebody else pumps gas for you is a bad thing?

Imagine pretending that you are disabled while you are obviously not, and yet the helping guy chooses to pretend he didn't notice.
Pure painful cringe.

I imagine in USA you'd also have to magnify that cringe with the need to give a tip.

 

[RisingFury]

Science question: why do hydrogen and hydrogen compounds such as water make good neutron shields? Does the hydrogen absorb the neutrons? What goes on there?

Particle interactions are governed by their respective cross-sections.

Think of a target. If its cross-section is larger, you stand a higher chance of hitting it. So it is with particles, that the odds of an interaction increase in certain circumstances.

As conditions change, the cross-sections change as well. So what works for capturing slow neutrons (also called thermal neutrons, because their average kinetic energy comes from their thermal motion, governed by temperature) might not work for capturing fast neutrons.

Hydrogen 1 has a decent enough cross-section for capturing neutrons that any substance with a lot of hydrogen that can stand the heat is a decent and cheap shield. That being said, there are better materials to use:

https://en.wikipedia.org/wiki/Neutron_cross_section#Typical_cross_sections

Notice that the table gives cross-sections for scattering, capture and fission. Also notice how wildly the number differs between thermal and fast neutrons.


So while you can use stuff like Gold or Cobolt, it's cheap and easy to use water.

Notice that Hydrogen is stuck in the "Moderators" category. That's because its cross-section for scattering neutrons is higher than for capture. It can therefore decrease neutron energy by taking some of the kinetic energy during an interaction. So it's a good thing if you're trying to slow neutrons down.

Thermal neutrons are easier to capture and trigger nuclear reactions more easily. Check the capture cross-sections of neutrons for U-238 and for U-235 for fast neutrons, then for thermal neutrons. Notice that for fast neutrons it's:
1.) Difficult to capture them
2.) The cross-section is about the same for U-238 and for U-235

U-238 will capture a neutron without fission, turning into U-239, but U-235 will cause fission. So U-238 is kind of a sink of neutrons. But if you slow them down into thermal neutrons, U-235 becomes ~50 times more likely to capture neutrons than U-238, so fission can continue without a giant loss of neutrons.

 

[Andy44]

Imagine pretending that you are disabled while you are obviously not, and yet the helping guy chooses to pretend he didn't notice.
Pure painful cringe.

I imagine in USA you'd also have to magnify that cringe with the need to give a tip.

Nope, tipping gas station attendants is not expected.

And my point was that people are comfortable if they grow up with it. Thus my grandfather's reaction as compared with MaverickSawyer's.

 

[Urwumpe]

I feel seriously de-skilled by letting somebody else do something as simple as putting the right liquid into the tank of my car. I understand it is a job somebody is paid for, but it is a job I feel more satisfied about when I did this myself.

(And I can understand the NY guys. I needed 5 minutes figuring out how an automatic gas station works in Denmark)

 

[Linguofreak]

Sitting in your warm car while somebody else pumps gas for you is a bad thing?

Not having the option to pump your own gas when all the attendants are busy is. I can't imagine any scenario where full service would be faster than pay-at-the-pump self service, and quite a few where it could be drastically slower (though I have admittedly never filled up at a full service station).

 

[Notebook]

http://www.bbc.co.uk/news/uk-scotland-glasgow-west-42565363

Second only to the Independence debate.

N.

 

[Notebook]

It seems 9 out of 10 folk can't tell the difference between the recipes. That was an unbiased poll between Scots as a hangover cure.


N.

 

[Urwumpe]

It seems 9 out of 10 folk can't tell the difference between the recipes. That was an unbiased poll between Scots as a hangover cure.

Somehow, all British people seem to be very scientific about their hangover cures. Here its just weapon-grade coffee and what you have left in your fridge...

 

[statickid]

From Facebook :facepalm:

 

[Andy44]

For the last week or so much of the continental US has been in a cold snap with some areas getting the deep freeze treatment. Here in the DC area the temperatures have been dipping into the single digits (F) at night, and staying below freezing during daylight hours. I visited the Potomac River bank today to find the river frozen over; there were people walking on the surface trying to play hockey in 19degF and bitter cold wind.

All good as far as I'm concerned, I generally love the cold, although when it's this cold I have to take measures to make sure the pipes don't freeze in my house. Crank up the heater higher than usual, and let the water drip in key places to keep it moving.

Unfortunately for one of my neighbors, they didn't follow this routine. They appear to have left on a trip some days ago without turning off the water or taking any other precautions. The other night walking past their house I noticed there was a glacier of ice on the walk about 2 inches thick leading back up the steps to their front door. Looked a little closer with a flashlight and there was water dripping out of the siding across the entire front of the house. Big thick icicles have formed underneath the living room bay window. Peering around at the back of the house, there are icicles hanging from the sliding glass door at the same level, leading into the kitchen. The windows have ice formed inside them on the window sills, and are all frosted up.

So their living room, kitchen, downstairs finished basement, and possibly parts of the upstairs bedroom level, are all completely ruined, and these poor souls don't even know this is waiting for them when they return home!

Somebody called the water company, who apparently turned off the water main and left a note on the front door, so at least the bleeding has stopped, but that is going to be, I'm guessing, tens of thousands of dollars in damage to the house itself, not to mention how much of their furniture and other belongings are totally trashed as well. And, of course, they will have to find a place to live in the meantime, since the house will be uninhabitable until at least some of the water damage is repaired. What an awful thing to see.

 

[Artlav]

Well, as we joke around here in Moscow under the rain and +4*C on New Year's day, you Americans should really stop stealing our winter if you don't know how to use it.

 

[Notebook]

Its been 3 or 4 degrees here, a hard wind blowing off the North Sea, and I'm FREeezing!
N.

 

[MaverickSawyer]

I was in shirtsleeves today in Seattle. I am DEEPLY enjoying this warmer spell.