Question: The physicist born in 1871 who worked on the identification of alpha radiation as the nucleus of the helium atom, was considered by Encyclopedia Britannica to be the greatest experimentalist since who ?

Context articles: Ernest Rutherford
Helium compounds
Lithium atom
Helium atom
Alpha decay
Fermi heap and Fermi hole
Alpha particle
Neutron howitzer
Antiprotonic helium
Thomas Royds

Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist who came to be known as the father of nuclear physics. "
Encyclopædia Britannica" considers him to be the greatest experimentalist since Michael Faraday (1791–1867).
Helium is the most unreactive element, so it was commonly believed that helium compounds do not exist at all.
 Helium's first ionization energy of 24.57 eV is the highest of any element.
 Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons or join with anything to make covalent compounds.
 The electron affinity is 0.080 eV, which is very close to zero.
 The helium atom is small with the radius of the outer electron shell at 0.29 Å.
 The atom is very hard with a Pearson's hardness of 12.3 eV.
 It has the lowest polarizability of any kind of atom.
 However very weak van der Waals forces exist between helium and other atoms.
 This force may exceed repulsive forces.
 So at extremely low temperatures helium may form van der Waals molecules. Also its atomic number is 2 and atomic mass is 4
A lithium atom is an atom of the chemical element lithium.
 Lithium is composed of three electrons bound by the electromagnetic force to a nucleus containing three protons along with either three or four neutrons, depending on the isotope, held together by the strong force.
 Similarly to the case of the helium atom, a closed-form solution to the Schrödinger equation for the lithium atom has not been found.
 However, various approximations, such as the Hartree–Fock method, can be used to estimate the ground state energy and wavefunction of the atom.
 The quantum defect is a value that describes the deviation from hydrogenic energy levels.
A helium atom is an atom of the chemical element helium.
 Helium is composed of two electrons bound by the electromagnetic force to a nucleus containing two protons along with either one or two neutrons, depending on the isotope, held together by the strong force.
 Unlike for hydrogen, a closed-form solution to the Schrödinger equation for the helium atom has not been found.
 However, various approximations, such as the Hartree–Fock method, can be used to estimate the ground state energy and wavefunction of the atom.
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two.
 An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons.
 It has a charge of +2e and a mass of 4u.
 For example, uranium-238 decays to form thorium-234.
 Alpha particles have a charge +2, but as a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms – the charge is not usually shown.
Fermi heap and Fermi hole refer to two closely related quantum phenomena that occur in many-electron atoms.
 They arise due to the Pauli exclusion principle, according to which no two electrons can be in the same quantum state in a system (which, accounting for electrons' spin, means that there can be up to two electrons in the same orbital).
 Due to indistinguishability of elementary particles, the probability of a measurement yielding a certain eigenvalue must be invariant when electrons are exchanged, which means that the probability amplitude must either remain the same or change sign.
 For instance, consider an excited state of the helium atom in which electron 1 is in the 1s orbital and electron 2 has been excited to the 2s orbital.
 It is not possible, even in principle, to distinguish electron 1 from electron 2.
 In other words, electron 2 might be in the 1s orbital with electron 1 in the 2s orbital.
 As they are fermions, electrons must be described by an anti-symmetric wavefunction which must change sign under electron exchange, resulting in either a Fermi hole (having a lower probability of being found close to each other) or a Fermi heap (having a higher probability of being found close to each other).
 Since electrons repel one another electrically, Fermi holes and Fermi heaps have drastic effects on the energy of many-electron atoms, although the effect can be illustrated in the case of the helium atom.
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus.
 They are generally produced in the process of alpha decay, but may also be produced in other ways.
 Alpha particles are named after the first letter in the Greek alphabet, α.
 The symbol for the alpha particle is α or α.
 Because they are identical to helium nuclei, they are also sometimes written as He2+ or 42He2+ indicating a helium ion with a +2 charge (missing its two electrons).
 If the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom 42He .
The name neutron howitzer was given to a neutron source that was developed after it was discovered in the 1930s that alpha radiation that strikes the beryllium nucleus would release neutrons.
 The high speed of the alpha is sufficient to overcome the relatively low Coulomb barrier of the beryllium nucleus, the repulsive force due to the positive charge of the nucleus, which contains only four protons, allowing for fusion of the two particles, releasing energetic neutrons.
Antiprotonic helium is a three-body atom composed of an antiproton and an electron orbiting around a helium nucleus.
 It is thus made partly of matter, and partly of antimatter.
 The atom is electrically neutral, since both electrons and antiprotons each have a charge of −1, whereas helium nuclei have a charge of +2.
 The antiprotonic helium atom is called an atomcule, as it has a structure like an atom, but has two nuclei like a molecule.
Thomas Royds (April 11, 1884 – May 1, 1955) was a Solar physicist who worked with Ernest Rutherford on the identification of alpha radiation as the nucleus of the helium atom, and who was Director of the Kodaikanal Solar Observatory.