Low energy nuclear physics with active targets and time projection chambers

doi:10.1016/j.ppnp.2020.103790

Progress in Particle and Nuclear Physics

Volume 114, September 2020, 103790

https://doi.org/10.1016/j.ppnp.2020.103790 Get rights and content

Abstract

This article aims at covering various low energy nuclear physics themes that can benefit from taking advantage of active targets and time projection chambers. They are naturally oriented towards the study of short-lived radioactive nuclei, for which high efficiency and thick targets are necessary to boost the luminosity of the experiments due to the weak intensity of the available beams. The use of active targets is particularly crucial when the recoil energy of the kinematically important particle is small and looses too much energy or does not emerge from a solid target.

Introduction

The past decade has seen a rapid increase of the number of active targets implemented in time projection chambers used in low energy nuclear physics experiments. This growth is directly linked to two main factors: the availability of radioactive beams with good emittance properties, and the technological advances in time projection chambers used as active targets. Because many nuclear reactions performed with radioactive beams are done in inverse kinematics, the energies of the recoil particles that carry the kinematic information of the reaction can vary over a wide range. The low intensities of these beams severely limit the luminosity of experiments that use inert- or passive -materials as targets. An increase in target thickness can mitigate this limitation, but at the expense of the resolutions that can be achieved, and a difficult compromise has to be reached between luminosity and resolution that can impact the quality of the data and scientific reach of the experiment.

Active targets directly address this issue by using the target material as the detector medium simultaneously. As the vertex of the reactions can be determined for each event, there is no impact of the target thickness on the determination of the energies of the particles before and after the reaction. Likewise, recoil particles of low energies do not need to escape a layer of inert target material to be detected, therefore the target thickness can be increased without impacting the energy and angular resolutions. In addition, the implementation of active targets in time projection chambers allows a large solid angle coverage of the emitted reaction products, which further contributes to the increase in luminosity.

Although the number of applications of active targets and time projection chambers keeps increasing, they have now reached a level from which the physics themes they cover can be reviewed. It is the aim of this work to provide the reader with an overview of some of the nuclear physics subjects that can take advantage of this new experimental technique. For more details on existing active targets that are in operation and the technologies they employ, the reader is referred to previous reviews [1] and [2], respectively. The topics covered in the following chapters is a collection of low energy nuclear physics themes related to the study of the nucleus in its various degrees of freedom. After a section dedicated to the experimental methods and observables that are relevant to active targets, the subsequent sections are organized in a topical manner: the study of shell evolution in nuclei as their isospin is varied (Section 3), followed by the effects of pairing on the strong force that binds nuclei together (Section 4), and clustering effect in nuclei (Section 5). Then comes a section on studies of exotic decay modes (Section 6), fusion–fission process (Section 7) and studies of reactions that are of interest for nuclear astrophysics (Section 8). Finally, the last section is devoted to other direct reactions, in particular those that involve higher beam energies (Section 9). Each section ends with a short summary that captures the main motivations for using this type of detector for this particular topic.

There is a number of active target time projection chambers that are mentioned in this review. To give an overview and facilitate readability and cross reference, they are listed in Table 1, indicating their (primary) location, (primary) use, reference and section(s) where they appear.

Section snippets

Experimental methods and observables

The purpose of this section is to introduce a number of general remarks on the experimental methods and observables that are most relevant with active targets, since the methods used to perform these measurements are common to all physics themes covered in this article.

Shell evolution

It is now well established that the shell closures observed in stable nuclei are not conserved across the chart of nuclei, and that the corresponding magic numbers can vanish with changing numbers of neutrons or protons, while new ones can appear [24]. The breakdown of the N=28 neutron shell closure for instance is well known and illustrated by the evolution of collectivity across the N=28 shell closure for different isotopic chains. Fig. 4 shows the evolution of the first 2 $^{+}$ states and the

Pairing

As discussed earlier, by combining both the target and detector in one device, active targets provide large efficiency and excellent resolving power to maximize the physics reach of exotic beam facilities.

