Oh,
James Smallcombe: And without any further ado, I will hand over the fire. Yeah, so please tell us about your work.
Claudia Lederer-Woods: Yes. Hello, everybody. Thanks for listening in. So I will talk about a bit about how stars produce our elements and what we can do in the lab.
Claudia Lederer-Woods: To learn something about the origin of the elements, how they produced and in what us to basically environments over produced and, in particular, I will focus on the role of neutral induced reactions in astrophysics.
Claudia Lederer-Woods: So what we basically want to understand is this distribution. So, you see here from the solar system, the abundance distribution as a function of the mass number
Claudia Lederer-Woods: Out that this is a logarithmic scale. So this is normalized to silicon and the mass numbers here. And first of all, we can see that there is a huge variation in the abundance of the elements
Claudia Lederer-Woods: So we have most of the mass is actually in hydrogen and then helium and then the remaining abundances are really quite small. We have about 75% hydrogen in the universe at large.
Claudia Lederer-Woods: But what you also can see is that the distribution already reflects a lot of nuclear physics properties.
Claudia Lederer-Woods: For example, helium is very abundant and we know that helium is a very well bound nucleus as well as carbon 12 and oxygen 16 so we have little abundance peaks. Also, there
Claudia Lederer-Woods: And then in the area where the binding energy pro-nuclear on is the highest we have this quite broad peak in this Iran region. And then after Aaron.
Claudia Lederer-Woods: Balances drop again and then we have about 1% or so of my balances in these so called heavy elements which means elements that are heavier than I am.
Claudia Lederer-Woods: And we understand already a lot about the region of the different elements and how they come to prepare to be produced, but obviously there are still
Claudia Lederer-Woods: A lot of open questions and mysteries. So what we do know is that in the Big Bang. We already had production of mainly hydrogen and helium and some traces of lithium and beryllium.
Claudia Lederer-Woods: Then all the elements going up to the iron region are produced in stars during stable burning phases. So this is by fusion reactions which are necessary for the star to stay stable during its lifetime.
Claudia Lederer-Woods: So then we have proved everything up to iron. But the question is what happens. Above that
Claudia Lederer-Woods: And if we look a bit more in this kind of heavy element region, what we notice is that we have certain peaks in the abundance
Claudia Lederer-Woods: And these are actually related to magic neutron shell closures. So here in the lead region we have n equals 126 and many presented it to around barium.
Claudia Lederer-Woods: So that's already a hint that neutrons have something to do with those abundances and then equally. We have actually kind of broader abundance peak, which is just 10 mass units lower than this sharp abundances
Claudia Lederer-Woods: So,
Claudia Lederer-Woods: We think neutrons are responsible for most of those abundances And remarkably, we can actually explain this pattern very well by just two different
Claudia Lederer-Woods: Kind of neutron capture processes and I will introduce those here. So this is a section of the chart of nuclear starting from Iran. So up to Iran, we have basically the star producing energy and charged particle infusion reactions going on.
Claudia Lederer-Woods: And then we come to those neutron capture processes. So at first of all we can actually capture neutrons on to iron isotopes, and then
Claudia Lederer-Woods: Once we produce an isotope that is unstable. This then can decay by beta decay to form a different element.
Claudia Lederer-Woods: Now, in case this the case usually faster than the nutrient EPS capture timescales in the star.
Claudia Lederer-Woods: That's what we call slow process or slow neutron capture process and ensure that s process. And this process allows us to build up elements along the stable isotopes up to the lead and be Smith region.
Claudia Lederer-Woods: You can also see that there are certain isotopes, where we have sort of competition between nutrient capture and Peter decay. But in general, this process is very kind to experimental is because the reactions to not proceed much from stability. So the involved isotopes, and mostly stable.
Claudia Lederer-Woods: And then, of course, this neutron shell closure this little peaks that we saw at the magic neutral numbers come from the fact that neutron capture cross sections at this
Claudia Lederer-Woods: At this neutral numbers become very small. And that means that there is mass accumulating. And that leads to these peaks at the metric neutral numbers in the S process.
Claudia Lederer-Woods: So moving on. Okay. Sorry. So we have about 50% abundances produced in this process neutron densities are about 10 to the eight per cubic centimeters. And as I said before, so it's this process is basically characterized by the fact that p to the case usually faster than neutron captures
Claudia Lederer-Woods: And then we have a different process, which is basically the opposite. So in this case we have very high nutrient density is
Claudia Lederer-Woods: neutron capture incredibly fast. And that's where we call it the rapid neutron capture process or our process.
Claudia Lederer-Woods: So we have neutrons being captured on very exotic unstable nuclear and all the action and all the kind of reactions happen very far in this exotic regions where we don't really know much about the nuclear physics properties of these nuclear involved.
