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Nuclear Physics

Most commonly known for its applications in nuclear energy and nuclear weapons, Nuclear Physics also has applications in medicine and archaeology. This category is for questions about the branch of physics that deals with the study of the forces, reactions, and internal structures of atomic nuclei, Nuclear Physics.

3,164 Questions

Does a radioactive substance continue to decay after its half life is over?

No, a radioactive substance does not remain radioactive forever. But we should dig a bit deeper and learn some things about what it means when something is radioactive.

Radioactive substances, which are sometimes called radionuclides, are atoms with an unstable atomic nuclear structure. Every unstable atomic nucleus will eventually decay spontaneously, and the only question is when. The time it takes for a given atom of a given radioisotope to decay cannot ever be given, but we've found a way to talk about the length of time it takes for a radionuclide to decay, and that's the half-life. The half-life is the time it takes for half of a large number of atoms of the same radionuclide to decay.

When an unstable atomic nucleus decays, a "new" atomic nucleus it formed. This new nucleus is what is called a daughter. The daughter may or may not be radioactive. If it is, it too will eventually decay into another daughter. And so on, and so on until a stable atomic nucleus is arrived at. In this light, no radioactive substance remains radioactive forever. But there's a catch.

What if the half-life of a radioisotope is, say, a billion years? Or more? There are some particularly long-lived radionuclides, and they have half-lives longer than the (calculated) length of time the universe itself has been around. That's a long time! Though it may be that nothing stays radioactive forever, an observer might be waiting a long, long, long, time for something like, say, 209Bi (Bismuth-209). This stuff has a half-life of 19 (+ or - 2) x 1018 years. That's about 20 quintillion years! Longer than the universe is calculated to have been here - and by roughly a billion times! Don't hold your breath waiting for 209Bi to alpha decay!

What is stellar nucleosynthesis?

Supernova nucleosynthesis is the process where new elements heavier than iron are created through nuclear fusion when a star goes supernova. During the "normal" life of a star, it fuses hydrogen into helium, and also fuses lighter nuclei together to make heavier nuclei, at least up through iron. But after the star completes the fusion of much of its bulk into iron, it no longer continues to function as a fusion engine. The fusion processes up through those that produce iron are all exothermic, and this released energy sustains further fusion throughout the life of the star. Toward the end of its life, the star can no longer operate the "regular" way it was in normal stellar nucleosynthesis. Recall that fusion is releasing huge quantities of energy and trying to "blow up" the star, but massive gravity keeps everything together. These two forces, fusion and gravity, operate at equilibrium. After exhausting most of it fuel creating iron, gravity wins and the star collapses. This collapse adds to the star's energy, and the collapse will add tremendous quantities of heat to the stellar plasma. This heat will provide energy for the endothermic fusion reactions that create the trans-iron elements and the star will go supernova, if it is of sufficient mass. With all the extra heat provided by the collapse of a sufficiently massive star, the fusion engine will be jump started. The heat-consuming fusion reactions that create the trans-iron elements will have the energy they need to drive them, and the supernova will create lots of material with nuclei heavier than iron. Additionally, this material will be blown across the universe to fertilize other newly forming solar systems. Links are provided below for more information.

Why light waves doesn't require a medium for its propogation but sound waves require?

Light waves are electromagnetic waves that can propagate through vacuum since they do not require a medium for transmission. Sound waves, on the other hand, are mechanical waves that require a medium (such as air, water, or solids) to propagate because they rely on the particles in the medium to transfer energy from one point to another.

Why did Rutherford say the deflection of an alpha particle was like?

Rutherford said the deflection of an alpha particle was like firing a bullet at tissue paper and having it bounce back. This analogy conveyed the unexpected result that particles were being deflected backwards, suggesting the presence of a concentrated positive charge in the atom's nucleus.

Why is the process of dating fossils often an example of circular reasoning?

I don't know how you arrived at that conclusion. But let say you're correct and there are some scientist that resort to circular reasoning; the finding will surely be debunked by other scientist and the original scientist will surely be disgraced. This is what separate evolution from creation; Creation is based on the supernatural and the faithful should believe the inerrancy of the Bible no matter what.

When do a nuclear reactor become critical or subcritical?

Critical is that point when the population of fission events is neither growing nor decreasing, and that it is sustained by its own means. In this state, on a large scale statistical basis, exactly one neutron produces one fission, which goes one to produce one neutron, which goes on to produce one fission, and so on and so forth. Subcritical is the state where that population is decreasing, and supercritical is where that population is increasing.

Criticality is also related to power output, as the number of fission events is directly tied to energy or power output. When you ramp a nuclear reactor up in power, you go slightly supercritical while you increase the population, and therefore the energy output, but once you achieve your target power, you let your moderator step in and modulate the power in a self-modulating cycle. Similarly, as you trim power down, you go slightly subcritical while you decrease the population, and then you let the moderator kick back in, that is, unless you lose control and you initiate a trip/scram, taking the reactor to shutdown, which is way-way-subcritical.

How are alpha particles written?

An alpha particle can be written as ¸He«+ (Sorry, but it will not print properly on this answer page. The notation should be a superscript 4 over a subscript 2, followed by He, and then a superscript 2 over a subscript 2, followed by a superscript + sign).

How does the sun produce energy and how is it transferred to the earth?

The sun produces energy via nuclear fusion. Electromagnetic energy in the form of light travels through the vacuum of space to reach earth via what we call radiation.

