Maximum Recoil Research Articles

Mössbauer experiments with Coulomb excited 61 Ni and 73 Ge after recoil implantation

This paper is to report from the point of view of ion implantation the results of Mossbauer measurements in 61 Ni and 73 Ge after Coulomb excitation of the relevant nuclear energy levels. The experiments were performed in cooperation with G. Czjzek, F. E. Obenshain and J. L. C. Ford, Jun., from the Oak Ridge National Laboratory (Seyboth, Obenshain & Czjzek 1965; Czjzek et al. 1966) and G. Ischenko, H. Jena, H. Kilian and B. H. Zimmermann from the University of Erlangen-Niirnberg (Zimmermann et al. 1968). I also wish to draw your attention to recent results of the Oak Ridge Group on 73 Ge (Czjzek et al. 1967, 1968). Our Mossbauer experiments after Coulomb excitation were carried out like ‘classical’ Mossbauer studies. Instead of a radioactive source, however, a target was used containing the same isotope as the absorber. The target nuclei were Coulomb excited by bombardment with oxygen ions of 20 to 30 MeV from a tandem Van de Graaff. The projectiles transfer recoil energy to the excited nuclei. The maximum recoil energy in the laboratory system was about 15 MeV in our experiments. The Mossbauer atom leaves its lattice site and moves through the target material. In this way it can be implanted into the target substrate. The slowing down process is finished in a time short compared to the lifetime of the excited level. The final environment of the excited Mossbauer nucleus determines such details of the Mossbauer effect as the recoilless fraction, the isomer shift and the hyperfine splitting. The chosen cryogenic target chamber made it possible to keep target and absorber close to liquid nitrogen temperature, though the heat input due to the oxygen ions was about 25 W.

Effect of 50 MeV Electrons of the Ultimate Fermi Level in Germanium

p-type Ge doped with Ga and In to resistivities ranging from 0.001 to 30 Ω·cm and n-type Ge doped with Sb and As to resistivities ranging from 0.1 to 30 Ω·cm were irradiated with 50 MeV electrons to various doses up to a maximum total integrated flux of 1.0×1019 electrons/cm2. Electrical measurements were performed to determine the effect of irradiation on the temperature dependence (78° to 320°K) of the conductivity, carrier concentration, and Fermi level. After irradiation to relatively high doses (≳1018 electrons/cm2), both types of Ge reach a saturation in the hole concentration which is accompanied by an ultimate value for the Fermi level at Ev+0.220±0.010 eV for all samples studied. Comparison of this result with studies made using fast neutrons shows that the position of the ultimate Fermi level strongly depends on the damaging or ``disordering'' capabilities of the incident radiation. We find that the ultimate Fermi level is positioned closer to the valence band as a result of irradiation by particles capable of imparting a larger maximum recoil energy to the Ge atom. Finally, a comparison is made with the work of others on the ultimate position of the Fermi level for Ge irradiated by 60Co gamma rays and 4.5 MeV electrons which are not sufficiently energetic to produce disordered regions comparable to what is observed in fast-neutron and 50 MeV electron irradiation of Ge.

3He Neutron Spectrometer Using Pulse Risetime Discrimination

A 3He filled proportional counter can be used for neutron detection in the range 100 keV to 8 MeV by using the 3He(n,p)T reaction. The major limitation as a neutron spectrometer is that the 3He recoil distribution, arising from the elastic scattering of the higher energy neutrons present, masks the 3He(n,p)T peaks due to lower energy neutron groups. Since a 3He recoil and a proton of equal energies have difference specific ionizations and, therefore, different ranges in the counter filling, one thus has a means to distinguish between pulses from the 3He(n,p)T and 3He(n,n)3He reactions. For appropriate operating conditions the risetime of the pulses for these two events will be different. By converting this risetime to a pulse height and only accepting pulses with long risetimes [which correspond to protons from the 3He(n,p)T reaction], one has a neutron spectrometer useful in an energy interval between the maximum neutron energy present and that energy for which the proton range equals the range of the maximum energy 3He recoil. Spectra of monoenergetic neutrons obtained with a 3He filled proportional counter and the pulse risetime discrimination are presented to illustrate the energy range over which this detector may be used as a neutron spectrometer. Under typical operating conditions, spectra of the 24Mg(d,n)25Al, 28Si(d,n)29P, 32S(d,n)33Cl reactions were obtained to illustrate the performance of the spectrometer.

An absolute measurement of the 6He decay energy

The end-point of the energy spectrum of recoil ions from the β-decay of 6He was observed with a spectrometer which is calibrated in terms of a standard voltage cell. The average of two independent measurements gives a maximum β-energy of 3508±4 keV. This result is weighted with other measurements to give a maximum β-energy of 3508.4±3.8 keV. Addition of the 1.4 keV maximum recoil energy yields the decay energy 3509.8±3.8 keV.

Flow elasticity of hyaluronate solutions

With the oestroscope technique of Scott-Blair (1) solutions of pure potassium hyaluronate have been shown to give a well-defined elastic recoil. Recoil and viscosity were measured at several concentrations, and maximum recoil was found with a 0.25% solution. The stable and well-defined solutions are well suited to examine the phenomena of flow elasticity and elastic recoil, and some preliminary results are reported. The common raw materials of hyaluronate, human umbilical cord extract and bovine synovial fluid, were also tested and showed elastic recoil, which disappeared on incubation with testicular hyaluronidase. A model is proposed which ascribes the elasticity to cross-linking and the flow to the fact that the cross-links are the fairly labile hydrogen bonds.

Nuclear Recoil Following Neutrino Emission from Beryllium 7

The nuclear recoil spectrum of the electron capture isotope ${\mathrm{Be}}^{7}$ was measured from nearly monolayer deposits of the isotope on lithium fluoride and wolfram surfaces. The recoil spectrum was measured with an electrostatic analyzer having a two percent resolution. The spectra exhibited a peak at the high energy end of the spectrum consistent with the hypothesis of single neutrino emission in ${\mathrm{Be}}^{7}$. The maximum recoil ion energy observed was 55.9\ifmmode\pm\else\textpm\fi{}1.0 electron volts.

The Relative Ionization Produced by Low Energy Protons, Deuterons and Alpha-Particles in Various Gases

Mono-energetic neutrons have been used to produce recoil protons, deuterons and α-particles in a proportional counter The maximum pulse sizes produced by the different recoil particles are compared with the accurately known ratios of maximum recoil energies From the results for protons and deuterons it can be inferred that, for protons between 200 and 550 keV energy, the ionization is proportional to the energy with a deviation of less than 1% The total ionization in argon produced by a proton is about 8% greater than that of an α-particle of equal energy, for energies between 200 and 400 keV.

On the Recoil of the Nucleus in Beta-Decay ofKr88.

The maximum energy and the average energy of the recoil atoms from ${\mathrm{Kr}}^{88}$, which emits $\ensuremath{\beta}$- and probably also $\ensuremath{\gamma}$-rays, have been determined to 51.5\ifmmode\pm\else\textpm\fi{}2 ev and 29\ifmmode\pm\else\textpm\fi{}1 ev, respectively. The maximum recoil energy agrees closely with the maximum energy 2.4 Mev for the $\ensuremath{\beta}$-particles.