8-O-16(n,xα)

Requester (Each request should be "owned" by a single individual)

Michaël PETIT (IRSN / EURADOS associated member)

Quantity (Quantity of the reaction process that is of concern to the requester, e.g., cross section, resonance parameter, spectrum, average multiplicity, etc.)

• all the differential cross-sections for branching ratio reactions up to a contribution sum of 95% of the total

Incident energy range (Energy range of the incident particle in the laboratory)

20 MeV – 200 MeV

• if using the ⁷Li(p,n)⁷Be reaction on a thin target for neutron production: the minimum point request measurements are: 20 MeV, 50 MeV, 100 MeV, 150 MeV and 200 MeV.
• if using a neutron white spectrum, as at the nToF or LANSCE facilities: the energy bin width is left up to the discretion of the lead experimenter. However, avoiding bins greater than 5% of the incident beam energy (i.e. 1 MeV at 20 MeV and 10 MeV at 200 MeV) is highly recommended.

Secondary energy/angle (If differential or double-differential data are requested, then the energy and angular ranges for the emitted particle need to be specified)

Measurement of the secondary particle energy should begin at 1 MeV (or as low as possible) and should go up to the incident particle energy. The double differential cross section, including both energy and angle, should be as detailed as possible depending on the experimental conditions. The measurements should make it possible to deduce the angular distribution of the different branching reactions. The data requested here is similar to the results obtained in the results obtained in the work presented in [1] (but for an ¹⁶O nucleus target and over a large energy range). However, any improvement on this example of experimental data would be welcome, particularly in terms of the angle covered.

Impact documentation (Impact of the requested data improvement for the application in terms of safety, reliability, cost, etc.)

The data required must allow for the construction of a complete model of the nuclear interaction between a nucleon (neutron or proton to begin with) and the light nuclei (¹²C and ¹⁶O in particular). This model must have an energy range application of up to a few hundred MeV or more. It must consider all the possible nuclear reaction pathways (charged particles and neutrons) by including differential cross sections.

It is ambitious to expect the models to accurately describe the nuclear interactions of other possible incident particles (alpha, deuteron; photon, etc.) as well as of other target nuclei of interest (¹⁴N and ¹⁹F in particular).

In this way, an initial nuclear intersection model based on the measurements carried out would make it possible to significantly improve the entire domain of medical application using nucleus charged particle beams (such as protontherapy). The aim is to have an accurate description of the deposited dose by the charged particles. This model will also lead to improved production and transport of neutrons in the body, which induce secondary doses during medical treatment or exposure to cosmic radiation.

The additional measurements required to determine the interactions between ¹²C and neutrons are similar when they are requested for the calculation of the detector response. In any case, both will help to improve the model.

Requested accuracy on the reaction quantity (in %, split into different energy/angle ranges if necessary)

For a double differential measurement over a wide energy range, it is unreasonable to request a specific value for the accuracy on the reaction quantity. So, accuracy is left to the discretion of the lead experimenter, but it is hoped to be “as accurate as possible”. The final requirement is to have a predictive nuclear interaction model, based on these measurements with an overall accuracy of around 5%.

Justification documentation (The need for these data, inadequacy of existing information, etc., should be clearly established – Quantitative support, e.g. from sensitivity studies, is required for high priority requests)

Light nuclei such as ¹H, ¹²C, ¹⁴N or ¹⁶O are extremely abundant in nature. ¹⁶O alone represents 46% of the mass of the earth's crust and even more considering planetary surface water. These elements are fundamental for all life on the planet. About ~96% by mass of the human body is composed of these four isotopes and even reaches ~75% for ¹⁶O alone in the cell nucleus. Any radiation transport calculation in the context of radiation protection, focusing on man and nature, is therefore completely dependent on nuclear data concerning these isotopes.

Neutron energy does not exceed about 20 MeV for fusion or fission application, but in other situations it is possible for the proton or neutron energy to reach up to several tens, or even hundreds of MeV, or even greater. For example, the neutron spectra at high altitudes which is induced by very high energy cosmic photons, can reach as high as 1000 MeV while having a maximum intensity probability at around 100 MeV. This radiation is usually the primarily dose contribution in the space and aviation fields. In addition, in some radiotherapy procedures, charged particles are directed towards a patient's body after being accelerated to energies up to several hundred MeV.

Currently, in neutron physics, the nuclear data for light nuclei such as ¹²C and ¹⁶O are well-established up to the threshold energies of reaction involving the emission of secondary charged particles, i.e. at about 6-8 MeV. Beyond that, an incident nucleon has enough energy to generate so-called "secondary" reactions, e.g. (n,xa), (n,xp) etc… In general, these reactions are poorly described outside a narrow energy range, if data exists at all.

For incident nucleons with energies up to 20 MeV the gaps in the nuclear data have already been identified and have been the subject of recent work or requests (see [2] for ¹²C and [3] for ¹⁶O). However, while these datasets are suitable for reactors and most industrial applications, they are insufficient as regards the full spectrum of radiation protection applications, both in terms of reaction description and energy range.

Code and/or model comparisons have been carried out in the framework of the EURADOS working groups [4]. This work has brought together measurements and calculations has demonstrated that there exist significant inaccuracies in the resulting calculations. Moreover, they are not compatible with the calculation requirements of either neutron detector response function or proton therapy secondary dose. These inaccuracies are concentrated at energies above 10 MeV, usually between 20 and 200 MeV, and can be of by a factor of 3 or more.

These inaccuracies could stem from differences in the basic assumption used to construct available nuclear models such as Bertini [5], ISABEL [6], etc... Indeed, these models have generally been constructed to describe the reactions of much heavier nuclei (Fe, Pb, etc.). So, the application of these models to light nuclei (as ¹²C and ¹⁶O) nuclear interactions could be problematic in two ways. The first of these is the small number of nucleons which might not fit well with the evaporation model established for heavier nuclei. Furthermore, the light nuclei of interest are necessarily influenced by the nuclear "magic" or "semi-magic" numbers (i.e. 2, 6 and 8) which implies a specific type of modelling for these strong nuclear forces.

References

[1] “Nucleon-induced reactions at intermediate energies: New data at 96MeV and theoretical status”. V. Blideanu et al. Phys. Rev. C 70, 014607 – Published 15 July 2004

[2] A. R. Garcia, E. Mendoza, D Cano-Ott, R. Nolte, T. Martinez, A. Algora, J.L. Tain, K. Baerjee and C. Bhattacharya. “New physics in GEANT4 for simulation of neutron interactions with organic scintillation detectors”. Nuclear Inst. And Methods in Physics Research, A868 (2017) 73-81

[3] High Priority request List : https://www.oecd-nea.org/dbdata/hprl/hprlview.pl?ID=417 with the document Arnaud Courcelle  “Need for 16O(n, α) Measurement and Evaluation in the Range 2.5 to 10 MeV” July 2005 working document.

[4] https://eurados.sckcen.be/working-groups/wg6-computational-dosimetry

[5] Aatos Heikkinen, Nikita Stepanov and Johannes Peter Wellisch “Bertini intra-nuclear cascade implementation in Geant4” Computing in High Energy and Nuclear Physics, 24-28 March 2003, La Jolla, California

[6] ISABEL - INC Model for High-Energy Hadron-Nucleus Reactions Y.Yariv “ICTP-IAEA Advanced Workshop on Model Codes for Spallation Reactions Miramare, Trieste, Italy 4-8 February 2008