The author is pleased to express his gratitude to the staff of the Kellogg Radiation Laboratory for the opportunity to conduct this research. This work was supported by the Office of ~'nval Research and the Atomic Energy Commission.. decay at followed by alpha particle deexcitation) the following levels were investigated: 7. These large values for log are consistent with the assigned spin and parity levels involved in beta-decay process.
Nucl.i all a function of the distance to the target surface in the direction of the solid-state counter. The target nuclei, u~:t, were Bll, ~5 and F19; the rest of the relevant data are shown in Table I. The energy evolved from the helium burning process is largely produced during the part of the atar's life when it is a red giant.
At this time, about 1% of the atar's luminosity is believed to be due to the helium burning process. However, if there is a weak internucleon interaction of the (V. A) type, we would expect the nearby 2 + level to mix with the Z-level as a positive parity impurity to 8.
7) and
The ratio of the counters in the •• two 8calers8 was used to determine the lile time of the alpha particles t Appendix 1. The spectrometer field was modified and the height of the alpha particle pool was plotted against alpha particle energy. To accurately determine the solid angle of the semiconductor counter, the target was assumed to be a point source.
The two effects are correlated in that the dynamics of the decay are such that the alpha particle loses. This integration was then performed for different values of L yielding the density of recoil nuclei a8 a function of the distance from the target surface in the direction of the alpha particle counter. One possibility i8 that the small angle scattering from the beam-defining slits in front of the target chamber may somehow contribute to the low-energy background.
Bscattering from the sunbeam of the target as for the ca.e where the beam is scattered by the target by 5%. Y • Z ER J l.) in order to emphasize the dependence of the cross section on the variable parameters.
39- Table Ul
The value of lnAl was then determined by taking the value of lnAl at constant log" j and fitting a fifth-order polynomial to this set of points. Nineteen values of InAi were calculated for 2 center-o£ values. The mass energy is given in Table III.
41- order polynomial in log "
The value of log f corresponding to the peak of the alpha particle spectrum is log f = O."!. Since the theoretical spectrum of the 9.85- Mev level is narrow, r 02 = 800 ev, the barrier permeability and beta- decay phase space eaecta will not shift the peak and one can obtain a limit for the A relation for the strength of the parity non-bonding term in the internucleon potential haa been given in equation 8.
SS.Mev level will not be reduced by any effect that reduces the width of 2 + levels. Confidence in the resulting value for r V is enhanced by the fact that the independent haa particle model successfully predicted the branching ratios of the amm rays. for, the spoiling of the scent by a. aa-Mev level, and the position of a. The spectrometer entrance aperture was adjusted for maximum yield for each beam setting that defines sUts.
800, and the counting rate was recorded as a function of the distance from the surface of the magnet. Typical curves of the count rate variations in the target chamber are shown in Figure 23. Alpha particles were then scattered from a gold l:iank and the alternating gradient spectrometer was calibrated from the position of the scattered alpha particle stage.
This control was achieved by measuring the displacement of the proton step, propagated through the background material, due to the CaF layer. There is a consistently high value of the low energy spectrum during the runs compared to the low energy spectrum during the background checks. This gives a total energy re-solution of 2.8%, which is indicated by the width of the theoretical spectrum.
To obtain an estimate of the log ft of decay to the two excited states, the alpha decay &8 deexcitation mode is assumed. This would have corresponded to 10% of the total spectrum based on the above assumed theoretical calculations. 63-Mev level directly to the ground state will be hampered by the high multipolarity of the required radiation.
APPENDIX I
Using the above assumption, we can equate Aj with B j' and then the ratio, R. From the reaction dynamics, we get the energy of displacement N 16 for a given value of the reflection angle r. The energy spectrum of alpha particles from these two states is shown in Figure 3.
This figure illustrates the geometric arrangement of the counters and the target room protection system. The surface of this hole and its distance from the target determines the solid angle of the counter. WBeen the beam is turned off, the shield drops and the fiat tantalum plate covers the target chamber's entrance opening.
This plate intercepts any residual beams that may pass down the beam tube during the counting portion of the cycle. Solenoid, target and shield are shown in perspective, viewed from slightly above the beam axis in the direction of the incident beam. The bias on the solid-state counter is applied immediately after the beam leaves the target, so that any built-up charges can be swept from the barrier region before opening the gates to the scalers.
As the target angle fa.) is reduced from fa.):11 48-to CIa • 0-, the number of recoil N16 nuclei escaping from the target surface increases from none to half the induced activity. See Section UI.I 0 The N16 nuclei escaping the surface during bombardment are captured on the tantalum shield and removed from the field of view of the solid state counter when the shield falls. If this factor for the angular dependence of the number of Nl6 formed is factored out of the observed gamma ray yield, the resulting yield should decrease with target angle iIi proportional to the number of recoil N16 nuclei escaping from the target surface.
The effect on the target response function of the N's distribution in the target is not considered. The counter was then exposed to a group of particles at the imaging point of the alternating gradient spectrometer. It can be easily deduced from the graph that the population in: the high energy is 01.
The dependence of the shape of the spectrum on the interaction radius, a , i.e. shown for a single set of values of I. • 1,. The interaction radius also affects the asymmetric properties of the spectrum.
The dependence of the spectrum shape on the choices of resonance energy is illustrated in this graph as follows. The dependence of the shape of the theoretical spectrum on variations in the reduced width ie. illustrated in figure 18. The upper plot illustrates the variation of level parameters that is necessary to maintain a good fit between the semi-empirical points and the theoretical spectrum when different response functions are used.
The lower family of curves shows the variation of the level shift Aa.l as a function of the energy of the center of mass for different values of the interaction radius a. Using the response function obtained in the target chamber figure l1.b J curve (1), one obtains curve (a). The response function number lZb)curve (1.) produces curve (b). The levels have spin and parity assignments of 3 - and 1 - respectively, according to the results of the Chalk River Tandem Accelerator Group (Chalk River 1961).
To obtain results that are reasonably insensitive to beam position variation. It can be seen that the position of maximum output is approximately 1/20 inch to the right of the target axis, which is indicated by the intersection of the three target corners. The magnet settings were converted to energy and the fine attenuator setting on the amplifier was adjusted to place the peak in the center channel of the pulse height analyzer.
Power values versus attenuator setting were plotted against each other for constant values of high phototube voltage. To place this peak in the center of the pulse height analyzer, it is determined from figure Z4 that the high voltage should be 1080 volts and the fine attenuator should be set to 40. The thickness of the CaF layer Z was determined by observing the pitch shift of of elastically scattered protons on the copper base due to the vaporized CaF Z layer.
This difference was then multiplied by two to account for the fact that the spectrometer's momentum window allows only half of the spectrum to pass through. SO-Mev levels, it is necessary to know how many FZO nuclei have decayed during the alpha particle observation period. The factor of two was obtained by extrapolating the recorded spectrum to zero gamma ray energy, passing a horizontal Une through the intersection of the spectrum and setting the bias setting.
This assumption a8- may be in error' by a {actor of two and the error is included in the error of the log ft values. The dashed curve was obtained by placing a 0.0064 mm aluminum foil in front of the solid-state counter and recording the spectrum for the same number of monitor counts as recorded during the foil-free runs.
