The Use of Coincidence Counting Methods in Determining Nuclear Disintegration Schemes

Abstract

I. INTRODUCTIOÑOR some years the author and his collaborators'* have been using coincidence counting techniques as an aid in the determination of nuclear disintegration schemes. The information obtained by this method, when taken together with that obtained with the help of a magnetic analyzermagnetic lens or 180' type magnetic spectrographis at present one of the best methods of obtaining nuclear disintegration schemes, or the energy levels of radioactive nuclei. A comparison of the two methods gives a picture of the advantages and disadvantages of each.Any magnetic analyzer, to be sure, has much greater resolving power than does the coincidence method. In principle, a resolution (AHp/Hp) in momentum of the electrons measured of i -2 percent can be obtained. Measurement of gamma-ray energies can be obtained to an accuracy of 1 to 5 percent by measuring the energy of photoelectrons produced in some radiator, such as lead. It is not difhcult to measure the energies of the electrons ejected from the Z and I. shell by some gamma-ray and thereby obtain the energy of the gamma-ray. In addition, one can measure the momentum distribution of Compton electrons produced in an element of Iow atomic number, say copper or aluminum, by the gamma-rays under investigation. This method can serve as a check on gamma-ray energies obtained by the photo-effect and is particularly useful in the two cases: (I) when the energy of the gamma-ray is so high that the probability of production of photoelectrons becomes small; and, (2) when two gamma-rays are so situated that the Iline of one is superimposed on the X line of the other, for some particular radiator.The energy of gamma-rays can be measured with considerable accuracy by this method, *References are to be found in the bibliography at the end of this article. provided sources of high activity are available.The problem is to determine the energy level scheme from this information which is, at the same time, consistent with the spectrum of the disintegration electrons.The determination of the momentum distribution of the disintegration electrons (beta-ray spectra) poses a somewhat different problem. The thickness of the source and the material upon which it is mounted influence the shape of the distribution especially at the low energy end of the spectrum. One is therefore forced to use sources of very high specihc activity in order to obtain the best results. When the distribution is measured, a "Fermi Plot" is made of the results, and a decision made as to whether the spectrum is simple or complex. If the spectrum consists of two groups, a determination of the two end points can be made with fair accuracy.If more than two groups are present, the accuracy of determining the end points of the lower energy groups is considerably less.With the help of the information from the gamma-ray spectra and that of the beta-ray analysis, including the occurrence of internal conversion lines, one attempts to draw up a self-consistent energy level diagram. This method does not allow one to be cer...

On Nuclear Dipole Vibrations

“…Such a resonance was observed in carbon at 30 Mev, 1 in copper at 22 Mev, 1 in tantalum at 16 Mev, 2 and for photofission in thorium and in uranium at 16-18 Mev. 1 The suggestion was made that this phenomenon may be due to the interplay of increasing level density and increasing competition from other processes such as, for instance, the (y y 2n) process. Recent experiments 3 show, however, that in the case of Cu 63 as well as other nuclei the decrease in the (y,n) cross section in the high energy region is not compensated to any considerable extent by an increase in the (T,2W) cross section.…”

Development of a minicomputer system for on-line processing of gamma--gamma coincidence events and measurements of E2/M1 mixing ratios in /sup 110/Cd and /sup 134/Ba

“…The reorientation parameters U, (y ) for the n transition depend on I , I , and on the multipole intensities (but not the interference terms) of the'unobserved radiation: I V)Ln (i n ! n "k +l ir A i |In> 2 L IT I n+1 ii+l nj U k (y n ) = -i -Ji (1)(2)(3)(4)(5)(6) A <-> Ln p In •"KHI^II^ 2 1 n+1 n+1 n'…”