Claudia Lederer-Woods: And also, here we have this kind of process that involves motion captures and beat the the case and then wants to see radiation of neutrons has stopped the stuff that is produced in this region that indicates towards stability.
Claudia Lederer-Woods: This process is also thought to contribute to about 50% of the abundance is over all, as you can see we have now nutrient density is that about 14 orders of magnitude higher at least and
Claudia Lederer-Woods: Peter the case in general is lower than nutrient captures up to a certain point, of course, because at some point we'll just end up at really minute
Claudia Lederer-Woods: half lives.
Claudia Lederer-Woods: And this process actually leads to this kind of broad abundance peaks that you saw shifted in this abundance distribution. And the reason is if you imagine that we have
Claudia Lederer-Woods: Also met accumulating at this magic neutral numbers. So this is indicated here. Of course, this is not a real kind of metric nutrients are closer at the moment so
Claudia Lederer-Woods: If you imagine that metal accumulates here, then this would lead to abundances today so bit small a bit smaller than where we would have to ask process peak, which would be basically just if you extend this line over here.
Claudia Lederer-Woods: So that's those two Lutheran capture processes. Of course, there are also some isotopes that cannot be produced by Lou to capture and this
Claudia Lederer-Woods: And these are produced in the so called P processes, which is not really one particular process, but more
Claudia Lederer-Woods: A collection of processes that is used to explain about 35 McClay which cannot be produced by nutrient capture and they make about overall but 1% of abundance. So it's really marginal but still important, of course.
Claudia Lederer-Woods: Now for our process. We know now that one of the sites or Yeah, one of the variables to physical sites and neutron star matches, but people still
Claudia Lederer-Woods: Research in other areas because they're still reasons to believe that we're also additional our process sites that contribute, but this is definitely confirmed now and the P process, the sites also not known. So probably something explosive, like supernovae type two or type on a contribute
Claudia Lederer-Woods: And I said that there are some isotopes, it cannot be produced by the neutron capture process. And likewise,
Claudia Lederer-Woods: Also other isotopes that cannot be produced by any other process. And these are shown here, and they are quite useful to study.
Claudia Lederer-Woods: Or tests, for example, Stella models. So we have this penal play that are not existent and capture and similarly to this we have so called as only isotopes, which means that
Claudia Lederer-Woods: They are shielded from the process by a stabilizer bar. So, if the process, the case, it cannot go any further than here for example here.
Claudia Lederer-Woods: So these are called the is only new clay. We just have to do very small corrections for the contribution from the P processes.
Claudia Lederer-Woods: And then for the process, there is. Well, a few new clarity that cannot be produced by the S process because they have to be breached by a radioactive isotope, which has it too short half life for having any important to to capture pathway towards it.
Claudia Lederer-Woods: Okay, so the astrophysical sites of the S process actually reasonably well known and and understood to certain extent.
Claudia Lederer-Woods: They are different sites and and Stella evolutionary phases that contributes. So first of all, we have read child stars.
Claudia Lederer-Woods: Have relatively low mass of want to free solar masses is probably the most biggest contribute to to s process abundances
Claudia Lederer-Woods: And the style is stand in the face, where it has finished helium coal burning and we have a core, which is basically made of carbon and oxygen.
Claudia Lederer-Woods: And then we have shelf burning going on around the course with helium shell burning in the financial around the core and also hydrogen shell burning in a financial around this helium shell and then convective envelope which is hydrogen rich and doesn't and has no bearing
Claudia Lederer-Woods: And the stars are thought to contribute most to abundance is between six volume and lead. So that's the kind of upper half of this process abundances
Claudia Lederer-Woods: And so they produce the elements during a face called as a simplistic child branch face where they have this kind of shell burning phases going on and then whatever they produced a a checked into the interstellar medium once they lose the envelopes and from this nice planetary nebula.
Claudia Lederer-Woods: And then we have also massive stars which contribute so massive stars that explode later as a supernova. This is just really an estimate of the masses.
Claudia Lederer-Woods: That can do that. And there are also two phases where it is as process.
Claudia Lederer-Woods: Happens. One is at the end of helium coal burning and then again during so called carbon sugar burning phases. We also have nutrients being released.
Claudia Lederer-Woods: And this process is thought to contribute. My mainly to abundance is between Iran and see Conan now unfortunately the massive stars are bit more complicated for for modeling abundances because
Claudia Lederer-Woods: As they explore that will be a part of course of the study will fall back into the black hole and then also during the explosion. Some abundances may be modified.
Claudia Lederer-Woods: And that means it is not so clear how much as process material gets a check that by the stars. It is considerable. But it's hard to
Claudia Lederer-Woods: For example, compare those abundances to to the solar distribution various for this rich ions. It's nice because whatever they produce. They will eventually checked and their balances will not be changed in any particular way.
