Why does Water Expand when it Freezes?

11 October 2009

The Nobel prizes feature on the Naked Scientists this week alongside a bumper crop of your science questions! We find out why water expands when it freezes, whether animals have regional accents, and how many rockets you would need to crash into the moon to knock it off course. Plus, how the insects splattered on windscreens are helping scientists to study biodiversity, the virus linked to chronic fatigue syndrome and the prospect of a paper-thin digital camera. Also, We find out how India is coping with the IT boom, and show you how to make a spud gun from stationery!

In this episode

Can Plants get Cancer?

Chris - Cancer in the context of a human has got a specialist disorder. What we mean by cancer, our cells that have lost the ability to obey the normal signals that control and dictate how things grow and move and obey signals that tell them not to go to other places in the body and not to grow through boundaries of tissues and not to disobey 'kill yourself' signals. Because every cell in the body is programmed to die unless it's told otherwise.Cancer cells ignore that signal and so, they are immortal as Richard Van Noorden was saying, and they also disobey all those normal regulatory signals that can spread to other bits of the body and cause secondary tumours. And it's usually those secondary tumours that cause problems. Now, plants don't have a disease like that. They don't get secondary spread through their system of disease which starts in one part of the plant and goes elsewhere, at least in the form of the cells from the plant itself. But they can get localized growths, a cancer-like phenomenon and just like some human cancers which can be triggered by microorganisms, cervical cancer for example is caused by infection with a virus, human papilloma virus. Also, gastric cancer in the stomach is caused by bacterial infection, Helicobacter pylori, is strongly associated with gastric cancers.In plants, there is an environmental organism, it's called Agrobacterium tumefaciens, this is a soil dwelling bacterium and it has something called a transposon. This is a piece of genetic material which the bacterium injects into the plant's own genetic material and that transposon carries genes which code for growth factors. And it causes the plant cells to begin to grow out of control. And the idea is to produce a big growth locally on the plant that then gives a home and provides protection to bacteria and that's a Gall. And it's very, very common, it's called Crown Gall disease when the plants actually have it, but it doesn't spread predictly to other bits of the plant. So there are some similarities between human cancers and animal cancers and plant tumours like Crown Gall disease, but it's not the same disease. There's nothing systemic as far as I know that does the same thing but it's a very good question.

Why is glass transparent?

Well if you look very, very carefully at a single grain of sand, especially if you've polished up the surfaces, it is actually transparent. I've looked through lumps of sand, quartz- white sand, through microscopes. As long as it's polished, you can see through it. Sand is intrinsically transparent. The reason why you can't see through it on a beach is because it is in lots of lumps. If you ever looked at the world through a glass or a piece of glass, especially if it's curved, everything looks distorted behind it because when light hits it, it slows down, it bends, it goes around a corner it gets refracted, and the light kind of gets bounced off. Now, if you're looking at something large, you can still make up a picture behind that. But if you've got thousands and thousands of very small glasses, the light would all get refracted off one. It would get refracted offsome others, and all the pictures will get mixed up and mixed up and mixed up, until eventually they get overlaid over one another and it looks white. Chris - So it must be the same phenomenon as snow looking white, but the water it's made from - if you see it in fish tank, is transparent. Dave - Yeah and even in ice it's also transparent. Helen - And then you've got sort of yellow sands, black sands, and the other impurities that are giving it that kind of tinge of a different colour path. Dave - Yeah, you get different rocks in it. Black sands are normally from basalts which is intrinsically black and those just aren't transparent and yeah, a bit of patchy clays and all sorts of things in there.

How do cold-blooded species cope in cold water?

The answer is to do with their metabolic rates and the fact that they can operate at those low temperatures. I actually want to go into detail a little bit on what you call at the end, the freezing species. This is the most interesting thing that was discovered back in the 1960s which is that there are fish in the Antarctic that create antifreeze and that's how they live in very cold temperatures. Because the crazy thing about the sea is that it doesn't actually freeze until -1.9 degrees centigrade where as normally water freezes at zero, we know that. But it's because of those salts and the various impurities in seawater that means that ocean temperatures can get extremely low indeed especially down there in the southern ocean. And so these Antarctic cod it was discovered that they have glycoproteins in their blood. That means that their tissues their fluids inside them don't freeze until -2 degrees centigrade, so they are safe in the sea. The glycoproteins work in a very clever way by actually attaching to the surface of small ice crystals by plugging gaps if you like between them. And that stops them from getting any bigger so the fish themselves don't actually freeze despite the fact that they are sub zero in temperaturesand that's really rather cool. But then there are other reasons why they don't actually manage to swim around all the time and they are affected to some extent by what temperature there is and what's going on in the environment. Because it was discovered last year that some fish in the Antarctic hibernate. The first fish that were shown to actually slow down, slow their heart rate, slow their movements when it's very cold and dark. And that could actually be because it's dark and they need to be able to see to be able to catch their food. So in fact what they do is say, "Okay fine we'll have a bit of rest while we can't find our food and wake up when it gets warmer and lighter."

