[Paper Review] Simulations of Doppler Eects in Nuclear Reactions for AGATA Commissioning Experiments

Ali Al-Adili|arXiv (Cornell University)|Sep 25, 2009

Nuclear Physics and Applications18 references3 citations

TL;DR

This study simulates inverse kinematics nuclear reactions for AGATA gamma-ray tracking spectrometer commissioning, using Monte Carlo simulations and Geant4 to evaluate Doppler effects and energy resolution. The reaction d(V-51,n)Cr-52 is identified as optimal due to strong Doppler shifts and minimal target-induced background from energy and angular straggling.

ABSTRACT

The purpose of this master thesis is to simulate suitable nuclear reactions for a commissioning experiment, to be performed with the AGATA gamma-ray tracking spectrometer. The main aim of the work is to find a reaction, which gives large Doppler effects of the emitted gamma rays, with as small contribution as possible due to the energy and angular spread of the nuclei emitting the gamma rays. Inverse kinematics heavy-ion (HI) fusion reactions of the type (HI,gamma), (HI, n) on proton and deuteron targets have been studied. Target effects were investigated using the program TRIM in order to determine the impact on the Doppler effects caused by energy and angular straggling in the target material. The cross sections of a large number of reactions of protons and deuterons on nuclei with mass numbers in the range A=20-100 have been evaluated using the TALYS reaction code. The fusion-evaporation reactions, d(V-51,n)Cr-52 and d(Cl-37,n)Ar-38 were simulated in detail using the Monte Carlo code evapOR. The interactions in AGATA of the gamma rays emitted in these reactions were simulated using Geant4. The energy resolution of the gamma rays after gamma-ray tracking and Doppler correction were determined as a function of the interaction position resolution of the germanium detectors. The conclusion of this work is that of the two reactions d(V-51,n)Cr-52 is more suitable for an AGATA commissioning experiment.

Motivation & Objective

• To identify nuclear reactions with strong Doppler effects suitable for AGATA spectrometer commissioning.
• To minimize contributions from target-induced energy and angular spread that degrade Doppler correction accuracy.
• To evaluate reaction cross sections and gamma-ray emission characteristics using the TALYS code.
• To simulate gamma-ray interactions and energy resolution in AGATA using Geant4.
• To optimize detector performance by assessing energy resolution as a function of interaction position resolution.

Proposed method

• Simulated inverse kinematics fusion-evaporation reactions (HI,γ) and (HI,n) on proton and deuteron targets using TALYS for cross-section evaluation.
• Employed TRIM to model energy and angular straggling effects in target materials, quantifying their impact on Doppler broadening.
• Conducted detailed Monte Carlo simulations of d(V-51,n)Cr-52 and d(Cl-37,n)Ar-38 using the evapOR code to model nuclear de-excitation and gamma-ray emission.
• Simulated AGATA detector responses to emitted gamma rays using Geant4, including gamma-ray tracking and Doppler correction.
• Quantified energy resolution degradation due to position resolution limitations in germanium detectors.
• Compared the two candidate reactions based on Doppler shift magnitude and background contributions from target effects.

Experimental results

Research questions

• RQ1 Which nuclear reaction produces the largest Doppler shifts in gamma-ray emissions while minimizing background from target-induced energy and angular spread?
• RQ2 How do energy and angular straggling in the target material affect Doppler broadening and correction accuracy in AGATA?
• RQ3 What is the achievable energy resolution after gamma-ray tracking and Doppler correction as a function of detector position resolution?
• RQ4 How do the simulated gamma-ray spectra and Doppler effects compare between d(V-51,n)Cr-52 and d(Cl-37,n)Ar-38?
• RQ5 To what extent do target effects degrade the performance of AGATA commissioning experiments?

Key findings

• The reaction d(V-51,n)Cr-52 produces strong Doppler shifts in emitted gamma rays, making it highly suitable for commissioning AGATA.
• Target-induced energy and angular straggling significantly broaden Doppler effects, but these contributions are minimized in d(V-51,n)Cr-52 compared to d(Cl-37,n)Ar-38.
• Energy resolution after Doppler correction and gamma-ray tracking degrades with poorer position resolution, but remains acceptable for d(V-51,n)Cr-52 across the range of studied resolutions.
• The TALYS code predicted cross sections consistent with expected reaction behavior, supporting the validity of the simulation framework.
• Geant4 simulations confirmed that gamma-ray tracking performance is sufficient to resolve key features in the gamma-ray spectra from d(V-51,n)Cr-52.
• d(V-51,n)Cr-52 outperforms d(Cl-37,n)Ar-38 in terms of signal-to-background ratio and Doppler correction fidelity, making it the preferred choice for AGATA commissioning.