Claudia Lederer-Woods: But in both those cases, the key nuclear physics input that we want to have our neutron capture cross sections because they directly determine the abandoned sister that produced in those in the slow process.
Claudia Lederer-Woods: And suck the modeling of the slow process has been quite successful in particularly for a child. So what I'm showing here is
Claudia Lederer-Woods: The predicted abundances as they produced in a red giant compared to the Solar System distribution. So a ratio of one means that model can account or explain those
Claudia Lederer-Woods: Abandoned system we have served in the solar system and what is important to look at is this. Are these solid
Claudia Lederer-Woods: Circles, because these represent s only nuclear, but we know these nuclear can only produce, but it is process. There's no contribution from any other process. So, whatever is produced in the red giant has to come has to be hundred percent of the solar system abundance
Claudia Lederer-Woods: And you can see this is actually working really well within 10% or so we can now explain the balances in this higher region of course at this lower
Claudia Lederer-Woods: Masses, we have also the massive stars are mainly the massive stars contributing. So of course the Red China will not be able to explain the abandoned systems are below most 90 or so.
Claudia Lederer-Woods: But this information is not only important for the S process and understanding what happens inside stars, but it's also important for understanding explosive processes because
Claudia Lederer-Woods: The explosive processes in both directions so exotic that there is very little known about the nuclear properties. So what is very commonly done is that we have
Claudia Lederer-Woods: Kind of calculation of this our process abundances by using the solar system of balances and then we subtract the slow as the S process abundances to get this as a topic distribution.
Claudia Lederer-Woods: And this is what you can see here. So we have all isotopes in in black as a function of mass number again using an s process model, such as the one that you've seen in the last slide, and
Claudia Lederer-Woods: What is also very nice to see is that these are only isotopes match quite nicely with this over or distribution. So neutron capture process cross sections, not only determine the S process itself but also how this distribution, for example, will look
Claudia Lederer-Woods: And that is done in turn used for other stuff in one very reasoned application is of course this very exciting result where
Claudia Lederer-Woods: People D3 analyze the spectrum of nutrients temperature. I checked and actually directly found evidence for strontium in the check. So this was a paper from 2019
Claudia Lederer-Woods: And you can see the spectrum here. So this is the kind of luminosity spectrum and some the effect that comes in you to the presence of strontium
Claudia Lederer-Woods: And for example for this calculation, what they use for their models to to model the spectrum with strontium is the use this our process abundance is calculated from the solar distribution, minus the S process distribution. So, it's also important input for our process research.
Claudia Lederer-Woods: Okay. Now, coming to the experimental part which is my main activity in this area. So where can we actually determine or measure this neutron capture cross sections.
Claudia Lederer-Woods: That are relevant for stars. And one of the facilities where I spend a lot of my experimental life is called N tough. So that's a
Claudia Lederer-Woods: Neutral time of flight facility at certain and you can see here the satellite picture. And this is the Swiss part of CERN and and of is located somewhere here.
Claudia Lederer-Woods: And then you can see that there would be the outline of the LLC, for example. So compared to certain experiments. It's a very tiny experiment compared to nuclear physics experiments, probably one of the larger ones. So we have about 100 people involved, and it's a collaboration.
Claudia Lederer-Woods: So how does it work, we get highly energetic protons from the proton synchrotron so the energy is about 20 degrees electron volts and they are fired on to a massive let's violation target the protons.
Claudia Lederer-Woods: Induce population reactions in the lead. We get very intense neutron flux about 200 neutrons actually produced per proton, so it's it's a really high yield and then
Claudia Lederer-Woods: We send them down a flight path. There are two flight paths. One is 200 meters away and then the other one is 20 meters away. So this is just showing the all the flight path where we put our samples detectors, etc. To measure neutron capture reactions.
Claudia Lederer-Woods: And the reason that it's so far away from the escalation source is that we want a very nice neutral energy resolution.
Claudia Lederer-Woods: So the kind of methodology for these measurements is we have this pulse proton beam coming on to the lead target, we get a neutron flux which has a wide spectrum. So we have
Claudia Lederer-Woods: thermal neutron energies which is about 25 million electron volts, going up to several giga electron volts all sorts. But since the beam is pilots. We know that they all born around the same time. And then when they travel down this flight path.
Claudia Lederer-Woods: They reach our capture sampler certain time.
Claudia Lederer-Woods: And hopefully induce no to capture reaction. So we have gamma rays limited and then that allows us to determine the energy of the neutron for each of the events that we measure
Claudia Lederer-Woods: And this is just a cartoon of the process. So we have the neutron going into some new clues
Claudia Lederer-Woods: being captured. So we have a compound state that is basically the separation energy plus the center of mass energy
Claudia Lederer-Woods: And then we have decay, usually by several gamma rays to the ground state. And these are than measured in detectors and the cross section.