32:08 - Technology in India

Tech expert Chris Vallance looks at the technology highlights from over the summer and investigates the effect of the internet boom in India on its residents...

Technology in India
with Chris Vallance & Jamilla Knowles, BBC Correspondents

Helen -  Now it's been a while since we've had an update on the world of technology.  So it's time to join our resident expert Chris Vallance for a summary of what's been going on over the summer as well as insight into the social effects of the technology boom in India.

Chris V -   Well it has been a while since we spoke and in the intervening months I think there were two events which for me highlighted the way that technology is changing and I think we should talk about.  You'd have to have been hiding under a rock to miss the first one, that's the 40th anniversary of the Apollo Moon landing.  Obviously the Apollo Moon landing is important for technology as it's the early uses of things like integrated circuits, fuel cells.  Obviously people debated and discussed the contribution to technology that those landings made.  But certainly events that are very important for people with an interest in space and the technologies surrounding it.  And weThe moon fast-forward to September and we have the announcement that one of the new countries to enter into space exploration; India, the Indian Chandrayaan probe had discovered evidence of water on the moon.  Now it's interesting for us to talk about India at the moment because obviously everybody hears about the Indian tech boom and what that means for the country.  A lot of it focused around the city of Bangalore. One of my colleagues has just been there: Jamilla Knowles, who's been looking at what this most tech-enabled of Indian cities can say about how technology is changing, the social relations in India between the haves and the have-nots. Obviously a country where there is still a great gulf between those two groups.  What did you find?

Jamilla -   I found things that you would probably expect if you start reading about Bangalore the area of poverty, the population is as huge in comparison with those who are employed, say.  And also that there are huge areas throughout the city of migrant workers living in slums, basically building glass shiny edifices to technology that we use.  So it's quite stark but it's something that has been happening for the last decade or so.  So it's looking more at the kind of politics and the consciousness of people who are in Bangalore as a city.  I went across to the Centre for Internet and Society inspecting Nishant Shah there, who's the director of research.  And he was talking about a sort of a feeling and a consciousness generally of people having a relationship with the internet and that would be even people who have never even used a computer.

Nishant -   So the case study in Ahmdebad, which is where the people who were living in slums on the river front, on the Sabarmati river front, are now demolishing their own houses and are being employed by the state to do that in order to build an IT skyline for the city.  There is no resentment among the people, there seems to be no protest initiated by civil society organizations.  And when you kind of talk to the people they keep on telling you it's because of that internet.  And they've never seen a computer and they've never been online and they don't know what the internet is about.  But they imagine themselves as having access to the internet by building this particular kind of infrastructure.  These are the invisible people of the IT story.  These are people we no longer talk about.  We always talk about either people in call centres or in back processing offices or offshore development centres or you know start ups who are working on technology.  People who are visible and who have a voice and who are so quintessentially a part of technology that we forget that there is an entire support system which is also defined by internet technologies in India.  And then we start talking about IT cities and IT parks and so on but are these people who aspirationally or experientially a part of the internet paradigm but not the technology. bangalore city

Chris V -   So that's fascinating.  So people who are the very poorest people in Bangalore, completely separate from the tech boom have this idea of the internet but they've never actually used it.

Jamilla -   It's almost as though it's in the air, it's everyone from auto rickshaw drivers from children in schools that are really in need.  These are kids who live with their parents who move around the city looking for work as labourers and often suffering from skin conditions from malnutrition.  But they understand, they know why their city is changing.

Chris V -   Is the internet benefiting these people in any way apart from the economic benefits?

