The motion of energetic charged particles inside a monocrystalline solid can be strongly influenced by channeling and blocking effects. The present article reviews the theory, the experimental studies, and some of the applications of these effects. The coverage of the published literature extends through June 1973.

Channeling and related effects in the motion of charged particles through crystals

The experimental techniques of measuring the mean lifetimes tau of excited nuclear states is reviewed. Emphasis is put on direct measurements of tau in the region 10-18-10-6 s, especially on techniques involving the observation of Doppler energy shifts of gamma -rays. Indirect methods of obtaining tau by measuring the widths or partial widths are discussed. Comparisons are made of the applicability, accuracy and reliability of the different experimental techniques.

https://iopscience.iop.org/article/10.1088/0034-4885/42/1/001/pdf

The measurement of the lifetimes of excited nuclear states

The importance of lifetime measurements of nuclear levels has been recognized for a long time. The techniques employed to measure lifetimes, or absolute transition probabilities, are very simple conceptually but are ingeniously adapted to obtain sensitivity to the decay products and to cover an enormous time scale from 10−20 sec to many years. In this chapter, the techniques we discuss cover only a small fraction of this time scale, namely, ∼10−15−∼10−9 sec. Radiative lifetimes of excited nuclear levels in this range can be measured with some sensitivity and accuracy by the Doppler-shift methods, the recoil distance plunger method (RDM) and the Doppler-shift attenuation method (DSAM). It is an important range, particularly for obtaining information about the collective excitation modes of nuclei throughout the periodic table.

Lifetime Measurements of Excited Nuclear Levels by Doppler-Shift Methods

Position-sensitve semiconductor detectors

Tz = 12β-delayed proton precursors: (I). The decay of 69Se

COMPOUND NUCLEAR REACTION TIMES AND LEVEL DENSITIES FROM A BLOCKING EXPERIMENT IN Ge.

In this paper we discuss problems associated with the extraction of compound nuclear lifetimes from blocking dips. This is done with reference to our previous measurements of the70Ge(p, p′)70Ge (1.04 MeV, 2+) and72Ge(p, p′)72Ge (0.835 MeV, 2+) reaction times. Different methods that may be used to quantify the filling-in of a blocking dip in a finite-lifetime case are discussed and compared. The importance of multiple-scattering effects in the various types of analyses are investigated. Our results are compared to those of other authors to obtain an estimate of the overall accuracy of the technique.

Multiple-scattering effects in mean-lifetime experiments by blocking technique

The 〈111〉 axial blocking in a natural Mo crystal has been used to measure the92Mo(p,p′)92Mo* (1.5 MeV, 2+) reaction times at proton energies between 7.5 and 9.5 MeV. A computer simulation was employed to extract the mean reaction times which were found to range from 2 · 10−17 to 4 · 10−17 s with an accuracy of 15%. An analysis of the results has allowed us to extract the valuea=(10.06 ± 0.12) (MeV)−1 for the level density parameter of the compound nucleus93Tc in the excitation energy range from 11.5 to 13.5 MeV.

Compound nuclear reaction times and level densities from a blocking experiment in molybdenum

Recent developments (1,2,3) have made the use of the blocking effect of charged particles in a single crystal a viable technique with which to measure compound nuclear lifetimes in the range 10-16-1O-18 seconds. This is a lifetime range difficult to study by other techniques but one of considerable interest as the fine structure of medium mass nuclei has lifetimes of this order.

G. J. Clark

Papers

COMPOUND NUCLEAR REACTION TIMES AND LEVEL DENSITIES FROM A BLOCKING EXPERIMENT IN Ge.

Multiple-scattering effects in mean-lifetime experiments by blocking technique

Compound nuclear reaction times and level densities from a blocking experiment in molybdenum

Compound Nuclear Lifetimes from Blocking Experiments in Ge and Mo