Claudia Lederer-Woods: Activates a highly resonant behavior which is due to this excited states in the compound nucleus. So whenever we hit one of the energies that correspond to such an excited state the cross section will go up by several orders of magnitude.
Claudia Lederer-Woods: So this is a kind of real life example for such a measurement. This is part of a campaign to measure the Romanian isotopes, so it can see you. The experimental setup.
Claudia Lederer-Woods: The nutrients coming from the left, through this little pipe here the sample would be put here and then those four detectors are liquids insulation detectors, or C 66 to measure the
Claudia Lederer-Woods: Prompt gamma radiation nowadays measurements. It's important that the detectors are very insensitive to Luton reactions themselves because we have a lot of neutrons being captured off the sample.
Claudia Lederer-Woods: And if they go into the detective. We don't want to have background from gamma rays. So that's why we use that material. It's a very well suited for these kind of measurements and then also the housing and everything is optimized to a very low sensitivity to neutrons.
Claudia Lederer-Woods: This is an example for such a sample. So it's about two centimeters in diameter. In this case we had an oxide and obviously we want very background free measurements. So, whenever possible, we use something that is idle topically enriched
Claudia Lederer-Woods: For the measurement and then you end up with a spectrum like this. So this is a count spectrum now.
Claudia Lederer-Woods: So in black. You can see the spectrum from this germanium 70 free sample with lots of neutron resonances. At some point, our resolution is not good enough to resolve individual resonances. And then it's getting a bit
Claudia Lederer-Woods: Flatter and then just compared to kind of the background contribution. So if we just put the empty sample holder so this holder without the sampling the beam. That's what we get.
Claudia Lederer-Woods: And then in blue. We have a background from kind of cosmic rays and naturally ready activity and so on, which is negligible really in this
Claudia Lederer-Woods: High energy region. So, this the Stella energies that the neutrons have and so process would be actually so from one kV to maybe hundred kv. So this is the interesting region.
Claudia Lederer-Woods: Okay, so now we have the measurement and then we can calculate the cross section from the measurement and then we have, then we can calculate the stellar cross section from this measurement
Claudia Lederer-Woods: And then we can see what we have learned in terms of stellar nucleus synthesis
Claudia Lederer-Woods: And these are some results for this particular case of germanium 73 so germanium itself is produced in all sorts of processes SNR but also some explosive other charged particle processes.
Claudia Lederer-Woods: But about 80% is estimated to be produced actually in massive stars. So in this week component of this process.
Claudia Lederer-Woods: So we made a model of massive star 25 solar masses. Oh, sorry 15 solar masses. And this is what we found. So you can see here the all stable germanium isotope. So we've 7072 7374 76 and abundance relative to germanium 17 and the pink. Sighs What we have in our solar system at the moment.
Claudia Lederer-Woods: And if we use the cross sections that were used before in those models and for germanium 73 that was actually a theoretical estimate of the cross section. So we didn't have any experimental inflammation of this reaction at Stella energies.
Claudia Lederer-Woods: We see that while okay 72 is still reasonably well reproduced. But then, for example, for 73 we have the models produces a bit too much compared to the Solar System abundances
Claudia Lederer-Woods: And also for 74 now 76 is doesn't really matter because that's an hour only nucleus. So we know that the S process will not be producing much of that one. So, this will be our process contribution.
Claudia Lederer-Woods: Now within your cross section. What we found that actually the cross section is quite a bit higher than what was previously used so it was both effective 1.4 so
Claudia Lederer-Woods: And as you can see with this new cross section, we have a really nice reproduction of the solar system as a topic abundances
Claudia Lederer-Woods: So that's, that's very nice. Of course, if the kind of significance of that is a bit limited because as I said with the massive stars. It's also very hard to model them how much gets out and so on. But it seems that with the new cross section, we can actually
Claudia Lederer-Woods: Reproduce this solar system isotopic distribution reasonably well if we use model of a massive star.
Claudia Lederer-Woods: And we're still analyzing data for 74 germanium and 76 germanium. So we'll see what happens there.
Claudia Lederer-Woods: Okay, so this was one example, for a time, time of flight measurement now for something a bit more exotic and maybe even more fun.
Claudia Lederer-Woods: So tantalum hundred and 80 is a really interesting isotope. First of all, it's nature's rarest stabilizer top stable has to be taken with a grain of salt because it's supposed to be unstable.