Jamilla -   What are they getting direct benefits from the internet is difficult to say.  Some of the online companies will say yes because they will go to rural areas and show local people or farmers, "Here's the internet it's great," but essentially they'll put it on a bus which will then drive away again so it's quite difficult to see that.  Going back to things like education which seems to be underpinning their hopes for improvement.  They are doing things like sourcing information online in educational centres then burning CDs which become educational supplements for teachers in rural areas.  Because they may not have the skills in say the sciences or mathematics that maybe teachers who are in urban areas do, so they can actually record a lesson and send it out and supplement that with information that they found online.

Chris V -   Did you get a sense that there are almost two cities, the bright shining new city and there was the older city of people who didn't have access to the technology?

Jamilla -   Definitely and it's quite often the migrant workers from other states who don't have the access.  Local people in Bangalore have a slightly different argument with the fact that basically they've been overrun with people from all over the world and all over the country thinking of Bangalore as one of the places that might be paved with gold when it comes to employment.  And instead there's a great deal of unemployment and it's happening to them as well because the population has just exploded and they're not necessarily trained up to go and work in IT support, to go and work in a call centre, to go and work as a developer or coder.  I mean, that's far beyond the ken of many of the people who live there.

Why does water expand when it freezes?

The default is for things to shrink when they freeze. This is because, normally, if you make something hotter, it vibrates more. When it vibrates more, it tends to take up more space, so it tends to expand. Ice is very unusual that, as it gets colder, although the particles are vibrating less, it expands. The reason for that is due to the strange shape of water. If you've ever seen the picture of a water molecule, it looks like a Mickey Mouse head with an oxygen molecule where Mickey Mouse's face is, and then two hydrogen atoms where his ears are.

The oxygen atom is slightly negative, and the hydrogens are slightly positively charged, so water molecules tend to stick together forming what are called hydrogen bonds. And because of that shape of the molecule, the way water molecules tend to link together is actually a very open structure with big holes. That means, there's quite a lot of extra "empty" space. When water freezes it releases energy because lots of extra strong bonds can be made. But it does take up more space. And so, ice expands when it freezes.

Why can't the human body multi-task?

It's very, very difficult. You can do it with practice, but it is incredibly hard to do. If you try and do that number 6, you'll find that number 6 flips around, and you start drawing it backwards. And the reason for this is to do with the way your brain codes for movement. Because you can easily do that if you use the opposite sides of the body. If you've got a hand which you do a clockwise circle with and your right hand and then you use your left leg, you'll easily do a circle in the anticlockwise direction because you're using two different sides of your brain. If you're trying to use the same side of your body, the motor cortex which is the bit of the brain which codes for movements, the way this is working is that it doesn't actually code for a brain cell, telling a muscle what to do. The brain actually codes for movements by what's called a tuning curve. So you have a cluster of nerve cells which fire off when you want to make a movement with a part of the body into a certain direction in space. And those nerve cells don't just switch on muscles that move say, just the arm. They switch on muscles which would move your leg in the same direction too, but they turn them on a bit less than the motor neurons that control the arm. So basically, you're facilitating or making it easier for your leg to move in the same direction as your arm. But it takes a little bit more switch on to make the leg move as well. Therefore, if you try then to make a movement in the opposite direction with the leg, you're basically facilitating another group of nerve cells to move in the opposite direction. So the two things are trying to fight it out and it's, whichever one wins, actually ends up going in that direction, and the arm is such a dominant force that's somewhat brain devoted to it, that I think it probably overwhelms the signal for the leg which is why the leg finds it hard to be dominant in that way. But it's an amazing demonstration, isn't it? It's great fun. You can have a lot of fun with that at parties.

Are 'light' cigarettes better?