Can the half life of a radioactive isotope decrease as the isotope decays?

No, the half-life of a radioactive isotope is a constant property of that particular isotope and does not change as it decays. The half-life is defined as the time it takes for half of the atoms in a sample to decay. Once set, the half-life remains constant regardless of how many atoms have decayed.

What is the equations for the beta decay of radon-198?

Radon-198 does not decay via beta decay. It is thought to decay by alpha decay, but that is not certain. The equation would be ...

86198Rn -> (Alpha, T1/2 = 86 ms) -> 84194Po + 24He2+

How many Joules would it take to destroy anything within a 3 miles radius with a bomb?

I don't have the number of J, but the blast radius of a 10KTon yield bomb is about 3 miles. This is defined as 1 psi maximum overpressure. It will not result in total destruction in this area but all conventional housing would be demolished. Industrial buildings would be damaged but still standing outside the 5 psi radius.

On the other hand, the fireball size of a 10MTon yield is roughly 3 miles.

Why fast neutrons are not captured by nucleus?

Fast neutrons have high kinetic energy, making them less likely to interact with the nucleus compared to slow neutrons. The high energy of fast neutrons means they often pass through the nucleus without being captured. As a result, fast neutrons are less effective in inducing nuclear reactions compared to slower neutrons.

What is the formula to calculate the remaining mass of an isotope with a half life of 27 seconds after 24 hours?

The equation for half-life is ...

AT = A0 2(-T/H)

... where A0 is the starting activity, AT is the ending activity at some time T, and H is the half-life in units of T.

Given that A0 is 1, H is 27 seconds, and T is 86400 seconds (one day, or 24 hours), AT is simply 5.06x10-964.

This sounds a bit extreme, and perhaps the question was mis-stated, but that's what the equation produces.

What takes the most energy to generate microwave or ex ray?

X-rays take more energy to generate compared to microwaves. This is because x-rays are a form of ionizing radiation that requires higher frequencies and more powerful equipment to produce, whereas microwaves are a form of non-ionizing radiation that typically require less energy to generate.

What is linear decay?

Linear decay is a reduction in a value or quantity at a constant rate over time. In the context of machine learning or reinforcement learning, it can refer to a linear decrease in a parameter, weight, or value over a specified number of steps or episodes. Linear decay is often used to gradually decrease the impact of certain factors or actions in a model to help stabilize or optimize its performance.

What is the main difference between breeder nuclear fission and convention nuclear fission?

Breeder nuclear fission produces more fissile material than it consumes, while conventional nuclear fission produces energy without producing additional fuel. Breeder reactors can create more fuel (like plutonium) for use in other reactors, making them potentially more efficient in terms of fuel usage.

What is the difference between Alpha rays and beta rays?

Alpha rays are helium nuclei, two protons and two neutrons, an atomic mass number of 4, and a charge of +2. Beta rays are electrons or, in some cases, positrons, an atomic mass number of 1 / 1854, and a charge of -1, or +1 for the positron.

Why does the the relative importance of the coulomb force compared to the strong nuclear force increase at large mass numbers?

Because the effect of the strong nuclear force falls (SNF) off more steeply as a function of distance than does the electromagnetic (coulomb?) (EMF) force. The SNF is an attractive force, that tends to hold nuclei together, while the EMF is an attractive/repulsive force (depending on polarity of charge) that tends to blow nuclei (at least, protons) apart. In the short distances for small nuclei, the SNF wins, but, starting at atomic number 83, bismuth, the EMF starts to win based on distance, which is why all nuclides with atomic number greater the 82 (lead) are unstable (radioactive).

Not asked, but answered for completeness sake; even for smaller nuclei, such as carbon, the proton/neutron ratio can lead to an unstable, i.e. radioactive, configuration, based on the weak nuclear force, which also enters into the picture.

How does an element change into another element in a nuclear reactor?

In a nuclear reactor elements do not simply change into other elements fission occurs and they are split into two smaller nuclei. For example: Uranium when bombarded with a neutron splits into two smaller nuclei; Barium and Krypton. When this happens energy is release in the form of heat and this heat heats water turning it into steam and drives turbines creating electricity.

Elements only really "change" into other elements in fusion reactions when two smaller nuclei come together to form a larger element. However this fusion requires extremely high temperatures and as such only takes place in the centre of the sun.

Why do dead bobies not decay in bogs?

Bogs have acidic and low-oxygen environments, which slows down the decay process by inhibiting bacteria and fungi that typically break down organic matter. This low rate of decomposition, coupled with the cold temperatures and preservative properties of the bog water, can lead to excellent preservation of bodies found in bogs.

Why does a kidney scanner use gamma radiation rather than beta or alpha radiation?

A kidney scanner uses gamma radiation because it has higher penetration ability, allowing it to reach and image deep structures inside the body like the kidneys. Beta and alpha radiation have lower penetration abilities and would not be suitable for this purpose. Additionally, gamma radiation is less likely to be absorbed by surrounding tissues, providing clearer images of the kidneys.

How does nuclear energy relate to the sun?

We derive electromagnetic energy from the nuclear fusion reactions on the sun. We also apply nuclear energy (fission) on earth to generate lots of thermal energy, which we use in a steam cycle to generate lots of electric power.

Is gasoline radioactive?

Oil is not generally radioactive unless it was originally located near radioactive material when it was extracted. More often, it only becomes radioactive when exposed to or stored near radioactive materials post processing.