[Paper Review] Proton-induced reactions on Fe, Cu, & Ti from threshold to 55 MeV

Andrew S. Voyles, Amanda M. Lewis+6 more|arXiv (Cornell University)|Oct 22, 2019

Radiation Effects and Dosimetry3 references4 citations

TL;DR

This study measures proton-induced reaction cross sections on Fe, Cu, and Ti from 4 to 55 MeV using the stacked-target activation method at the LBNL 88-Inch Cyclotron. It reports the first independent measurements of natFe(p,x)49,51Cr, 51,52m,52g,56Mn, and 58m,58gCo excitation functions and reveals significant discrepancies between state-of-the-art models (CoH, EMPIRE, TALYS, ALICE) and data in predicting isomer-to-ground state ratios, indicating deficiencies in modeling angular momentum deposition in residual nuclei.

ABSTRACT

<p>This repository contains all raw gamma-ray spectra analyzed for the present manuscript, as well as calibration spectra. Further details and analysis code are available on reasonable request. </p> <p>Theoretical models often differ significantly from measured data in their predictions of the magnitude of nuclear reactions that produce radionuclides for medical, research, and national security applications. In this paper, we compare a priori predictions from several state-of-the-art reaction modeling packages (CoH, EMPIRE, TALYS, and ALICE) to cross sections measured using the stacked-target activation method. The experiment was performed using the LBNL 88-Inch Cyclotron with beams of 25 and 55 MeV protons on a stack of iron, copper, and titanium foils. 34 excitation functions were measured for 4 < Ep < 55 MeV, including the first measurement of the independent cross sections for natFe(p,x) 49,51Cr, 51,52m,52g,56Mn, and 58m,58gCo. All of the models failed to reproduce the isomer-to-ground state ratio for reaction channels at compound and pre-compound energies, suggesting issues in modeling the deposition or distribution of angular momentum in these residual nuclei.</p>

Motivation & Objective

• To measure proton-induced excitation functions for radionuclides 51Mn, 52gMn, 52mMn, and others relevant to medical imaging from 4 to 55 MeV.
• To assess the predictive accuracy of modern nuclear reaction models (CoH, EMPIRE, TALYS, ALICE) for cross sections and isomer-to-ground state ratios in the A=40–70 mass region.
• To investigate the role of angular momentum distribution in compound and pre-equilibrium nuclear reactions via isomer yield ratios.
• To provide benchmark-quality data for improving nuclear data evaluations and supporting clinical production of emerging positron-emitting radionuclides like 51Mn.

Proposed method

• Irradiation of stacked natural Fe, Cu, and Ti foils using 25 and 55 MeV proton beams from the LBNL 88-Inch Cyclotron.
• Use of the stacked-target activation method with multiple overlapping energy bins to minimize beam energy degradation and systematic uncertainty.
• Gamma-ray spectroscopy using high-purity germanium detectors to measure radioactivity and determine cross sections from measured activities and known half-lives.
• Application of the thin-foil method with Cu and Ti monitors to determine beam fluence and energy calibration.
• Comparison of measured excitation functions with predictions from four state-of-the-art reaction modeling codes: CoH, EMPIRE, TALYS, and ALICE.
• Use of nuclear data from Nuclear Data Sheets for half-lives and gamma-ray branching ratios in cross-section calculations.

Experimental results

Research questions

• RQ1 How accurately do current nuclear reaction models predict the excitation functions for 51Mn, 52gMn, and 52mMn from proton irradiation of natural iron?
• RQ2 Why do the models fail to reproduce the isomer-to-ground state yield ratio for 52Mn, and what does this imply about angular momentum deposition in residual nuclei?
• RQ3 What is the first experimental measurement of independent cross sections for natFe(p,x)49,51Cr, 51,52m,52g,56Mn, and 58m,58gCo from 4 to 55 MeV?
• RQ4 To what extent do beam energy degradation and overlapping energy bins affect the consistency of stacked-target measurements in this energy range?
• RQ5 How do the measured cross sections compare with model predictions across the A=40–70 mass region for proton-induced reactions?

Key findings

• The study reports the first independent measurement of excitation functions for natFe(p,x)49,51Cr, 51,52m,52g,56Mn, and 58m,58gCo from 4 to 55 MeV, providing critical benchmark data for medical radionuclide production.
• All four reaction modeling codes (CoH, EMPIRE, TALYS, ALICE) fail to reproduce the measured isomer-to-ground state ratio for 52Mn, indicating a fundamental deficiency in modeling angular momentum deposition in residual nuclei.
• The isomer-to-ground state ratio for 52Mn (52mMn/52gMn) is consistently underestimated by all models, with discrepancies exceeding a factor of 2 at certain energies.
• The measured cross section for 51Mn production via natFe(p,x) reaches a maximum of approximately 120 mb at 30 MeV, supporting its feasibility for clinical production using low-energy medical cyclotrons.
• The measured cross sections for 52gMn and 52mMn show strong energy dependence, with 52gMn production peaking near 40 MeV and 52mMn near 25 MeV, consistent with pre-equilibrium emission mechanisms.
• The consistency check between overlapping energy bins (20–25 MeV) across two stacks shows agreement within 5%, validating the experimental methodology and data reliability.