Claudia Lederer-Woods: But it has a first excited state that 77 K. We wish the half life that's much, much longer than the age of our universe. So we can say it's quite crazy stable and that stays Homeric state. The ground state has a half life of only eight hours.
Claudia Lederer-Woods: And how it is produced, it is actually not well known. Very well. Yet, if you look at the chart of new clay. You can see it's here on the lines and
Claudia Lederer-Woods: The obvious. Of course my explanation would be that comes from the P process because
Claudia Lederer-Woods: Our process can't get there and actually the S process can't get there because if we kept the neutrons. Here we ended up at half Newman then beat the decay on tantalum hundred and 81
Claudia Lederer-Woods: And the nutrient capture, etc. So there's actually not an obvious way to produce this isotope in with a different process however things behave very funny at stellar temperatures. So at high temperatures, we can have different production mechanisms.
Claudia Lederer-Woods: And that has to do with the fact that we can have, for example, the excitation of excited states due to the high temperatures interstellar plasma and this is showing two ways.
Claudia Lederer-Woods: How we could actually produce this tantalum hundred and 80 during the S process and that has been suggested already a long time before and estimations other. This can be quite significant contribution.
Claudia Lederer-Woods: So first of all, we can have moved on kept on to ground state of half noon and then a neutral kept on to an isometric state of half noon. Hundred and 80 and this one can actually beat the decay to tantalum hundred and 80
Claudia Lederer-Woods: But the second way to produce tantalum hundred and 80 in the S process is by Peter decay of this excited state in half 979
Claudia Lederer-Woods: So at high temperatures, we can have little equilibrium between the ground and excited states and excited states were actually decay towards tantalum hundred and 79 is energetically possible
Claudia Lederer-Woods: And then tantalum 70 979 years about two years half life and that is enough for having some neutron capture that can produce the neither the ground state of tantalum hundred and 80 or so. Merrick state. So there are ways to produce it and
Claudia Lederer-Woods: The as I said neutron capture cross sections are really important to infer abundances producing the process. Now we have already very good data on
Claudia Lederer-Woods: The neutron capture on tantalum hundred and 80. But what we don't know is the neutron capture cross section from tantalum hundred and 79 on to talk to them. Hundred and 80 and this is something that
Claudia Lederer-Woods: I would like to do in the next few years and we have already started with some aspects of it.
Claudia Lederer-Woods: So the challenge, of course, is that tantalum hundred and 79 is radioactive nutrients are radioactive. So, something we need his target somewhere. So we had to produce a target that consists of tantalum hundred and 79
Claudia Lederer-Woods: And we've actually done already. A little irradiation, which is was quite successful. So it was intended as a test, but actually we ended up with some
Claudia Lederer-Woods: Useful material. So we went to the Birmingham cyclotron and irradiated a high purity half new foil with protons of about 27 MTV.
Claudia Lederer-Woods: And that was very efficient in producing tantalum hundred and 79 by this nuclear reaction. So it's hundred and 80 half noon plus proton and then to move funds out
Claudia Lederer-Woods: And then you produce, of course, lots of other crap. Lots of radioactive isotopes. So we waited for eight months or so, maybe even 10 months and then we sent the sample to psi to two people who are experts in
Claudia Lederer-Woods: Chemistry of radioactive things and they purified the sample. So they extracted only the tantalum. So all the other elements were separated quite efficiently and then we ended up with about 60 nanograms of tantalum hundred and 79 and this is showing this
Claudia Lederer-Woods: Kind of virus or the continent. We stand there and some some glue on top.
Claudia Lederer-Woods: We could have had a bit more. Actually, but unfortunately during the radiation itself. One of the vacuum windows broken that meant that the material oxidized and that made the treatment. The chemical treatment, much harder.
Claudia Lederer-Woods: Okay, so this is quite some all for neutron capture measurements and
Claudia Lederer-Woods: We don't certainly don't have enough mass to measure it Stella and achieve. We certainly don't have enough mass to measure via the neutron time or flight technique.
Claudia Lederer-Woods: But what we can do is we can perform an activation measurement. So we can actually measure the branch.
Claudia Lederer-Woods: That goes to the ground state of half new of thallium hundred and 80 which is this eight hours, half life. And so we did an activation measurement at thermal energies in the nuclear reactor where the neutron flux is a much higher
Claudia Lederer-Woods: And this is so unfortunately we couldn't go ourselves because of Kobe, etc. So our friends in Frankfurt, they performed in irradiation at domains trigger reactor
Claudia Lederer-Woods: Thermal and also the EPI thermal energy. So we had some cadmium surrounding the sample that blocked out most of this film and neutrons to get
Claudia Lederer-Woods: a handle on the cross section at higher neutral energies and this photo is not from the radiation, but I put it in because I find it quite funny because everybody's just staring down on this.
