Digging self into a hole nowBade wrote:^ why would dislodging electrons require more energy than dislodging something from inside a nucleus ?
On second thought, what I said is wrong as small potential difference across a conductor causes electric flow. The protons are held together with electrostrong forces, right? What causes the neutrons to stick together?That would be an incorrect way to look at it.matrimc wrote:The protons are held together with electrostrong forces, right? What causes the neutrons to stick together?
OK, "held together" is the wrong wording. Repulsive forces are overcome by ... . Rest of it has gone whoosh over my head. Will ruminate over it (and do some background reading, I guess?).Bade wrote:That would be an incorrect way to look at it.matrimc wrote:The protons are held together with electrostrong forces, right? What causes the neutrons to stick together?
AmberG jiAmber G. wrote:^^^ If you can get a chance, (and if you have not done so), I will strongly urged you to check out Feynman's lectures. The book, IMO, gives an excellent perspective on what you are asking.
You may like to get a copy of the book "Six easy pieces" (which takes six "easy" chapters).. .. or since Bill Gates has bout Feynman on line, you may be able to use that.
Thank you Amber G for the recommendation. I have briefly read Feynman's lectures and believe me, he is one of my gods, probably the highest of them all. And honestly, the more I think about the interplay between math and physics, no doubt I will fall in line with "The Unreasonable Effectiveness of Mathematics in the Natural Sciences".Amber G. wrote:^^^ If you can get a chance, (and if you have not done so), I will strongly urged you to check out Feynman's lectures. The book, IMO, gives an excellent perspective on what you are asking.
You may like to get a copy of the book "Six easy pieces" (which takes six "easy" chapters).. .. or since Bill Gates has bout Feynman on line, you may be able to use that.
Another good resource is Mr. Tomkins in Wonderland (By George Gamow)
(These books are old, and they made a very big impression on me)
Yes, I think it covers 6 chapters taken from the original .. including class lecturers (on CD) and notes...which are more understandable for non-physics majors.matrimc wrote: AmberG ji
I have the lectures (3 volumes - Indian edition). Are these a subset of the Lectures? thanks
I remember from high school , something very vaguely of how the total Neutron to Atomic Mass ratio and there is a think band along which the stable atoms are and the others are unstable such that when hit by a neutron , the nucleus sort of fissions or when hit by a neutron get from being unstable to the table no of Nuetrons to Atomic mass ratio.Amber G. wrote:But why slow neutron do not cause fission in ..U232, U234 or , U238
But they do in U233 and U235 ...
kasthuri wrote:Oh boy, I like this quote,
There is only one thing which is more unreasonable than the unreasonable effectiveness of mathematics in physics, and this is the unreasonable ineffectiveness of mathematics in biology. — Israel Gelfand
IMHO, this comes about due to the fact that things are almost mathematical. What I mean by that is that in bio there are a large number of special cases. Due to this abstraction is difficult leading to theorems becoming too specific and thus applicable to only a few (and in some cases only one) situations.This is also a main MIT newsACKGROUND: In the event of a nuclear accident, people are exposed to elevated levels of continuous low dose-rate radiation. Nevertheless, most of the literature describes the biological effects of acute radiation. Our major aim is to reveal potential genotoxic effects of low dose-rate radiation.
OBJECTIVES: DNA damage and mutations are well established for their carcinogenic effects. Here, we assessed several key markers of DNA damage and DNA damage responses in mice exposed to low dose-rate radiation.
METHODS: We studied low dose-rate radiation using a variable low dose-rate irradiator consisting of flood phantoms filled with 125Iodine-containing buffer. Mice were exposed to 0.0002 cGy/min (~400X background radiation) continuously over the course of 5 weeks. We assessed base lesions, micronuclei, homologous recombination (using fluorescent yellow direct repeat [FYDR] mice), and transcript levels for several radiation-sensitive genes.
RESULTS: Under low dose-rate conditions, we did not observe any changes in the levels of the DNA nucleobase damage products hypoxanthine, 8-oxo-7,8-dihydroguanine, 1,N6-ethenoadenine or 3,N4-ethenocytosine above background. The micronucleus assay revealed no evidence that low dose-rate radiation induced DNA fragmentation. Furthermore, there was no evidence of double strand break-induced homologous recombination. Finally, low dose-rate radiation did not induce Cdkn1a, Gadd45a, Mdm2, Atm, or Dbd2. Importantly, the same total dose, when delivered acutely, induced micronuclei and transcriptional responses.
CONCLUSIONS: Together, these results demonstrate in an in vivo animal model that lowering the dose-rate suppresses the potentially deleterious impact of radiation, and calls attention to the need for a deeper understanding of the biological impact of low dose-rate radiation.
