The partial support of the Atomic Energy Commission and the interest of Dr. The ratio of photoproduction cross sections of neutral pions from neutrons to that from protons was obtained at average photon energies of 750, 875 and 1050 mev at a pion CM angle of 600 and at average photon energies of 875 and 1050 mev at a CM angle pion of 90 o. The cross sections for neutral pion photoproduction from neutrons are derived from the ratio .,-no / .,-0 and. Caltech data on neutral pion photoproduction from hydrogen. Detailed measurements of total cross sections and differential cross sections for the photoproduction of positive pions and neutral pions from hydrogen have been made up to 1 Bev for energy.
The differential photoproduction cross sections of positive pions and neutral pions become more complex as the energy of the incident photons increases. Its interpretation in relation to the neutral pion productions from protons and neutrons is uncertain. In view of the above situation regarding neutral pion production from neutrons, this experiment was designed to directly measure the ratio of photoproduction of neutral pions from bound neutrons to the ratio from bound protons in the energy range 500-1000 mev with.
EQUIPMENT
The function b(k/E) was measured by J. The target used was deuterium gas at high pressure in a nickel-plated steel cylinder with hemispherical ends. To reduce the background, the target was shielded so that the counters only saw the central part of the target. A liquid nitrogen tank located on top of the target was used to cool the target.
The temperature was given by an iron-constant thermocouple on the outer surface of the target near. A diagram of the counters is shown in Figure 4. Pions were detected by a set of three scintillation counters C1, C2 and C3. the sizes of these counters and the spacing between them are shown in Table 2. This efficiency varied from 40% to 80% depending on the energy and angle of the neutral pion.
I Fast F ast
PROCEDURE
Due to the physical limitations of our laboratory, the difference in time for a nucleon produced at a laboratory angle of 50 by o a photon of 1000 mev and a photon. For a fast coincidence circuit to operate with a resolution of this order of magnitude requires that the amplitudes of the input pulses have very small dispersion - a condition that is not valid in this experiment since the pulse amplitude of a neutral pion four times can be as large as the pulse amplitude of a charged pion. The difference of the two sets of data, when each is properly normalized, represents the contributions due to photons of energy between the two values of the endpoint energies.
As mentioned earlier, the output of the random circuit system also served an important function as an event trigger. The output of this coincidence was placed in slow coincidence with the output of the fast coincidence system C2, C3 and C5. The deviation of the absolute efficiency value from 100% is probably due to the inefficiency of the individual meters.
The expression for the resolution of the electronic circuitry as a function of photon energy with hydrogen as the target is similar to the expression for deuterium in Part II, except for the factors that take into account the internal motion of the nucleons in the deuteron. . When D2 was used as a target, the resolution curve was smeared due to the internal motion of the nucleons in the deuterons. Resolution function of the random circuit system as a function of photon energy k, for hydrogen and deuterium with Bremsstrahlung endpoint energy E :0: 1150 Mev.
The position of the line was digitized and the number could be punched directly onto a paper tape by a machine manufactured by Datex Co. The information recorded on the tape was the height of the peaks of the five pulses and the baseline of the pulse train. The upper and lower energy data were taken alternately as often as possible in compromise with the efficiency of the operation of the syn-.
The stability of the high voltage in the phototubes and the gain of the phototubes could be checked by their pulse height spectrum and they showed very little drift.
DATA REDUCTION A) Biases
The probability of a photon from the decayed neutral pawn being converted into the target or into the paraffin shield in front of the counters was 30%. The ratio between the number of detected paired productions of charged pions and the number of single productions of positive pions ranges from 0.10 to 0.20. First, the nucleon counters can detect one of the pions and the pion counters can detect the other.
Second, nucleon counters can detect one of the pions and pion counters detect a nucleon. Third, nucleon counters can detect a nucleon, and pion counters can detect one of the pions. To simplify the calculation, the effects of in-. the internal motion of nucleons in deuterium was not taken into account.