Chris - James Bond said that giving up smoking is actually really easy. He'd done it hundreds of times. The thing with smoking is of course, everyone takes these or uses these 'light' or kind of 'smooth' cigarette brands. They first surfaced in the '50s and '60s. I was doing a bit of research of this because I thought they were more recent than this. But they first surfaced in the '50s and '60s actually, coinciding with when Richard Doll first published studies, showing that smoking is bad for you. So, it was a sort of response in the part of cigarette manufacturers to try to market a product that gave the impression that it was in fact much healthier. And in fact, 80% of the cigarettes that gets smoked worldwide are now of the 'light' variety. And the way they make them 'light' is that they put little holes in the filter. And so, as the person takes a drag on the cigarette, it draws in some air with the smoke. But what that means is, this can actually lead to a change in behaviour on the part of the person. And in fact, the statistics show that in fact, smoking 'light' cigarettes is no better for you than smoking full strength cigarettes. And the reason is, people change their smoking behaviour to accommodate the fact that they're getting a lower nicotine dose.There was a study which got published in the journal, Neuropsychopharmacology was a guy in UCLA in America, Arthur Brody did this last year. They got people who smoked into the laboratory and they did a thing called a PET scan. This is a way of imaging the brain and they got them to smoke cigarettes and they compared people smoking cigarettes that had nicotine in them with cigarettes that have very little nicotine in them or much lower doses, to see how many of the receptors for nicotine in the brain got filled by these different varieties of cigarettes. And they found almost the same amount of occupancy. The receptors are getting stimulated, just as much. Probably because the people were smoking the 'light' cigarettes harder to get the dose up. Because at the end of the day, the cigarette has got nicotine in it and that's the thing you want. So, people will just titrate up or increase their dose of cigarettes, in order to get their nicotine levels to what they want it to be, to satisfy their craving.I went looking for any actual evidence that light cigarettes are better on the internet and I found this site, the US National Cancer Institute. This is a government organization. They've got a very interesting analysis on this on their website and I'll just read it to you because I couldn't add anything to this. I couldn't put it better myself, but this is really quite staggering. Listen to this:"Tobacco companies designed light cigarettes with tiny pinholes on their filters. These "filter vents" dilute cigarette smoke with air so that when lit cigarettes are "puffed" by smoking machines, and that's how they get their tar numbers in the nicotine values which they then report in the packet, these causes the machine to measure an artificially low tar and nicotine level. But many smokers do not know that their cigarettes have these vent holes and the filter vents are uncovered when the cigarettes are smoked on the smoking machines, but the filter vents are placed just millimetres from where a smoker puts their lips or fingers when they're smoking. And as a result, many smokers block the vents when they smoke and this actually turns the light cigarette into a regular cigarette. Some cigarette makers also increased the length of the paper wrapped around the outside of the cigarette filter and this decreases the number of puffs that occur during a machine test. Although the tobacco under the filter is still available to the smoker and this tobacco is not burned during the machine test. As a result, the machine measures less tar and nicotine than is actually available when the person smokes."And here's the real clincher. Because smokers, unlike machines, crave nicotine, they will inhale more deeply, take larger, more rapid, or more frequent puffs or smoke a few extra cigarettes each day to get enough nicotine to satisfy their craving, and this is called "compensating," and it means that smokers end up inhaling more tar, nicotine, and other harmful chemicals than the machines would actually have you believe. So that's actually on the U.S. National Cancer Institute's cancer.gov website. So, I think the answer to your question is, 'light' cigarettes are basically a way of making you smoke and think you're doing yourself some good. There's no evidence that actually help people improve their health or give up.

Why does it get dark at night?

Dave - It's actually a really quite a deep question. If the universe is infinite, then any direction you look in, you ought to end up hitting a star. And therefore surely, the whole sky ought to be bright white. The simple answer is, because the universe is expanding, the universe is expanding really quite fast. So, the further away you go, it's expanding as if you're blowing up a balloon. So the further away you go, the faster things are moving away from us. If you go a really long way, tens of billions of light years away, they're moving away so fast that all light coming from it has been really, really red-shifted. So, it's been so red shifted,that we can't see it. In fact, it has been so red shifted that it's in the microwave region in the spectrum. So you can see light in every direction, but it's been so red shifted that our eyes can't see it. So the sky looks dark.

How many LCROSS NASA missions would it take to change the orbit of the moon by 1%?

Dave - Interesting question. What they were doing was firing the top stage of a centaur rocket and crashing it into the moon. They've been trying to watch the plume of stuff that comes up from that to see if there is water in that plume.Now the centaur rocket weights about 2.3 tons and it's going at about 10,000 kilometres per hour, that's 2,800 metres per second, which means it's got 6.4 million (6.4 x 106) kilogram metres per second of momentum. That's an awful lot of momentum. For anything on Earth, that's a scary amount of momentum. However, the moon has got awful lot more momentum than that. It's moving at a kilometre per second and it weighs 7.3 x1022 kilograms. That means the moon has got 7.3 x 1025 kilogram metres per second of momentum.So, how many LCROSS's crashing into it would change it's momentum by 1%?7.3x1025 minus 6.4x106 is roughly 1x1019So about 1019 collisions. So that's 1 with 19 zeros after it (10,000,000,000,000,000,000!).And actually, an LCROSS's momentum compared to the moon is about the same as 1 millilitre of water compared to all the water in all the earth's oceans.

