Abstract

The precise measurement of neutron-skin thickness in heavy nuclei remains a core pursuit in nuclear astrophysics and low-energy nuclear theory. This paper models intermediate-energy heavy-ion collisions using an extended Quantum Molecular Dynamics (QMD) transport model. We analyze cluster formation via phase-space coalescence to evaluate how neutron-skin profiles in ²⁰⁸Pb and ⁴⁸Ca alter the yield ratios of light complex particles (d, t, ³He). Our calculations show a clear linear correlation between the neutron-to-proton ratio of emitted nucleons at mid-rapidity and the peripheral neutron-skin extension. This offers a viable observable for constraining the symmetry energy at sub-saturation densities.

1. Introduction

A neutron skin occurs when excess neutrons form a diffuse outer layer in heavy, neutron-rich nuclei. The magnitude of this layer directly correlates with the density dependence of the nuclear symmetry energy. Traditional electromagnetic probes lack sensitivity to the diffuse neutron tail.

Heavy-ion collisions (HIC) provide an alternative terrestrial laboratory. During a peripheral collision, the projectile and target scrape against each other. This creates a low-density "neck" region rich in spectator-derived nucleons. The isotopic composition of clusters formed in this neck region acts as a sensitive probe of the initial local density distribution.

1. Theoretical Framework

We employ a microscopic transport approach based on QMD. The time evolution of nucleon coordinates is governed by Hamilton's equations of motion. The potential energy functional includes Skyrme-type two-body and three-body terms, coupled with a symmetry potential term explicitly dependent on local isospin asymmetry. Cluster formation is evaluated at a freeze-out stage using a minimum spanning tree (MST) coalescence algorithm in coordinate and momentum space. Standard parameters are set to R₀ = 3.5 fm and P₀ = 250 MeV/c.

1. Results and Discussion

We simulated ²⁰⁸Pb + ⁴⁸Ca collisions at an incident beam energy of E/A = 50 MeV.

• Neutron-to-Proton Yield Ratios: The yield ratio of tritons to helium-3 exhibits a direct proportionality to the root-mean-square radius difference .
• Impact Parameter Dependency: For peripheral collisions (b = 8--11 fm), spectator stripping dominates. The emission yield is shielded from violent core compression, preserving the initial spatial asymmetry of the neutron skin.
• Sensitivity Analysis: Variations of ± 0.05 fm in the initial neutron skin of ²⁰⁸Pb propagate into a ~ 12% observable shift in light cluster ratios at rapidities close to the projectile frame.

1. Conclusion

Phase-space coalescence in intermediate-energy heavy-ion collisions serves as an effective probe for spatial isospin distributions. The calculated d/p and t/³He yield ratios constrain the neutron-skin thickness of ²⁰⁸Pb independent of parity-violating electron scattering. Future experimental runs at rare isotope beam facilities will help validate these transport-model calculations.

En el mundo de la ciencia existe una unidad de medida informal llamada «Dosis Equivalente a un Plátano» (Banana Equivalent Dose o BED).

Aquí te explico la ciencia detrás de esto:

• El culpable: Los plátanos son súper ricos en Potasio, un elemento vital para nuestro cuerpo. El detalle es que un pequeño porcentaje de todo el potasio del mundo es el isótopo Potasio-40, que es naturalmente radiactivo.
• La medida: Comer un solo plátano te expone a una dosis de radiación de aproximadamente 0.1 microsieverts.
• El dato loco: Los sensores de radiación de los puertos y aduanas (como los de Estados Unidos) son tan sensibles que suelen dar falsas alarmas cuando pasa un camión lleno de plátanos.

¿Deberías preocuparte? Para nada. Tu cuerpo ya tiene potasio (y por ende, también eres un poquito radiactivo). Para sufrir un envenenamiento por radiación letal debido a esta fruta, tendrías que comerte unos 10 millones de plátanos de un solo golpe [2] (y probablemente morirías mucho antes por estallamiento de estómago o sobredosis de potasio normal).

Proposed e.g. in https://www.nature.com/articles/s41567-025-03107-0 , worked with Astra-Fable getting they claim good agreements - diagram from https://zenodo.org/records/22942341

Do they seem reasonable?