Citation: Olipitz W, Wiktor-Brown D, Shuga J, Pang B, McFaline J, Lonkar P, et al. 2012. Integrated Molecular Analysis Indicates Undetectable DNA Damage in Mice after Continuous Irradiation at ~400-fold Natural Background Radiation. Environ Health Perspect :-. http://dx.doi.org/10.1289/ehp.1104294
Pay attention to the following quote from Jacqueline Yanch, MITA new study from MIT scientists suggests that the guidelines governments use to determine when to evacuate people following a nuclear accident may be too conservative.
The study, led by Bevin Engelward and Jacquelyn Yanch and published in the journal Environmental Health Perspectives, found that when mice were exposed to radiation doses about 400 times greater than background levels for five weeks, no DNA damage could be detected.
Current U.S. regulations require that residents of any area that reaches radiation levels eight times higher than background should be evacuated. However, the financial and emotional cost of such relocation may not be worthwhile, the researchers say.
“There are no data that say that’s a dangerous level,” says Yanch, a senior lecturer in MIT’s Department of Nuclear Science and Engineering. “This paper shows that you could go 400 times higher than average background levels and you’re still not detecting genetic damage. It could potentially have a big impact on tens if not hundreds of thousands of people in the vicinity of a nuclear powerplant accident or a nuclear bomb detonation, if we figure out just when we should evacuate and when it’s OK to stay where we are.”
Until now, very few studies have measured the effects of low doses of radiation delivered over a long period of time. This study is the first to measure the genetic damage seen at a level as low as 400 times background (0.0002 centigray per minute, or 105 cGy in a year). { for perceptive, this is about 1000 mSV /Yr = 10000000 bed /yr - about 1000 times 1mSV insisted by some.. about 50 times the current limit when one is forced to evacuate .. about 4 times the limit allowable (which they increased to 250 mSV) for emergency workers in Japan..Amber G notes }
“Almost all radiation studies are done with one quick hit of radiation. That would cause a totally different biological outcome compared to long-term conditions,” says Engelward, an associate professor of biological engineering at MIT.
<snip:
(Background radiation . add up to about 3 mSV per year in US)
“Exposure to low-dose-rate radiation is natural, and some people may even say essential for life. The question is, how high does the rate need to get before we need to worry about ill effects on our health?” Yanch says.
Previous studies have shown that a radiation level of 10.5 cGy, the total dose used in this study, does produce DNA damage if given all at once. { This is what I said in one of VERY early message - I said that below this one does not see any symptoms ... LNT predicts about 4% increased risk of cancer in life time } However, for this study, the researchers spread the dose out over five weeks, using radioactive iodine as a source. The radiation emitted by the radioactive iodine is similar to that emitted by the damaged Fukushima reactor in Japan.
At the end of five weeks, the researchers tested for several types of DNA damage, using the most sensitive techniques available. Those types of damage fall into two major classes: base lesions, in which the structure of the DNA base (nucleotide) is altered, and breaks in the DNA strand. They found no significant increases in either type.
<snip - Technical details about DNA damage >
... “My take on this is that this amount of radiation is not creating very many lesions to begin with, and you already have good DNA repair systems.
Doug Boreham, a professor of medical physics and applied radiation sciences at McMaster University, says the study adds to growing evidence that low doses of radiation are not as harmful as people often fear.
“Now, it’s believed that all radiation is bad for you, and any time you get a little bit of radiation, it adds up and your risk of cancer goes up,” says Boreham, who was not involved in this study. “There’s now evidence building that that is not the case.”
Most of the radiation studies on which evacuation guidelines have been based were originally done to establish safe levels for radiation in the workplace,.....
....“when you’ve got a contaminated environment, then the source is no longer controlled, and every citizen has to pay for their own dose avoidance,” Yanch says. “They have to leave their home or their community, maybe even forever. They often lose their jobs, like you saw in Fukushima. And there you really want to call into question how conservative in your analysis of the radiation effect you want to be. Instead of being conservative, it makes more sense to look at a best estimate of how hazardous radiation really is.”
Those conservative estimates are based on acute radiation exposures, and then extrapolating what might happen at lower doses and lower dose-rates, Engelward says. “Basically you’re using a data set collected based on an acute high dose exposure to make predictions about what’s happening at very low doses over a long period of time, and you don’t really have any direct data. It’s guesswork,” she says. “People argue constantly about how to predict what is happening at lower doses and lower dose-rates.”
....
“It is interesting that, despite the evacuation of roughly 100,000 residents, the Japanese government was criticized for not imposing evacuations for even more people. From our studies, we would predict that the population that was left behind would not show excess DNA damage — this is something we can test using technologies recently developed in our laboratory,” she adds.
<snip>
****"Instead of being conservative, it makes more sense to look at a best estimate of how hazardous radiation really is."
{ One can become instant guru..what kind of isotope may be good nuclear fuelAccording to the fissile rule, heavy isotopes with 90 ≤ Z ≤ 100 and 2 × Z – N = 43 ± 2, with few exceptions, are fissile (where N = number of neutrons and Z = number of protons).