How do we know how much the moon weighs?

Dave - We know quite accurately because we've sent things to orbit around the moon and the speed at which something orbits around an object is related to its mass and you can do it with a load of maths and workout exactly how much it weighs.

Do animals speak regional languages?

Helen - Good question. Animals do indeed. Some of them do have regional accents, if you like, or dialects. And whether or not your dog would understand another dog might come down to breeds, rather than necessarily where it's living in the world. But yes, animals do. We know that some birds have regional accents, some amphibians do, and if you jump into the oceans, there are creatures there that definitely have different languages and accents of their own. And that is the whales and dolphins, the cetaceans. And various studies have shown that if you listen to the sounds that some of these great whales are making, you can actually work out pretty well where it came from. Blue whales are one example and scientists have worked out that there are about nine regional populations of blue whales that seem to have their own distinct languages. And so, that might be something that has implications for things like conservation. Maybe we have to think about those nine populations as being slightly separate and different. Chris - Is that because the baby whales learn to speak by imitation from parents and that's how this regionality arises? Helen - Probably. I mean, we know so little really about these amazing creatures, given the huge area of ocean that they live in, things like that. So these sorts of questions, we don't yet know. For example, we also don't know if they could understand each other between these regions. We don't know that yet. Killer whales are another example of fantastic regional dialects. Along the eastern pacific coast of North America, there's been a lot of study of killer whales living around Vancouver and Alaska. And these guys also have regional dialects. In fact, you can tell whether or not the individual killer whale belongs to a residential population, whether it's a transient individual that's coming through or whether it's one from offshore because all these different killer whales basically speak with different accents, a little bit like different accents throughout the UK. We could tell where someone comes from, from the way they sound. I think this is fantastic.They've also shown that there's a genetic link which is fantastic which shows that there seems to be some way that killer whales can tell how related they are to each other. And therefore, try and avoid problem with things like inbreeding, just by the way that they're talking to each other. So I think that's just really fantastic.

Jelly fish swim in groups. How do they communicate to stay together?

Helen - I don't think they do actually. Jellyfish are in some ways extremely simple creatures. They don't have a brain, so they don't really have the ability to process inputs and sensory inputs like that.

So, I think, usually, when you see large numbers of jellyfish together, it's probably more likely to be the fact that the currents and the ocean currents are actually moving them together and keeping them in similar places.

Or also, they can respond to things like the availability of food in the water and chemicals and things like that.

So possibly, they're all following food sources, and that's why they're all ending up together.

But I don't think we yet have an idea that jellyfish can actually communicate to each other.

Although some of them do have quite complex eyes, which is quite exciting and box jellyfish have eyes...

Chris - What do they do with them?

Helen - That's a very good question. They have eyes quite a lot like humans and in fact, some of the genes they have are very similar to human genes for creating parts of the eye, but we think that happens in parallel and wasn't from a common ancestor, but we arrived at the same solution to having eyes and what do they see?

We know they certainly respond to daylight, light and dark. They need to know basically, what time of day it is because they tend to come up the water column at nighttime when they're less easily seen by predators and when it's light, they actually go further down the water column. So, they respond to light and dark. And even though they have quite complex eyes, it's actually a very good eye at detecting things like diffuse light to figure out, is it light or dark? What time is it? Should I be up or down in the water column?

How far would electricity carry in the sea?