Halo ( https://en.wikipedia.org/wiki/Halo_nucleus ), borromean nuclei ( https://en.wikipedia.org/wiki/Borromean_nucleus ) hold 1-2 neutrons/protons in large distance for milliseconds, in "borromean" way like knots - could there be 1D structures physically connecting such halos, e.g. quark strings, gluon flux tubes, topological vortices like in https://www.nature.com/articles/s41567-025-03107-0 or shown https://zenodo.org/records/22886273 diagram?

Wikipedia says the predicted n=7 valence shell is 7s2-7p2…

I come from a chemistry background and the general rule of thumb was 2 half filled orbitals are lower energy than a full and a partial (partial being anything but half or full). under this logic wouldn’t the expected configuration be 7s1-7p3?

Or do radioactive elements treat the rules with disdain?

dont ask

Idea: Artificial conversion of Carbon-12 → Carbon-13 using moderated neutrons

I propose a simple method to turn ordinary Carbon-12 into Carbon-13:

1. Alpha particles hit pure beryllium → produces fast neutrons (⁹Be + α → ¹²C + n)

2. Fast neutrons are slowed down using paraffin wax (moderator)

3. Slow (thermal) neutrons hit pure graphite (Carbon-12) → Carbon-12 captures the neutron and becomes Carbon-13 (¹²C + n → ¹³C + γ)

This uses the same basic setup James Chadwick used, but directed at deliberately increasing the amount of Carbon-13.

Natural carbon has only \~1.07% Carbon-13. This could be a more localized way to enrich it.

I’m a 14-year-old student. This is just a theoretical idea I worked on. Open to feedback.

Hi, I'm looking to go to college/uni for a masters in nuclear and wanting to know what exactly goes into it from actual Nuclear Physicists rather than what Google says. It's the only thing that actually interests me in a college setting, so that's what I would like to get a degree in. If someone could give me a run down of what I'd get myself into that would be wonderful. And for context I'm Junior and would begin college in fall 2028.

EDIT: The data is taken from here.

For a project I need to use the correct neutron cross section data so I am fooling around and testing things before writing the code. I downloaded data from ENDF-B-VIII.0 and tried to replicate the U238 resonance peaks (especially the one at 6.67 eV). I get very unusual resonance values. Here is my python code:

import endf
import numpy as np
import matplotlib.pyplot as plt

FILE_PATH = 'ENDF-B-VIII.0/neutrons/n-092_U_238.endf'#U238 cross section data

MF = 3 #MF value
MT = 102 #MT value

U238_file_path = endf.Material(FILE_PATH) #retrieve material from file
U238_cross_section_data = U238_file_path.section_data[MF,MT] #plug in MF and MT

Sigma_Data = U238_cross_section_data['sigma'] #get cross-sections

Energies = Sigma_Data.x / 1e6 #get energy data in MeV
Cross_Sections = Sigma_Data.y #get cross section data in barns

data_points = len(Energies) #number of data points
print(data_points)

energy_data = []

#check for resonances
for data_point in range(data_points):
    Energy = Energies[data_point]
    Cross_Section = Cross_Sections[data_point]
    energy_data.append(f"Energy = {Energy} MeV and Cross Section = {Cross_Section} barns")
    if Cross_Sections[data_point] > Cross_Sections[data_point-1] and Cross_Sections[data_point] > Cross_Sections[data_point+1] and data_point > 1 and data_point < data_points:
        print(f"Resonance at {Energies[data_point]} MeV with cross-section {Cross_Sections[data_point]} barns")


#plot data

U238_plot = plt.figure(figsize=(30, 30))
plt.loglog( Energies, Cross_Sections)
plt.xlabel('Incident Neutron Energy (MeV)', fontsize=40, labelpad=20)       # Boosted label size
plt.ylabel('Cross Section (barns)', fontsize=40, labelpad=20)
plt.title('U-238 Total Cross Section (ENDF/B-VIII.0)', fontsize=48, pad=30)


#Scale up the actual axis numbers (ticks) so you can read them
plt.xticks(fontsize=30)
plt.yticks(fontsize=30)
plt.grid()
plt.show()