} In general, most actinide isotopes with an odd neutron number are fissile. Most nuclear fuels have an odd atomic mass number (A = the total number of protons and neutrons), and an even atomic number (Z = the number of protons). This implies an odd number of neutrons. Isotopes with an odd number of neutrons gain an extra 1 to 2 MeV of energy from absorbing an extra neutron, from the pairing effect which favors even numbers of both neutrons and protons. This energy is enough to supply the needed extra energy for fission by slower neutrons, which is important for making fissionable isotopes also fissile.
More generally, elements with an even number of protons and an even number of neutrons, and located near a well-known curve in nuclear physics of atomic number vs. atomic mass number are more stable than others; hence, they are less likely to undergo fission. They are more likely to "ignore" the neutron and let it go on its way, or else to absorb the neutron but without gaining enough energy from the process to deform the nucleus enough for it to fission. These "even-even" isotopes are also less likely to undergo spontaneous fission, and they also have relatively much longer half-lives for alpha or beta decay. Examples of these elements are uranium-238 and thorium-232. On the other hand, isotopes with an odd number of neutrons and an odd number of protons (odd Z, odd N) are short-lived because they readily decay by beta-particle emission to an isotope with an even number of neutrons and an even number of protons (even Z, even N) becoming much more stable. The physical basis for this phenomenon also comes from the pairing effect in nuclear binding energy, but this time from both proton-proton and neutron-neutron pairing. The short half-life of such odd-odd heavy isotopes means that they are not available in quantity and are highly radioactive
Very true. Rate does matter, but looking *purely* from genomics perspective, tumor occurrence due to radiation is relatively a rare event even with modest levels of radiation. I am not sure if the LNT model incorporates any genomics, leave alone biology (and mechanistic cell cycle) roles. One can die of secondary smoke than due to radiation, in a high probability. I think people who campaign for radiation safety will serve a better purpose if they rather do for quitting smoking. World will be a far better place that way...Amber G. wrote:
Also, you may already know this but CRITICAL difference between above study and say radiation for tumors is the RATE ... is the dose given in a short time or distributed over long period.
This story (both in ndtv and dailymail where it is taken from) looks like written by some ddm who has no idea about the related field ...no details are are given a comment in dailmail puts it aptly
I tried to look at the article, it is not published but just written and submitted to school so I couldn't even tell.You realise you're a newspaper? Say atleast vaguely what it is that he's solved! "His solutions mean that scientists can now calculate the flight path of a thrown ball and then predict how it will hit and bounce off a wall." No they don't. That has been doable for hundreds of years using very simple vectors and conservation of momentum and every child doing A level maths or physics will know how to do it. What has he done? Made it more accurate? Is it even related to that at all, because since it definitely isn't that I don't see why I would believe that the story is even close to accurate
Yes, not only the type of radiation (energy and type) but which organ of the body.. Radiation of toes is less dangerous than, say stomach or bone marrow cells..SaiK wrote:btw, what type of radiation also matters right?
Few comments:rsingh wrote:As I understand gravity is universal property of mass. Weight is due to gravity. Sun is millions times bigger then Earth and therefore Earth revolves around sun. That is simple for amm Abdul like me. Now the question : do we weigh less during day (because of Sun's gravitational field) and more during night. There has to be a difference. The difference may be very small ( may be 1/10000000th of a gram but there has to be. And if we can find that difference it will be a big thing. I want to design an experiment but I do not have access to very sensitive balance.
Please let me know if I made some wrong assumptions.
4. But the effect of sum makes you weigh less at noon as well as midnight .. (you weigh more in Evening or morning.. why?do we weigh less during day (because of Sun's gravitational field) and more during night.
To simplify let's take 1kg Iron........why it would weigh more in Evening?4. But the effect of sum makes you weigh less at noon as well as midnight .. (you weigh more in Evening or morning.. why?
If we forget (ignore) effects due to everything else.. (that is assume earth is a perfect sphere .. no spin - hence no centrifugal force --- no air, no moon .. nothing else.. just earth and sun)rsingh wrote:Amber G. thanks for the comments.
<snip>
To simplify let's take 1kg Iron........why it would weigh more in Evening?
Can you guess?Which experiment are you talking about?
AmberG is it because during the midnight Moon's gravity actually adds up with the earth's gravitational pull whereas during the noon it actually adds up to the Sun's gravitational pull ?For most, it is intuitive that at midday it will weigh less but why at midnight ?
If we forget (ignore) effects due to everything else.. (that is assume earth is a perfect sphere .. no spin - hence no centrifugal force --- no air, no moon .. nothing else.. just earth and sun)
Then at midday and midnight..
Then, If I understand you correctly at midnight one will weigh more.. (which is different than what I said)negi wrote:Ok then , during noon if g2 is the acceleration due to gravitational pull exerted by Sun on an object of mass m on earth and 'g' due to the earth , then net weight of the object will be |mg-mg2| during midnight the two will get added.