Dave - Seawater conducts electricity reasonably well, but not very well. It's about a 10 millionth as good as copper. So, you will get electricity flowing through it, but it will also depend on where the other cable is because electricity always moves from one place to another place. And if the other connection to the circuit is an awful long way away, then you get very, very small currents and it's not going to do a lot of damage. If you've got two contacts a foot apart and a fish swims between them then it's almost certainly going to get electrocuted. So, I think it depends an awful lot about how you set up this test. Helen - I just like to say, I don't want anyone to go and try this for the sake of the fish and the sake of any divers that might be there. Just in case. Dave - And of course, with a toaster, if it's got a proper three pronged plug, then you got an earth in there as well, so most of the currents can flow within the toaster from the live parts of the toaster to the earth. So, it's probably not... Chris - It probably would just melt the cable, wouldn't it? Dave - It's probably going to draw a very large current and blow the fuse. Chris - I have heard of someone turning a lot of electricity into about a million gallons of very hot water in Australia when a flood happened in Adelaide at a Medical Research Institute and it flooded the basement and flooded the power board, and it didn't trip out for some reason. It just passed a very large current through a large amount of water and made the largest Jacuzzi you've ever seen. So there we are.

Could I use a torch to push me in space?

Chris - Yeah and the answer is, it does work. In fact, there's something called the YORP effect, Yarkovsky-O'Keefe-Radzievskii-Paddack effect in honour of the four scientists who described this first of all. If you look at asteroids and they are spinning in space and they're irregularly shaped, when they have one surface facing at the sun, which is a different size, say to the other face, then that face gets a disproportionately big push compared with when the object then turns on its side for example. And what this does is to create a push or a torque effect, which tends to steer the asteroid and change its path through space. And this is one effect which is thought to have unleashed this barrage of asteroids on earth that destroyed the dinosaurs 65 million years ago because out in vestiges of the early solar system near mars are whole remnants of bits of planet that failed to form. And there are these fairly big objects out there and they are subject to the YORP effect. So light can definitely push things along, and that could go for a person too. We know we can push spacecrafts via the same thing. This is the whole concept of solar sailing. You have a very big collector. And when photons are incident on it, then they can give it a bit of a nudge and we can work out how much of a nudge a photon, when it arrives, gives something. We know from the Planck constant, if you times that by the frequency of the light, you can work out how much energy is imparted by a photon, a particle of light hitting something, and I have to say very big thank you to Light Arrow on our forum who suggested a very neat solution to this problem. So basically, yes. Light can give things a push. If our astronaut who's drifting around in space were armed with a laser beam and he were armed with a 3 kilowatt laser beam, then the energy, the nudge that he would get would be given by the equation F=w/c, where F is the force and it's equal to W, the wattage of the beam divided by the speed of light. And if we put the numbers in, 3 kilowatts is 3 x103 that's power of a laser. You divide that by the speed of light, 3 x 108. That would tell you that the force that the astronaut would feel through firing the laser would be about 10-5 newtons. On Earth, that would be the equivalent of holding up 1 milligram. In other words, about 1,000th of a gram. So, very small push but nonetheless, over enough time, given enough time, it would push the astronaut through space. You would have to point the laser in the direction opposite to which he wanted to travel. Dave - This is actually the ultimate rocket. You get the maximum push for every kilogram of stuff you throw out the back. So, if you want to travel a very, very long way, this is the way to do it.

60:44 - Why should we sit far from the TV?

When I was younger I was told not to sit too close to the TV. Is it an urban myth that it's dangerous to sit too close? Or does the TV emit radiation? Does this still apply to modern...

Why should we sit far from the TV?

We put this question to Andy Karam, adjunct professor at the Rochester Institute of Technology...Andy - Televisions really do give off radiation. But having said that, it's only a little bit of radiation and it's not that dangerous. What happens is that anything with a cathode ray tube, a tube where you shoot high-energy electrons at some sort of screen, when those electrons hit the screen, they give off very low energy x-ray radiation. This is the same way that x-rays are produced in regular x-ray tubes. So, if you're sitting close to a cathode ray tube, whether a computer monitor, a television screen, a radar set or anything else with that type of technology, you're going to be getting low doses of x-ray radiation.Now having said that, I've got to emphasize, they're low doses of radiation. It's not enough to be dangerous and in fact, if you watch your television for several hours a day all year, you're getting less radiation than you would from a single medical x-ray and less radiation than you get from the radioactivity that's just naturally within your body. So, it's something that we can measure, but it's not something that's harmful.LCD and plasma screens don't give off any radiation at all. They don't use high-energy electrons. It's a different type of technology. I could not say that they're safer because I don't consider the radiation from cathode ray tubes to be a risk, but I can say that they give off less radiation. As far as sitting too close to the television goes, the further back you are, the lower the radiation dose will be. But having said that, I don't consider the radiation dose even at a distance of just one metre to be dangerous.

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