Energy Distribution Of Α-particles Research Articles

Structure effects in (n, α) reactions on Nd isotopes

The angular and energy distributions of α-particles from the reactions142,144Nd(n, α)139,141Ce have been measured at incident neutron energies of ≈ 14.2 and 18.1 MeV. The comparison of the angle-integrated α spectra with those from the reaction143Nd(n, α)140Ce, shows that the 83th valence neutron of143Nd acts as a spectator in the (n, α) process, while the two paired neutrons outside theN= 82 shell of144Nd play an active role. This result, together with analogous data from (p, α) reactions, clearly indicates that the protons and the neutrons of the emitted α in a (nucleon, α) reaction must be already paired in the target nucleus.

High resolution alpha particle spectroscopy using CR-39 plastic track detector

We present a technique for high resolution alpha particle spectroscopy using CR-39 plastic. An energy resolution, δE, close to the range straggling limit is reported on particles of energy ≳3 MeV under typical etch conditions. For 6 MeV α-particles δE is ∼35 keV on individual tracks. For groups of particles δE∼20 keV can be achieved using certain data selection criteria. The technique is based on the determination of track length in the plastic from measurement of the etch track parameters. The etch track data can be analysed by two methods. Method 1 employs all five parameters of the etched track: track depth, Z; major axis M j; minor axis, M i overall track length, X and the diameter of the etched out end, m, which is equal to zero in the case of a non-etched out track. Method 2 employs only the horizontal measurements of the projected parameters X, M i and m. The experimental data presented include (1) V T-range curves at etch temperatures of 50, 75 and 100°C in 6.25N NaOH for CR-39 available commercially and for material manufactured to specific temperature-time curing profiles. (2) The variation of etch induction time with etch temperature and α-particle energy. The theoretical analysis includes (1) a full discussion of α-particle track structure in CR-39 as a function of particle energy, dip angle and degree of etching including a comparative simulation of etched tracks, (2) a description of the methods of track analysis. The energy resolution attainable using the methods of analysis described is discussed fully. As an example of the best resolution achievable using selection criteria on a group of tracks the energy distribution of α-particles from a 252Cf source is considered. The 6.076 and 6.119 MeV α-particles are clearly resolved: δE=±20 keV.

On the knock-on mechanism for (n, α) reactions induced by fast neutrons on the deformed doubly even nuclei

A method for the calculation of the energy distribution of α-particles from the (n, α) reaction on deformed doubly even nuclei is developed. The Feynman triangular diagram is used for the calculation. The resulting energy distributions for the 14 MeV (n, α) reactions in 160Dy, 162Dy, 164Dy, 166Er and 168Er are compared with the experimental data. The agreement suggests the dominance of the knock-on mechanism in the investigated reactions.

Angular and energy distributions of α-particles in LRA fission

Detailed experimental studies have been made on the angular and energy distributions of the long-range α-particles (LRA) emitted from 252Cf during spontaneous fission. They show that the α-particle angular distribution is peaked at an angle (made by the trajectory of the α-particle with that of either of the main fragments) of about 90° and has a FWHM of 20–30. The α-particle energy spectrum is peaked at about 15 MeV and has a FWHM of 13 MeV. We have carried out computer calculations of the trajectories of the three particles produced in LRA fission. Such calculations lead to predictions of angular and energy distributions which may be compared with the experimental ones. The calculations were carried out using a set of initial conditions determined by the statistical theory of nuclear fission. The comparison with experimental results therefore provides a test of the statistical theory. The calculated results show that the statistical theory leads to an energy spectrum which is in good agreement with the experimental one, and that reasonable agreement between the calculated and the experimental angular distribution may be obtained if it is assumed that the α-particle is emitted within a short period of time, of the order of 3 × 10 −22 s after the instant of scission.

Fragments alpha produits par spallation de bismuth par des protons de 240 à 600 MeV

From secondary reaction measurements on Bi nuclei bombarded by high energy protons the cross sections for α-particle emission were deduced. The values are 110, 220 and 320 mb at incident energies of 240, 420 and 550 MeV, respectively. The energy distributions of α-particles emitted in the forward or in the backward directions have been determined, and it could be shown that the following two processes are involved: 1. a)An isotropic emission in the centre-of-mass system the cross section of which increases from 25 to 210 mb when the incident energy goes from 240 to 550 MeV. 2. b)A process in which α-particles are emitted mainly in the forward direction. Calculations were carried out with a IBM 7094 computer, assuming that α substructures are “knocked-out” from the surface of the nucleus by cascade nucleons. The probability for the occurrence of such α structures was found to be 0.7 ± 0.1.

Das α-Spektrum aus dem Zerfall des Li8

The energy distribution of α-particles from the β-a-decay of Li8 over the first excited state of Be8 can be determined by means of the normalization integral over the α-α-scattering solution. Relating the relevant part of this integral to the phase shift, the α-spectrum may be obtained using one phenomenological parameter only. The calculation gives a correct fit to the experimental energy distribution, excepting a small region around the maximum.

Note on the α particle energy spectrum in Li 8 decay

An attempt is made to correlate the asymmetry in the energy distribution of α-particles from Li 8 decay with the asymmetry in the behaviour of the phase shift in the J = 2 state. A phenomenological potential of the Haefner type is used and the nuclear matrix element is evaluated using the mean value theorem. It is found that the two sets of data can only be correlated if the repulsive core is weakened as the energy increases.