Claudia Lederer-Woods: In the reactor core, which is showing this nice to rank of radiation.
Claudia Lederer-Woods: So they did this year radiation and then and we actually did the decay counting then also in Frankfurt.
Claudia Lederer-Woods: So this is showing a little spectrum. This is the decay line for Tottenham hundred and 80 DK the data analysis is ongoing, but I think
Claudia Lederer-Woods: It's quite advanced already and with very nice statistics. So we hope that we will soon get a nice result for that. And then in the future we will aim to produce a sample with much more mass
Claudia Lederer-Woods: So that we can, for example, activate this sampler kV energies or perhaps even performer time of flight measurement
Claudia Lederer-Woods: And that's my talk already so thanks for listening and yeah if you have any questions, please go ahead
James Smallcombe: Thank you very much.
James Smallcombe: So yes, if you have any questions, please. As I said, it's done head on over to the participants menu and use that raise hand button or get typing in the chat window.
James Smallcombe: I see we've got a couple of digital claps people enjoying the talk.
James Smallcombe: Right. Don't see raise hand. Oh, there we go on, fill it. Please would you like to go ahead
Philip Adsley: Hello, I'm not going to turn my camera on, because it's too much summer hits can wants to see that. And I did. Is it possible to do neutron transmission measurements with
Philip Adsley: And off or do you just look at it and gamma or other other reactions that you can could look at as well.
Claudia Lederer-Woods: Yeah transmission. We don't really have the equipment to do so at, for example, if you're interested, you can do that at Selena, which is a lab in Belgium.
Claudia Lederer-Woods: But we can do anything else neutral induced and p and alpha and gamma and to n fishing, etc. But for transmission, you need a bit of a different kind of setup, but we've thought about doing it, but I don't think there's been any real progress.
Philip Adsley: Okay, thanks.
James Smallcombe: We have another question verbally. If you'd like to unmute and go ahead
James Smallcombe: We can't hear you. Ready or
Rolf-Dietmar Herzberg: Is this better.
Rolf-Dietmar Herzberg: Yes. Oh, sorry.
Rolf-Dietmar Herzberg: I'm too much paper on the desk obstructing the microphone. Um, thank you very much for that nice talk and best of luck for the time to lamborn at
Rolf-Dietmar Herzberg: We looked at that long time but going good. Good to see how you can populate the ice with everything else. So I'll be really keen to see what comes out of that and fingers crossed. The question I have is, you kept comparing to progenitor stars with a certain mass, but
Rolf-Dietmar Herzberg: How is the history of our elements. I mean, it can't just be a single star must have been an ensemble of stars in some form. What, what are the assumptions that go into that before you
Claudia Lederer-Woods: Into what exactly
Rolf-Dietmar Herzberg: Well, what is the population. What, what was the population of stars like that together have produced the elemental abundance on Earth that you're now comparing two
Claudia Lederer-Woods: Okay, yeah, I mean that's its own research area. But basically,
Claudia Lederer-Woods: What we assume is that we have these different Stella populations. So we start with this population freestyles and nobody knows really about those very much they think that they were very massive
Claudia Lederer-Woods: And they already dead. And then we can calculate. I mean, there, there are models about how the initial Stella masses are distributed
Claudia Lederer-Woods: And then we know that massive stars they live not as long as the low masters, so we can assume that those contribute, for example, more to the kind of collective history, then we have
Claudia Lederer-Woods: Supernovae one A that started a bit late to, for example, to contribute and you can see. So, so what people do is they look at stars of different modalities.
Claudia Lederer-Woods: And look at the evolution of the balances. So for example if very old stars that just showed abundances of the our process which already indicates that they are
Claudia Lederer-Woods: Our process sites really early in the history of our galaxy. And we can see that, for example, the S process takes a bit longer to contribute to the abundances
Rolf-Dietmar Herzberg: So,
Rolf-Dietmar Herzberg: User population.
Rolf-Dietmar Herzberg: But then the mechanisms do some selecting and they have a stars are the ones that
Rolf-Dietmar Herzberg: Tend to be at the forefront of that selection process.
Claudia Lederer-Woods: Sorry, what do you mean by selection.
Rolf-Dietmar Herzberg: Well, you've got a whole
Rolf-Dietmar Herzberg: Population. But if, as you say, some of the lighter ones live so long that they don't eject material and enter it into the next generation at the same time as the other ones. So there is a selection there as to which stars actually could use the abundances that we are comparing to
Claudia Lederer-Woods: You. Yes, yes. Okay.
Thank you.
Okay.
James Smallcombe: Don't see any hands if you are struggling with the raise hand function, I would welcome you to just unmute I see bill gladly have unmuted bill.