It measures the loss of the count rate per deuteron due to the internal motion of the nucleons in the deuteron. Since the synchrotron beam has a period of 25 nanoseconds between its maximum intensity due to the fact that R. They are too small to count in view of the large statistical errors of this experiment.
However, it is most interesting to express the result in terms of the average photon energy K in the nucleon rest system. Due to the internal motion of the nucleon in the deuteron, the energy of the photon that initiates a certain reaction is different for the two coordinate systems. Thus, the average photon energy K for each point in the nucleon rest system differs from the average energy k.
The sum of the integrands at a given K gives the relative contribution to the counting rate of photons with energy K. The calculation of the average pion emission angle in the CM system of the target nucleon and the incident photon is e.g. - extremely long-lasting. Given the large statistical errors of our data and the close proximity of K and k, no calculation was made.
RESULTS
As one can see from the resolution function plotted in Figure 19, the average photon energy of the data taken with the synchrotron running at 950 mev and the delay set for point 1 is very close to the average photon energy of point 2 when the data was observed. - retained by subtracting the 800 ms data from the 950 ms data with the delay of C5 set to 31. The fact that the results of points 2' and 3' match those of points 2 and 3 respectively indicates that the ratio of (Tno to (To) does not change rapidly within the energy interval of each point. Furthermore, this gives confidence in the operation of the fast electronic circuits, and in the belief that efficiencies n's defined in Section II do not ' a big influence on the data.
It shows that even on the slope of the resolution of the coincidence circuits, where the efficiency is not .. 100%, the change in the amplitudes of the input pulses does not significantly affect the operation of the coincidence circuits. One of the advantages of this experiment is that it eliminates many experimental errors in measuring the ratio.
DISCUSSION
The present experiment suffers in the same way as Bingham's in requiring the use of synchrotron subtraction to determine the energy of the incident photon. A better way to do this experiment, at least in the forward direction of the outgoing pion, would be to use two lead glass total absorption Cerenkov counters to detect the two photons from the decaying neutral pion. The opening angle of the two lead glass counters would determine the minimum torque of the neutral pion.
The maximum neutral pion momentum will be determined by the maximum synchrotron photon energy. In this section, the ratio of counting efficiency for neutrons to that of protons and the ratio of counting efficiency for neutral pions to that for charged pions are evaluated. From the derivation in Section II, we obtain the expressions for the count rates of the four reactions.
The reason why the values of pn/pp at points 1, Z and 3a are greater than those at points 3b, 4 and 5 is probably the result of the absorption of the proton by the l/Zn lead plate. The reason that the value of p n / p p at point 3b is greater than that at points 4 and 5 is probably due to the increase of the neutron. The values of pO S 0 / p ~ at points 4 and 5 are approximately 1/2 of the geometric efficiency for counting iTo.
C~)p '" y - . o . where y):!::"P is the efficiency of counting the specific pair production, determined by the resolution of the coincidence circuit system, and S is the number of possible ways to find the particular pair end products. Kinematically it is possible to have protons of the above description in the production of pion pairs. ESTIMATE OF PAIR PRODUCTIONS IN DEUTERIUM In this section the corrections for the pair productions in.
The following expression can be derived from the last equation in Appendix II by appropriate substitution if the effects of the internal motion of the nucleons in the deuteron are neglected.
APPENDIX IV
There is some probability that the results of each successive cascade shower initiated by a photon from the decaying neutral pion passing through 1/3 radiation length of paraffi~, 2.4 radiation lengths of lead and 1. To estimate this correction we calculate the probability that the number of electrons is 1 after each successive burst. For each probability we assume a Poisson distribution for the number of electrons of all energies at depth t in a shower.
The results are shown in Table 12 where PI is the probability that the number of electrons is 1 after a photon has traveled through 1/3 radiation length of paraffin~ P2 is the probability that the number of electrons is 1 after an electron has traveled through 2.4 radiation lengths has of lead, P3 is the probability that the number of electrons is 1 after an electron has passed through 1.