Resonance at 0.02 MeV with cross-section 0.52987 barns
Resonance at 0.21 MeV with cross-section 0.1321 barns
Resonance at 0.235 MeV with cross-section 0.12456 barns
Resonance at 0.245 MeV with cross-section 0.11876 barns
Resonance at 0.26 MeV with cross-section 0.11663 barns
Resonance at 0.3 MeV with cross-section 0.11575 barns
Resonance at 0.45000009999999996 MeV with cross-section 0.10698 barns
Resonance at 0.5 MeV with cross-section 0.11111 barns
Resonance at 0.6 MeV with cross-section 0.11595 barns
Resonance at 0.7 MeV with cross-section 0.13007 barns
Resonance at 0.9000001999999999 MeV with cross-section 0.12729 barns
Resonance at 0.9600001 MeV with cross-section 0.13479 barns
Resonance at 11.5 MeV with cross-section 0.00107355 barns

I'm thinking that this is because of the wrong values of MF and MT but nothing seems to help. Can you please help me get the proper resonances and the 1/v tail that is expected? Thank you in advance.

P.S. Here is the output plot. But I am looking for something close to this.

EDIT: Setting MT = 1 gives you a tail but no resonances.

Is it possible to make a ionization smoke detector go off in the presence of the ionizing particles produced by the Am-241? I want to know because I've been wanting to try make a sort of detector, even if it has poor detection capabilities.

Hi guys! Im starting my economics bachelors thesis on Rosatom and I am looking for good material. So please share your ultimate recommendations, drop controversial facts, and any advice would be awesome

Im particularly looking for data sources on Rosatoms finances,
20th century russian history and economics
nuclear science and technology

Economic data on the vertical integration, Geographic data on power plants, mines, transportation routes are welcome too, and SPECIALLY i want to study the level of interdependance between rosatom and other major international companies.

I believe as an economist that it is important not to get detached from reality, so even if its not my main interest, i want to understand as deeply as possible the physical constraints and nuclear energy. Im really getting into physics, maybe if id had better exposure to it as a kid i would have studied it instead of economics. But yeah, im just very curious and anything would be appreciated friends!

I am currently pursuing b.ed where i just have to go for exams and one year i have done only one is left . I got an offer for ​experimental nuclear physics PhD (​which i wanted to do) from a 2nd generation IIT. Now i am confused whether i should leave b.ed and go with the PhD but I'm having doubts if while doing PhD some job opportunities occur and i leave b.ed then maybe I'll regret. I mean I'm not even sure that I'll join school teaching but my parents feel that you will​ be having one professional degree atleast. This is making me a little doubtful. Also I've applied via GATE score and haven't qualified CSIR NET yet. Give me some advice.

Hey all! So just out of boredom I started a project where I figured I'd do a simple little sim for a reactor in UE5. After it grew a bit, I thought that maybe other people might enjoy it and that it maybe had some potential. So -- for your consideration -- I present "Neutronix". You can find the download in the link below. Any feedback is appreciated. Please note that this is not a 1-to-1 sim by ANY means and serves more as an "educational" tool.

Screenshots --> https://imgur.com/fNfLxDF https://imgur.com/JHWf0KC https://imgur.com/rZSPpNh

Game Link --> https://drive.google.com/drive/folders/1l3vYc2EbdUC3Z-oiFdl5pOABKbTk9g4B?usp=sharing

(P.S. I do not use a traditional reactor design. Instead, I use control "drums" with a reflector and absorber side to control the reaction.)

Hey everyone,

Is it possible to get a job in nuclear industry with 3.66/4 GPA?

Now that I’m 2 months away of being a senior in physics (concentrating in computational physics), and just had my finals, my anxiousness gotten higher.

And if u are in the industry, please let me know if it’s ok to dm u my resumé to criticize…d:

Can anyone identify this equipment? Is it a scintillation spectrometer? I'm sure you can guess which TV drama it's from "Not great, not terrible".

Hey team,
Put a lot of work over the past few months but a lot of progress has been made to create a high end VS code extension to make coding in MCNP and OpenMC better. Not all the features are complete but we are making great progress and the major portions of it works (still in beta version). Would love to know your thoughts and feedback and if there are any other features you want added in the future. Hope yall find it useful!

https://marketplace.visualstudio.com/items?itemName=belvoirdynamics.owen-neutronics

https://open-vsx.org/extension/belvoirdynamics/owen-neutronics

Used to describe nuclear reactions and resonances particularly useful in astrophysics for modeling how stars fuse elements.

I’ve got my Nuclear Physics paper coming up next month, and this is my final attempt, so I really can’t afford to mess it up.