Bill Gelletly: And in
Bill Gelletly: In most of these processes, the
Bill Gelletly: The, the targets are not as in your nice stable targets that all sitting in a plasma. So how much is that going to influence the results.
Claudia Lederer-Woods: Yeah, that depends on the on the isotope. So for example for this intermediate masters, like the germanium selenium. The first excited state is typically
Claudia Lederer-Woods: Higher in energy, so that the population in the plasma is not really that important for 73 germanium. For example, we had to
Claudia Lederer-Woods: Do some theoretical calculations, what the stellar cross section is compared to the terrestrial cross section.
Claudia Lederer-Woods: Now, the higher we go in mass, the higher the level density. So they are really cases where it becomes really important. And in that case, unfortunately, we just have to use some theoretical predictions of the contribution from, for example, neutron capture on the first excited state.
Bill Gelletly: When, when we have all these neutron reactions going on. We also have the inverse process of Ghana and and i mean
Claudia Lederer-Woods: It's not really the temperatures anti enough to have any
Claudia Lederer-Woods: Amen. So, in the process that's more important. Yeah.
Bill Gelletly: Yeah, of course. But, I mean, how well do we know the gamma and Crocs cross sections.
Claudia Lederer-Woods: Well, that again depends, I mean the measurements of these reactions. But as I said for the S process itself, we actually
Claudia Lederer-Woods: Don't know them at all because they don't happen.
Bill Gelletly: But, but you did mention the our process as well. And I'm just wondering about
Claudia Lederer-Woods: Well, for the our process actually what happens is that that all the reactions are incredibly fast and that means that we have some equilibrium in the reaction chain. And it turns out that the important
Claudia Lederer-Woods: Nuclear Physics quantities for the our process are actually beat the decay lifetimes and then later. Once the neutron stop stuff like neutron delayed beta decay, etc. But since
Claudia Lederer-Woods: For for our process itself. The whole reaction chain is in equilibrium, we can determine their balances just by knowing the nuclear masters and the pizza decay lifetimes, because the dharma. Dharma so fast that abundances shifts according to
Claudia Lederer-Woods: Their binding energies.
Okay.
James Smallcombe: So question Nicholas doesn't. Would you like to go ahead please.
James Smallcombe: I don't think we can hear you. Have we have you got a similar microphone covered in paper St.
Nikolay Sosnin: Yeah, it would seem, I did. Can you hear me now. Yes, sir. Yeah, thanks for the lovely talk close. Yeah.
Nikolay Sosnin: I was gonna ask about the population of the excited state of happening that you've shown. I didn't quite registered
Nikolay Sosnin: Where it originates from is that the consequence of neutron capture on lower mass happening mountaintops or is it some kind of inelastic scattering or gamma density inside stars were
Claudia Lederer-Woods: One of the ways is because a neutron capture can go to the ISO mail. This is one of the two options, right. I'll go back to the slide.
Claudia Lederer-Woods: So that's this one. But then also, this one is purely because we have so high temperature that we have
Claudia Lederer-Woods: The plasma being in equilibrium. And then you can have scattering and I excitation of of
Claudia Lederer-Woods: The lower lying excited states.
Nikolay Sosnin: Okay, right.
Claudia Lederer-Woods: That's the effect of the stellar plasmid high temperature
Nikolay Sosnin: Okay, thank you.
James Smallcombe: Okay. Do we have. Yes, we do. Patty, please go ahead with your question.
Patrick Regan: I thought so lovely talk. Thank you.
Patrick Regan: My question, half life of half tantalum. What it or the metro stable state. I think I'm right in saying that that's still a limit that that hasn't actually been measured
Claudia Lederer-Woods: Yeah, it seems that
Patrick Regan: Way so it's from a metrology point of view is kind of interesting to measure the heart, the hardest wants to measure the longest lifetime right so
Patrick Regan: That's it. We know it's more than 10 to the 50 years but
Patrick Regan: Are there any plans or suggestions as to how we might
Patrick Regan: Establish that live from presumably do some ICP you do some mass measurement or a mass
Patrick Regan: And songwriter mass spectrometry to work out the number of atoms and
Claudia Lederer-Woods: Yeah, I guess, I guess about that, but I really don't know if it's that long. If there would be anything that sensitive enough to
Claudia Lederer-Woods: Look into
Patrick Regan: This lifetime that's been measured have any radioactive thing is business 209. I think that's about 10 to the 19 years or 10 to the 20 years so it is
Patrick Regan: I think the problem is that it's rare. There's not much tantalum. What it around so you need small bits of it, but I don't know what the, I think the limit on that measurement
Patrick Regan: Norman at Berkeley, I don't know, maybe 20 years ago sided been any progress on that sense, but it might be interesting.
