Excitation functions for (p,x) reactions of niobium in the energy range of Ep = 40–90 MeV

Abstract

A stack of thin Nb foils was irradiated with the 100 MeV proton beam at Los Alamos National Laboratory's Isotope Production Facility, to investigate the 93 Nb(p,4n) 90 Mo nuclear reaction as a monitor for intermediate energy proton experiments and to benchmark state-of-the-art reaction model codes. A set of 38 measured cross sections for nat Nb(p,x) and nat Cu(p,x) reactions between 40-90 MeV, as well as 5 independent measurements of isomer branching ratios, are reported. These are useful in medical and basic science radionuclide productions at intermediate energies. The nat Cu(p,x) 56 Co, nat Cu(p,x) 62 Zn, and nat Cu(p,x) 65 Zn reactions were used to determine proton fluence, and all activities were quantified using HPGe spectrometry. Variance minimization techniques were employed to reduce systematic uncertainties in proton energy and fluence, improving the reliability of these measurements. The measured cross sections are shown to be in excellent agreement with literature values, and have been measured with improved precision compared with previous measurements. This work also reports the first measurement of the nat Nb(p,x) 82m Rb reaction, and of the independent cross sections for nat Cu(p,x) 52g Mn and nat Nb(p,x) 85g Y in the 40-90 MeV region. The effects of nat Si(p,x) 22,24 Na contamination, arising from silicone adhesive in the Kapton tape used to encapsulate the aluminum monitor foils, is also discussed as a cautionary note to future stacked-target cross section measurements. A priori predictions of the reaction modeling codes CoH, EMPIRE, and TALYS are compared with experimentally measured values and used to explore the differences between codes for the nat Nb(p,x) and nat Cu(p,x) reactions. 2 68 Ga, 82 Rb, and 123 I. These accelerators also produce non-medical radionuclides with commercial value, such as 22 Na, 73 As, 95m Tc, and 109 Cd [3,4]. Novel applications are being explored for several radionuclides whose production methodologies are not established, but their production requires accurate, high-fidelity cross section data. Candidate isotopes to meet these needs have been identified based on their chemical and radioactive decay properties [2,5,6], and a series of campaigns are underway to perform targeted, high-priority measurements of thin-target cross sections and thick-target integral yields. These studies will serve to facilitate the production of clinically relevant quantities of radioactivity.Accurate cross section measurements using activation methods benefit from well-characterized monitor reactions. Currently there is a paucity of such data at intermediate energies, and much of what exists have high uncertainties (>15%). Indeed, the development of new monitor reaction standards and the improved evaluation of existing standards is one of the areas of greatest cross-cutting need for nuclear data [6]. New reactions can expand the available range of options for the monitoring of charged particle beams. This work is an attempt to characterize a new monitor reaction for proton beams in exce...

Proton-induced reactions on Fe, Cu, and Ti from threshold to 55 MeV

“…The work described herein follows the methods utilized in our recent work and established by Graves et al for monitor reaction characterization of beam energy and fluence in stacked target irradiations [7,16]. Preliminary results were reported in a Master's thesis [17]; here we report the final analysis of that work.…”

“…As in our previous work, these activities were used to calculate cumulative and independent cross sections [16]. For the first product nuclide in a mass chain with observable decay gammas, its (p,x) cross section is reported as a cumulative cross section (σ c ), which is the sum of direct production of that nucleus, as well as decay of its precursors and any other independent cross sections leading to that nucleus.…”

Measurement of 139La(p,x) cross sections from 35–60 MeV by stacked-target activation

“…This monitor foil variance minimization technique was also performed with the Monte Carlo code MCNP [28]. This corresponded to a 15% enhancement in the degrader areal density, which is significantly higher than comparable values in the literature [16,17]. These results suggest a systematic issue in the low-energy charged-particle stopping power tables used by MCNP, and that a detailed comparison between the Anderson & Ziegler and MCNP stopping powers should be further explored in this intermediate energy range.…”

“…In this work we used the stacked-target activation technique, in which one can measure a reaction cross section by quantifying the activity induced within a thin foil of known areal density, using a beam of known intensity [16,17]. In a single irradiation, many foils can be placed in a "stack" (along with monitor foils), yielding cross section measurements at multiple energies by lowering the energy of the primary beam as it traverses the stack.…”

“…The minimum value of χ 2 ν yields the energy assignments which give the best agreement between the proton current derived from the various monitor reaction channels. This "variance minimization" technique was performed in a manner consistent with Graves (2016) and Voyles (2018) [16,17]. Afterwards, because the discrepancy was still quite large for foils in the high-energy portion of the stack (≈30%), the incident beam energy was also treated as a free parameter and this same minimization was performed on density and incident energy simultaneously.…”