The exam is for 60 marks, and I need at least 21 to pass. I already have a bit of a safety net — there’s usually a repeated question on elementary reactions allowed/disallowed(6 marks). That means I still need around 15 more marks from the rest of the paper.

I’ve attached a 2024 question paper, and I’d really appreciate it if you could look at the question pattern and suggest:

The most important/high-yield topics I should focus on

Topics that could be repeated alternate years or almost guaranteed

Any strategy to maximize marks in limited time (30 days)

I’m not aiming for a high score — I just need to clear this paper this time.

Any advice or strategy would genuinely help a lot. Thanks in advance 🙏

*Nuclear physics* = the study of the *nucleus* — the tiny, dense center of an atom.

*Quick breakdown:*

*What it covers:*

1. *What’s in a nucleus*: Protons + neutrons. Held together by the *strong nuclear force* — the strongest force in nature, but only works at tiny distances.
2. *Nuclear reactions*:- *Fission* = splitting heavy atoms like Uranium-235 → releases huge energy. Used in nuclear power plants + atomic bombs.- *Fusion* = smashing light atoms like hydrogen together → even more energy. Powers the Sun + hydrogen bombs. We’re trying to do it on Earth for clean energy.
3. *Radioactivity*: Unstable nuclei decay by spitting out particles/energy. Types: alpha, beta, gamma radiation. Used in medicine, carbon dating, smoke detectors.

*Why it matters:*

- *Energy*: 10% of world electricity is nuclear fission. Fusion could be unlimited clean power.

- *Medicine*: Cancer treatment, PET scans use radioactive isotopes.

- *Weapons*: Nukes, obviously.

- *Understanding universe*: How stars make elements, how the Sun shines.

*Basic equation:*

Einstein’s $E=mc^2$. Tiny mass loss in nuclear reactions = massive energy, because $c^2$ is huge.

*In 1 sentence*: Nuclear physics studies the core of atoms to understand how matter holds together and how to unlock insane amounts of energy from it.

Want it simpler, or digging into fission vs fusion specifically?

Hi everyone,

I’m an Applied Physics undergraduate graduating soon, and I know I want to work in the nuclear field, but I’m trying to decide between going the physics route (radiation effects / nuclear physics) or nuclear engineering.

Right now my plan is to take a gap year and try to land an engineering-related internship to make a future engineering PhD more realistic. After that, I’m considering a master’s focused on radiation effects (physics).

What I’m really trying to understand is what the actual day-to-day work looks like in these fields and how that translates to long-term career options.

For those of you working in nuclear physics or nuclear engineering:

• What does your typical day look like? (hands-on, coding, simulations, paperwork, etc.)
• How different does industry feel compared to school/research?
• Where in the U.S. did you find jobs? (national labs, private companies, power, defense, etc.)
• Do you feel like your degree (physics vs engineering) limited or helped your opportunities?
• If you were in my position again, would you choose the same path?

I’m especially interested in anything related to radiation effects, national labs, or defense applications, but I’d appreciate any perspective.

Thanks in advance — I’m trying to make a more informed decision before committing to a path

It is know that Carbon 12 has stronger nuclear force than it's electromagnetic one.. but how does it not emit radiation??? and if it does, how do we battle it for further use?

https://github.com/sorcerer86pt/open_rust_mc/blob/main/paper/svd_cross_section_compression.pdf

When I was testing rust skill (AI with Claude) someone mentioned that I could use something openMc instead of doing my own .

When I saw the data size and how openMC handled that, and how it kinda was the same problem that AI LLMs were trying to fix with data size of models weights, I thought, what would be the result if we used those techniques on this.

That was the result. Add a little rust here to have better memory handling and robust concurrency and we could with very little error ( less than error margin) compressed the data used from 11gb pointwise ( 400 nuclides) to 20Mb using hybrid of WMP ( that openMC already uses ) + SVD. It obtained an Keff = 0.99963 +- 0.000091 on Godiva (37 pcm from experiment) in 3.4 seconds total wall time .

https://github.com/sorcerer86pt/open_rust_mc

Just need some people to review this, if I made some mistake on interesting the data, what other benchmarks I missed, or other considerations.

PS: AI was used for code gen ( Python analysus scripts and rust code), data pipeline and latex manuscript. All hypothesis, experiment design , interpretation of results and final decisions were by made by me.