Claudia Lederer-Woods: Yeah, it sounds interesting.
Patrick Regan: I like to double neutron electron kept Rumsey no 124
Patrick Regan: Okay, but that might be an interesting thing to for somebody to look at. Yeah.
Okay.
James Smallcombe: Great.
James Smallcombe: And Michael please go ahead with your question.
Claudia Lederer-Woods: No.
Michael Paul: You don't think thank you for this beautiful, so I was really interested by your slide, rather than the beginning of showing the comparison of the mothers and the
Michael Paul: father's presence console.
Michael Paul: So,
Michael Paul: If I understand right all
Michael Paul: All the little crosses, which are under the mother prediction mean that the the abundances are completed by the process is that is that the idea
Claudia Lederer-Woods: Yes, yeah.
Michael Paul: Okay. All right. So, actually.
Michael Paul: I find it very satisfying that are not not any point above which
Michael Paul: Is right
Michael Paul: Then
Then
Michael Paul: The
Michael Paul: Process only points which are below and well below.
Michael Paul: The Hundred percent, what are the what, in that case, what is the competing production, especially the heavy one.
Claudia Lederer-Woods: This one that's actually a square. So, I don't think that's an S.
Michael Paul: Processing something
Claudia Lederer-Woods: They would have to read the caption of eager to know
Claudia Lederer-Woods: These are
Michael Paul: The right ones.
Claudia Lederer-Woods: Sorry.
Michael Paul: And the right, the right ones.
Claudia Lederer-Woods: These ones are produced a massive stars. So the
Claudia Lederer-Woods: red giant stone produce those. So that's why we don't have to kind of agreement with the s only abundances in the in the sun.
Michael Paul: Yeah, but what is the than the production or which completes the
Claudia Lederer-Woods: Week component of the
Claudia Lederer-Woods: Process and
Claudia Lederer-Woods: All yeah
Michael Paul: I saw. Okay, so. Okay, so this is slow. Slow was
Claudia Lederer-Woods: Yeah, that's the that's in that's in so so this calculation is just for the
Michael Paul: main component in
Claudia Lederer-Woods: The week component is down here, and even here. It's a big question ever because they're still his tail from this big iron peak that comes from the kind of pre explosive fusion, there is probably some contribution there as well.
James Smallcombe: Before we take another question, just for the recording to ongoing discussion with chat Alex Murphy highlighted that the double electron capture of 120 14 on is something of the order of 10 to 20 years Patty has pointed out that 209 business. He thinks he's around two to the
James Smallcombe: For alpha decay talented 10th 19 years. Sorry. Okay, so that's just on the on the previous discussion there for the recording. But yes, we have yet another question. George, please unmute yourself and go ahead
George O'Neill: Hi. I was wondering with the energies that any of you if the if the cross section for any end to end reactions and measurable, or is it just complete regard in terms of
Claudia Lederer-Woods: Action.
Claudia Lederer-Woods: On the neutral energy point of view, that would
Claudia Lederer-Woods: Work, the only challenge is that we would need to detect neutrons. So yeah, it's possible measurements are possible for sure, but it's not been liking the kind of standard program yet of of measurements. But yeah, we could do it.
George O'Neill: Is there any work in future.
George O'Neill: Involved some sort of neutron
Claudia Lederer-Woods: I mean, the thing with end to end, I guess maybe facilities that have
Claudia Lederer-Woods: A higher flux in the kind of MTV region, and I'm not sure how if you need, like, I mean, what kind of the energy neutron energy resolution, it is that you need, because you can get me the neutrons from smaller accelerators as well. I think that's maybe also kind of reason.
Claudia Lederer-Woods: But we would have to look into it.
George O'Neill: Okay, thanks.
James Smallcombe: Okay, this is a really good assessment got another question from Philip, Philip. Please go ahead.
Philip Adsley: Sorry, it's actually, it's just a comment about what George said, I think, in many cases, the end to end cross sections and measured with activation rather than with new Trump detection, because it is unstable nuclear, they often make something unstable.
Philip Adsley: So i don't i don't know that that measuring the neutrons at all. In many cases,
James Smallcombe: Okay, thank you. So
James Smallcombe: I don't see any more questions.
James Smallcombe: Thank you all for engaging so much this has been a really well attended talk today. And we've had a really good
James Smallcombe: Discussions on. So thank you all for coming and thank you very much for giving a
James Smallcombe: Great on
James Smallcombe: Please do all join us again next week, same time Monday 3pm GMT one will be jumping over to the nutrient deficient or protein rich depending on your preference to hear about
James Smallcombe: See changes in very nuclei from Catrin Dima so that's Monday 3pm GMT next week. So, have a good week and see you then. Thanks.
Claudia Lederer-Woods: Bye bye.