In this section we discuss the unique opportunities offered by active target time projection chambers to study pairing correlations in exotic nuclei, which is a topic that has received much attention in recent years. Following a short introduction, we will discuss specific examples regarding

Clustering in nuclei

Nuclei have been known to exhibit cluster structure especially in the light mass region. There has been much progress in understanding the nature of clustering theoretically and this has spurred experimental work to find evidence to test theoretical predictions. Ultimately, a deep understanding of clustering from a fundamental and microscopic perspective is desired. A recent review of understanding nuclear clusters from a microscopic perspective can be found in Ref. [90] as well as various

Decay processes

How a radioactive nuclei gets rid of the excess of neutrons or protons on its way towards stability depends very much on its location in the nuclear landscape. Usually, the $β$ -decay process dominates how a nucleus is transformed into another. In the $β^{-}$ -decay process, which usually happens in neutron-rich nuclei, a neutron is converted into a proton, with the emission of an electron and electron anti-neutrino. On the other side, proton-rich nuclei may undergo $β^{+}$ -decay converting a proton into a

Fission

Nuclear fission, discovered in 1938 [172], provides a tool to study the nuclear potential energy and its evolution. Fission is a field that involves a unique combination of macroscopic and microscopic effects. The macroscopic effects are illustrated by the liquid drop model that predicts the onset of fission where the Coulomb forces lead first to strong deformation and then to fission. However, by adding microscopic corrections one is able to reproduce properties such as fission isomers [173].

Nuclear astrophysics

Dependable prediction of nucleosynthesis yields and other astrophysical observables require stringently constrained nuclear input data. Out of various nuclear physics inputs, nuclear reactions play a vital role, especially capture reactions, for example (n, $γ$ ) and (p, $γ$ ) in $r$ -process and in $r p$ -process, respectively, and also in quiescent burning. In many astrophysical environments, the $α$ -particle induced reactions, which includes ( $α$ , $γ$ ), ( $α$ ,p) and ( $α$ ,n) type reactions, play a pivotal role. Out

Direct reactions at higher energy

This last section departs from the preceding ones that regroup applications of active targets by physics theme. Here we cover various experimental ideas that could not fit in the previous sections, but are nonetheless worthy of being mentioned here, particularly because they make use of radioactive beams that are produced at high energy from projectile fragmentation. Although most applications of active-target time projection chambers in nuclear physics are concentrated on processes that

Conclusion

In this review we have presented the potential uses of time projection chambers in general and active-target time projection chambers in particular for low energy nuclear physics experiments. Although it does not attempt to be exhaustive, the variety of themes covered illustrates the versatility of active-target time projection chambers and the vast amount of physics applications that can take advantage of their potential 4 $π$ solid angle detection coverage and excellent resolution and separation

Acknowledgments

This material is based upon work supported by the U.S. National Science Foundation under grant No. PHY-1565546 (NSCL) and PHY-1713857 (ND), and the U.S. Department of Energy, Office of Science , Office of Nuclear Physics under Contract No. DE-AC02-05CH11231 (LBNL).

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ReviewLow energy nuclear physics with active targets and time projection chambers

Abstract

Introduction

Section snippets

Experimental methods and observables

Shell evolution

Pairing

Clustering in nuclei

Decay processes

Fission

Nuclear astrophysics

Direct reactions at higher energy

Conclusion

Acknowledgments

Prog. Part. Nucl. Phys.

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. B

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nuclear Phys. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Nucl. Instrum. Methods Phys. Res. A

Prog. Part. Nucl. Phys.

Prog. Part. Nucl. Phys.

Nucl. Instrum. Methods Phys. Res. A

Phys. Lett. B

Phys. Lett. B

Nuclear Phys. A

Nuclear Phys.

Prog. Part. Nucl. Phys.

Prog. Part. Nucl. Phys.

Phys. Lett. B

Phys. Lett. B

Nuclear Phys. A

Nuclear Phys. A

Nuclear Phys. A

Phys. Lett. B

Nucl. Instrum. Methods Phys. Res. A

Phys. Rep.

Prog. Part. Nucl. Phys.

Prog. Part. Nucl. Phys.

The European Physical Journal A

The SpecMAT active target

J. Phys. Conf. Ser.

EPJ Web Conf.

J. Radioanal. Nucl. Chem.

Scholarpedia

Rev. Modern Phys.

J. Phys. G: Nucl. Part. Phys.

Phys. Rev. Lett.

Phys. Rev. Lett.

Phys. Rev. Lett.

Physica Scripta

Computational Quantum Mechanics for Nuclear Physics

Phys. Rev. Lett.

Phys. Rev. C

Phys. Rev. C

Review
Low energy nuclear physics with active targets and time projection chambers